NFSv4                                                     D. Noveck, Ed.
Internet-Draft                                                    NetApp
Updates: 8881, 7530 (if approved)                       24 December 2021
Intended status: Standards Track
Expires: 27 June 2022


                    Security for the NFSv4 Protocols
                    draft-dnoveck-nfsv4-security-04

Abstract

   This document describes the core security features of the NFSv4
   family of protocols, applying to all minor versions.  The discussion
   includes the use of security features provided by RPC on a per-
   connection basis.

   This preliminary version of the document, is intended, in large part,
   to result in working group discussion regarding existing NFSv4
   security issues and to provide a framework for addressing these
   issues and obtaining working group consensus regarding necessary
   changes.

   When a successor document is eventually published as an RFC, it will
   supersede the description of security appearing in existing minor
   version specification documents such as RFC 7530 and RFC 8881.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   This Internet-Draft will expire on 27 June 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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Table of Contents

   1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.1.  Document Motivation . . . . . . . . . . . . . . . . . . .   5
     1.2.  Document Annotation . . . . . . . . . . . . . . . . . . .   5
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   7
     2.1.  Keyword Definitions . . . . . . . . . . . . . . . . . . .   7
     2.2.  Special Considerations  . . . . . . . . . . . . . . . . .   7
   3.  Introduction to this Update . . . . . . . . . . . . . . . . .   8
     3.1.  Per-connection Security Features  . . . . . . . . . . . .   8
     3.2.  Handling of Multiple Minor Versions . . . . . . . . . . .   9
     3.3.  Handling of Minor-version-specific features . . . . . . .  10
     3.4.  Features Needing Extensive Clarification  . . . . . . . .  12
     3.5.  Process Going Forward . . . . . . . . . . . . . . . . . .  15
   4.  Introduction to NFSv4 Security  . . . . . . . . . . . . . . .  17
     4.1.  NFSv4 Security Terminology  . . . . . . . . . . . . . . .  19
     4.2.  NFSv4 Security Scope Limitations  . . . . . . . . . . . .  23
   5.  Structure of NFSv4 Access Control Lists . . . . . . . . . . .  26
     5.1.  Access Control Entries  . . . . . . . . . . . . . . . . .  26
     5.2.  ACE Type  . . . . . . . . . . . . . . . . . . . . . . . .  27
     5.3.  ACE Access Mask . . . . . . . . . . . . . . . . . . . . .  28
     5.4.  Uses of Mask Bits . . . . . . . . . . . . . . . . . . . .  29
     5.5.  Requirements and Recommendations Regarding Mask
            Granularity  . . . . . . . . . . . . . . . . . . . . . .  39
     5.6.  Handling of Deletion  . . . . . . . . . . . . . . . . . .  41
       5.6.1.  Previous Handling of Deletion . . . . . . . . . . . .  42
     5.7.  ACE flag bits . . . . . . . . . . . . . . . . . . . . . .  43



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     5.8.  Details Regarding ACE Flag Bits . . . . . . . . . . . . .  45
     5.9.  ACE Who . . . . . . . . . . . . . . . . . . . . . . . . .  46
     5.10. Automatic Inheritance Features  . . . . . . . . . . . . .  49
     5.11. Attribute 13: aclsupport  . . . . . . . . . . . . . . . .  51
     5.12. Attribute 12: acl . . . . . . . . . . . . . . . . . . . .  52
   6.  Authorization in General  . . . . . . . . . . . . . . . . . .  53
   7.  User-based File Access Authorization  . . . . . . . . . . . .  54
     7.1.  Attributes for User-based File Access Authorization . . .  54
     7.2.  Handling of Multiple Parallel File Access Authorization
           Models  . . . . . . . . . . . . . . . . . . . . . . . . .  55
     7.3.  Posix Authorization Model . . . . . . . . . . . . . . . .  57
       7.3.1.  Attribute 33: mode  . . . . . . . . . . . . . . . . .  57
       7.3.2.  NFSv4.1 Attribute 74: mode_set_masked . . . . . . . .  58
     7.4.  ACL-based Authorization Model . . . . . . . . . . . . . .  59
       7.4.1.  Processing Access Control Entries . . . . . . . . . .  59
       7.4.2.  V4.1 Attribute 58: dacl . . . . . . . . . . . . . . .  61
   8.  Common Considerations for Both File access Models . . . . . .  61
     8.1.  Server Considerations . . . . . . . . . . . . . . . . . .  62
     8.2.  Client Considerations . . . . . . . . . . . . . . . . . .  65
   9.  Combining Authorization Models  . . . . . . . . . . . . . . .  66
     9.1.  Background for Combined Authorization Model . . . . . . .  66
     9.2.  Needed Attribute Coordination . . . . . . . . . . . . . .  69
     9.3.  Computing a Mode Attribute from an ACL  . . . . . . . . .  72
     9.4.  Alternatives in Computing Mode Bits . . . . . . . . . . .  73
     9.5.  Handling of UNIX ACLs . . . . . . . . . . . . . . . . . .  75
     9.6.  Setting Multiple ACL Attributes . . . . . . . . . . . . .  75
     9.7.  Setting Mode and not ACL (overall)  . . . . . . . . . . .  75
       9.7.1.  Setting Mode and not ACL (vestigial)  . . . . . . . .  76
       9.7.2.  Setting Mode and not ACL (Discussion) . . . . . . . .  77
       9.7.3.  Setting Mode and not ACL (Proposed) . . . . . . . . .  78
     9.8.  Setting ACL and Not Mode  . . . . . . . . . . . . . . . .  83
     9.9.  Setting Both ACL and Mode . . . . . . . . . . . . . . . .  84
     9.10. Retrieving the Mode and/or ACL Attributes . . . . . . . .  84
     9.11. Creating New Objects  . . . . . . . . . . . . . . . . . .  84
     9.12. Use of Inherited ACL When Creating Objects  . . . . . . .  86
     9.13. Combined Authorization Models for NFSv4.2 . . . . . . . .  86
   10. Labelled NFS Authorization Model  . . . . . . . . . . . . . .  87
   11. State Modification Authorization  . . . . . . . . . . . . . .  87
   12. Other Uses of Access Control Lists  . . . . . . . . . . . . .  88
     12.1.  V4.1 Attribute 59: sacl  . . . . . . . . . . . . . . . .  88
   13. Identification and Authentication . . . . . . . . . . . . . .  89
     13.1.  Identification vs. Authentication  . . . . . . . . . . .  89
     13.2.  Items to be Identified . . . . . . . . . . . . . . . . .  89
     13.3.  Authentication Provided by specific RPC Auth Flavors . .  90
     13.4.  Authentication Provided by other RPC Security
            Services . . . . . . . . . . . . . . . . . . . . . . . .  91
   14. Security of Data in Flight  . . . . . . . . . . . . . . . . .  91




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     14.1.  Data Security Provided by Services Associated with Auth
            Flavors  . . . . . . . . . . . . . . . . . . . . . . . .  91
     14.2.  Data Security Provided for a Connection by RPC . . . . .  91
   15. Security Negotiation  . . . . . . . . . . . . . . . . . . . .  92
     15.1.  Dealing with Multiple Connections  . . . . . . . . . . .  93
   16. Future Security Needs . . . . . . . . . . . . . . . . . . . .  94
   17. Security Considerations . . . . . . . . . . . . . . . . . . .  95
     17.1.  Changes in Security Considerations . . . . . . . . . . .  95
       17.1.1.  Wider View of Threats  . . . . . . . . . . . . . . .  96
       17.1.2.  Connection-oriented Security Facilities  . . . . . .  97
       17.1.3.  Necessary Security Changes . . . . . . . . . . . . .  97
       17.1.4.  Compatibility and Maturity Issues  . . . . . . . . .  98
       17.1.5.  Discussion of AUTH_SYS . . . . . . . . . . . . . . .  98
     17.2.  Security Considerations Scope  . . . . . . . . . . . . .  99
       17.2.1.  Discussion of Potential Classification of
               Environments  . . . . . . . . . . . . . . . . . . . .  99
       17.2.2.  Discussion of Environments . . . . . . . . . . . . . 100
       17.2.3.  Insecure Environments  . . . . . . . . . . . . . . . 101
     17.3.  Major New Recommendations  . . . . . . . . . . . . . . . 101
       17.3.1.  Recommendations Regarding Security of Data in
               Flight  . . . . . . . . . . . . . . . . . . . . . . . 101
       17.3.2.  Recommendations Regarding Client Peer
               Authentication  . . . . . . . . . . . . . . . . . . . 102
       17.3.3.  Recommendations Regarding Superuser Semantics  . . . 103
       17.3.4.  Issues Regarding Valid Reasons to Bypass
               Recommendations . . . . . . . . . . . . . . . . . . . 103
     17.4.  Threat Analysis  . . . . . . . . . . . . . . . . . . . . 104
       17.4.1.  Threat Analysis Scope  . . . . . . . . . . . . . . . 104
       17.4.2.  Threats based on Credential Compromise . . . . . . . 104
       17.4.3.  Threats Based on Rouge Clients . . . . . . . . . . . 106
       17.4.4.  Threats Based on Rouge Servers . . . . . . . . . . . 107
       17.4.5.  Data Security Threats  . . . . . . . . . . . . . . . 108
       17.4.6.  Authentication-based threats . . . . . . . . . . . . 108
       17.4.7.  Disruption and Denial-of-Service Attacks . . . . . . 111
   18. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 112
     18.1.  New Authstat Values  . . . . . . . . . . . . . . . . . . 112
     18.2.  New Authentication Pseudo-Flavors  . . . . . . . . . . . 113
   19. References  . . . . . . . . . . . . . . . . . . . . . . . . . 114
     19.1.  Normative References . . . . . . . . . . . . . . . . . . 114
     19.2.  Informative References . . . . . . . . . . . . . . . . . 115
   Appendix A.  Changes Made . . . . . . . . . . . . . . . . . . . . 115
     A.1.  Motivating Changes  . . . . . . . . . . . . . . . . . . . 116
     A.2.  Other Major Changes . . . . . . . . . . . . . . . . . . . 116
   Appendix B.  Issues for which Consensus Needs to be
           Ascertained . . . . . . . . . . . . . . . . . . . . . . . 117
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 128
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . 129




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1.  Overview

   This document is intended to form the basis for a new description of
   NFSv4 security applying to all NFSv4 minor versions.  The motivation
   for this new document and the need for major improvements in NFSv4
   security are explained in Section 1.1.

   Because this document anticipates making major changes in material
   covered in previous standards-track RFCs, extensive working group
   discussion will be necessary to make sure that there is a working
   group consensus to make the changes being proposed.  These changes
   include the major improvements mentiontioned above and changes
   necessary to suitably describe features currently in an
   unsatisfactory state as described in Section 3.4

1.1.  Document Motivation

   A new treatment of security is necessary because:

   *  Previous treatments paid insufficient attention to security issues
      regarding data in flight.

   *  The presentation of AUTH_SYS as an "'OPTIONAL' means of
      authentication" obscured the significant security problems that
      come with its use.

   *  The security considerations sections of existing minor version
      specifications contain no threat analyses and focus on particular
      security issues in a way that obscures, rather than clarifying,
      the security issues that need to be addressed.

   *  The availability of RPC-with-TLS (described in [12]) provides
      facilities that NFSv4 clients and servers will need to use to
      provide security for data in flight and mitigate the lack of user
      authentication when AUTH_SYS is used.

1.2.  Document Annotation

   The first version of this preliminary document contained many notes
   with headers in brackets, requesting comments regarding confusing or
   otherwise dubious passages in existing documents and noting other
   choices that need to made.  Comments about and working group
   discussion of these issues will be important in arriving at an
   adequate RFC candidate.  In this version, those specific items have
   been removed and are replaced by the sorts of items described below
   which show the troublesome existing text, explain the issues with it,
   and and provide a proposed replacement.




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   In order to make further progress on these difficult issues,
   including many whose resolution will probably involve compatibility
   issues with existing implementations, the author has tried his best
   to resolve these issues, even though there is no assurance that the
   resolution adopted by consensus will match the author's current best
   efforts.  To provide a possible resolution that might be the basis of
   discussion while not foreclosing other possibilities, proposed
   changes are organized into a series of consensus items, which are
   listed in Appendix B.

   For such pending issues, the following annotations will be used:

   *  A paragraph headed "[Author Aside]:", provides the author's
      comments about possible changes and will probably not appear in an
      eventual RFC.

      This paragraph can specify that certain changes within the current
      section are to be implicitly considered as part of a specific
      consensus item.

      The paragraph can indicate that all unannotated material in the
      current section is to be considered either the previous treatment
      or the proposed replacement text for a specific consensus item.

   *  A paragraph headed "[Consensus Needed (Item #NNx)]:", provides the
      author's preferred treatment of the matter and will only appear in
      the eventual RFC if working group consensus on the matter is
      obtained allowing the necessary changes to be made permanent,
      without being conditional on a future consensus.

      The item id, represented above by "NNx" consists of a number
      identifying the specific consensus item and letter which is unique
      to appearance of that consensus item in a particular section.  In
      cases in which a pending item is cited with no part of the
      discussion appearing in the current section, an item id of the
      form "#NN" is used.

   *  A paragraph headed "[Previous Treatment]:", indicates text that is
      provided for context but which the author believes, need not
      appear in the eventual RFC, because it is expected to be
      superseded by a corresponding consensus item

      The corresponding consensus item is often easily inferred, but can
      be specified explicitly, as it is for items associated with the
      consensus item itself.






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   Each of the annotations above can be modified by addition of the
   phrase, "Including List" to indicate that it applies to a following
   bulleted list as well as the current paragraph or the phase "Entire
   Bulleted Item" to indicate it applies to all paragraphs within a
   specific bulleted item.

2.  Requirements Language

2.1.  Keyword Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as specified in BCP 14 [1] [5] when,
   and only when, they appear in all capitals, as shown here.

2.2.  Special Considerations

   Because this document needs to revise previous treatments of its
   subject, it will need to cite previous treatments of issues that now
   need to be dealt with in a different way.  This will take the form of
   quotations from documents whose treatment of the subject is being
   obsoleted, most often direct but sometimes indirect as well.

   Paragraphs headed "[Previous Treatment] or otherwise annotated as
   having that status, as described in Section 1, can be considered
   quotations in this context.

   Such treatments in quotations will involve use of these BCP14-defined
   terms in two noteworthy ways:

   *  The term may have been used inappropriately (i.e not in accord
      with RFC2119 [1]), as has been the case for the "RECOMMENDED"
      attributes, which are in fact OPTIONAL.

      In such cases, the surrounding text will make clear that the
      quoted text does not have a normative effect.

      Some specific issues relating to this case are described below
      Section 7.1.

   *  The term may been used in accord with RFC2119 [1], although the
      resulting normative statement is now felt to be inappropriate.

      In such cases, the surrounding text will need to make clear that
      the text quoted is no longer to be considered normative, often by
      providing new text that conflicts with the quoted, previously
      normative, text.




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      An important instance of this situation is the description of
      AUTH_SYS as an "'OPTIONAL' means of authentication".  For detailed
      discussion of this case, see Sections 13 and 17.1.5

3.  Introduction to this Update

   There are a number of noteworthy aspects to the updated approach to
   NFSv4 security presented in this document:

   *  There is a major rework of the security framework to take
      advantage of work done in RPC-with-TLS, as described in
      Section 1.1.

      NFSv4 security is still built on RPC, as had been done previously.
      However, it is now able to take advantage of security-related
      facilities provide on a per-connection basis For more information
      about this transformation, see Section 3.1.

      For an overview of changes made so far as part of this rework, see
      Appendix A.1.

   *  This document deals with all minor versions together, although
      there is a need for exceptions to deal with, for example, pNFS
      security.

      For more detail about how minor version differences will be
      addressed, see Sections 3.2 and 3.3.

   *  There is a new Security Considerations section including a threat
      analysis.

   *  There has been extensive work to clarify the multiple types of
      authorization within NFSv4 and deal more completely with the co-
      ordination of ACL-based and mode-based file access authorization.

3.1.  Per-connection Security Features

   There are a number of security-related facilities that can be
   provided on a per-connection basis, eliminating the need to provide
   such support on a per-request basis, based on the RPC auth flavor
   used.

   These will initially be provided, in mosr cases, by RPC-with-TLS but
   similar facilities might be provided by new versions of existing
   transports or new RPC transports.






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   *  The transport or a layer above it might provide encryption of
      requests and replies, eliminating the need for privacy and
      integrity services to be negotiated later and applied on a per-
      request basis.

      While clients might choose to establish connections with such
      encryption, servers can establish policies allowing access to
      certain pieces of the namespace using such security facilities, or
      limiting access to those providing privacy, allowing the use of
      either per-connection encryption or privacy services provided by
      RPCSEC_GSS.

   *  The transport or a layer above it might provide mutual
      authentication of the client and server peers as part of the
      establishment of the connection This authentication is distinct
      from the the mutual authentication of the client user and server
      peer, implemented within the GSSSEC_RPC framework.

      This form of authentication is of particular importance when when
      the server allows the use of the auth flavors AUTH_SYS and
      AUTH_NONE, which have no provision for the authentication of the
      user requesting the operation.

      While clients might choose, on their own,to establish connections
      with such peer authentication, servers can establish policies a
      limiting access to certain pieces of the namespace without such
      peer authentication or only allowing it when using RPCSEC_GSS.

   To enable server policies to be effectively communicated to clients,
   the security negotiation framework now allows connection
   characteristics to be specified using pseudo-flavors returned as part
   of the response to SECINFO and SECINFO_NONAME.  See Section 15 for
   details.

3.2.  Handling of Multiple Minor Versions

   In some cases, there are differences between minor versions in that
   there are security-related features, not present in all minor
   versions.

   To deal with this issue, this document will focus on a few major
   areas listed below which are common to all minor versions.

   *  File access authorization (discussed in Section 7) is the same in
      all minor versions together with the identification/
      authentication infrastructure supporting it (discussed in
      Section 13) provided by RPC and applying to all of NFS.




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      An exception is made regarding labelled NFS, an optional feature
      within NFSv4.2, described in RFC7862 [10].  This is discussed as a
      version-specific feature in this document in Section 10

   *  Features to secure data in-flight, all provided by RPC, together
      with the negotiation infrastructure to support them are common to
      all NFSv4 minor versions, are discussed in Section 15

      However, the use of SECINFO_NONAME, together with changes needed
      for connection-based encryption, paralleling those proposed here
      for SECINFO, is treated as a version-specific feature and, while
      mentioned here, will be fully documented in new NFSv4.1
      specification documents.

   *  The protection of state data from unauthorized modification is
      discussed in Section 11) is the same in all minor versions
      together with the identification/ authentication infrastructure
      supporting it (discussed in Section 13 by security services such
      as those provided by RPC-with-TLS.

      It needs to be noted that state protection based on RPCSEC_GSS is
      treated as a version-specific feature and will continue to be
      described by RFC8881[8] or its successors.  Also, it needs to be
      noted that the use of state protection was not discussed in
      RFC7530 [6].

3.3.  Handling of Minor-version-specific features

   There are a number of areas in which security features differ among
   minor versions, as discussed below.  In some cases, a new feature
   requires specific security support while in others one version will
   have a new feature related to enhancing the security infrastructure.

   How such features are dealt with in this document depends on the
   specific feature.

   *  In addition to SECINFO, whose enhanced description appears in this
      document, NFSv4.1 added a new SECINFO_NONAME operation, useful for
      pNFS file as well as having some non-pNFS uses.

      While the enhanced description of SECINFO mentions SECINFO_NONAME,
      this is handled as one of a number of cases in which the
      description has to indicate that different actions need to be
      taken for different minor versions.







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      The definitive description of SECINFO_NONAME, now appearing in
      RFC8881 [8] needs to be modified to match the description of
      SECINFO appearing in this document.  It is expected that this will
      be done as part of the rfc5661bis process.

      The security implications of the security negotiation facilities
      as a whole will be addressed in the security considerations
      section of this document.

   *  The OPTIONAL pNFS feature added in NFSv4.1 has its own security
      needs which parallel closely those of non-pNFS access but are
      distinct, especially when the storage access protocol used are not
      RPC protocols.  As a result, these needs and the means to satisfy
      them are not discussed in this document.

      The definitive description of pNFS security will remain in RFC8881
      [8] and its successors (i.e. the rfc5661bis document suite).
      However, because pNFS security relies heavily on the
      infrastructure discussed here, it is anticipated that the new
      treatment of pNFS security will deal with many matters by
      referencing the overall NFS security document.

      The security considerations section of rfc5661bis will deal with
      pNFS security issues.

   *  In addition to the state protection facilities described in this
      document, NFS has another set of such facilities that are only
      implemented in NFSv4.1.

      While this document will discuss the security implications of
      protection against state modification, it will not discuss the
      details of the NFSv4.1-specific features to accomplish it.

   *  The additional NFSv4.1 acl attributes, sacl and dacl, are
      discussed in this document, together with the ACL inheritance
      features they enable.

      As a result, the responsibility for the definitive description of
      these attributes will move to overall NFS security document, with
      the fact that they are not available in NFSv4.0 duly noted.  While
      these attributes will continue to be mentioned in NFSv4.1
      specification documents, the detailed description appearing in
      RFC8881 [8] will be removed in successor documents.

   *  Both NFSv4.0 and NFSv4.1 specifications discussed the coordination
      of the values the mode and ACL-related attributes.  While the
      treatment in RFC8881 [8] is more detailed, the differences in the
      approaches are quite minor.



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      [Consensus Item #25a]: This document will provide a unified
      treatment of these issues, which will note any differences of
      treatment that apply to NFSv4.0.  Changes applying to NFSv4.2 will
      also be noted.

      As a result, this document will override the treatment within
      RFC7530 [6] and RFC8881 [8].  This material will be removed in the
      rfc5661bis document suite and replaced by a reference to the
      treatment in the NFSv4 security RFC.

   *  The protocol extension defined in RFC8257 [15], now part of
      NFSv4.2, is also related to the issue of co-ordination of acl and
      mode attributes and will be discussed in that context.

      Nevertheless, the description in RFC8257 [15] will remain
      definitive.

   *  The NFSv4.1 attribute set-mode-masked attribute is mentioned
      together with the other attributes implementing the POSIX
      authorization model.

      Because this attribute. while related to security, does not
      substantively modify the security properties of the protocol, the
      full description of this attribute, will continue to be the
      province of the NFSv4.1 specification proper.

   *  There is a brief description of the v4.2 Labelled NFS feature in
      Section 10.  Part of that description discusses the limitations in
      the description of that feature within RFC7862 [10].

      Because of some limitations in the description, it is not possible
      to provide an appropriate security considerations section for that
      feature in this document.

      As a result, the responsibility for providing an appropriate
      Security Considerations section remains, unrealized for now, with
      the NFSv4.2 specification document and its possible successors.

3.4.  Features Needing Extensive Clarification

   For a number of authorization-related features, the existing
   descriptions are inadequate for various reasons:

   *  In the description of the the use of the mode attribute in
      implementing the POSIX-based authorization model, critical pieces
      of the semantics are not mentioned, while, ironically, the
      corresponding semantics for ACL-based authorization are discussed.




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      This includes the authorization of file deletion and of
      modification of the mode, owner and owner-group attributes.  For
      ACL-based authorization, there is a an attempt to provide the
      description.

      The situation for authorization of RENAME is similar, although, in
      this case, the corresponding semantics for the ACL case are also
      absent.

   *  The description of authorization for ACLs is more complete but it
      needs further work, because the previous specifications make
      extensive efforts, in my view misguided, to allow an enormous
      range of server behaviors, making it hard for a client to know
      what the effect of many actions, and the corresponding security-
      related consequences, might be.

      Troublesome in this connection are the discussion of ACE mask bits
      which essentially treats every mask bit, as its own OPTIONAL
      feature, the use of "SHOULD" and "SHOULD NOT" in situations which
      it is unclear what valid reasons to ignore the recommendation
      might be, and cases in which it is is simply stated that some
      servers do some particular thing, leaving the unfortunate
      implication that clients need to be prepared for a vast range of
      server behaviors.

      This approach essentially treated ACLs in a manner appropriate to
      an experimental feature.

   *  Similar issues apply to descriptions related to the need to co-
      ordinate the values of the mode attribute and the ACL-related
      attributes.

      Although the need for such coordination is recognized.  There are
      multiple modes of mapping an ACL to a corresponding mode together
      with multiple sources of uncertainty about the reverse mapping.

      In addition, certain of the mapping algorithms have flaws in that
      their behavior under unusual circumstances give results that
      appear erroneous.

   Dealing with these issues is not straightforward, because the
   appropriate resolution will depend on:

   *  The actual existence of server implementations with non-preferred
      semantics.






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      In some cases in which "SHOULD" was used, there may not have been
      any actual severs choosing to ignore the recommendation,
      eliminating the possibility of compatibility issues when changing
      the "SHOULD" to a formulation that restricts the server's choices.

   *  The difficulty of modifying server implementations to eliminate or
      narrow the effect of non-standard semantics.

      One aspect of that difficulty might be client or application
      expectations based on existing server implementations, even if the
      existing specifications give the client no assurance that that
      server's behavior is mandated by the standard.

   *  Whether the existing flaw in some existing recommended actions to
      be performed by the server is sufficiently troublesome to justify
      changing the specification at this point.

   This sort of information will be used in deciding whether to:

   *  Narrow the scope of allowable server behavior to those actually
      used by existing severs.

   *  Limiting the negative effects of unmotivated SHOULDs by limiting
      valid reasons to ignore the recommendation to the difficulty of
      changing existing implementations.

      This would give significant guidance to future implementations,
      while forcing clients to live with the uncertainty about existing
      servers

   *  Tie a more restricted set of semantics to nominally unrelated
      OPTIONAL features such as implementation of dacl and sacl.

      This would provide a way to allow the development of newer servers
      to proceed in a way that

   *  Provide means that clients to use to determine, experimentally,
      what semantics are provided by the server.

      Would need to be supported by a requirement/assurance that a
      server behave uniformly, at least within the scope of a single
      file system.

   *  Allow the provision of other ways for the client to know the
      semantics choices made by the server.






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   Despite the difficulty of addressing these issues, if the protocol is
   to be secure and ACLs are to be widely available, these problems have
   to be addressed.  While there has not been significant effort to
   provide client-side ACL APIs and there might not be for a while, we
   cannot have a situation if which the security specification makes
   that development essentially impossible.

3.5.  Process Going Forward

   Because of the scope of this document, and the fact that it is
   necessary to modify previous treatments of the subject previously
   published as Proposed Standards, it is necessary that the process of
   determining whether there is Working Group Consensus to submit it for
   publication be more structured than that used for the antecedent
   documents.

   In order to facilitate this process, the necessary changes which need
   to be made, beyond those clearly editorial in nature, are listed in
   Appendix B.  As working group review and discussion of this document
   and its successors proceeds, there will be occasion to discuss each
   of these changes, identified by the annotations described in
   Section 1.2.

   Based on working group discussions, successive document versions will
   do one of the following for some set of consensus items:

   *  Deciding that the replacement text is now part of a new working
      group consensus.

      When this happens, future drafts of the document will be modified
      to remove the previous treatment, treat the proposed text as
      adopted, and remove Author Asides or replace them by new text
      explaining why a new treatment of the matter has been adopted or
      pointing the reader to an explanation in Appendix A.

      At this point, the consensus item will be removed from Appendix B
      and an explanation for the change will be added to Appendix A.

   *  Deciding that the general approach to the issue, if not
      necessarily the specific current text has reached the point of
      "general acceptance" as defined in Appendix B

      In this case, to facilitate discussion of remaining issues, the
      text of the document proper will remain as it is.







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      At this point, the consensus item will be marked within the table
      in Appendix B as having reached general acceptance, indicating the
      need to prioritize discussion in the next document cycle, aimed at
      arriving at final text to address the issue.

      In addition, an explanation for the change will be added to
      Appendix A.

   *  Deciding that modification of the existing text is necessary to
      facilitate eventual consensus, based on the working group's input.

      In this case, there will be changes to the document proper in the
      next draft revision.  In some cases, because of the need for a
      coherent description, text outside the consensus item may be
      affected.

      The table in Appendix B will be updated to reflect the new item
      status while Appendix A is not expected to change.

   *  Deciding that the item is best dropped in the next draft.

      In this case, the changes to the document proper will be the
      inverse of those when a change is accepted by consensus.  The
      previous treatment will be restored as the current text while the
      proposed new text will vanish from the document at the next draft
      revision.  The Author Aside will be the basis for an explanation
      of the consequences of not dealing with the issue.

      At this point, the consensus item will be removed from Appendix B.

   The changes that the working group will need to reach consensus on,
   either to accept (as-is or with significant modifications) or reject
   can be divided into three groups.

   *  A large set of changes, all addressing issues mentioned in
      Section 1.1, were already present in the initial I-D so that there
      has been the opportunity for working group discussion of them,
      although that discussion has been quite limited so far.

      As a result, a small set of these changes is marked, in
      Appendix B, as having reached general acceptance.

      That subset of these changes changes, together with the
      organizational changes to support them are described in
      Appendix A.1.






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   *  Another large set of changes were made in draft -02.  These mostly
      concern the issues mentioned in Section 3.4 None of these changes
      is yet considered to have reached general acceptance.

      The organizational changes to support these changes are described
      in Appendix A.2.

   *  There remain a set of potential changes for which a need is
      expected but for which no text is yet available.

      Such changes have associated Author Asides and are listed in
      Appendix B.

      The text for these changes is expected to be made available in
      future document revisions and they will be processed then, in the
      same way as other changes will be processed now.

      If and when such changes reach general acceptance, they will be
      explained in the appropriate subsection of Appendix A.

4.  Introduction to NFSv4 Security

   Because the basic approach to security issues is so similar for all
   minor versions, this document applies to all NFSv4 minor versions.
   The details of the transition to an NFSv4-wide document are discussed
   in Sections 3.2 and 3.3.

   NFSv4 security is built on facilities provided by the RPC layer,
   including various auth flavors and and other security-related
   services provided by RPC.

   [Consensus Needed, Including List (Item #1a)}: Support for multiple
   auth flavors can be provided.  Not all of these actually provide
   authentication, as discussed in Section 13.

   *  Support for RPCSEC_GSS is REQUIRED, although use of other auth
      flavors is provided for.

      This auth flavor provides for mutual authentication of the
      principal making the request and the server performing it.

      This auth flavor allows the client to request the provision of
      encryption-based services to provide privacy or integrity for
      specific requests.  Although such services are often provided, on
      a per-connectio basis, by RPC, this support is useful, when such
      services are not supported or are otherwise unavailable.





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   *  AUTH_SYS, provides identification of the principal making the
      request but SHOULD NOT be used unless the client peer sending the
      request can be authenticated and there is protection against the
      modification of the request in flight.

      Both of the above require specific RPC support such as that
      provided by RPC-with-TLS [12].

   *  AUTH_NONE does not provide identification of the principal making
      the request so would only be used for requests for which there is
      no such principal or for which it would irrelevant.

      The restrictions mentioned above for AUTH_SYS apply to AUTH_NONE
      as well.

   [Consensus Needed, Including List (Item #1a)}: There are important
   services that can be provided by RPC, when RPC-with-TLS or similar
   transport-level facilities are available.

   *  Such services can provide data security to all requests on the
      connection.  This is to be preferred to data security provided by
      the RPC auth flavor because it provides protection to the request
      headers, because it applies to requests using all authentication
      flavors, and because it is more likely to be offloadable.

   *  These services can authenticate the server to the client peer.
      This is desirable since that authentication applies even when
      AUTH_SYS or AUTH_NONE is used.

   *  The client-peer can be authenticated to the server at the time the
      connection is set up.  This is essential to allow AUTH_SYS to be
      used with a modicum of security, based on the server's level of
      trust with regard to the client peer.

   [Consensus Needed (Item #2a)}: Because important security-related
   services depend on the security services, rather the auth flavor, the
   process of security negotiation, described in Section 15, has been
   extended to provide for the negotiation of a appropriate connection
   characteristics at connection time if the server's policy limits the
   range of transports being used and also when use of a particular auth
   flavor on a connection with inappropriate security characteristics
   causes NFS4ERR_WRONGSEC to be returned,

   [Consensus Needed (Item #1a)}: The authentication provided by RPC, is
   used to provide the basis of authorization, which is discussed in
   general in Section 6.  This includes file access authorization,
   discussed in Sections 7 through 9 and state modification
   authorization, discussed in Section 11



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   File access is controlled by the server support for and client use of
   certain recommended attributes, as described in Section 7.1.
   Multiple file access model are provided for and the considerations
   discussed in Section 8 apply to all of them.

   *  The mode attribute provides a POSIX-based authorization model, as
      described in Section 7.3

   *  The ACL-related attributes acl, sacl, and dacl (the last two
      introduced in NFSv4.1) support a finer grained authorization model
      and provide additional securiy-related services.  The structure of
      ACLs is described in Section 5.

      The ACL-based authorization model is described in Section 7.4

      The additional security-related services are described in
      Section 12.  These also rely on the authentication provided by
      RPC.

   *  Because there are two different approaches to file-access
      authorization, servers might implement both, in which case the
      associated attributes need to be coordinated as described in
      Section 9.

   *  NFSv4.2 provides an file access authorization model oriented
      toward Mandatory Access Control.  It is described in Section 10.
      For reasons described there, its security properties are hard to
      analyze in detail and this document will not consider it as part
      of the NFSv4 threat analysis.

   Authorization of locking state modification is discussed in
   Section 11.  This form of authorization relies on the authentication
   of the client peer as opposed to file access authorization, which
   relies on authentication of the client principal.

4.1.  NFSv4 Security Terminology

   In this section, we will define the security-related terminology used
   in this document.  This is particularly important for NFSv4 because
   many of the terms terms related to security in previous specification
   may be hard to understand because their meanings have changed or have
   been used inconsistently, resulting in confusion.

   The following terms are listed in alphabetical order:







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   *  "Access Control" denotes any control implemented by a server peer
      to limit or regulate file system access to file system objects.
      It includes but is not limited to authorization decisions.  Access
      control features can be divided into those wich are "Dicretionary"
      or "Mandatory" as described below.

   *  "ACL" or "Access Control List" denotes a structure used, like the
      mode (see below), to defines the privileges that individual users
      have with respect to a given file.  These structures provide more
      options than modes with regard to the association of privileges
      with specific users or group and often provide a finer-graned
      privilege structure as well.  This specification will have need to
      refer to two types of ACLs.

      The ACLs present in the acl, sacl, and dacl attributes are called
      "NFSv4 ACLs".  This ACL format, was modeled on the the semantics
      of the SMB ACL format which provide a privilege model
      substantially finer-grained than that provided by POSIX modes.

      [Consensus needed (Item #56a)]: Another ACL type derives from an
      attempt to define, within POSIX, a UNIX-oriented approach to ACLs
      which was published as a draft (POSIX 1003.1e draft 17), but
      subsequently withdrawn.  Despite the withdrawal of this draft and
      the working group's decision to adopt a native NFsv4 ACL format
      based on SMB ACLs, this document will have to discuss these ACLs,
      which we will term "UNIX ACLs" because many server file systems do
      not support the finer-grained privilege model needed by the the
      NFSv4 ACL model and because many clients are built on systems
      whose only ACL-related API is based on the UNIX ACL model.

   *  "authentication" refers to a reliable determination that one
      making a request is in fact who he purports to be.  Often this
      involves cryptographic means of demonstrating identity.

      This is to be distinguished from "identification" which simply
      provides a specified identity without any evidence to verify that
      the identification is accurate.

      In the past, these terms have been confused, most likely because
      of confusion engendered by th use of the term "authentication
      flavor" including flavors for which only identification is
      provided or which do not provide even identification.

   *  "authorization" refers to the process of determining whether a
      request is authorized, depending on the resources (e.g. files) to
      be accessed, the identity of the entity on whose behalf the
      request was issued, and the particular action to be performed.




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      Depending on the type of request, the entity whose identity is
      referenced can be a user, a peer, or a combination of both.

      Authorization is distinct from authentication.  However,
      performing authorization based on identities which have not been
      authenticated makes secure operation impossible since use of
      unauthenticated identities allows acceptance of requests that are
      not properly authorized if the sender has the ability, as it
      typically does, to pretend to be an authorized user/peer.

   *  "client" refers to the entity responsible for setting up a
      connection.  In most cases the client and the requester reside on
      the same node but this not always the case for NFSv4 because of
      the possibility of callback requests in which the server makes
      some request of the client.

   *  "confidentiality" refers to the assurance provided, typically
      through encryption, that the contents of requests and responses
      are not inadvertently disclosed to unauthorized parties.

   *  "Discretionary Access Control" denotes forns of acces control,
      that rely on a user, such as the owner, specifyling the privileges
      that varous users are to have.

   *  "Mandatory Access Control" denotes forms of access control that
      reflecct choices made by the server peer and based on its policy
      and that are typicall based on the identity of the client peer
      rather than the specfic user making a request.  While such access
      control is discussedin this document, it is important to note that
      many forms of mandatory access control are discussed by other
      NFsv4 documents and that there forms that are not standardized.

   *  [Consensus Needed, Entire Bulleted Item (Item #21a)]: "Mode"
      designates a set of twelve flag bits used by POSIX-based systems
      to control access to the file with which it is associated.  In
      NFSv4, there are represented by an OPTIONAL attribute, which, in
      practical terms, is always supported by servers and expected by
      clients.

      The three high-order flags are generally accessed only by the
      client while low-order bits are divided into three three-bit
      fields, which give, in order of decreasing numeric value, the
      privileges to be associated with, the owner of the file, other
      users in the group owning the file, and users not in the above two
      categories.






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      In most cases, the privileges associated with each successive
      group are no greater than those for the previous group.  Modes
      whose privileges are of this form are referred to as "forward-
      slope modes" because the privilege level proceeds downward as
      successive groups of users are specified.  Cases in which the
      contrary possibility is realized are referred to as "reverse-slope
      modes".

   *  "peer" refer to the entity which is charged with requesting or
      performing a specified request as opposed to the entity on whose
      behalf the request is requested or performed, the principal;

   *  "principal" refers to the specific entity 9e.g. user) on whose
      behalf a request is being made.

   *  "privacy", has in the past been used to refer, to what is now
      referred to as "confidentiality".

      over time, this usage has changed so that the word most often
      refers to applicability of data to a single individual and
      person's right to prevent its unauthorized disclosure

      As a result, many references to "privacy" in previous are no
      longer appropriate and really refer to confidentiality.

      The NFSv4 protocol has no way to determine whether particular data
      items raise privacy concerns (In the new sense).  NFSv4 provides
      confidentiality whatever type of data is being accessed so that
      private data is kept private.

   *  "integrity" refers to the assurance that data in a request has not
      been modified in the process of transmission.  Such an assurance
      is generally provided b means of a cryptographic hash of the
      requests or response.

   *  "requester" is the entity making a request, whether that entity is
      on the client-side, as it most often is (forward-direction
      request) or the server side, in th case of callback (reverse-
      direction requests)

   *  "responder" is the entity performing a request, whether that
      entity is on the server side, as it most often is (forward-
      direction request) or the client side, in the case of callbacks
      (reverse-direction requests.







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   *  "server" refers to the entity to which the client connects.  In
      most cases the client and the responder reside on the same node
      but this not always the case for NFSv4 because of the possibility
      of callback requests in which the server makes some request of the
      client.

4.2.  NFSv4 Security Scope Limitations

   This document describes the security features of the NFSv4 protocol
   and is unable to address security threats that are inherently outside
   the control of the protocol implementors.  Such matters as out of
   this document's scope.

   As a way of clarifying the threats that this document, and the threat
   analysis in Section 17.4 can and cannot deal with, we list below the
   potential threats discussed Section 3.1 of [14] and review how, if at
   all, it is discussed in the current document.  In cases in which the
   threat is dealt with in this document, distinctions are to be made
   between cases in which the issues have been dealt with directly or
   have been delegated to a lower layer on which the protocol is built
   and whether the issue has been addressed by the changes to NFSv4
   security made by this document.

   *  Regarding the possibility of "Credential Theft or Compromise",
      this is not a matter that the NFSv4 protocols concern themselves
      with or can address directly, despite its importance for security.
      Depending on the auth flavor chosen, either the client (for
      AUTH_SYS) or a third-party (for RPCSEC_GSS), usually Kerberos,
      will be responsible for credential verification.

      Since experience has shown that credential compromise (e.g.
      through "phishing" attacks) is a common occurrence, this problem
      cannot be ignored, even though it the NFSv4's reliance on RPC
      facilities for authentication might be thought to make it out-of-
      scope as it would be RPC if had an effective solution to the
      issue.  However, that the urgency of the situation this issue is
      such that will be discussed in Section 17.4.2, even though no
      definitive solutions to this issue are likely before this document
      is completed and published.

      Regardless of such issues, the likelihood of such compromise has
      had a role in decisions made regarding the acceptance and use of
      "superuser" credentials.  The possibility of such compromise is
      also relevant to implementation of means to synchronize
      credentials when they are managed by the client, as described in
      Section 17.4.6.1





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   *  Regarding the possibility of "Cracking Encryption", prevention of
      this is responsibility of the NFSv4 protocols but it is one which
      has been delegated to RPC, so that its discussion in Security
      Considerations will rely on ..... and ... to manage encryption so
      as to limit the possibility of such unwanted encryption key
      discovery.

   *  Regarding the possibility of "Infection of Malware and
      Ransomware", NFSv4 has no direct role in preventing such
      infection, but does have an important role in limiting its
      consequences, by limiting the the ability of Malware to access or
      modify data, through the file access authorization model supported
      by NFSv4 to limit access to authorized users.  Of course, malware
      will be able to execute on behalf of the user mistakenly invoking
      it but the authorization model will server to limit the potential
      damage.

      The possibility of vertical privilege escalation is of concern as
      regard the possible elevation to "superuser" privileges.  For this
      reason, this document recommends that any such escalation not be
      effective on the server, even if it happens on local clients for
      which NFSv4 has no role.

      Execution of a ransomeware-based attack requires the attacker to
      have the ability to read existing data and replacing it with an
      encrypted version together with the ability to temporarily hide
      the encryption from ongoing operations by intercepting requests to
      read encrypted data and substitute the unencrypted data.

   *  Regarding the possibility of "Backdoors and Unpatched
      Vulnerabilities", it needs to be noted that the NFSv4 protocols do
      not specify any backdoors even though it is possible that might
      choose to provide such backdoors.  Since it is not practical to
      specifically prohibit the existence of such backdoors nor would
      they be enforceable if written, this document will not attempt to
      do so.  Instead, Section 17.2.3 will note the possibility of such
      backdoors and recommend against any such implementation, and
      include implementations containing backdoors in the category of
      insecure use that will not be dealt with in Section 17.4.

      Although it is expected that vulnerabilities will be due to
      incorrect implementations and thus outside the scope of this
      document, the possibility of a protocol design errors cannot be
      excluded.  In dealing with such eventualities, it is likely that
      complete remediation would require co-ordinated changes on the
      client and server





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   *  Regarding the possibility of "Privilege Escalation", NFSv4 has
      dealt with the possibility of vertical escalation by not allowing
      a client-local escalation to superuser privileges to be effective
      on the server.

      With regard to horizontal "escalation", NFSv4 provides for the use
      of various means RPC authentication of principals but relies on
      the client operating system to make sure that one user principal
      cannot masquerade as another.

   *  Regarding the possibility of "Human Error and Deliberate
      Misconfiguration", the approach taken is to limit the need for the
      server to make complicated decisions regarding the security
      requirements of each section of its namespace, with many
      opportunities for misconfiguration, if the chosen security
      requirements are insufficiently restrictive.  This is in contrast
      to previous specifications which made such configuration the
      centerpiece of the security approach.

      Although it is possible to create configurations where certain
      data, generally publicly accessible, are to be made available
      without encryption, this is expected to be a rarely used option
      with the possibility of in-transit modification kept in mind
      before adopting such use.

   *  Regarding the possibility of "Physical Theft of Storage Media",
      this a matter which, while of concern to those deploying NFSv4
      server, will be considered out-of-scope since there is nothing
      that the protocol could do to deal with this threat.

   *  Regarding the possibility of "Network Eavesdropping", when the
      protocol implementation follows the recommendations in this
      document, the protocol's use of RPC facilities is designed,
      through the consistent use of encryption to make it difficult for
      an attacker to have access to the data being transmitted, to
      modify it, or inject requests into an existing data stream.

      The possibility of an attacker with access to the network creating
      a new connection is best considered as a case of the attacker
      pretending to be a client and is addressed in Section 17.4.3.

   *  Regarding the possibility of "Insecure Images, Software and
      Firmware", while attention to such matters is important for those
      deploying NFSv4, it is important to note that these are matters
      outside the control the NFSv4, which has to assume that the
      infrastructure it is built is working properly.  As a result, this
      document will not deal with the possibility of such threats.




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5.  Structure of NFSv4 Access Control Lists

   NFSv4 Access Control Lists consisting of multiple Access Control
   Elements, while originally designed to support a more flexible
   authorization model, have multiple uses within NFSv4, with the use of
   each element depending on its type, as defined in Section 5.2

   *  They may be used to provide a more flexible authorization model as
      described in Section 7.4.  This involves use of Access Control
      Entries of the ALLOW and DENY types.

   *  They may be used to provide the security-related services
      described in Section 12.  This involves use of Access Control
      Entries of the AUDIT and ALARM types.

   Subsections of this section define the structure of NFSv4 ACLs and
   discuss ACL-related matters that apply to multiple uses of NFSv4
   ACLs, including the definitions of the acl and aclsupport attributes.

   Matters that relate to only a single one of these use classes,
   including the definition of the NFSv4.1-specific attributes dacl and
   sacl, are discussed in subsections of Sections 7.4 or 12.

5.1.  Access Control Entries

   The attributes acl, sacl (v4.1 only) and dacl (v4.1 only) each
   contain an array of Access Control Entries (ACEs) that are associated
   with the file system object.  The client can set and get these
   attributes attribute, the server is responsible for using the ACL-
   related attributes to perform access control.  The client can use the
   OPEN or ACCESS operations to check access without modifying or
   explicitly reading data or metadata.

   The NFS ACE structure is defined as follows:

   typedef uint32_t        acetype4;

   typedef uint32_t aceflag4;

   typedef uint32_t        acemask4;

   struct nfsace4 {
           acetype4        type;
           aceflag4        flag;
           acemask4        access_mask;
           utf8str_mixed   who;
   };




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5.2.  ACE Type

   The constants used for the type field (acetype4) are as follows:

   const ACE4_ACCESS_ALLOWED_ACE_TYPE      = 0x00000000;
   const ACE4_ACCESS_DENIED_ACE_TYPE       = 0x00000001;
   const ACE4_SYSTEM_AUDIT_ACE_TYPE        = 0x00000002;
   const ACE4_SYSTEM_ALARM_ACE_TYPE        = 0x00000003;

   All four are permitted in the acl attribute.  For NFSv4.1 and beyond,
   only the ALLOWED and DENIED types may be used in the dacl attribute,
   and only the AUDIT and ALARM types.x used in the sacl attribute.







































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   +==============================+==============+====================+
   | Value                        | Abbreviation | Description        |
   +==============================+==============+====================+
   | ACE4_ACCESS_ALLOWED_ACE_TYPE | ALLOW        | Explicitly grants  |
   |                              |              | the ability to     |
   |                              |              | perform the action |
   |                              |              | specified in       |
   |                              |              | acemask4 to the    |
   |                              |              | file or directory. |
   +------------------------------+--------------+--------------------+
   | ACE4_ACCESS_DENIED_ACE_TYPE  | DENY         | Explicitly denies  |
   |                              |              | the ability to     |
   |                              |              | perform the action |
   |                              |              | specified in       |
   |                              |              | acemask4 to the    |
   |                              |              | file or directory. |
   +------------------------------+--------------+--------------------+
   | ACE4_SYSTEM_AUDIT_ACE_TYPE   | AUDIT        | Log (in a system-  |
   |                              |              | dependent way) any |
   |                              |              | attempt to         |
   |                              |              | perform, for the   |
   |                              |              | file or directory, |
   |                              |              | any of the actions |
   |                              |              | specified in       |
   |                              |              | acemask4.          |
   +------------------------------+--------------+--------------------+
   | ACE4_SYSTEM_ALARM_ACE_TYPE   | ALARM        | Generate an alarm  |
   |                              |              | (in a system-      |
   |                              |              | dependent way) any |
   |                              |              | attempt to         |
   |                              |              | perform, for the   |
   |                              |              | file or directory, |
   |                              |              | any of the actions |
   |                              |              | specified in       |
   |                              |              | acemask4.          |
   +------------------------------+--------------+--------------------+

                                 Table 1

   The "Abbreviation" column denotes how the types will be referred to
   throughout the rest of this document.

5.3.  ACE Access Mask

   The bitmask constants used for the access mask field of the ACE are
   as follows:





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   const ACE4_READ_DATA            = 0x00000001;
   const ACE4_LIST_DIRECTORY       = 0x00000001;
   const ACE4_WRITE_DATA           = 0x00000002;
   const ACE4_ADD_FILE             = 0x00000002;
   const ACE4_APPEND_DATA          = 0x00000004;
   const ACE4_ADD_SUBDIRECTORY     = 0x00000004;
   const ACE4_READ_NAMED_ATTRS     = 0x00000008;
   const ACE4_WRITE_NAMED_ATTRS    = 0x00000010;
   const ACE4_EXECUTE              = 0x00000020;
   const ACE4_DELETE_CHILD         = 0x00000040;
   const ACE4_READ_ATTRIBUTES      = 0x00000080;
   const ACE4_WRITE_ATTRIBUTES     = 0x00000100;
   const ACE4_WRITE_RETENTION      = 0x00000200;
   const ACE4_WRITE_RETENTION_HOLD = 0x00000400;

   const ACE4_DELETE               = 0x00010000;
   const ACE4_READ_ACL             = 0x00020000;
   const ACE4_WRITE_ACL            = 0x00040000;
   const ACE4_WRITE_OWNER          = 0x00080000;
   const ACE4_SYNCHRONIZE          = 0x00100000;

   Note that some masks have coincident values, for example,
   ACE4_READ_DATA and ACE4_LIST_DIRECTORY.  The mask entries
   ACE4_LIST_DIRECTORY, ACE4_ADD_FILE, and ACE4_ADD_SUBDIRECTORY are
   intended to be used with directory objects, while ACE4_READ_DATA,
   ACE4_WRITE_DATA, and ACE4_APPEND_DATA are intended to be used with
   non-directory objects.

5.4.  Uses of Mask Bits

   [Author Aside]: Because this section has been moved to be part of a
   general description of ACEs, not limited to authorization, the
   descriptions no longer refer to permissions but rather to actions.
   This is best considered a purely editorial change, but, to allow for
   possible disagreement on the matter, it will be considered, here and
   in Appendix B, as consensus item #3.

   [Author Aside]: In a large number of places, SHOULD is used
   inappropriately, since there appear to be no valid reasons to allow a
   server to ignore what might well be a requirement.  Such changes are
   not noted individually below.  However, they will be considered, here
   and in Appendix B, as consensus item #4a.

   [Author Aside}: In a significant number of cases the ACCESS operation
   is not listed as a operation affected by the mask bit.  These
   additions are not noted individually below.  However, they will be
   considered, here and in Appendix B, as consensus item #5a.




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   [Author Aside, Including List]: In a number of cases, there are
   additional changes which go beyond editorial or arguably do so.
   These will be marked as their own consensus items usually with an
   accompanying author aside but without necessarily citing the previous
   treatment.  These include:

   *  Revisions were necessary to clarify the relationship between
      READ_DATA and EXECUTE.  These are part of consensus item #7a.

   *  Revisions were necessary to clarify the relationship between
      WRITE_DATA and APPEND_DATA.  These are part of consensus item #8a.

   *  Clarification of the handling of RENAME by ADD_SUBDIRECTORY.  This
      is part of consensus item #9a.

   *  Revisions in handling of the masks WRITE_RETENTION and
      WRITE_RETENTION_HOLD.  These are parts of consensus items #10a.

   [Author Aside]: Because of the need to address sticky-bit issues as
   part of of the ACE mask descriptions, it is appropriate to introduce
   the subject here.

   [Consensus Item (Item #6a)]: Despite the fact that NFSv4 ACLs and
   mode bits are separate means of authorization, it has been necessary,
   even if only for the purpose of providing compatibility with earlier
   implementations, to introduce the issue here, since reference to this
   mode bit are necessary to resolve issues regard directory entry
   deletion, as is done in Section 5.6.

   [Consensus Item, Including List (Item #6a): The full description of
   the role of the sticky-bit appears in Section 7.3.1.  In evaluating
   and understanding the relationship between the handling of this bit
   when NFSv4 ACLs are used and when they are not, the following points
   need to be kept in mind:

   *  This is troublesome in that it combines data normally assigned to
      two different authorization models and breaks the overall
      architectural arrangement in which the mask bits represent the
      mode bits but provide a finer granularity of control.

   *  It might have been possible to conform to the existing
      architectural model if a new mask bit were created to represent to
      directory sticky bit.  It is probably too late to so now, even
      though it would be allowed as an NFSv4.2 extension.







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   *  The new treatment in Section 5.6 is more restrictive than the
      previous one appearing in Section 5.6.1.  This raises potential
      compatibility issues since the new treatment, while designed to
      address the same issues was designed to match existing Unix
      handling of this bit.

   *  This handling initially addresses REMOVE and does not address
      directory sticky bit semantics with regard to RENAME.  Whether it
      will do so is still uncertain.

   *  The handling of this mode bit was not documented in previous
      specifications.  However, there is a preliminary attempt to do so
      in Section 7.3.1.  The reason for doing so, is that given the Unix
      orientation of the mode attribute, it is likely that servers
      currently implement this, even though there is no NFSv4
      documentation of this semantics

      This treatment needs to be checked for compatibility issues and
      also to establish a model that we might adapt to the case of NFSv4
      ACLs.

   *  In the long term, it would make more sense to allow the client
      rather than the server to have the primary role in determining the
      semantics for things like this.  That does not seem possible right
      now but it is worth considering.

   ACE4_READ_DATA

      Operation(s) affected:
         READ

         OPEN

         ACCESS

      Discussion:
         The action of reading the data to the data of the file.

         [Previous Treatment (Item #7a)]: Servers SHOULD allow a user
         the ability to read the data of the file when only the
         ACE4_EXECUTE access mask bit is allowed.

         [Author Aside]: The treatment needs to be clarified to make it
         appropriate to all ACE types.

         [Consensus Needed (Item #7a)]: When used to handle READ or OPEN
         operations, the handling MUST be identical whether this bit,
         ACE4_EXECUTE, or both are present, as the server has no way of



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         determining whether a file is being read for execution are not.
         The only occasion for different handling is in construction of
         a corresponding mode or in responding to the ACCESS operation.

   ACE4_LIST_DIRECTORY

      Operation(s) affected:
         READDIR

      Discussion:
         The action of listing the contents of a directory.

   ACE4_WRITE_DATA

      Operation(s) affected:
         WRITE

         OPEN

         ACCESS

         SETATTR of size

      Discussion:
         [Author Aside]: Needs to be revised to deal with issues related
         to the interaction of WRITE_DATA and APPEND_DATA.

         [Consensus Needed (Item #8a)]: The action of modifying existing
         data bytes within a file's current data.

         [Consensus Needed (Item #8a)]: As there is no way for the
         server to decide, in processing an OPEN or ACCESS request,
         whether subsequent WRITEs will extend the file or not, the
         server will, in processing an OPEN treat masks containing only
         WRITE_DATA, only APPEND_DATA, or both identically.

         [Consensus Needed (Item #8a)]: In processing a WRITE request,
         the server is presumed to have the to determine whether the
         current request extends the file and whether it modifies bytes
         already in the file.

         [Consensus Needed (Item #8a)]: ACE4_WRITE_DATA is required to
         process a WRITE which spans pre-existing byte in the file,
         whether the file is extended or not.

   ACE4_ADD_FILE

      Operation(s) affected:



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         CREATE

         LINK

         OPEN

         RENAME

      Discussion:
         The action of adding a new file in a directory.  The CREATE
         operation is affected when nfs_ftype4 is NF4LNK, NF4BLK,
         NF4CHR, NF4SOCK, or NF4FIFO.  (NF4DIR is not included because
         it is covered by ACE4_ADD_SUBDIRECTORY.)  OPEN is affected when
         used to create a regular file.  LINK and RENAME are always
         affected.

   ACE4_APPEND_DATA

      Operation(s) affected:
         WRITE

         ACCESS

         OPEN

         SETATTR of size

      Discussion:
         [Author Aside]: Also needs to be revised to deal with issues
         related to the interaction of WRITE_DATA and APPEND_DATA.

         The action of modifying a file's data, but only starting at
         EOF.  This allows for the specification of append-only files,
         by allowing ACE4_APPEND_DATA and denying ACE4_WRITE_DATA to the
         same user or group.

         [Consensus Needed (Item #8a)]: As there is no way for the
         server to decide, in processing an OPEN or ACCESS request,
         whether subsequent WRITEs will extend the file or not, the
         server will treat masks containing only WRITE_DATA, only
         APPEND_DATA or both, identically.










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         [Consensus Needed (Item #8a)]: If the server is processing a
         WRITE request and the area to be written extends beyond the
         existing EOF of the file then the state of APPEND_DATA mask bit
         is consulted to determine whether the operation is permitted or
         whether alarm or audit activities are to be performed.  If a
         file has an NFSv4 ACL allowing only APPEND_DATA (and not
         WRITE_DATA) and a WRITE request is made at an offset below EOF,
         the server MUST return NFS4ERR_ACCESS.

         [Consensus Needed (Item #8a)]: If the server is processing a
         WRITE request and the area to be written does not extend beyond
         the existing EOF of the file then the state of APPEND_DATA mask
         bit does not need to be consulted to determine whether the
         operation is permitted or whether alarm or audit activities are
         to be performed.  In this case, only the WRITE_DATA mask bit
         needs to be checked to determine whether the WRITE is
         authorized.

   ACE4_ADD_SUBDIRECTORY

      Operation(s) affected:
         CREATE

         RENAME

      Discussion:
         [Author Aside]: The RENAME cases need to be limited to the
         renaming of directories, rather than saying, "The RENAME
         operating is always affected."

         [Consensus Needed (Item #9a)]: The action of creating a
         subdirectory in a directory.  The CREATE operation is affected
         when nfs_ftype4 is NF4DIR.  The RENAME operation is always
         affected when directories are renamed and the target directory
         NFSv4 ACL contains the mask ACE4_ADD_SUBDIRECTORY.

   ACE4_READ_NAMED_ATTRS

      Operation(s) affected:
         OPENATTR

      Discussion:
         The action of reading the named attributes of a file or of
         looking up the named attribute directory.  OPENATTR is affected
         when it is not used to create a named attribute directory.
         This is when 1) createdir is TRUE, but a named attribute
         directory already exists, or 2) createdir is FALSE.




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   ACE4_WRITE_NAMED_ATTRS

      Operation(s) affected:
         OPENATTR

      Discussion:
         The action of writing the named attributes of a file or
         creating a named attribute directory.  OPENATTR is affected
         when it is used to create a named attribute directory.  This is
         when createdir is TRUE and no named attribute directory exists.
         The ability to check whether or not a named attribute directory
         exists depends on the ability to look it up; therefore, users
         also need the ACE4_READ_NAMED_ATTRS permission in order to
         create a named attribute directory.

   ACE4_EXECUTE

      Operation(s) affected:
         READ

         OPEN

         ACCESS

         REMOVE

         RENAME

         LINK

         CREATE

      Discussion:
         The action of reading a file in order to execute it.

         Servers MUST allow a user the ability to read the data of the
         file when only the ACE4_EXECUTE access mask bit is allowed.
         This is because there is no way to execute a file without
         reading the contents.  Though a server may treat ACE4_EXECUTE
         and ACE4_READ_DATA bits identically when deciding to permit a
         READ or OPEN operation, it MUST still allow the two bits to be
         set independently in NFSv4 ACLs, and distinguish between them
         when replying to ACCESS operations.  In particular, servers
         MUST NOT silently turn on one of the two bits when the other is
         set, as that would make it impossible for the client to
         correctly enforce the distinction between read and execute
         permissions.




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         As an example, following a SETATTR of the following NFSv4 ACL:

            nfsuser:ACE4_EXECUTE:ALLOW

         A subsequent GETATTR of acl attribute for that file will
         return:

            nfsuser:ACE4_EXECUTE:ALLOW

         and MUST NOT return:

            nfsuser:ACE4_EXECUTE/ACE4_READ_DATA:ALLOW

   ACE4_EXECUTE

      Operation(s) affected:
         LOOKUP

      Discussion:
         The action of traversing/searching a directory.

   ACE4_DELETE_CHILD

      Operation(s) affected:
         REMOVE

         RENAME

      Discussion:
         The action of deleting a file or directory within a directory.
         See Section 5.6 for information on now ACE4_DELETE and
         ACE4_DELETE_CHILD are to interact.

   ACE4_READ_ATTRIBUTES

      Operation(s) affected:
         GETATTR of file system object attributes

         VERIFY

         NVERIFY

         READDIR

      Discussion:
         The action of reading basic attributes (non-ACLs) of a file.
         On a UNIX system, such basic attributes can be thought of as
         the stat-level attributes.  Allowing this access mask bit would



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         mean that the entity can execute "ls -l" and stat.  If a
         READDIR operation requests attributes, this mask need s to be
         be allowed for the READDIR to succeed.

   ACE4_WRITE_ATTRIBUTES

      Operation(s) affected:
         SETATTR of time_access_set, time_backup, time_create,
         time_modify_set, mimetype, hidden, system.

      Discussion:
         The action of changing the times associated with a file or
         directory to an arbitrary value.  Also permission to change the
         mimetype, hidden, and system attributes.  A user having
         ACE4_WRITE_DATA or ACE4_WRITE_ATTRIBUTES will be allowed to set
         the times associated with a file to the current server time.

   ACE4_WRITE_RETENTION

      Operation(s) affected:
         SETATTR of retention_set, retentevt_set.

      Discussion:
         The action of modifying the durations for event and non-event-
         based retention.  Also includes enabling event and non-event-
         based retention.

         [Author Aside]: The use of "MAY" here ignores the potential for
         harm which unexpected modification of the associated attributes
         might cause for security/compliance.

         [Previous Treatment]: A server MAY behave such that setting
         ACE4_WRITE_ATTRIBUTES allows ACE4_WRITE_RETENTION.

         [Consensus Needed (Items #10a, #11a)]: Options for coarser-
         grained treatment involving this mask bit are discussed in
         Section 5.5

   ACE4_WRITE_RETENTION_HOLD

      Operation(s) affected:
         SETATTR of retention_hold.

      Discussion:
         The action of modifying the administration retention holds.

         [Previous Treatment]: A server MAY map ACE4_WRITE_ATTRIBUTES to
         ACE_WRITE_RETENTION_HOLD.



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         [Author Aside]: The use of "MAY" here ignores the potential for
         harm which unexpected modification of the associated attributes
         might cause for security/compliance.

         [Consensus Needed (Items #10a, #11a)]: Options for coarser-
         grained treatment of this mask bit are discussed in Section 5.5

   ACE4_DELETE

      Operation(s) affected:
         REMOVE

      Discussion:
         The action of deleting the associated file or directory.  See
         Section 5.6 for information on how ACE4_DELETE and
         ACE4_DELETE_CHILD are to interact.

   ACE4_READ_ACL

      Operation(s) affected:
         GETATTR of acl, dacl, or sacl

         NVERIFY

         VERIFY

      Discussion:
         The action of reading the NFSv4 ACL.

   ACE4_WRITE_ACL

      Operation(s) affected:
         SETATTR of acl and mode

      Discussion:
         The action of modifying the acl or mode attributes.

   ACE4_WRITE_OWNER

      Operation(s) affected:
         SETATTR of owner and owner_group

      Discussion:
         The action of modifying the owner or owner_group attributes.
         On UNIX systems, this done by executing chown() and chgrp().

   ACE4_SYNCHRONIZE




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      Operation(s) affected:
         NONE

      Discussion:
         Permission to use the file object as a synchronization
         primitive for interprocess communication.  This permission is
         not enforced or interpreted by the NFSv4.1 server on behalf of
         the client.

         Typically, the ACE4_SYNCHRONIZE permission is only meaningful
         on local file systems, i.e., file systems not accessed via
         NFSv4.1.  The reason that the permission bit exists is that
         some operating environments, such as Windows, use
         ACE4_SYNCHRONIZE.

         For example, if a client copies a file that has
         ACE4_SYNCHRONIZE set from a local file system to an NFSv4.1
         server, and then later copies the file from the NFSv4.1 server
         to a local file system, it is likely that if ACE4_SYNCHRONIZE
         was set in the original file, the client will want it set in
         the second copy.  The first copy will not have the permission
         set unless the NFSv4.1 server has the means to set the
         ACE4_SYNCHRONIZE bit.  The second copy will not have the
         permission set unless the NFSv4.1 server has the means to
         retrieve the ACE4_SYNCHRONIZE bit.

5.5.  Requirements and Recommendations Regarding Mask Granularity

   This is new section which replaces material formerly in the previous
   section, cited here as "Previous Treatment.  The new material,
   constituting the remainder of the section is proposed to replace it.
   All such unannotated material is to be considered as part of
   consensus item #11b.

   [Previous Treatment (Item #11b)]: Server implementations need not
   provide the granularity of control that is implied by this list of
   masks.  For example, POSIX-based systems might not distinguish
   ACE4_APPEND_DATA (the ability to append to a file) from
   ACE4_WRITE_DATA (the ability to modify existing contents); both masks
   would be tied to a single "write" permission bit.  When such a server
   returns attributes to the client that contain such masks, it would
   show ACE4_APPEND_DATA and ACE4_WRITE_DATA if and only if the the
   write permission bit is enabled.

   [Previous Treatment (Item #11b)]: If a server receives a SETATTR
   request that it cannot accurately implement, it should err in the
   direction of more restricted access, except in the previously
   discussed cases of execute and read.  For example, suppose a server



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   cannot distinguish overwriting data from appending new data, as
   described in the previous paragraph.  If a client submits an ALLOW
   ACE where ACE4_APPEND_DATA is set but ACE4_WRITE_DATA is not (or vice
   versa), the server should either turn off ACE4_APPEND_DATA or reject
   the request with NFS4ERR_ATTRNOTSUPP.

   [Author Aside]: Giving servers a general freedom to to not support
   the masks defined in this section creates an unacceptable level of
   potential interoperability problems.  With regard to the specific
   example given, it is hard to imagine a server incapable of
   distinguishing a write to an offset within existing file and one
   beyond it.  This applies whether the server in question is
   implemented within a POSIX-based system or not.  It is true that a
   server that used the unmodified POSIX interface to interact with the
   file system, rather than a purpose-built VFS, would face this
   difficulty, but it not clear that that fact justifies the client
   compatibility issues that accommodating this behavior in the protocol
   would generate.  A further difficulty with the previous treatment is
   that it at variance with the approach to other cases in which ACEs
   are stored with the understanding that implementations of other
   protocols might be responsible for enforcement.

   [Author Aside]: A replacement clearly needs to be based on the idea
   that these mask bits were included in NFSv4 for a reason, and that
   exceptions need to be justified, and take interoperability issues
   into account.  The treatment below attempts to do that.

   All implementations of the acl, dacl, and sacl attributes SHOULD
   follow the definitions provided above in Section 5.4, which allow
   finer-grained control of the actions allowed to specific users than
   is provided by the mode attribute.  Valid reasons to bypass this
   guidance include the need for compatibility with clients expecting a
   coarser-grained implementation.

   The specific cases in which servers may validly provide coarser-
   grained implementations are discussed below.

   Servers not providing the mask granularity described in Section 5.4
   MUST NOT treat masks other than described in that section except as
   listed below.

   *  Servers that do not distinguish between WRITE_DATA and APPEND_DATA
      need to make it clear to clients that support for append-only
      files is not present.  To do that, requests to set NFSv4 ACLs
      where the handling for these two masks are different for any
      specified user or group are to be rejected with
      NFS4ERR_ATTRNOTSUPP.




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   *  [Consensus Needed (Items #10b, #11b)]: Servers that combine either
      of the masks WRITE_RETENTION or WRITE_RETENTION_HOLD with
      WRITE_ATTRIBUTES need to make it clear to clients that the finer-
      grained treatment normally expected is not available.  To do that,
      requests to set NFSv4 ACLs in which the two combined masks are
      explicitly assigned different permission states (i.e. one is
      ALLOWED while the other is DENIED) for any specific user or group
      are to be rejected with NFS4ERR_ATTRNOTSUPP.

   The above are in line with the requirement that attempts to set NFSv4
   ACLs that the server cannot enforce, it needs to be clear that there
   are cases in which such ACLs need to be set with the expectation that
   enforcement will be done by the local file system or by another file
   access protocol.  In particular,

   *  In handling the mask bit SYNCHRONIZE, the server is not
      responsible for enforcement and so can accept NFSv4 ACLs it has no
      way of enforcing.

   *  When mask bits refers to an OPTIONAL feature that the server does
      not support such as named attributes or retention attributes, the
      server is allowed to accept NFSv4 ACLs containing mask bits
      associated with the unimplemented feature, even though there is no
      way these cold be enforced.  The expectation is that the files
      might be accessed by other protocols having such support or might
      be copied, together with associated ACLs to servers capable of
      enforcing them.

5.6.  Handling of Deletion

   [Author Aside]: This section, exclusive of subsections contains a
   proposal for the revision of the ACL-based handling of requests to
   delete directory entries.  All unannotated material within it is to
   be considered part of consensus item #12a.

   [Author Aside]: The associated previous treatment is to be found in
   Section 5.6.1

   This section describes the handling requests of that involve deletion
   of a directory entry.  It needs to be noted that:

   *  Modification or transfer of a directory, as happens in RENAME is
      not covered.

   *  The deletion of the file's data is dealt with separately as this,
      like a truncation to length zero, requires ACE4_WRITE_DATA.





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   In general, the recognition of such an operation for
   authorization/auditing/alarm depends on either of two bits mask bits
   being set: ACE4_MASK_DELETE on the file being deleted and
   ACE4_MASK_DELETE_CHILD on the directory from which the entry is being
   deleted.

   In the case of authorization, the above applies even when one of the
   bits is allowed and the other is explicitly denied.

   [Consensus Items, Including List (#6b, #12a): When neither of the
   mask bits is set, the result is normally negative.  That is,
   permission is denied and no audit or alarm event is recognized.
   However, in the case of authorization, the server MAY make permission
   dependent on the setting of MODE4_SVTX if the mode attribute is
   supported, as follows:

   *  If that bit not set, allow the removal if and only if
      ACE4_ADD_FILE is permitted.

   *  If that bit is set, allow the removal if and only if ACE4_ADD_FILE
      is permitted and the requester is the owner of the target.

5.6.1.  Previous Handling of Deletion

   [Author Aside]: This section contains the former content of
   Section 5.6.  All unannotated paragraphs within it are to be
   considered the Previous Treatment associated with consensus item
   #12b.

   [Author Aside, Including List]: Listed below are some of the reasons
   that I have tried to replace the existing treatment rather than
   address the specific issues mentioned here and in later asides.

   *  The fact that there is no clear message about what servers are to
      do and about whether behavior clients might rely rely on.  This
      derives in turn from the use of "SHOULD" in contexts in which it
      is clearly not appropriate, combined with non-normative reports of
      what some systems do, and the statement that the approach
      suggested is a way of providing "something like traditional UNIX-
      like semantics".

   *  The complexity of the approach without any indication that there
      is a need for such complexity makes me doubtful that anything was
      actually implemented, especially since the text is so wishy-washy
      about the need for server implementation.  The probability that it
      would be implemented so widely that clients might depend on it is
      even more remote.




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   *  The fact that how audit and alarm issues are to be dealt with is
      not addressed at all.

   *  The fact that this treatment combines ACL data with mode bit
      information in a confused way without any consideration of the
      fact that the mode attribute is OPTIONAL.

   Two access mask bits govern the ability to delete a directory entry:
   ACE4_DELETE on the object itself (the "target") and ACE4_DELETE_CHILD
   on the containing directory (the "parent").

   Many systems also take the "sticky bit" (MODE4_SVTX) on a directory
   to allow unlink only to a user that owns either the target or the
   parent; on some such systems the decision also depends on whether the
   target is writable.

   Servers SHOULD allow unlink if either ACE4_DELETE is permitted on the
   target, or ACE4_DELETE_CHILD is permitted on the parent.  (Note that
   this is true even if the parent or target explicitly denies one of
   these permissions.)

   If the ACLs in question neither explicitly ALLOW nor DENY either of
   the above, and if MODE4_SVTX is not set on the parent, then the
   server SHOULD allow the removal if and only if ACE4_ADD_FILE is
   permitted.  In the case where MODE4_SVTX is set, the server may also
   require the remover to own either the parent or the target, or may
   require the target to be writable.

   This allows servers to support something close to traditional UNIX-
   like semantics, with ACE4_ADD_FILE taking the place of the write bit.

5.7.  ACE flag bits

   The bitmask constants used for the flag field are as follows:

   const ACE4_FILE_INHERIT_ACE             = 0x00000001;
   const ACE4_DIRECTORY_INHERIT_ACE        = 0x00000002;
   const ACE4_NO_PROPAGATE_INHERIT_ACE     = 0x00000004;
   const ACE4_INHERIT_ONLY_ACE             = 0x00000008;
   const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG   = 0x00000010;
   const ACE4_FAILED_ACCESS_ACE_FLAG       = 0x00000020;
   const ACE4_IDENTIFIER_GROUP             = 0x00000040;
   const ACE4_INHERITED_ACE                = 0x00000080;








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   [Author Aside]: Although there are multiple distinct issues that
   might need to be changed, in the interest of simplifying the review,
   all such issues within this section will be considered part of
   Consensus Item #13a with a single revised treatment addressing all
   the issues noted.

   [Previous Treatment]: A server need not support any of these flags.

   [Author Aside]: It is hard to understand why such broad license is
   granted to the server, leaving the client to deal, without an
   explicit non-support indication, with 256 possible combinations of
   supported and unsupported flags.  If there were specific issues with
   some flags that makes it reasonable for a server not to support them,
   then these need to be specifically noted.  Also problematic is the
   use of the term "need not", suggesting that the server does not need
   any justification for choosing these flags, defined by the protocol.
   At least it needs to be said that the server SHOULD support the
   defined ACE flags.  After all they were included in the protocol for
   a reason.

   [Previous Treatment]: If the server supports flags that are similar
   to, but not exactly the same as, these flags, the implementation may
   define a mapping between the protocol-defined flags and the
   implementation-defined flags.

   [Author Aside]: The above dealing how an implementation might store
   the bits it supports, while valid, is out-of-scope and need to be
   deleted.

   [Previous Treatment]: For example, suppose a client tries to set an
   ACE with ACE4_FILE_INHERIT_ACE set but not
   ACE4_DIRECTORY_INHERIT_ACE.  If the server does not support any form
   of ACL inheritance, the server should reject the request with
   NFS4ERR_ATTRNOTSUPP.  If the server supports a single "inherit ACE"
   flag that applies to both files and directories, the server may
   reject the request (i.e., requiring the client to set both the file
   and directory inheritance flags).  The server may also accept the
   request and silently turn on the ACE4_DIRECTORY_INHERIT_ACE flag.

   ]Author Aside]: What is the possible for justification for accepting
   a request asking you do something and then, without notice to the
   client do, something else.  I believe there is none.

   Consensus Needed (Item #13a)]: Servers SHOULD support the flag bits
   defined above as described in Section 5.8.  When a server which does
   not support all the flags bits receives a request to set an NFSv4 ACL
   containing an ACE with an unsupported flag bit set the server MUST
   reject the request with NFS4ERR_ATTRNOTSUPP.



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   Consensus Needed (Item #13a)]: The case of servers which do not
   provide support for particular flag combinations is to be treated
   similarly.  If a server supports a single "inherit ACE" flag that
   applies to both files and directories, receives a request set an
   NFSv4 ACL with ACE ACE4_FILE_INHERIT_ACE set but
   ACE4_DIRECTORY_INHERIT_ACE not set, it MUST reject the request with
   NFS4ERR_ATTRNOTSUPP.

5.8.  Details Regarding ACE Flag Bits

   ACE4_FILE_INHERIT_ACE
      Any non-directory file in any sub-directory will get this ACE
      inherited.

   ACE4_DIRECTORY_INHERIT_ACE
      Can be placed on a directory and indicates that this ACE is to be
      added to each new directory created.

      If this flag is set in an ACE in an NFSv4 ACL attribute to be set
      on a non-directory file system object, the operation attempting to
      set the ACL SHOULD fail with NFS4ERR_ATTRNOTSUPP.

   ACE4_NO_PROPAGATE_INHERIT_ACE
      Can be placed on a directory.  This flag tells the server that
      inheritance of this ACE is to stop at newly created child
      directories.

   ACE4_INHERIT_ONLY_ACE
      Can be placed on a directory but does not apply to the directory;
      ALLOW and DENY ACEs with this bit set do not affect access to the
      directory, and AUDIT and ALARM ACEs with this bit set do not
      trigger log or alarm events.  Such ACEs only take effect once they
      are applied (with this bit cleared) to newly created files and
      directories as specified by the ACE4_FILE_INHERIT_ACE and
      ACE4_DIRECTORY_INHERIT_ACE flags.

      If this flag is present on an ACE, but neither
      ACE4_DIRECTORY_INHERIT_ACE nor ACE4_FILE_INHERIT_ACE is present,
      then an operation attempting to set such an attribute SHOULD fail
      with NFS4ERR_ATTRNOTSUPP.

   ACE4_SUCCESSFUL_ACCESS_ACE_FLAG and ACE4_FAILED_ACCESS_ACE_FLAG
      The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG (SUCCESS) and
      ACE4_FAILED_ACCESS_ACE_FLAG (FAILED) flag bits may be set only on
      ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) and ACE4_SYSTEM_ALARM_ACE_TYPE
      (ALARM) ACE types.  If during the processing of the file's NFSv4
      ACL, the server encounters an AUDIT or ALARM ACE that matches the
      principal attempting the OPEN, the server notes that fact, and the



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      presence, if any, of the SUCCESS and FAILED flags encountered in
      the AUDIT or ALARM ACE.  Once the server completes the ACL
      processing, it then notes if the operation succeeded or failed.
      If the operation succeeded, and if the SUCCESS flag was set for a
      matching AUDIT or ALARM ACE, then the appropriate AUDIT or ALARM
      event occurs.  If the operation failed, and if the FAILED flag was
      set for the matching AUDIT or ALARM ACE, then the appropriate
      AUDIT or ALARM event occurs.  Either or both of the SUCCESS or
      FAILED can be set, but if neither is set, the AUDIT or ALARM ACE
      is not useful.

      The previously described processing applies to ACCESS operations
      even when they return NFS4_OK.  For the purposes of AUDIT and
      ALARM, we consider an ACCESS operation to be a "failure" if it
      fails to return a bit that was requested and supported.

   ACE4_IDENTIFIER_GROUP
      Indicates that the "who" refers to a GROUP as defined under UNIX
      or a GROUP ACCOUNT as defined under Windows.  Clients and servers
      MUST ignore the ACE4_IDENTIFIER_GROUP flag on ACEs with a who
      value equal to one of the special identifiers outlined in
      Section 5.9.

   ACE4_INHERITED_ACE
      Indicates that this ACE is inherited from a parent directory.  A
      server that supports automatic inheritance will place this flag on
      any ACEs inherited from the parent directory when creating a new
      object.  Client applications will use this to perform automatic
      inheritance.  Clients and servers MUST clear this bit in the acl
      attribute; it may only be used in the dacl and sacl attributes.

5.9.  ACE Who

   The "who" field of an ACE is an identifier that specifies the
   principal or principals to whom the ACE applies.  It may refer to a
   user or a group, with the flag bit ACE4_IDENTIFIER_GROUP specifying
   which.

   There are several special identifiers that need to be understood
   universally, rather than in the context of a particular DNS domain.

   [Author Aside, including list]: so far, so good, but the following
   problems need to be addressed:

   *  Lack of clarity about which special identifiers can be understood
      by NFSv4.

   *  Confusion of "authentication" and "identification".



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   [Previous treatment (Item #50a)]: Some of these identifiers cannot be
   understood when an NFS client accesses the server, but have meaning
   when a local process accesses the file.  The ability to display and
   modify these permissions is permitted over NFS, even if none of the
   access methods on the server understands the identifiers.

   [Consensus Needed (Item #50a)]: These identifiers, except for OWNER@,
   GROUP@, EVERONE@, cannot be reliably understood when an NFS client
   accesses the server, but might have meaning when a local process
   accesses the file or when protocols other than NFSv4 are used As a
   result, when ACEs containing these who values are encountered, the
   server is free to make its own judgment as to whether any particular
   request will be treated as matching.

   [Consensus Needed (Item #50a)]: The ability to display and modify
   these permissions is provide for by NFSv4, even though they are not
   useful when processing NFSv4 requests,


































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     +===============+==============================================+
     | Who           | Description                                  |
     +===============+==============================================+
     | OWNER         | The owner of the file.                       |
     +---------------+----------------------------------------------+
     | GROUP         | The group associated with the file.          |
     +---------------+----------------------------------------------+
     | EVERYONE      | [Previous treatment (Item #50a)]: The world, |
     |               | including the owner and owning group.        |
     |               |                                              |
     |               | [Consensus Needed (Item #50a)]: All          |
     |               | requesters, including the owner, members of  |
     |               | the owning group, and requests for which no  |
     |               | user information is available.               |
     +---------------+----------------------------------------------+
     | INTERACTIVE   | Accessed from an interactive terminal.       |
     +---------------+----------------------------------------------+
     | NETWORK       | Accessed via the network.                    |
     +---------------+----------------------------------------------+
     | DIALUP        | Accessed as a dialup user to the server.     |
     +---------------+----------------------------------------------+
     | BATCH         | Accessed from a batch job.                   |
     +---------------+----------------------------------------------+
     | ANONYMOUS     | [Consensus Needed (Item #50a)]: Accessed     |
     |               | without any authentication of the user       |
     |               | principal.                                   |
     +---------------+----------------------------------------------+
     | AUTHENTICATED | [Consensus Needed (Item #50a)]: Any          |
     |               | authenticated user (opposite of ANONYMOUS).  |
     +---------------+----------------------------------------------+
     | SERVICE       | Accessed from a system service.              |
     +---------------+----------------------------------------------+

                                 Table 2

   To avoid conflict, these special identifiers are distinguished by an
   appended "@" and will appear in the form "xxxx@" (with no domain name
   after the "@"), for example, ANONYMOUS@.

   {Previous treatment (Item #51a)]: The ACE4_IDENTIFIER_GROUP flag MUST
   be ignored on entries with these special identifiers.  When encoding
   entries with these special identifiers, the ACE4_IDENTIFIER_GROUP
   flag SHOULD be set to zero.

   [Author Aside]: I don't understand what might be valid reasons to
   ignore this or how a server would respond in the case the that it was
   ignored.




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   [Consensus Needed (Item #51a)]: The ACE4_IDENTIFIER_GROUP flag MUST
   be ignored on entries with these special identifiers.  When encoding
   entries with these special identifiers, the ACE4_IDENTIFIER_GROUP
   flag MUST be set to zero.

   It is important to note that "EVERYONE@" is not equivalent to the
   UNIX "other" entity.  This is because, by definition, UNIX "other"
   does not include the owner or owning group of a file.  "EVERYONE@"
   means literally everyone, including the owner or owning group.

5.10.  Automatic Inheritance Features

   The acl attribute consists only of an array of ACEs, but the sacl
   (Section 12.1) and dacl (Section 7.4.2) attributes also include an
   additional flag field.

   struct nfsacl41 {
           aclflag4        na41_flag;
           nfsace4         na41_aces<>;
   };

   The flag field applies to the entire sacl or dacl; three flag values
   are defined:

   const ACL4_AUTO_INHERIT         = 0x00000001;
   const ACL4_PROTECTED            = 0x00000002;
   const ACL4_DEFAULTED            = 0x00000004;

   and all other bits are to be cleared.  The ACE4_INHERITED_ACE flag
   can be set in the ACEs of the sacl or dacl (whereas it always needs
   to be cleared in the acl).

   Together these features allow a server to support automatic
   inheritance, which we now explain in more detail.

   Inheritable ACEs are normally inherited by child objects only at the
   time that the child objects are created; later modifications to
   inheritable ACEs do not result in modifications to inherited ACEs on
   descendants.

   However, the dacl and sacl provide an OPTIONAL mechanism that allows
   a client application to propagate changes to inheritable ACEs to an
   entire directory hierarchy.

   A server that supports this feature performs inheritance at object
   creation time in the normal way, and SHOULD set the
   ACE4_INHERITED_ACE flag on any inherited ACEs as they are added to
   the new object.



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   A client application such as an ACL editor may then propagate changes
   to inheritable ACEs on a directory by recursively traversing that
   directory's descendants and modifying each NFSv4 ACL encountered to
   remove any ACEs with the ACE4_INHERITED_ACE flag and to replace them
   by the new inheritable ACEs (also with the ACE4_INHERITED_ACE flag
   set).  It uses the existing ACE inheritance flags in the obvious way
   to decide which ACEs to propagate.  (Note that it may encounter
   further inheritable ACEs when descending the directory hierarchy and
   that those will also need to be taken into account when propagating
   inheritable ACEs to further descendants.)

   The reach of this propagation may be limited in two ways: first,
   automatic inheritance is not performed from any directory ACL that
   has the ACL4_AUTO_INHERIT flag cleared; and second, automatic
   inheritance stops wherever an ACL with the ACL4_PROTECTED flag is
   set, preventing modification of that ACL and also (if the ACL is set
   on a directory) of the ACL on any of the object's descendants.

   This propagation is performed independently for the sacl and the dacl
   attributes; thus, the ACL4_AUTO_INHERIT and ACL4_PROTECTED flags may
   be independently set for the sacl and the dacl, and propagation of
   one type of acl may continue down a hierarchy even where propagation
   of the other acl has stopped.

   New objects are to be created with a dacl and a sacl that both have
   the ACL4_PROTECTED flag cleared and the ACL4_AUTO_INHERIT flag set to
   the same value as that on, respectively, the sacl or dacl of the
   parent object.

   Both the dacl and sacl attributes are Recommended, and a server MAY
   support one without supporting the other.

   A server that supports both the old acl attribute and one or both of
   the new dacl or sacl attributes MUST do so in such a way as to keep
   all three attributes consistent with each other.  Thus, the ACEs
   reported in the acl attribute will be the union of the ACEs reported
   in the dacl and sacl attributes, except that the ACE4_INHERITED_ACE
   flag will be cleared from the ACEs in the acl.  And of course a
   client that queries only the acl will be unable to determine the
   values of the sacl or dacl flag fields.

   When a client performs a SETATTR for the acl attribute, the server
   SHOULD set the ACL4_PROTECTED flag to true on both the sacl and the
   dacl.  By using the acl attribute, as opposed to the dacl or sacl
   attributes, the client signals that it may not understand automatic
   inheritance, and thus cannot be trusted to set an ACL for which
   automatic inheritance would make sense.




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   When a client application queries an NFSv4 ACL, modifies it, and sets
   it again, it needs to leave any ACEs marked with ACE4_INHERITED_ACE
   unchanged, in their original order, at the end of the NFSv4 ACL.  If
   the application is unable to do this, it needs to set the
   ACL4_PROTECTED flag.  This behavior is not enforced by servers, but
   violations of this rule may lead to unexpected results when
   applications perform automatic inheritance.

   If a server also supports the mode attribute, it SHOULD set the mode
   in such a way that leaves inherited ACEs unchanged, in their original
   order, at the end of the ACL.  If it is unable to do so, it SHOULD
   set the ACL4_PROTECTED flag on the file's dacl.

   Finally, in the case where the request that creates a new file or
   directory does not also set permissions for that file or directory,
   and there are also no ACEs to inherit from the parent's directory,
   then the server's choice of ACL for the new object is implementation-
   dependent.  In this case, the server SHOULD set the ACL4_DEFAULTED
   flag on the ACL it chooses for the new object.  An application
   performing automatic inheritance takes the ACL4_DEFAULTED flag as a
   sign that the ACL is to be completely replaced by one generated using
   the automatic inheritance rules.

5.11.  Attribute 13: aclsupport

   A server need not support all of the above ACE types.  This attribute
   indicates which ACE types are supported for the current file system.
   The bit mask constants used to represent the above definitions within
   the aclsupport attribute are as follows:

   const ACL4_SUPPORT_ALLOW_ACL    = 0x00000001;
   const ACL4_SUPPORT_DENY_ACL     = 0x00000002;
   const ACL4_SUPPORT_AUDIT_ACL    = 0x00000004;
   const ACL4_SUPPORT_ALARM_ACL    = 0x00000008;

   [Author Aside]: Even though support aclsupport is OPTIONAL, there has
   been no mention of the possibility of it not being supported.

   [Consensus Needed (Item #14a)]: If this attribute is not supported
   for a server, the client is entitled to assume that if the acl
   attribute is supported, support for ALLOW and DENY ACEs is present.
   Thus, if such a server supports the the sacl attribute, clients are
   not likely to use it if aclsupport is not supported by the server.

   [Previous Treatment]: Servers that support either the ALLOW or DENY
   ACE type SHOULD support both ALLOW and DENY ACE types.





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   [Author Aside]: It needs to be made clearer what the harm is that is
   to be prevented by this.  Further if such harm exists, it is not
   clear what are the valid reasons not do this?

   [Consensus Needed (Item #15a)]: There is little point in implementing
   a server which supports either ALLOW or DENY ACE types without
   supporting both.  For reasons explained in Section 7.1 the ACL-based
   authorization cannot be used if only a single ACE type is available.

   Clients are not to attempt to set an ACE unless the server claims
   support for that ACE type.  If the server receives a request to set
   an ACE that it cannot store, it MUST reject the request with
   NFS4ERR_ATTRNOTSUPP.

   [Previous Treatment (Item #12c)]: If the server receives a request to
   set an ACE that it can store but cannot enforce, the server SHOULD
   reject the request with NFS4ERR_ATTRNOTSUPP.

   [Author Aside]: Beyond the issues with the use of SHOULD, it is
   better to centralize this material and be clearer about the whole
   issue of ACL enforcement.

   [Consensus Needed (Item #12c)]: The case of ACEs that cannot be
   enforced is similar, with the details of enforcement discussed in
   Section 5.5.

   Support for any of the ACL attributes is OPTIONAL, although
   Recommended.  However, a server (NFSv4.1 and above) that supports
   either of the new ACL attributes (dacl or sacl) MUST allow use of the
   new ACL attributes to access all of the ACE types that it supports.
   In other words, if a server which supports sacl or dacl supports
   ALLOW or DENY ACEs, then it MUST support the dacl attribute, and if
   it supports AUDIT or ALARM ACEs, then it MUST support the sacl
   attribute.

5.12.  Attribute 12: acl

   The acl attribute, as opposed to the sacl and dacl attributes,
   consists only of an ACE array and does not support automatic
   inheritance.

   The acl attribute is recommended and there is no requirement that a
   server support it.  However, when the dacl attribute is supported, it
   is a good idea to provide support for the acl attribute as well, in
   order to accommodate clients that have not been upgraded to use the
   dacl attribute.





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   [Author Aside]: Although it has generally been assumed that changes
   to sacl and dacl attributes are to be visible in the acl and vice
   versa, NFSv4.1 specification do not appear to document this fact.

   [Consensus Item, Including List (Item #16a)]: For NFSv4.1 servers
   that support Both the acl attribute and one or more of the sacl and
   dacl attributes, changes to the ACE's need to be immediately
   reflected in the other supported attributes:

   *  The result of reading the dacl attribute MUST consist of a set of
      ACEs that are exactly the same as the ACEs ALLOW and DENY ACEs
      within the the acl attribute, in the same order.

   *  The result of reading the sacl attribute MUST consist of a set of
      ACEs that are exactly the same as the ACEs AUDIT and ALARM ACEs
      within the the acl attribute, in the same order.

   *  The result of reading the acl attribute MUST consist of a set of
      ACEs that are exactly the same as the union of ACEs within the
      sacl and dacl attributes.  Two ACEs that both appear in one of the
      sacl or dacl attributes will appear in the same order in the acl
      attribute.

6.  Authorization in General

   There are three distinct methods of checking whether NFSv4 requests
   are authorized:

   *  The most important methods of authorization is used to effect
      user-based file access control, as described in Section 7.  These
      methods are often termed "Discretionary access control" because
      they rely on attributes set by particular users, to control
      acceptable file access.

      This requires the identification of the user making the request.
      Because of the central role of such access control in providing
      NFSv4 security, server implementations SHOULD NOT use such
      identifications when they are not authenticated.  In this context,
      valid reasons to do otherwise are limited to the compatibility and
      maturity issues discussed in Section 17.1.4

   *  NFSv4.2, via the labelled NFS feature, provides an additional
      potential requirement for request authorization.  The labelled NFS
      provides "Mandatory access control" not under the control of
      individual users.






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      For reasons made clear in Section 10, there is no realistic
      possibility of the server using the data defined by existing
      specifications of this feature to effect request authorization.
      While it is possible for clients to provide this authorization,
      the lack of detailed specifications makes it impossible to
      determine the nature of the identification used and whether it can
      appropriately be described as "authentication".

   *  Since undesired changes to server-maintained locking state (and,
      for NFSv4.1, session state) can result in denial of service
      attacks (see Section 17.4.7), server implementations SHOULD take
      steps to prevent unauthorized state changes.  This can be done by
      implementing the state authorization restrictions discussed in
      Section 11.  Because these restrictions apply on a per-peer basis
      rather than being affected by the identity of the user making the
      request, it is better to consider them as part of "Mandatory
      access control".

7.  User-based File Access Authorization

7.1.  Attributes for User-based File Access Authorization

   NFSv4.1 provides for multiple authentication models, controlled by
   the support for particular recommended attributes implemented by the
   server, as discussed below:

   *  Consensus Needed (Item #18a)]: The attributes owner, owning_group,
      and mode enable use of a POSIX-based authorization model, as
      described in Section 7.3.  When all of these attributes are
      supported, this authorization model can be implemented.

      Consensus Needed (Item #18a)]:When none of these attributes or
      only a proper subset of them are supported, this authorization
      model is unavailable.

   *  [Consensus Needed (Item #17a)]: The acl attribute (or the
      attribute dacl in NFSv4.1) can provide an ACL-based authorization
      model as described in Section 7.4 as long as support for ALLOW and
      DENY ACEs is provided.

      [Consensus Needed (Items #17a, #18a)]: When some of these ACE
      types are not supported or the owner or owning_group attribute is
      not supported, this authorization model is unavailable, since
      there are some modes that cannot be represented as a corresponding
      NFSv4 ACL, when using only a single ACE type.  See Section 9.2 for
      details.





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7.2.  Handling of Multiple Parallel File Access Authorization Models

   NFSv4 ACLs and modes represent two well-established models for
   specifying user-based file access permissions.  NFSv4 provides
   support for either or both depending on the attributes supported by
   the server and, in cases in which both NFSv4 ACLs and the mode
   attribute are supported, the actual attributes set for a particular
   object.

   *  [Consensus Needed (item #18b)]: When the attributes mode, owner,
      owner group are all supported, the posix-based authorization
      model, described in Section 7.3 can be used.

   *  [Consensus Needed (Items #17b, #18b)]: When the acl (or dacl)
      attribute is supported together with both of the ACE types ALLOW
      and DENY, the acl based authorization model, described in
      Section 7.4 can be used as long as the attributes owner and
      owner_group are also supported.

   [Consensus Needed (item #18b)]: While formally recommended
   (essentially OPTIONAL) attributes, it appears that the owner and
   owner_group attributes need to be available to support any file
   access authorization model.  As a result, this document will not
   discuss the possibility of servers that do not support both of these
   attributes and clients have no need to support such servers.

   When both authorization models can be used, there are difficulties
   that can arise because the ACL-based model provides finer-grained
   access control than the POSIX model.  The ways of dealing with these
   difficulties appear later in this section while more detail on the
   appropriate handling of this situation, which might depend on the
   minor version used, appears in Section 9.

   The following describe NFSv4's handling in supporting multiple
   authorization models for file access.

   *  If a server supports the mode attribute, it needs to provide the
      appropriate POSIX semantics if no ACL-based attributes have ever
      been assigned to object.  These semantics include the restriction
      of the ability to modify the mode, owner and owner-group to the
      current owner of the file.

   *  If a server supports ACL attributes, it needs to provide NFSv4 ACL
      semantics as described in this document for all objects for which
      the ACL attributes have actually been set.  This includes the ACL-
      based restrictions on the authorization to modify the mode, owner
      and owner_group attributes.




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   *  On servers that support the mode attribute, if ACL attributes have
      never been set on an object, via inheritance or explicitly, the
      behavior is to be the behavior mandated by POSIX, including the
      those provisions that restrict the setting of authorization-
      related attributes.

   *  On servers that support the mode attribute, if the ACL attributes
      have been previously set on an object, either explicitly or via
      inheritance:

      -  [Previous Treatment]: Setting only the mode attribute should
         effectively control the traditional UNIX-like permissions of
         read, write, and execute on owner, owner_group, and other.

         [Author Aside]: It isn't really clear what the above paragraph
         means, especially as it governs the handling of aces
         designating specific users and groups which are not the owner
         and have no overlap with the owning group

         {Consensus Needed (Item #19a)]: Setting only the mode
         attribute, will result in the access of the file being
         controlled just it would be if the existing acl did not exist,
         with file access decisions as to read made in accordance with
         the mode set.  The ALLOW and DENY aces in the ACL will reflect
         the modified security although there is no need to modify AUDIT
         and ALARM aces or mask bits not affected by the mode bits, such
         as SYNCHRONIZE.

         [Author Aside]: the above may need to modified to reflect the
         resolution of Consensus Item #??.

      -  [Previous Treatment]: Setting only the mode attribute should
         provide reasonable security.  For example, setting a mode of
         000 should be enough to ensure that future OPEN operations for
         OPEN4_SHARE_ACCESS_READ or OPEN4_SHARE_ACCESS_WRITE by any
         principal fail, regardless of a previously existing or
         inherited ACL.

         [Author Aside]: We need to get rid of or provide some some
         replacement for the subjective first sentence.  While the
         specific example give is unexceptionable, it raises questions
         in other cases as to what would constitutes "reasonable
         semantics".  While the resolution of such questions would be
         subject to dispute, the author believes that consensus item
         #19a deals with the matter adequately.  As a result he
         proposes, that the that this bullet be removed and the second-
         level list collapsed to single paragraph.




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   *  Although RFCs 7530 [6] and 8881 [8] present different descriptions
      of the specific semantic requirements relating to the interaction
      of mode and ACL attributes, the difference are quite small, with
      the most important ones deriving from the absence of the
      set_mode_masked attribute.  The unified treatment in Section 9
      will indicate where version-specific differences exist.

7.3.  Posix Authorization Model

7.3.1.  Attribute 33: mode

   The NFSv4.1 mode attribute is based on the UNIX mode bits.  The
   following bits are defined:

   const MODE4_SUID = 0x800;  /* set user id on execution */
   const MODE4_SGID = 0x400;  /* set group id on execution */
   const MODE4_SVTX = 0x200;  /* save text even after use */
   const MODE4_RUSR = 0x100;  /* read permission: owner */
   const MODE4_WUSR = 0x080;  /* write permission: owner */
   const MODE4_XUSR = 0x040;  /* execute permission: owner */
   const MODE4_RGRP = 0x020;  /* read permission: group */
   const MODE4_WGRP = 0x010;  /* write permission: group */
   const MODE4_XGRP = 0x008;  /* execute permission: group */
   const MODE4_ROTH = 0x004;  /* read permission: other */
   const MODE4_WOTH = 0x002;  /* write permission: other */
   const MODE4_XOTH = 0x001;  /* execute permission: other */

   Bits MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR apply to the principal
   identified by the owner attribute.  Bits MODE4_RGRP, MODE4_WGRP, and
   MODE4_XGRP apply to principals belonging to the group identified in
   the owner_group attribute but who are not identified by the owner
   attribute.  Bits MODE4_ROTH, MODE4_WOTH, and MODE4_XOTH apply to any
   principal that does not match that in the owner attribute and does
   not belong to a group matching that of the owner_group attribute.
   These nine bits are used in providing authorization information.

   [Previous Treatment]: The bits MODE4_SUID, MODE4_SGID, and MODE4_SVTX
   do not provide authorization information and do not affect server
   behavior.  Instead, they are acted on by the client just as they
   would be for corresponding mode bits obtained from local file
   systems.

   [Consensus needed (Item #6c)]: For objects which are not directories,
   the bits MODE4_SUID, MODE4_SGID, and MODE4_SVTX do not provide
   authorization information and do not affect server behavior.
   Instead, they are acted on by the client just as they would be for
   corresponding mode bits obtained from local file systems.




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   [Consensus needed (Item #6c)]: For directories, the bits MODE4_SUID
   and MODE4_SGID, do not provide authorization information and do not
   affect server behavior.  Instead, they are acted on by the client
   just as they would be for corresponding mode bits obtained from local
   file systems.  The mode bit MODE_SVTX does have an authorization-
   related role as described later in this section

   [Consensus Needed, Including List (Item #6c]): When handling RENAME
   and REMOVE operations the check for authorization depends on the
   setting of MODE_SVTX for the directory.

   *  When MODE_SVTX is not set on the directory, authorization requires
      write permission on both the file being renamed and the source
      directory.

   *  When MODE_SVTX is not on the directory, authorization requires, in
      addition that the requesting principal be the owner of the file to
      be named or removed.

   [Consensus needed (Item #6c)]: It needs to be noted that this
   approach is similar to the ACL-based approach documented in
   Section 5.6.  However there are some semantic differences whose
   motivation remains unclear and the specification does not mention
   RENAME, as it needs to.

   [Author Aside]: Bringing the above into more alignment with the ACL-
   based semantics is certainly desirable but the necessary work has not
   been done yet.  For tracking purposes, that realignment will be
   considered Consensus Item #20.

   Bits within a mode other than those specified above are not defined
   by this protocol.  A server MUST NOT return bits other than those
   defined above in a GETATTR or READDIR operation, and it MUST return
   NFS4ERR_INVAL if bits other than those defined above are set in a
   SETATTR, CREATE, OPEN, VERIFY, or NVERIFY operation.

   [Consensus Needed (Item #21b)]: As will be seen in Sections 9.3 and
   9.7, many straightforward ways of dealing with mode that work well
   with forward-slope modes need adjustment to properly deal with
   reverse-slope modes, as defined in Section 4.1

7.3.2.  NFSv4.1 Attribute 74: mode_set_masked

   The mode_set_masked attribute is a write-only attribute that allows
   individual bits in the mode attribute to be set or reset, without
   changing others.  It allows, for example, the bits MODE4_SUID,
   MODE4_SGID, and MODE4_SVTX to be modified while leaving unmodified
   any of the nine low-order mode bits devoted to permissions.



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   When minor versions other than NFSv4.0 are used, instances of use of
   the set_mode_masked attribute such that none of the nine low-order
   bits are subject to modification, then neither the acl nor the dacl
   attribute needs to be automatically modified as discussed in Sections
   9.7 and 9.9.

   The mode_set_masked attribute consists of two words, each in the form
   of a mode4.  The first consists of the value to be applied to the
   current mode value and the second is a mask.  Only bits set to one in
   the mask word are changed (set or reset) in the file's mode.  All
   other bits in the mode remain unchanged.  Bits in the first word that
   correspond to bits that are zero in the mask are ignored, except that
   undefined bits are checked for validity and can result in
   NFS4ERR_INVAL as described below.

   The mode_set_masked attribute is only valid in a SETATTR operation.
   If it is used in a CREATE or OPEN operation, the server MUST return
   NFS4ERR_INVAL.

   Bits not defined as valid in the mode attribute are not valid in
   either word of the mode_set_masked attribute.  The server MUST return
   NFS4ERR_INVAL if any such bits are set to one in a SETATTR.  If the
   mode and mode_set_masked attributes are both specified in the same
   SETATTR, the server MUST also return NFS4ERR_INVAL.

7.4.  ACL-based Authorization Model

7.4.1.  Processing Access Control Entries

   To determine if a request succeeds, the server processes each nfsace4
   entry of type ALLOW or DENY in turn as ordered in the array.  Only
   ACEs that have a "who" that matches the requester are considered.  An
   ACE is considered to match a given requester if at least one of the
   following is true:

   *  The "who' designates a specific user which is the user making the
      request.

   *  The "who" specifies "OWNER@" and the user making the request is
      the owner of the file.

   *  The "who" designates a specific group and the user making the
      request is a member of that group.

   *  The "who" specifies "GROUP@" and the user making the request is a
      member of the group owning the file.

   *  The "who" specifies "EVERYONE@".



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   *  The "who" specifies "INTERACTIVE@", "NETWORK@", "DIALUP@",
      "BATCH@", or "SERVICE@" and the requester, in the judgment of the
      server, feels that designation appropriately describes the
      requester.

   *  The "who" specifies "ANONYMOUS@" or "AUTHENTICATED@" and the
      requestor's authentication status matches the who, using the
      definitions in Section 5.9

   Each ACE is processed until all of the bits of the requester's access
   have been ALLOWED.  Once a bit (see below) has been ALLOWED by an
   ACCESS_ALLOWED_ACE, it is no longer considered in the processing of
   later ACEs.  If an ACCESS_DENIED_ACE is encountered where the
   requester's access still has unALLOWED bits in common with the
   "access_mask" of the ACE, the request is denied.  When the ACL is
   fully processed, if there are bits in the requester's mask that have
   not been ALLOWED or DENIED, access is denied.

   Unlike the ALLOW and DENY ACE types, the ALARM and AUDIT ACE types do
   not affect a requester's access, and instead are for triggering
   events as a result of a requester's access attempt.  AUDIT and ALARM
   ACEs are processed only after processing ALLOW and DENY ACEs if any
   exist.  This is necessary since the handling of AUDIT and ALARM ACEs
   are affected by whether the access attempt is successful.

   [Previous Treatment]: The NFSv4.1 ACL model is quite rich.  Some
   server platforms may provide access-control functionality that goes
   beyond the UNIX-style mode attribute, but that is not as rich as the
   NFS ACL model.  So that users can take advantage of this more limited
   functionality, the server may support the acl attributes by mapping
   between its ACL model and the NFSv4.1 ACL model.  Servers must ensure
   that the ACL they actually store or enforce is at least as strict as
   the NFSv4 ACL that was set.  It is tempting to accomplish this by
   rejecting any ACL that falls outside the small set that can be
   represented accurately.  However, such an approach can render ACLs
   unusable without special client-side knowledge of the server's
   mapping, which defeats the purpose of having a common NFSv4 ACL
   protocol.  Therefore, servers should accept every ACL that they can
   without compromising security.  To help accomplish this, servers may
   make a special exception, in the case of unsupported permission bits,
   to the rule that bits not ALLOWED or DENIED by an ACL must be denied.
   For example, a UNIX-style server might choose to silently allow read
   attribute permissions even though an ACL does not explicitly allow
   those permissions.  (An ACL that explicitly denies permission to read
   attributes should still be rejected.)






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   [Author Aside]: While the NFSv4.1 provides that many might not need
   or use, it is the one that the working group adopted by the working
   group, and I have to assume that alternatives, such as the withdrawn
   POSIX ACL proposal were considered but not adopted.  The phrase
   "unsupported permission bits" with no definition of the bit whose
   support might be dispensed with, implies that the server is free to
   support whatever subset of these bits it chooses.  As a result,
   clients would not be able to rely on a functioning server
   implementation of this OPTIONAL attribute.  If there are specific
   compatibility issues that make it necessary to allow non-support of
   specific mask bits, then these need to be limited and the client
   needs guidance about determining the set of unsupported mask bits.

   [Previous Treatment]: The situation is complicated by the fact that a
   server may have multiple modules that enforce ACLs.  For example, the
   enforcement for NFSv4.1 access may be different from, but not weaker
   than, the enforcement for local access, and both may be different
   from the enforcement for access through other protocols such as SMB
   (Server Message Block).  So it may be useful for a server to accept
   an ACL even if not all of its modules are able to support it.

   [Author Aside]: The following paragraph does not provide helpful
   guidance and takes no account of the need of the the client to be
   able to rely on the server implementing protocol-specifying semantics
   and giving notice in those cases in which it is unable to so

   [Previous Treatment]: The guiding principle with regard to NFSv4
   access is that the server must not accept ACLs that appear to make
   access to the file more restrictive than it really is.

7.4.2.  V4.1 Attribute 58: dacl

   The dacl attribute is like the acl attribute, but dacl allows only
   ALLOW and DENY ACEs.  The dacl attribute supports automatic
   inheritance (see Section 5.10).

8.  Common Considerations for Both File access Models

   [Author Aside, Including List]: This subsections within this section
   are derived from Section 6.3 of 8881, entitled "Common Methods.
   However, its content is different because it has been rewritten to
   deal with issues common to both file access models, which now appears
   to have not been the original intention.  Nevertheless, the following
   changes have been made:

   *  The section "Server Considerations" has been revised to deal with
      both the mode and acl attributes, since the points being made
      apply, in almost all cases, to both attributes.



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   *  The section "Client Considerations" has been heavily revised,
      since what had been there did not make any sense to me.

   *  The section "Computing a Mode Attribute from an ACL" has been
      moved to Section 9.3 since it deals with the co-ordination of the
      posix and acl authorization models.

8.1.  Server Considerations

   The server uses the mode attribute or the acl attribute applying the
   algorithm described in Section 7.4.1 to determine whether an ACL
   allows access to an object.

   [Author Aside, Including List]: The list previously in this section
   (now described as "Previous Treatment" combines two related issues in
   a way which obscures the very different security-related consequences
   of two distinct issues:

   *  In some cases an operation will be authorized but is not allowed
      for reasons unrelated to authorization.

      This has no negative effect on security.

   *  The converse case does have troubling effects on security which
      are mentioned in this section and discussed in more detail in
      Section 17

   [Author Aside, Including List]: The items in that list have been
   dealt with as follows:

   *  The first and sixth items fit under the first (i.e. less
      troublesome) of these issues.  They have have been transferred
      into an appropriate replacement list.

   *  The third item is to be deleted since it does not manifest either
      of these issues.  In fact, it refers to the semantics already
      described in Section 5.4.  is already described in ...

   *  The second, fourth and fifth items need to be addressed in a new
      list dealing with the potentially troublesome issues arising from
      occasions in which the access semantics previously described are
      relaxed, for various reasons.

      Included are cases in which previous specifications explicitly
      allowed this by using the term "MAY" and others in which the
      existence of servers manifesting such behavior was reported, with
      the implication that clients need to prepared for such behavior.




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   [Previous Treatment, Including List (Items #22a, #41a, #52a)]:
   However, these attributes might not be the sole determiner of access.
   For example:

   *  In the case of a file system exported as read-only, the server
      will deny write access even though an object's file access
      attributes would grant it.

   *  Server implementations MAY grant ACE4_WRITE_ACL and ACE4_READ_ACL
      permissions to prevent a situation from arising in which there is
      no valid way to ever modify the ACL.

   *  All servers will allow a user the ability to read the data of the
      file when only the execute permission is granted (e.g., if the ACL
      denies the user the ACE4_READ_DATA access and allows the user
      ACE4_EXECUTE, the server will allow the user to read the data of
      the file).

   *  Many servers implement owner-override semantics in which the owner
      of the object is allowed to override accesses that are denied by
      the ACL.  This may be helpful, for example, to allow users
      continued access to open files on which the permissions have
      changed.

   *  Many servers provide for the existence of a "superuser" that has
      privileges beyond an ordinary user.  The superuser may be able to
      read or write data or metadata in ways that would not be permitted
      by the ACL or mode attributes.

   *  A retention attribute might also block access otherwise allowed by
      ACLs (see Section 5.13 of RFC8881 [8]).

   [Consensus Needed, Including List (Item #22a)]: It needs to be noted
   that, even when an operation is authorized, it may be denied for
   reasons unrelated to authorization.  For example:

   *  In the case of a file system exported as read-only, the server
      will deny write access even though an object's file access
      attributes would authorize it.

   *  A retention attribute might also block access otherwise allowed by
      ACLs (see Section 5.13 of RFC8881 [8]).

   [Consensus Needed, (Item #22a)]: There are also cases in which the
   converse issue arises, so that an operation which is not authorized
   as specified by the mode and ACL attributes is, nevertheless,
   executed as if it were authorized.  Because previous NFSv4
   specifications have cited the cases listed below without reference to



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   the security problems that they create, it is necessary to discuss
   them here to provide clarification of the security implications of
   following this guidance, which is now superseded.  These cases are
   listed below and discussed in more detail in Section 17.1.3.

   [Consensus Needed, Including List (Item #22a, #41a, #52a)]: In the
   following list, the treatment used in RFC8881 [8] is quoted, while
   the corresponding text in RFC7530 [6]is essentially identical.

   *  RFC8881 [8] contains the following, which is now superseded:

         Server implementations MAY grant ACE4_WRITE_ACL and
         ACE4_READ_ACL permissions to prevent a situation from arising
         in which there is no valid way to ever modify the ACL.

      While, as a practical matter, there do need to be provisions to
      deal with this issue, the "MAY" above is too broad,in that it
      describes the motivation without any limits providing appropriate
      restriction on the steps that might be taken to deal with the
      issue.  See Section 17.1.3 for the updated treatment of this
      issue.

   *  RFC8881 [8] contains the following, which is now superseded:

         Many servers implement owner-override semantics in which the
         owner of the object is allowed to override accesses that are
         denied by the ACL.  This may be helpful, for example, to allow
         users continued access to open files on which the permissions
         have changed.

      Regardless of the truth of the first sentence above, either when
      it was written or today, it needs to be stressed that the fact
      that a server manifests a particular behavior does not imply that
      it is valid according to the protocol specification.  In this
      case, the supposed "owner-override semantics" clearly are not
      valid, since they contradict the specification of both the mode-
      based and ACL-based approaches to file access authorization.

      With regard to the second sentence of the quotation above, it is
      not clear whether it is helpful or hurtful to allow continued
      access to open files which have become inaccessible due to changes
      in security and it is not clear that the working group will make a
      decision on the matter in this document, despite the obvious
      security implications.  In any case, the resolution is unlikely to
      depend on whether the owner is involved.

   *  RFC8881 [8] contains the following, which is now superseded:




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         Many servers have the notion of a "superuser" that has
         privileges beyond an ordinary user.  The superuser may be able
         to read or write data or metadata in ways that would not be
         permitted by the ACL or mode attributes.

      While many (or almost all) systems in which NFSv4 servers are
      embedded, have provisions for such privileged access to be
      provided, it does not follow that NFSv4 servers, as such, need to
      have provision for such access.

      Providing such access as part of the NFSv4 protocols, would
      necessitate a major revision of the semantics of ACL including
      such troublesome matters as the proper handling of AUDIT and ALARM
      ACEs in the face of such privileged access.

      Because of the effect such unrestricted access might have in
      facilitating and perpetuating attacks, Section 17.1.3 will the new
      approach to this issue, while Section 17.4.1, will explain how
      such access is addressed in the threat analysis.

8.2.  Client Considerations

   [Previous Treatment]: Clients SHOULD NOT do their own access checks
   based on their interpretation of the ACL, but rather use the OPEN and
   ACCESS operations to do access checks.  This allows the client to act
   on the results of having the server determine whether or not access
   is to be granted based on its interpretation of the ACL.

   [Author Aside]: With regard to the use of "SHOULD NOT" in the
   paragraph above, it is not clear what might be valid reasons to
   bypass this recommendation.  Perhaps "MUST NOT" or "are not advised
   to" would be more appropriate.

   [Consensus Needed (Item #23a)]: Clients are not expected to do their
   own access checks based on their interpretation of the ACL, but
   instead use the OPEN and ACCESS operations to do access checks.  This
   allows the client to act on the results of having the server
   determine whether or not access is to be granted based on its
   interpretation of the ACL.

   [Previous Treatment]: Clients must be aware of situations in which an
   object's ACL will define a certain access even though the server will
   not enforce it.  In general, but especially in these situations, the
   client needs to do its part in the enforcement of access as defined
   by the ACL.






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   [Author Aside]: Despite what is said later, the only such case I know
   of is the use of READ and EXECUTE where the client, but not the
   server, has any means of distinguishing these.  I don't know of any
   others.  If there were, how could ACCESS or OPEN be used to verify
   access?

   [Consensus Needed (Item #23a)]; Clients need to be aware of
   situations in which an object's ACL will define a certain access even
   though the server is not in position to enforce it because the server
   does not have the relevant information, such as knowing whether a
   READ is for the purpose of executing a file.  Because of such
   situations, the client needs to do be prepared to do its part in the
   enforcement of access as defined by the ACL.

   To do this, the client will send the appropriate ACCESS operation
   prior to servicing the request of the user or application in order to
   determine whether the user or application is to be granted the access
   requested.

   [Previous Treatment (Item #24a)]: For examples in which the ACL may
   define accesses that the server doesn't enforce, see Section 8.1.

   [Author Aside]: The sentence above is clearly wrong since that
   section is about enforcement the server does do.  The expectation is
   that it will be deleted as part of Consensus Item #24a.

9.  Combining Authorization Models

9.1.  Background for Combined Authorization Model

   Both RFCs 7530 [6] and 8881 [8] contain material relating to the
   need, when both mode and ACL attributes are supported, to make sure
   that the values are appropriately co-ordinated.  Despite the fact
   that these discussions are different, they are compatible and differ
   in only a small number of areas relating to the existence absence of
   the set-mode-masked attribute.

   Such co-ordination is necessary is necessary since it is expected
   that servers providing both sets of attributes will encounter users
   who have no or very limited knowledge of one and need to work
   effectively when other users changes that attribute.  As a result,
   these attributes cannot each be applied independently since that
   would create an untenable situation in which some users who have the
   right to control file access would find themselves unable to do so.







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   [Author Aside]: From this point on, all paragraphs in this section,
   not other annotated are to be considered part of Consensus Item #25b.
   The description in this section of changes to be made reflects the
   author's proposal to address this issue and related issues.  It might
   have to be adjusted based on working group decisions.

   As a result, in this document, we will have a single treatment of
   this issue, in Sections 9.2 through 9.12.  In addition, an
   NFSv4.2-based extension related to attribute co-ordination will be
   described in Section 9.13.

   The current NFSv4.0 and NFSv4.1 descriptions of this co-ordination
   share an unfortunate characteristic in that they are both written to
   give server implementations a broad latitude in implementation
   choices while neglecting entirely the need for clients and users to
   have a reliable description of what servers are to do in this area.

   As a result, one of the goals of this new combined treatment will be
   to limit the uncertainty that the previous approach created for
   clients, while still taking proper account of the possibility of
   compatibility issues that a more tightly drawn specification might
   give rise to.

   The various ways in which these kinds of issues have been dealt with
   are listed below together with a description of the needed changes
   proposed to address each issue.

   *  In some cases, the term "MAY" is used in contexts where it is
      inappropriate, since the allowed variation has the potential to
      cause harm in that it leaves the client unsure exactly what
      security-related action will be performed by the server.

      The new treatment will limit use use of MAY to cases in which it
      is truly necessary, in order to give clients proper notice of
      cases in which server behavior cannot be determined and limit the
      work necessary to deal with a large array of possible behaviors.

   *  There are also cases in which no RFC2119-defined keywords are used
      but it is stated that certain server implementations do a
      particular thing, leaving the impression that that action is to be
      allowed, just as if "MAY" had been used.










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      If the flexibility is necessary, MAY will be used.  In other
      cases, SHOULD will be used with the understanding that maintaining
      compatibility with clients that have adapted to a particular
      approach to this issue is a valid reason to bypass the
      recommendation.  However, in no case will it be implied, as it is
      in the current specifications, that the server MAY do whatever it
      chooses, with the client having no option but to adapt to that
      choice.

   *  There was a case, in Section 9.2, in which the term "SHOULD" was
      explicitly used intentionally, without it being made clear what
      the valid reasons to ignore the guidance might be, although there
      was a reference to servers built to support the now-withdrawn
      draft definition of POSIX ACLs, which are referred to in this
      document as "UNIX ACLs", ass described in Section 4.1.  A
      discussion of the issues for support of for these ACLs appears in
      Section 9.5.

      [Author Aside]: Despite the statement, now cited in Section 9.2,
      that this was to accommodate implementations "POSIX" ACLs, it now
      appears that this was not complete.  I've been given to understand
      that this was the result of two groups disagreeing on the
      appropriate mapping from ACLs, and specifying both, using the
      "intentional" "SHOULD" essentially as a MAY, with the text now in
      Section 9.2 discouraging such use as potentially confusing, not
      intended to be taken seriously.  Since the above information might
      not be appropriate in a standards-track RFC, we intend to retain
      this as an Author Aside which the working group might consider as
      it discusses how to navigate our way out of this situation.

      The new approach will use the term "RECOMMENDED" without use of
      the confusing term "intentional".  The valid reasons to bypass the
      recommendation will be clearly explained as will be the
      consequences of choosing to do other than what is recommended.

   *  There are many case in which the terms "SHOULD" and "SHOULD NOT"
      are used without any clear indication why they were used.  In this
      situation it is possible that the "SHOULD" was essentially treated
      as a "MAY" but also possible that servers chose to follow the
      recommendation.











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      In order to deal with the many uses of these terms in Section 9
      and included subsections, which have no clear motivation, it is to
      be assumed that the valid reasons to act contrary to the
      recommendation given are the difficulty of changing
      implementations based on previous analogous guidance, which may
      have given the impression that the server was free to ignore the
      guidance for any reason the implementer chose.  This allows the
      possibility of more individualized treatment of these instances
      once compatibility issues have been adequately discussed.

      [Author Aside]: In each subsection in which the the interpretation
      of these term in the previous paragraph applies there will be an
      explicit reference to Consensus Item #25, to draw attention to
      this change, even in the absence of modified text.

9.2.  Needed Attribute Coordination

   On servers that support both the mode and the acl or dacl attributes,
   the server needs to keep the two consistent with each other.  The
   value of the mode attribute (with the exception of the high-order
   bits reserved for client use as described in Section 7.3.1) are to be
   determined entirely by the value of the ACL, so that use of the mode
   is never required for anything other than setting and interrogating
   the three high-order bits.  See Sections 9.7 through 9.9 for detailed
   discussion.

   [Previous Treatment (Item #25c)]: When a mode attribute is set on an
   object, the ACL attributes may need to be modified in order to not
   conflict with the new mode.  In such cases, it is desirable that the
   ACL keep as much information as possible.  This includes information
   about inheritance, AUDIT and ALARM ACEs, and permissions granted and
   denied that do not conflict with the new mode.

   [Author Aside]: one the things that this formulation leaves
   uncertain, is whether, if the ACL specifies permission for a named
   user group or group, it "conflicts" with the node.  Ordinarily, one
   might think it does not, unless the specified user is the owner of
   the file or a member of the owning group, or the specified group is
   the owning group.  However, while some parts of the existing
   treatment seem to agree with this, other parts, while unclear, seem
   to suggest otherwise, while the treatment in Section 9.7 is directly
   in conflict.

   [Previous Treatment (Item #26a)]: The server that supports both mode
   and ACL must take care to synchronize the MODE4_*USR, MODE4_*GRP, and
   MODE4_*OTH bits with the ACEs that have respective who fields of
   "OWNER@", "GROUP@", and "EVERYONE@".




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   [Author Aside]: This sentence ignores named owners and group, giving
   the impressions that there is no need to change them.

   [Previous Treatment (Item #26a)]: This way, the client can see if
   semantically equivalent access permissions exist whether the client
   asks for the owner, owner_group, and mode attributes or for just the
   ACL.

   [Author Aside, Including List:] The above sentence, while hard to
   interpret for a number a reasons, is worth looking at in detail
   because it might suggest an approach different from the one in the
   previous sentence from the initial paragraph for The Previous
   Treatment of Item #26a.

   *  The introductory phrase "this way" adds confusion because it
      suggests that there are other valid ways of doing this, while not
      giving any hint about what these might be.

   *  It is hard to understand the intention of "client can see if
      semantically equivalent access permissions" especially as the
      client is told elsewhere that he is not to interpret the ACL
      himself.

   *  If this sentence is to have any effect at all it, it would be to
      suggest that the result be the same "whether the client asks for
      the owner, owner_group, and mode attributes or for just the ACL."

      If these are to be semantically equivalent it would be necessary
      to delete ACEs for named users, which requires a different
      approach form the first sentence of the original paragraph.

   {Consensus Needed, Including List (Items #26a, #28a)]: A server that
   supports both mode and ACL attributes needs to take care to
   synchronize the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with the
   ACEs that have respective who fields of "OWNER@", "GROUP@", and
   "EVERYONE@".  This requires:

   *  When the mode is changed, in most cases, the ACL attributes will
      need to be modified as described in Section 9.7.

   *  When the ACL is changed, the corresponding mode is determined and
      used to set the nine low-oder bits of the mode attribute.

      This is relatively straightforward in the case of forward-slope
      modes, but the case of reverse-slope modes needs to be addressed
      as well.  It is RECOMMENDED that the procedure presented in
      Section 9.3 be used or another one that provides the same results.




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      The valid reasons to bypass this recommendation together with a
      alternate procedures to be used are discussed in Section 9.4.

   {Consensus Needed (Item #26a)]: How other ACEs are dealt with when
   setting mode is described in Section 9.7.  This includes ACEs with
   other who values, all AUDIT and ALARM ACEs, and all ACES that affect
   ACL inheritance.

   [Previous Treatment (Item #27a)]: In this section, much depends on
   the method in specified Section 9.3.  Many requirements refer to this
   section.  It needs to be noted that the methods have behaviors
   specified with "SHOULD" and that alternate approaches are discussed
   in Section 9.4.  This is intentional, to avoid invalidating existing
   implementations that compute the mode according to the withdrawn
   POSIX ACL draft (1003.1e draft 17), rather than by actual permissions
   on owner, group, and other.

   [Consensus (Item #27a)]: In performing the co-ordinarion discussed in
   this section, the method used to compute the mode from the ACL has an
   important role.  While the approach specified in Section 9.3 is
   RECOMMENDED, it needs to be noted that the alternate approaches
   discussed in Section 9.4 are valid in some cases.  As discussed in
   that section, an important reason for allowing multiple ways of doing
   this is to accommodate server implementations that compute the mode
   according to the withdrawn POSIX ACL draft (1003.1e draft 17), rather
   than by actual permissions on owner, group, and other.  While, this
   means that a client, having no way of determining the method the
   server uses may face interoperability difficulties in moving between
   servers which approach this matter differently, these problems need
   to be accepted for the time being.  A more complete discussion of
   handling of the UNIX ACLs is to be found in Section 9.5.

   [Consensus Needed, Including List (Items #27a, #28a)]: All valid
   methods of computing the mode from an ACL use the following procedure
   to derive a set of mode bits from a set of three ACL masks, with the
   only difference being in how the set of ACL masks is constructed.
   The calculated mask for for each set of bits in mode are derived from
   the ACL mask for owner, group, other are derived as follows:

   1.  Set the read bit (MODE4_RUSR, MODE4_RGRP, or MODE4_ROTH) if and
       only if ACE4_READ_DATA is set in the corresponding mask.

   2.  Set the write bit (MODE4_WUSR, MODE4_WGRP, or MODE4_WOTH) if and
       only if ACE4_WRITE_DATA and ACE4_APPEND_DATA are both set in the
       corresponding mask.

   3.  Set the execute bit (MODE4_XUSR, MODE4_XGRP, or MODE4_XOTH), if
       and only if ACE4_EXECUTE is set in the corresponding mask.



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9.3.  Computing a Mode Attribute from an ACL

   [Previous Treatment (Item #27b)]: The following method can be used to
   calculate the MODE4_R*, MODE4_W*, and MODE4_X* bits of a mode
   attribute, based upon an ACL.

   [Author Aside]: "can be used" says essentially "do whatever you
   choose" and would make Section 9 essentially pointless.  Would prefer
   "is to be used" or "MUST", with "SHOULD" available if valid reasons
   to do otherwise can be found.

   [Consensus Needed (Items #27b, #28b)}: The following method (or
   another one providing exactly the same results) SHOULD be used to
   calculate the MODE4_R*, MODE4_W*, and MODE4_X* bits of a mode
   attribute, based upon an ACL.  In this case, one of the valid reasons
   to bypass the recommendation includes implementor reliance on
   previous specifications which ignored the cases of the owner having
   less access than the owning group or the owning group having less
   access than others.  Further, in implementing or the maintaining an
   implementation previously believed to be valid, the implementor needs
   to be aware that this will result invalid values in some uncommon
   cases.  Other reasons to bypass the recommendation are discussed in
   Section 9.4.

   [Author Aside, Including List]: The algorithm specified below, now
   considered the Previous Treatment associated with Item #24a, has an
   important flaw in does not deal with the (admittedly uncommon) case
   in which the owner_group has less access than the owner or others
   have less access than the owner-group.  In essence, this algorithm
   ignores the following facts:

   *  That GROUP@ includes the owning user while group bits in the mode
      do not affect the owning user.

   *  That EVERYONE includes the owning group while other bits in the
      mode do not affect users within the owning group.

   [Previous Treatment (Item #28b)]: First, for each of the special
   identifiers OWNER@, GROUP@, and EVERYONE@, evaluate the ACL in order,
   considering only ALLOW and DENY ACEs for the identifier EVERYONE@ and
   for the identifier under consideration.  The result of the evaluation
   will be an NFSv4 ACL mask showing exactly which bits are permitted to
   that identifier.

   [Previous Treatment (Item #28b)]: Then translate the calculated mask
   for OWNER@, GROUP@, and EVERYONE@ into mode bits for, respectively,
   the user, group, and other, as follows:




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   [Consensus Needed, including List(Item #28b)]: First, for each of the
   sets of mode bits (i.e., user, group other, evaluate the ACL in
   order, with a specific evaluation procedure depending on the specific
   set of mode bits being determined.  For each set there will be one or
   more special identifiers considered in a positive sense so that ALLOW
   and DENY ACE's are considered in arriving at the mode bit.  In
   addition, for some sets of bits, there will be one or more special
   identifiers to be considered only in a negative sense, so that only
   DENY ACE's are considered in arriving at the mode it.  The users to
   be considered are as follows:

   *  For the owner bits, "OWNER@" and "EVERYONE@" are to be considered,
      both in a positive sense.

   *  For the group bits, "GROUP@" and "EVERYONE@" are to be considered,
      both in a positive sense, while "OWNER@" is to be considered in a
      negative sense.

   *  For the other bit, "EVERYONE@" is to be considered in a positive
      sense, while "OWNER@" and "GROUP@" are to be considered in a
      negative sense.

   [Consensus Needed (Item #28b)]: Once these ACL masks are constructed,
   the mode bits for, user, group, and other can be obtained as
   described in Section 9.2 above.

9.4.  Alternatives in Computing Mode Bits

   [Author Aside]: All unannotated paragraphs within this section are to
   be considered the Previous Treatment corresponding to Consensus Item
   #27c.

   Some server implementations also add bits permitted to named users
   and groups to the group bits (MODE4_RGRP, MODE4_WGRP, and
   MODE4_XGRP).

   Implementations are discouraged from doing this, because it has been
   found to cause confusion for users who see members of a file's group
   denied access that the mode bits appear to allow.  (The presence of
   DENY ACEs may also lead to such behavior, but DENY ACEs are expected
   to be more rarely used.)

   [Author Aside]: The text does not seem to really discourage this
   practice and makes no reference to the need to standardize behavior
   so the clients know what to expect or any other reason for providing
   standardization of server behavior.





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   The same user confusion seen when fetching the mode also results if
   setting the mode does not effectively control permissions for the
   owner, group, and other users; this motivates some of the
   requirements that follow.

   [Author Aside]: The part before the semicolon appears to be relevant
   to Consensus Item #23 but does not point us to a clear conclusion.
   The statement certainly suggests that the 512-ACL approach is more
   desirable but the absence of a more direct statement to that effect
   suggest that this is a server implementer choice.

   [Author Aside]: The part after the semicolon is hard to interpret in
   that it is not clear what "this" refers to or which which
   requirements are referred to by "some of the requirements that
   follow".  The author would appreciate hearing from anyone who has
   insight about what might have been intended here.

   [Consensus Needed, Including List (Item #27c)]: In cases in which the
   mode is not computed as described in Section 9.3, one of the
   following analogous procedures or their equivalents, MUST be used.

   *  First, for each of the special identifiers OWNER@ and EVERYONE@,
      evaluate the ACL in order, considering only ALLOW and DENY ACEs
      for the identifier EVERYONE@ and for the identifier under
      consideration.

      For the special identifier GROUP@, ALLOW and DENY ACEs for GROUP@
      and EVERYONE@ are to be considered, together with ALLOW ACEs for
      named users and groups.

      This represents the approach previously recommended to compute
      mode in previous specification, as modified to reflect the UNIX
      ACL practice of reflecting permissions for named users and groups.
      It does not deal properly with reverse-slope modes.

   *  Compute a set of ACL mask according to the procedure in
      Section 9.3 and then, for the mask associated with GROUP@, or in
      the masks for all ALLOW ACEs for named users and groups.

      This represents the approach currently recommended to compute mode
      in Section 9.3 as modified to reflect the UNIX ACL practice of
      reflecting permissions for named users and groups.

   [Consensus Needed, Including List (Item #27c)]: In both cases, The
   results of the evaluation will be a set of NFSv4 ACL masks which can
   be converted to the set on nine low-order mode bits using the
   procedure appearing in Section 9.2 above.




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   [Consensus Needed, Including List (Item #27c)]: When the
   recommendation to use Section 9.3 is bypassed, it needs to be
   understood, that the modes derived will differ from the expected
   values and might cause interoperability issues.  This is particularly
   the case when clients have no way to determine that the server's
   behavior is other than standard.

9.5.  Handling of UNIX ACLs

   [Author Aside]: All paragraphs in this section are consider part of
   Consensus Item #56b.

   Although the working group did not adopt the acls in the withdrawn
   POSIX draft, their continued existence in UNIX contexts has created
   protocol difficulties that need to be resolved.  In many cases these
   ACLS and their associated semantics are the basis for ACL support in
   UNIX client APIs and in UNIX file systems supported by NFSv4

   Although the semantic range of UNIX ACLs is a subset of that for
   NFSv4 ACLs, expecting clients to perform that mapping on their own
   has not worked well, leading to the following issues which will, at
   some point, need to be addressed:

   *  There is a considerable uncertainty about the proper mapping from
      ACLs to modes.

   *  The corresponding mapping from modes to ACLs is dealt with
      different ways by different sections of the spec.

   *  These individual uncertainties are compounded since it is
      difficult, in this environment, to ensure that these independently
      chosen mappings are inverses of one another, as they are intended
      to be.

   Some possible approaches to these issues are discussed in Section 16,

9.6.  Setting Multiple ACL Attributes

   In the case where a server supports the sacl or dacl attribute, in
   addition to the acl attribute, the server MUST fail a request to set
   the acl attribute simultaneously with a dacl or sacl attribute.  The
   error to be given is NFS4ERR_ATTRNOTSUPP.

9.7.  Setting Mode and not ACL (overall)







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9.7.1.  Setting Mode and not ACL (vestigial)

   [Author Aside]: All unannotated paragraphs are to be considered the
   Previous treatment of Consensus Item #30a.

   [Previous Treatment (Item #?a)]: When any of the nine low-order mode
   bits are subject to change, either because the mode attribute was set
   or because the mode_set_masked attribute was set and the mask
   included one or more bits from the nine low-order mode bits, and no
   ACL attribute is explicitly set, the acl and dacl attributes must be
   modified in accordance with the updated value of those bits.  This
   must happen even if the value of the low-order bits is the same after
   the mode is set as before.

   Note that any AUDIT or ALARM ACEs (hence any ACEs in the sacl
   attribute) are unaffected by changes to the mode.

   In cases in which the permissions bits are subject to change, the acl
   and dacl attributes MUST be modified such that the mode computed via
   the method in Section 9.3 yields the low-order nine bits (MODE4_R*,
   MODE4_W*, MODE4_X*) of the mode attribute as modified by the
   attribute change.  The ACL attributes SHOULD also be modified such
   that:

   1.  If MODE4_RGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_READ_DATA.

   2.  If MODE4_WGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_WRITE_DATA or ACE4_APPEND_DATA.

   3.  If MODE4_XGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_EXECUTE.

   Access mask bits other than those listed above, appearing in ALLOW
   ACEs, MAY also be disabled.

   Note that ACEs with the flag ACE4_INHERIT_ONLY_ACE set do not affect
   the permissions of the ACL itself, nor do ACEs of the type AUDIT and
   ALARM.  As such, it is desirable to leave these ACEs unmodified when
   modifying the ACL attributes.








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   Also note that the requirement may be met by discarding the acl and
   dacl, in favor of an ACL that represents the mode and only the mode.
   This is permitted, but it is preferable for a server to preserve as
   much of the ACL as possible without violating the above requirements.
   Discarding the ACL makes it effectively impossible for a file created
   with a mode attribute to inherit an ACL (see Section 9.11).

9.7.2.  Setting Mode and not ACL (Discussion)

   [Author Aside]: All unannotated paragraphs are to be considered
   Author Asides relating to Consensus Item #30b.

   Existing documents are unclear about the changes to be made to an
   existing ACL when the nine low-order bits of the mode attribute are
   subject to modification using SETATTR.

   A new treatment needs to apply to all minor versions.  It will be
   necessary to specify that, for all minor versions, setting of the
   mode attribute, subjects the low-order nine bits to modification.

   One important source of this lack of clarity is the following
   paragraph from Section 9.7.1, which we refer to later as the trivial-
   implementation-remark".

      Also note that the requirement may be met by discarding the acl
      and dacl, in favor of an ACL that represents the mode and only the
      mode.  This is permitted, but it is preferable for a server to
      preserve as much of the ACL as possible without violating the
      above requirements.  Discarding the ACL makes it effectively
      impossible for a file created with a mode attribute to inherit an
      ACL (see Section 9.11).

   The only "requirement" which might be met by the procedure mentioned
   above is the text quoted below.

      In cases in which the permissions bits are subject to change, the
      acl and dacl attributes MUST be modified such that the mode
      computed via the method in Section 9.3 yields the low-order nine
      bits (MODE4_R*, MODE4_W*, MODE4_X*) of the mode attribute as
      modified by the attribute change.

   While it is true that this requirement could be met by the specified
   treatment, this fact does not, in itself, affect the numerous
   recommendations that appear between the above requirement and the
   trivial-implementation-remark.






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   It may well be that there are are implementations that have treated
   the trivial-implementation-remark as essentially allowing them to
   essentially ignore all of those recommendations, resulting in a
   situation in which were treated as if it were a trivial-
   implementation-ok indication.  How that issue will be dealt with in a
   replacement for Section 9.7.1 will be affected by the working group's
   examination of compatibility issues.

   The following specific issues need to be addressed:

   *  Handling of inheritance.

      Beyond the possible issues that arise from the trivial-
      implementation-ok interpretation, the treatment in Section 9.7.1,
      by pointing specifically to existing INHERIT_ONLY ACEs obscures
      the corresponding need to convert ACE's that specify both
      inheritance and access permissions to be converted to INHERIT_ONLY
      ACEs.

   *  Reverse-slope modes

   *  Named users and groups.

   *  The exact bounds of what within the ACL is covered by the low-
      order bits of the mode.

   It appears that for many of the issues, there are many possible
   readings of the existing specs, leading to the possibility of
   multiple inconsistent server behaviors.  Furthermore, there are cases
   in which none of the possible behaviors described in existing
   specifications meets the needs.

   As a result of these issues, the existing specifications do not
   provide a reliable basis for client-side implementations of the ACL
   feature which a Proposed Standard is normally expected to provide.

9.7.3.  Setting Mode and not ACL (Proposed)

   [Author Aside]: This proposed section is part of Consensus Item #30c
   and all unannotated paragraphs within it are to be considered part of
   that Item.  Since the proposed text includes support for reverse-
   slope modes, treats all minor versions together and assumes decisions
   about handling of ACEs for named users and groups, the relevance of
   consensus items #26, #28, and #29 needs to be noted.

   [Author Aside]: As with all such Consensus Items, it is expected that
   the eventual text in a published RFC might be substantially different
   based on working group discussion of client and server needs and



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   possible compatibility issues.  In this particular case, that
   divergence can be expected to be larger, because the author was
   forced to guess about compatibility issues and because earlier
   material, on which it is based left such a wide range of matters to
   the discretion of server implementers.  It is the author's hope that,
   as the working group discusses matters, sufficient attention is
   placed on the need for client-side implementations to have reliable
   information about expected server-side actions.

   This section describes how ACLs are to be updated in response to
   actual or potential changes in the mode attribute, when the
   attributes needed by both of the file access authorization models are
   supported.  It supersedes the discussions of the subject in RFCs 7530
   [6] and 8881 [8], each of which appeared in Section 6.4.1.1 of the
   corresponding document.

   It is necessary to approach the matter differently than in the past
   because:

   *  Organizational changes are necessary to address all minor versions
      together.

   *  Those previous discussions are often internally inconsistent
      leaving it unclear what specification-mandated actions were being
      specified..

   *  In many cases, servers were granted an extraordinary degree of
      freedom to choose the action to take, either explicitly or via an
      apparently unmotivated use of "SHOULD", leaving it unclear what
      might be considered "valid" reasons to ignore the recommendation.

   *  There appears to have been no concern for the problems that
      clients and applications might encounter dealing ACLs in such an
      uncertain environment.

   *  Cases involving reverse-slope modes were not adequately addressed.

   *  The security-related effects of SVTX were not addressed.













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   While that sort of approach might have been workable at one time, it
   made it difficult to devise client-side ACL implementations, even if
   there had been any interest in doing so.  In order to enable this
   situation to eventually be rectified, we will define the preferred
   implementation here, but in order to provide temporary compatibility
   with existing implementations based on reasonable interpretations of
   RFCs 7530 [6] and 8881 [8].  To enable such compatibility the term
   "SHOULD" will be used, with the understanding that valid reasons to
   bypass the recommendation, are limited to implementers' previous
   reliance on these earlier specifications and the difficulty of
   changing them now.

   When the recommendation is bypassed in this way, it is necessary to
   understand, that, until the divergence is rectified, or the client is
   given a way to determine the detail of the server's non-standard
   behavior, client-side implementations may find it difficult to
   implement a client-side implementation that correctly interoperates
   with the existing server.

   When mode bits involved in determining file access authorization are
   subject to modification, the server MUST, when ACL-related attributes
   have been set, modify the associated ACEs so as not to conflict with
   the new value of the mode attribute.

   The occasions to which this requirement applies, vary with the
   attribute being set and the type of object being dealt with:

   *  For all minor versions, any change to the mode attribute, triggers
      this requirement

   *  When the set_mode_masked attribute is being set on an object which
      is not a directory, whether this requirement is triggered depends
      on whether any of the nine low-order bits of the mode is included
      in the mask.

   *  When the set_mode_masked attribute is being set on a directory,
      whether this requirement is triggered depends on whether any of
      the nine low-order bits of the mode or the SVTX bit is included in
      the mask of bit whose values are to be set.

   When the requirement is triggered, ACEs need to be updated to be
   consistent with the new mode attribute.  In the case of AUDIT and
   ALARM ACEs, which are outside of file access authorization, no change
   is to be made.

   For ALLOW and DENY ACEs, changes are necessary to avoid conflicts
   with the mode in a number of areas:




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   *  The handling of ACEs that have consequences relating to ACL
      inheritance.

   *  The handling of ACEs with a who-value of OWNER@, GROUP@, or
      EVERYONE@ need to be adapted to the new mode.

   *  ACEs whose who-value is a named user or group, are to be retained
      or not based on the mode being set as described below.

   *  ACEs whose who-value is one of the other special values defined in
      Section 5.9 are to be left unmodified.

   In order to deal with inheritance issues, the following SHOULD be
   done:

   *  ACEs that specify inheritance-only need to be retained, regardless
      of the value of who specified, since inheritance issues are
      outside of the semantic range of the mode attribute.

   *  ACEs that specify inheritance, in addition to allowing or denying
      authorization for the current object need to be converted into
      inheritance-only ACEs.  This needs to occur irrespective of the
      value of who appearing in the ACE.

   For NFSv4 servers that support the dacl attribute, at least the first
   of the above MUST be done.

   Other ACEs are to be treated are classified based on the ACE's who-
   value:

   *  ACEs whose who-value is OWNER@, GROUP@, or EVERYONE@ are referred
      to as mode-directed ACEs and are subject to extensive
      modification.

   *  ACEs whose who-value is a named user or group are either left
      alone or subject to extensive modification, as described below.

   *  ACEs whose who-value is one of the other special values defined in
      Section 5.9 are left as they are.

   Mode-directed ACEs need to be modified so that they reflect the mode
   being set.

   In effecting this modification, the server will need to distinguish
   mask bits deriving from mode attributes from those that have no such
   connection.  The former can be categorized as follows:





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   *  For non-directory objects, the mask bits ACE4_READ_DATA (from the
      read bit in the mode), ACE4_EXECUTE (from the execute bit in the
      mode), and ACE4_WRITE_DATA together with ACE4_APPEND_DATA (from
      the write bit in the mode) are all derived from the set of three
      mode bits appropriate to the current who-value.

   *  For directories, analogous mask bits are included:
      ACE4_LIST_DIRECTORY (from the read in the mode), ACE4_EXECUTE
      (from the execute bit in the mode), and ACE4_ADD_FILE together
      with ACE4_ADD_SUBDIRECTORY and ACE4_DELETE_CHILD> (from the write
      bit in the mode) are all included based on the set of three mode
      bits appropriate to the current who-value.

      When the SVTX bit is set, ACE4_DELETE_CHILD is set, regardless of
      the values of the low-order nine bit of the mode.

   *  When named attributes are supported for the object whose mode is
      subject to change, ACE4_READ_NAMED_ATTRIBUTES is set based on the
      read bit and ACE4_WRITE_NAMED_ATTRIBUTES is set based on the write
      bit based on the set of three mode bits appropriate to the current
      who-value.

   *  In the case of OWNER@, ACE4_WRITE_ACL, ACE4_WRITE_ATTRIBUTES
      ACE4_WRITE_ACL, ACE4_WRITE_OWNER are all set.

   The union of these groups of mode bit are referred to as the mode-
   relevant mask bits.

   [Author Aside]: Except for the case of ACE4_SYNCHRONIZE, the handling
   of mask bits which are not mode-relevant is yet to be clarified.  For
   tracking purposes, the handling of mask bits ACE4_READ_ATTRIBUTES,
   ACE4_WRITE_RETENTION, ACE4_WRITE_RETENTION_HOLD, ACE4_READ_ACL will
   be dealt with as Consensus Item #31.

   If the mode is of forward-slope, then each set of three bits is
   translated into a corresponding set of mode bits.  Then, for each
   ALLOW ACE with one of these who values, all mask bits in this class
   are deleted and the computed mode bits for that who-value
   substituted.  For DENY ACEs, all mask bits in this class are reset,
   and, if none remain, the ACE MAY be deleted.

   In the case of reverse-slope modes, the following SHOULD be done:

   *  For mode-directed ACEs all mode-relevant mask bits are reset, and,
      if none remain, the ACE MAY be deleted.

   *  Then, proceeding from owner to others, ALLOW ACEs are generated
      based on the computed mode-relevant mask bits.



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      At each stage, if the mode-relevant mask bits for the current
      stage includes mask bits not set for the previous stage, then a
      DENY ACE needs to be added before the new ALLOW ACE.  That ACE
      will have a who-value based on the previous stage and a mask
      consisting of the bit included in the current stage that were not
      included in the previous stage.

   In cases in which the above recommendation is not followed, the
   server MUST follow a procedure which arrives at an ACL which behaves
   identically for all cases involving forward-slope mode values.

   When dealing with ACEs whose who-value is a named user or group, they
   SHOULD be processed as follows:

   *  DENY ACEs are left as they are.

   *  ALLOW ACES are subject to filtering to effect mode changes that
      deny access to any principal other than the owner.

      To determine the set of mode bits to which this filtering applies,
      the mode bits for group are combined with those for others, to get
      a set of three mode bits to determine which of the mode privileges
      (read, write, execute) are denied to all principals other than the
      owner, i.e. the set of bits not present in either the bits for
      group or the bits for others.

      Those three bits are converted to the corresponding set of mask
      bits, according to the rules above.

      All such mask bits are reset in the ACE, and, if none remain, the
      ACE MAY be deleted.

   In cases in which the above recommendation is not followed, the
   server MUST follow a procedure which arrives at an ACL which behaves
   identically for all cases involving forward-slope mode values.  This
   would be accomplished if the mask bits were reset based on the group
   bits alone, as had been recommended in earlier specifications.

9.8.  Setting ACL and Not Mode

   [Author Aside]: The handling of SHOULD in this section is considered
   as part of Consensus Item #25d.









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   When setting the acl or dacl and not setting the mode or
   mode_set_masked attributes, the permission bits of the mode need to
   be derived from the ACL.  In this case, the ACL attribute SHOULD be
   set as given.  The nine low-order bits of the mode attribute
   (MODE4_R*, MODE4_W*, MODE4_X*) MUST be modified to match the result
   of the method in Section 9.3.  The three high-order bits of the mode
   (MODE4_SUID, MODE4_SGID, MODE4_SVTX) SHOULD remain unchanged.

9.9.  Setting Both ACL and Mode

   When setting both the mode (includes use of either the mode attribute
   or the mode_set_masked attribute) and the acl or dacl attributes in
   the same operation, the attributes MUST be applied in the following
   order order: mode (or mode_set_masked), then ACL.  The mode-related
   attribute is set as given, then the ACL attribute is set as given,
   possibly changing the final mode, as described above in Section 9.8.

9.10.  Retrieving the Mode and/or ACL Attributes

   [Author Aside]: The handling of SHOULD in this section is considered
   as part of Consensus Item #25e.

   Some server implementations may provide for the existence of "objects
   without ACLs", meaning that all permissions are granted and denied
   according to the mode attribute and that no ACL attribute is stored
   for that object.  If an ACL attribute is requested of such a server,
   the server SHOULD return an ACL that does not conflict with the mode;
   that is to say, the ACL returned SHOULD represent the nine low-order
   bits of the mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) as
   described in Section 9.3.

   For other server implementations, the ACL attribute is always present
   for every object.  Such servers SHOULD store at least the three high-
   order bits of the mode attribute (MODE4_SUID, MODE4_SGID,
   MODE4_SVTX).  The server SHOULD return a mode attribute if one is
   requested, and the low-order nine bits of the mode (MODE4_R*,
   MODE4_W*, MODE4_X*) MUST match the result of applying the method in
   Section 9.3 to the ACL attribute.

9.11.  Creating New Objects

   [Author Aside]: The handling of SHOULD in this section is considered
   as part of Consensus Item #25f.

   If a server supports any ACL attributes, it may use the ACL
   attributes on the parent directory to compute an initial ACL
   attribute for a newly created object.  This will be referred to as
   the inherited ACL within this section.  The act of adding one or more



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   ACEs to the inherited ACL that are based upon ACEs in the parent
   directory's ACL will be referred to as inheriting an ACE within this
   section.

   Implementors need to base the behavior of CREATE and OPEN depending
   on the presence or absence of the mode and ACL attributes by
   following the directions below:

   1.  If just the mode is given in the call:

       In this case, inheritance SHOULD take place, but the mode MUST be
       applied to the inherited ACL as described in Section 9.7, thereby
       modifying the ACL.

   2.  If just the ACL is given in the call:

       In this case, inheritance SHOULD NOT take place, and the ACL as
       defined in the CREATE or OPEN will be set without modification,
       and the mode modified as in Section 9.8.

   3.  If both mode and ACL are given in the call:

       In this case, inheritance SHOULD NOT take place, and both
       attributes will be set as described in Section 9.9.

   4.  If neither mode nor ACL is given in the call:

       In the case where an object is being created without any initial
       attributes at all, e.g., an OPEN operation with an opentype4 of
       OPEN4_CREATE and a createmode4 of EXCLUSIVE4, inheritance SHOULD
       NOT take place (note that EXCLUSIVE4_1 is a better choice of
       createmode4, since it does permit initial attributes).  Instead,
       the server SHOULD set permissions to deny all access to the newly
       created object.  It is expected that the appropriate client will
       set the desired attributes in a subsequent SETATTR operation, and
       the server SHOULD allow that operation to succeed, regardless of
       what permissions the object is created with.  For example, an
       empty ACL denies all permissions, but the server need to allow
       the owner's SETATTR to succeed even though WRITE_ACL is
       implicitly denied.











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       In other cases, inheritance SHOULD take place, and no
       modifications to the ACL will happen.  The mode attribute, if
       supported, MUST be as computed in Section 9.3, with the
       MODE4_SUID, MODE4_SGID, and MODE4_SVTX bits clear.  If no
       inheritable ACEs exist on the parent directory, the rules for
       creating acl, dacl, or sacl attributes are implementation
       defined.  If either the dacl or sacl attribute is supported, then
       the ACL4_DEFAULTED flag SHOULD be set on the newly created
       attributes.

9.12.  Use of Inherited ACL When Creating Objects

   [Author Aside]: The handling of SHOULD in this section is considered
   as part of Consensus Item #25g.

   If the object being created is not a directory, the inherited ACL
   SHOULD NOT inherit ACEs from the parent directory ACL unless the
   ACE4_FILE_INHERIT_ACE flag is set.

   If the object being created is a directory, the inherited ACL is to
   inherit all inheritable ACEs from the parent directory, that is,
   those that have the ACE4_FILE_INHERIT_ACE or
   ACE4_DIRECTORY_INHERIT_ACE flag set.  If the inheritable ACE has
   ACE4_FILE_INHERIT_ACE set but ACE4_DIRECTORY_INHERIT_ACE is clear,
   the inherited ACE on the newly created directory MUST have the
   ACE4_INHERIT_ONLY_ACE flag set to prevent the directory from being
   affected by ACEs meant for non-directories.

   When a new directory is created, the server MAY split any inherited
   ACE that is both inheritable and effective (in other words, that has
   neither ACE4_INHERIT_ONLY_ACE nor ACE4_NO_PROPAGATE_INHERIT_ACE set),
   into two ACEs, one with no inheritance flags and one with
   ACE4_INHERIT_ONLY_ACE set.  (In the case of a dacl or sacl attribute,
   both of those ACEs SHOULD also have the ACE4_INHERITED_ACE flag set.)
   This makes it simpler to modify the effective permissions on the
   directory without modifying the ACE that is to be inherited to the
   new directory's children.

9.13.  Combined Authorization Models for NFSv4.2

   The NFSv4 server implementation requirements described in the
   subsections above apply to NFSv4.2 as well and NFSv4.2 clients can
   assume that the server follows them.








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   NFSv4.2 contains an OPTIONAL extension, defined in RFC8257 [15],
   which is intended to reduce the interference of modes, restricted by
   the umask mechanism, with the acl inheritance mechanism.  The
   extension allows the client to specify the umask separately from the
   mask attribute.

10.  Labelled NFS Authorization Model

   The labelled NFS feature of NFSv4.2 is designed to support Mandatory
   Access control.

   The attribute sec_label enables an authorization model focused on
   Mandatory Access Control and is described in Section 10.

   Not much can be said about this feature because the specification, in
   the interest of flexibility, has left important features undefined in
   order to allow future extension.  As a result, we have something that
   is a framework to allow Mandatory Access Control rather than one to
   provide it.  In particular,

   *  The sec_label attribute, which provides the objects label has no
      existing specification.

   *  There is no specification of the of the format of the subject
      label or way to authenticate them.

   *  As a result, all authorization takes place on the client, and the
      server simply accepts the client's determination.

   This arrangements shares important similarities with AUTH_SYS.  As
   such it makes sense:

   *  To require/recommend that an encrypted connection be used.

   *  To require/recommend that client and server peers mutually
      authenticate as part of connection establishment.

   *  That work be devoted to providing a replacement without the above
      issues.

11.  State Modification Authorization

   Modification of locking and session state data are not be done by a
   client other than the one that created the lock.  For this form of
   authorization, the server needs to identify and authenticate client
   peers rather than client users.





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   Such authentication is not directly provided by any RPC auth flavor.
   However, RPC can, when suitably configured, provide this
   authentication on a per-connection basis.

   NFSv4.1 defines a number of ways to provide appropriate authorization
   facilities.  These will not be discussed in detail here but the
   following points need to be noted:

   *  NFSv4.1 defines the MACHCRED mechanism which uses the RPCSEC_GSS
      infrastructure to provide authentication of the clients peer.
      However, this is of no value when AUTH_SYS is being used.

   *  NFSv4.1 also defines the SSV mechanism which uses the RPCSEC_GSS
      infrastructure to enable it to be reliably determined whether two
      different client connections are connected to the same client.  It
      is unclear whether the word "authentication" is appropriate in
      this case.  As with MACHCRED, this is of no value when AUTH_SYS is
      being used.

   *  Because of the lack of support for AUTH_SYS and for NFSv4.0, it is
      quite desirable for clients to use and for servers to require the
      use of client-peer authentication as part of connection
      establishment.

   When unauthenticated clients are allowed, their state is exposed to
   unwanted modification as part of disruption or denial-of-service
   attacks.  As a result, the potential burdens of such attacks are felt
   principally by clients who choose not to provide such authentication.

12.  Other Uses of Access Control Lists

   Whether the acl or sacl attributes are used, AUDIT and ALARM ACEs
   provide security-related facilities separate from the the file access
   authorization provide by ALLOW and DENY ACEs

   *  AUDIT ACEs provide a means to audit attempts to access a specified
      file by specified sets of principals.

   *  ALARM ACEs provide a means to draw special attention to attempts
      to access specified files by specified sets of principals.

12.1.  V4.1 Attribute 59: sacl

   The sacl attribute is like the acl attribute, but sacl allows only
   AUDIT and ALARM ACEs.  The sacl attribute supports automatic
   inheritance (see Section 5.10).





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13.  Identification and Authentication

   Various objects and subjects need to be identified for a protocol to
   function.  For it to be secure, many of these need to be
   authenticated so that incorrect identification is not the basis for
   attacks.

13.1.  Identification vs. Authentication

   It is necessary to be clear about this distinction which has been
   obscured in the past, by the use of the term "RPC Authentication
   Flavor" in connection with situation in which identification without
   authentication occurred or in which there was neither identification
   nor authentication involved.  As a result, we will use the term "Auth
   Flavors" instead

13.2.  Items to be Identified

   Some identifier are not security-relevant and can used be used
   without authentication, given that, in the authorization decision,
   the object acted upon needs only to be properly identified

   *  File names are of this type.

      Unlike the case for some other protocols, confusion of names that
      result from internationalization issues, while an annoyance, are
      not relevant to security.  If the confusion between LATIN CAPITAL
      LETTER O and CYRILLIC CAPITAL LETTER O, results in the wrong file
      being accessed, the mechanisms described in Section 7 prevent in
      appropriate access being granted.

      Despite the above, it is desirable if file names together with
      similar are not transferred in the clear as the information
      exposed may give attackers useful information helpful in planning
      and executing attacks.

   *  The case of file handles is similar.

   Identifiers that refer to state shared between client and server can
   be the basis of disruption attacks since clients and server
   necessarily assume that neither side will change the state corpus
   without appropriate notice.

   While these identifiers do not need to be authenticated, they are
   associated with higher-level entities for which change of the state
   represented by those entities is subject to peer authentication.





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   *  Unexpected closure of stateids or changes in state sequence values
      can disrupt client access as no clients have provision to deal
      with this source of interference.

      While encryption may make it more difficult to execute such
      attacks attackers can often guess stateid's since server generally
      not randomize them.

   *  Similarly, modification to NFSv4.1 session state information can
      result in confusion if an attacker changes the slot sequence by
      assuring spurious requests.  Even if the request is rejected, the
      slot sequence is changed and clients may a difficult time getting
      back in sync with the server.

      While encryption may make it more difficult to execute such
      attacks attackers can often guess slot id's and obtain sessinid's
      since server generally do not randomize them.


   it is necessary that modification of the higher-levell entities be
   restricted to the client that created them.

   *  For NFSv4.0, the relevant entity is the clientid.

   *  for NFSv4.1, the relevant entity is the sessionid.

   Identifiers describing the issuer of the request, whether in numeric
   or string form always require authentication.

13.3.  Authentication Provided by specific RPC Auth Flavors

   Different auth flavors differ quite considerably, as discussed below;

   *  When AUTH_NONE is used, the user making the request is neither
      authenticated nor identified to the server.

      Also, the server is not authenticated to the client and has no way
      to determine whether the server it is communicating with is an
      imposter.

   *  When AUTH_SYS is used, the user making is the request identified
      but there no authentication of that identification.

      As in the previous case, the server is not authenticated to the
      client and has no way to determine whether the server it is
      communicating with is an imposter.





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   *  When RPCSEC_GSS is used, the user making the request is
      authenticated as is the server peer responding.

13.4.  Authentication Provided by other RPC Security Services

   Depending on the connection type used, RPC may provide additional
   means of authentication.  In contrast with the case of RPC auth
   flavors, any authentication happens once, at connection
   establishment, rather than on each RPC request.  As a result, it is
   the client and server peers, rather than individual users that are
   authenticated.

   *  For many types of connections such as those created TCP without
      RPC-with-TLS and RPC-over-RDMA version 1, there is no provision
      for peer authentication.

      As a result use of AUTH_SYS using such connections is inherently
      problematic.

   *  Some connection types provide for the possibility of mutual peer
      authentication.  These currently include only those established by
      RPC-with-TLS.  However, given the value of peer authentication,
      there is reason to believe further means of providing such
      services will be defined.

14.  Security of Data in Flight

14.1.  Data Security Provided by Services Associated with Auth Flavors

   The only auth flavor providing these facilities is RPCSEC_GSS.  When
   this auth flavor is used, data security can be negotiated between
   client and server as described in Section 15.  However, when data
   security is provided for the connection level, as described in
   Section 14.2, the negotiation of privacy and integrity support,
   provided by the auth flavor, is unnecessary,

   Other auth flavors, such as AUTH_SYS and AUTH_NONE have no such data
   security facilities.  When these auth flavors are used, the only data
   security is provided on a per-connection basis.

14.2.  Data Security Provided for a Connection by RPC

   RPC, in many case, provide data security for all transactions
   performed on a connection, eliminating the need for that security to
   be provided or negotiated by the selection of particular auth
   flavors, mechanisms, or auth-flavor-associated services.





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15.  Security Negotiation

   [Author Aside]: All unannotated paragraphs in this section are
   considered part of Consensus Item #32a.

   Because of the availability of security-related services associated
   with the transport layer, the security negotiation process needs to
   be enhanced so that the server can indicate the services needed,
   rather than, as previously, depending on the specification of
   acceptable auth flavors and services provided by RPCSEC_GSS.

   The situations listed below needed to be provided for.  In each of
   them, there is a possibility that a new connection will be needed for
   new requests since the security issue might not be resolvable only by
   using a new auth flavor on an existing connection.  The possible
   existence of multiple connections with different security
   characteristics makes it necessary that clients direct requests to
   the correct connection and that servers be aware of the security
   characteristics of te connection on which requests were received.
   This issue id discussed in Section 15.1.

   *  When one or more of the auth flavors AUTH_NONE and and AUTH_SYS is
      accepted by a server, there is often a server policy requirement
      that it be used with encryption or peer authentication provided as
      a transport layer service.  In such cases, the pseudo-flavors
      defined in [13] can be used to indicate that the corresponding
      auth flavor may be validly used, but only when the connection's
      characteristics meet the requirements of the pseudo-flavor.

      As a result, when NFS4ERR_WRONGSEC is received as a result of
      using one of these auth flavors, the client will, if it wishes to
      continue using one of these flavors, establish a new connection,
      with the appropriate security characteristics.

   *  When the server's policy requirement is that encryption by used to
      access a region of the namespace, a secinfo entry will be returned
      identifying RPCSEC_GSS as an appropriate auth flavor to use while
      indicating that privacy/confidentiality is also needed.

      In that case, the client MAY obtain the necessary confidentiality
      either by sending requests requesting that confidentiality be
      provided by RPCSEC_GSS, or by making the requests on a connection
      for which confidentiality is provided at the transport layer.








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   *  When the server's policy requirement is that transport-level
      encryption be used, and a subsequent entry indicates that
      RPCSEC_GSS is an acceptable auth flavor, a section entry of type
      FL_GSS_CRYPT (described in Section 18.2) indicates that this auth
      flavor is only to be used on connections that provide this
      facility.

      Unlike the previous case, the client has no choice as to how
      confidentiality is to be provided as server has indicated, by
      using FL_GSS_CRYPT that transport-provide encryption required.
      Also, in this case, the information in the RPCSEC_GSS secinfo
      entry regarding regarding services to be provided by the auth
      flavor, is to be ignored.

   *  When the server's policy requirement is that mutual peer
      authentication be provided and the secinfo entry indicates that
      RPCSEC_GSS is an acceptable auth flavor, a previous section entry
      of type FL_GSS_MPA (described in Section 18.2) indicates that this
      auth flavor is only to be used on connections that provide this
      facility.

      Unlike the previous case, the information in the RPCSEC_GSS
      secinfo entry regarding regarding services to be provided by the
      auth flavor, is to be consulted and might be relevant if the
      transport provides mutual peer authentication without encryption.

15.1.  Dealing with Multiple Connections

   [Author Aside]: All unannotated paragraphs in this section are
   considered part of Consensus Item #32b.

   Because effective security will require both an appropriate auth
   flavor (and possibly services provide by the auth flavor) together
   with appropriate connection characteristics, it is often necessary
   that clients and server be aware of connection characteristics:

   *  When multiple connections with different security-related
      characteristics, are used to access a server, the clients needs to
      ensure that each request is issued on a an appropriate connection.

   *  Similarly, in such situations, the server needs to be aware of the
      security-related characteristics for the connection pn which each
      request is received, in order to enforce its security policy.

   Depending on how the client and server implementations are
   structured, implementations may have to be changed to accomplish the
   above.




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   In the case of NFSv4.1 and above, the protocol requires that requests
   associated with a given session only be issued on connections bound
   to that session and accepted by the server only when that binding is
   present.  This makes it likely that clients or servers will be able
   to correctly associate requests with the appropriate connections
   although additional work might be necessary to enable them to
   determine, for any given connection, its security characteristics.

   In the case of NFSv4.0, no such binding is present in the protocol so
   that, depending on existing implementations' layering, channel
   binding functionality might have to be added.

   This subject is discussed, in the context of pseudo-flavors
   associated with the auth flavors AUTH_SYS and AUTH_NONE in Section 4
   of [13].  That treatment is equally applicable to the pseudo-flavor
   defined in this document.

16.  Future Security Needs

   [Author Aside]: All unannotated paragraphs in this section are to be
   considered part of Consensus Item #35a.

   [Author Aside]: This section is basically an outline for now, to be
   filled out later based on Working Group input, particularly from
   Chuck Lever who suggested this section and has ideas about many of
   the items in it.

   *  Security for data-at-rest, most probably based on facilities
      defined within SAN.

   *  Support for content signing.

   *  Revision/extension of labelled NFS to provide true
      interoperability and server-based authorization.

   *  Work to provide more security for RDMA-based transports.  This
      would include the peer authentication infrastructure now being
      developed as part of RPC-over-RDMA version 2.  In addition, there
      is a need for an RDMA-based transport that provides for
      encryption, which might be provided in number of ways.

   *  Work, via extensions, to provide attributes describing server
      behavior to the client.  This is likely to have an important role
      in resolving security issues connected with ACLs where there is
      both a new preferred approach together with legacy implementations
      built when the specifications wither offered no preferred approach
      or treated that preference as easily dispensed with.




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   *  [Consensus Needed (Item #56c)]: Potential support for an optional
      attribute to provide a UNIX ACL attribute as an NFSv4 extension.

17.  Security Considerations

17.1.  Changes in Security Considerations

   Beyond the needed inclusion of a threat analysis as Section 17.4 and
   the fact that all minor versions are dealt with together, the
   Security Considerations in this section differ substantially from
   those in RFCs 7530 [6] and 8881 [8].  These differences derive from a
   number of substantive changes in the approach to NFSv4 security
   presented in RFCs 7530 [6] and 8881 [8] and that appearing in this
   document.

   These changes were made in order to improve the security of the NFSv4
   protocols because it had been concluded that the previous treatment
   of these matters was in error, leading to a situation in which
   NFSv4's security goals were not met.  As a result, this document
   supersedes the treatment of security in earlier documents, now viewed
   as incorrect.  However, it will, for the benefit of those familiar
   with the previous treatment of these matters, draw attention to the
   important changes listed here.

   *  There is a vastly expanded range of threats being considered as
      described in Section 17.1.1

   *  New facilities provided by RPC on a per-connection basis can be
      used to deal with security issues, as described in Section 17.1.2.
      These include the use encryption on a per-connection basis, and
      the use of peer mutual authentication, to mitigate the security
      problems that come with the use of AUTH_SYS.

   *  The handling of identities with superuser privileges is no longer
      part of NFSv4 semantics, even though many platforms on which NFSv4
      servers are implemented continue to depend, for local operation,
      on the existence of such identities.

      NFSv4 servers SHOULD NOT provide for such unrestricted access
      since doing so would provide a means by which an escalation-of-
      privilege on a client could be used to compromise a server to
      which it was connected, affecting all clients of that server.

      In connection with the use of "SHOULD NOT" above, and similar uses
      elsewhere, it is to be understood that valid reasons to do other
      than recommended are limited to the difficulty of promptly
      changing existing server implementations and the need to
      accommodate clients that have become dependent upon the existing



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      handling.  Further, those maintaining or using such
      implementations need to be aware of the security consequences of
      such use as well as the fact that clients who become aware of this
      characteristic may not be inclined to store their data on such a
      system.

   *  The appropriate handling of ACL-based authorization and necessary
      interactions between ACLs and modes is now specified in this
      standards-track document rather it being assumed that the behavior
      of server implementations needs to be accepted and deferred to.

17.1.1.  Wider View of Threats

   Although the absence of a threat analysis in previous treatments
   makes comparison most difficult, the security-related features
   described in previous specifications and the associated discussion in
   their security considerations sections makes it clear that earlier
   specifications took a quite narrow view of threats to be protected
   against and placed the burden of providing for secure use on those
   deploying such systems with very limited guidance as to how such
   secure use could be provided.

   One aspect of that narrow view that merits special attention is the
   handling of AUTH_SYS, at that time in the clear, with no client peer
   authentication.

   With regard to specific threats, there is no mention in existing
   security considerations sections of:

   *  Denial-of-service attacks.

   *  Client-impersonation attacks.

   *  Server-impersonation attacks.

   The handling of data security in-flight is even more troubling.

   *  Although there was considerable work in the protocol to allow use
      of encryption to be negotiated when using RPCSEC_GSS.  The
      existing security considerations do not mention the potential need
      for encryption at all.

      It is not clear why this was omitted but it is a pattern that
      cannot repeated in this document.

   *  The case of negotiation of integrity services is similar and uses
      the same negotiation infrastructure.




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      In this case, use of integrity is recommended but not to prevent
      the corruption of user data being read or written.

      The use of integrity services is recommended in connection with
      issuing SECINFO (and for NFSv4.1, SECINFO_NONAME).  The presence
      of this recommendation in the associated security considerations
      sections has the unfortunate effect of suggesting that the
      protection of user data is of relatively low importance.

17.1.2.  Connection-oriented Security Facilities

   Such RPC facilities as RPC-with-TLS provide important ways of
   providing better security for all the NFSv4 minor versions.

   In particular:

   *  The presence of encryption by default deals with security issues
      regarding data-in-flight, whether RPCSEC_GSS or AUTH_SYS is used
      for client principal identification.

   *  Peer authentication provided by the server eliminates the
      possibility of a server-impersonation attack, even when AUTH_SYS
      or AUTH_NONE is used to issue requests

   *  When mutual authentication is part of connection establishment,
      there is a possibility, where an appropriate trust relationship
      exists, of treating the uids and gids presented in AUTH_SYS
      requests, as effectively authenticated, based on the
      authentication of the client peer.

17.1.3.  Necessary Security Changes

   [Consensus Needed (Items #36a, #37a)]: For a variety of reasons,
   there are many cases in which a change to the security approach has
   been adopted but for which provisions have been made in order to give
   implementers time to adapt to the new approach.  In such cases the
   words "SHOULD", "SHOULD NOT", and "RECOMMENDED" are used to introduce
   the new approach while use of the previous approach is allowed on a
   temporary basis, by limiting the valid reasons to bypass the
   recommendation.  Such instances fall into two classes:

   *  [Consensus Needed (Item #36a)]: In adapting to the availability of
      security services provided by RPC on a per-connection basis,
      allowance has been made for implementations for which these new
      facilities are not available and for which, based on previous
      standards-track guidance, AUTH_SYS was used, in the clear, without
      client-peer authentication.




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   *  [Consensus Needed (Item #37a)]: In dealing with server
      implementations that support both ACLs and the mode attribute,
      previous specifications have allowed a wide range of possible
      server behavior in coordinating these attributes.  While this
      document now clearly defines the recommended behavior in dealing
      with these issues, allowance has been made to provide time for
      implementations to conform to the new recommendations.

   [Consensus Needed (Items #36a, #37a)]: The threat analysis within
   this Security Considerations section will not deal with older servers
   for which allowance has been made but will explore the consequences
   of the recommendations made in this document.

17.1.4.  Compatibility and Maturity Issues

   [Author Aside]: All unannotated paragraphs within this section are
   considered part of Consensus Item #38a.

   Given the need to drastically change the NFSv4 security approach from
   that specified previously, it is necessary for us to be mindful of:

   *  The difficulty that might be faced in adapting to the newer
      guidance because the delays involved in designing, developing, and
      testing new connection-oriented security facilities such as RPC-
      with-TLS.

   *  The difficulty in discarding or substantially modifying previous
      existing deployments and practices, developed on the basis of
      previous normative guidance.

   For these reasons, we will not use the term "MUST NOT" in some
   situations in which the use of that term might have been justified
   earlier.  In such cases, previous guidance together with the passage
   of time may have created a situation in which the considerations
   mentioned above in this section may be valid reasons to defer, for a
   limited time, correction of the current situation making the term
   "SHOULD NOT" appropriate, since the difficulties cited would
   constitute a valid reason to not allow what had been recommended
   against.

17.1.5.  Discussion of AUTH_SYS

   [Author Aside]: All unannotated paragraphs within this section are
   considered part of Consensus Item #39a.

   An important change concerns the treatment of AUTH_SYS which is now
   divided into two distinct cases given the possible availability of
   connection-oriented support from RPC.



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   When such support is not available, AUTH_SYS SHOULD NOT be used,
   since it makes the following attacks quite easy to execute:

   *  The absence of authentication of the server to the client allow
      server impersonation in which an imposter server can obtain data
      to be written by the user and supply corrupted data to read
      requests.

   *  The absence of authentication of the client user to the server
      allow client impersonation in which an imposter client can issue
      requests and have them executed as a user designated by imposter
      client, vitiating the server's authorization policy.

      With no authentication of the client peer, common approaches, such
      as using the source IP address can be easily defeated, allowing
      unauthenticated execution of requests made by the pseudo-clients

   *  The absence of any support to protect data-in-flight when AUTH_SYS
      is used result in further serious security weaknesses.

   In connection with the use of the term "SHOULD NOT" above, it is
   understood that the "valid reasons" to use this form of access
   reflect the Compatibility and Maturity Issue discussed above in
   Section 17.1.4 and that it is expected that, over time, these will
   become less applicable.

17.2.  Security Considerations Scope

17.2.1.  Discussion of Potential Classification of Environments

   [Author Aside]: All unannotated paragraphs within this section are
   considered part of Consensus Item #40a.

   This document will not consider different security policies for
   different sorts of environments.  This is because,

   *  Doing so would add considerable complexity to this document.

   *  The additional complexity would undercut our main goal here, which
      is to discuss secure use on the internet, which remain an
      important NFSv4 goal.

   *  The ubiquity of internet access makes it hard to treat corporate
      networks separately from the internet per se.







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   *  While small networks might be sufficiently isolated to make it
      reasonable use NFSv4 without serious attention to security issues,
      the complexity of characterizing the necessary isolation makes it
      impractical to deal with such cases in this document.

17.2.2.  Discussion of Environments

   [Author Aside]: All unannotated paragraphs within this section are
   considered part of Consensus Item #40b.

   Although the security goal for Nfsv4 has been and remains "secure use
   on the internet", much use of NFSv4 occurs on more restricted IP
   corporate networks with NFS access from outside the owning
   organization prevented by firewalls.

   This security considerations section will not deal separately with
   such environments since the threats that need to be discussed are
   essentially the same, despite the assumption by many that the
   restricted network access would eliminate the possibility of attacks
   originating inside the network by attackers who have some legitimate
   NFSv4 access within it.

   In organizations of significant size, this sort of assumption of
   trusted access is usually not valid and this document will not deal
   with them explicitly.  In any case, there is little point in doing
   so, since, if everyone can be trusted, there can be no attackers,
   rendering threat analysis superfluous.

   In corporate networks, as opposed to the Internet, there is good
   reason to be less concerned about denial-of-service attacks, since
   there is no tangible benefit to attackers inside the organization,
   and the anonymity that makes such attacks attractive to outside
   attackers will not be present.

   The above does not mean that NFSv4 use cannot, as a practical matter,
   be made secure through means outside the scope of this document
   including strict administrative controls on all software running
   within it, frequent polygraph tests, and threats of prosecution.
   However, this document is not prepared to discuss the details of such
   policies, their implementation, or legal issues associated with them
   and treats such matters as out-of-scope.










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   Nfsv4 can be used in very restrictive IP network environments where
   outside access is quite restricted and there is sufficient trust to
   allow, for example, every node to have the same root password.  The
   case of a simple network only accessible by a single user is similar.
   In such networks, many thing that this document says "SHOULD NOT" be
   done are unexceptionable but the responsibility for making that
   determination is one for those creating such networks to take on.
   This document will not deal further with NFSv4 use on such networks.

17.2.3.  Insecure Environments

   As noted in Section 17.2.2, NFSv4 is often used in environments of
   much smaller scope than the internet, with the assumption often being
   made, that the prevention of NFSv4 access from outside the
   organization makes the attention to security recommended by this
   document unnecessary, the possibility of insider attacks being
   explicitly or implicitly disregarded.

   As a result, there will be implementations that do not conform to
   these recommendations, many of which because the implementations were
   based on RFCs 3530 [6], 7530 [6], 5661 [16], or 8881 [8].  In
   addition to these cases in which the disregard of the recommendations
   is considered valid because implementors relied on existing normative
   guidance, there will be other cases in which implementors choose to
   ignore these recommendations,

   Despite the original focus of RFC2119 [1] on interoperability, many
   such implementations will interoperate, albeit without effective
   security, whether the reasons that the recommendations are not
   adhered to are considered valid or not.

   When such insecure use is mentioned in this Security Considerations
   section it will only be in explaining the need for the
   recommendations, by explaining the likely consequences of not
   following them.  The threat analysis, in Section 17.4 and included
   subsections, will not consider such insecure use and will concern
   itself with situation in which these recommendations are followed.

17.3.  Major New Recommendations

17.3.1.  Recommendations Regarding Security of Data in Flight

   [Author Aside]: All unannotated paragraphs within this section are
   considered part of Consensus Item #41b.







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   It is RECOMMENDED that requesters always issue requests with data
   security (i.e. with protection from disclosure or modification in
   flight) whether provided at the RPC request level or on a per-
   connection basis, irrespective of the responder's requirements.

   It is RECOMMENDED that implementers provide servers the ability to
   configure policies in which requests without data security will be
   rejected as having insufficient security.

   It is RECOMMENDED that servers use such policies over either their
   entire local namespace or for all file systems except those clearly
   designed for the general dissemination of non-sensitive data.

   When these recommendations are not followed, data, including data for
   which disclosure is a severe [problem is exposed to unwanted
   disclosure or modification in flight.  Depending on the server to be
   aware of the need for confidentiality or integrity, as expected by
   previous specifications, has not proved workable, making encryption
   by default as provided uniformly by RPC (e.g. through RPC-with-TLS)
   necessary.

17.3.2.  Recommendations Regarding Client Peer Authentication

   [Author Aside]: All unannotated paragraphs within this section are
   considered part of Consensus Item #41c.

   It is RECOMMENDED that clients provide authentication material
   whenever a connection is established with a server capable of using
   it to provide client peer authentication.

   It is RECOMMENDED that implementers provide servers the ability to
   configure policies in which attempts to establish connections without
   client peer authentication will be rejected.

   It is RECOMMENDED that servers adopt such policies whenever requests
   not using RPCSEC_GSS (i.e.  AUTH_NONE Or AUTH_SYS) are allowed to be
   executed.

   When these recommendations are not followed, it is possible for
   connections to be established between servers and client peers that
   have not been authenticated with the following consequences:

   *  The server will be in the position of executing requests where the
      identity used in the authorization of operations is not
      authenticated, including cases in which the identification has
      been fabricated by an attacker.





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   *  When no identification of a specific user is needed or present
      (i.e AUTH_NO is used) there is no way of verifying that the
      request was issued by the appropriate client peer.

   When the recommendations are followed, use of AUTH_SYS can be valid
   means of user authentication, so long as due attention is paid to the
   discussion in Section 17.4.6.1.  Despite this fact, the description
   of AUTH_SYS as an "OPTIONAL means of authentication"is no longer
   appropriate since choosing to use it requires heightened attention to
   security as discussed later in this document.

17.3.3.  Recommendations Regarding Superuser Semantics

   [Author Aside]: All unannotated paragraphs within this section are
   considered part of Consensus Item #52b.

   It is RECOMMENDED that servers adhere to the ACL semantics defined in
   this document and avoid granting to any remote user, however
   authenticated, unrestricted access capable of authorizing access
   where the file/directory ACL would deny it.

   Servers are free to conform to this recommendation either by
   implementing authorization semantics without provisions for
   superusers or by mapping authenticated users that would have
   superuser privileges to users with with more limited privileges (e.g.
   "nobody").

   It needs to b e understood that the second of these choices is
   preferable when there are NFsv4-accessible files owned by a special
   users (e.g. root) whose compromise might be taken advantage of by
   attackers to enable permanent unauthorized access to a server.

17.3.4.  Issues Regarding Valid Reasons to Bypass Recommendations

   [Author Aside]: All unannotated paragraphs within this section are
   considered part of Consensus Item #41d.

   Clearly, the maturity and compatibility issues mentioned in
   Section 17.1.4 are valid reasons to bypass the proposed
   recommendations requiring pervasive use of encryption, as long as
   these issues continue to exist.

   [Author Aside]: The question the working group needs to address is
   whether other valid reasons exist.

   [Author Aside]: In particular, some members of the group might feel
   that the performance cost of conection-based encryption constitutes,
   in itself, a valid reason to ignore the above recommendations.



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   [Author Aside]: I cannot agree and feel that accepting that as a
   valid reason would undercut Nfsv4 security improvement, and probably
   would not be acceptable to the security directorate.  However, I do
   want to work out an a generally acceptable compromise.  I propose
   something along the following lines:

   In dealing with recommendations requiring pervasive use of
   connection-based encryption, it needs to be understood that the
   connection-based encryption facilities are designed to be compatible
   with facilities to offload the work of encryption and decryption.
   When such facilities are not available, at a reasonable cost, to
   NFSv4 servers and clients anticipating heavy use of NFSv4, then the
   lack of such facilities can be considered a valid reason to bypass
   the above recommendations, as long as that situation continues.

17.4.  Threat Analysis

17.4.1.  Threat Analysis Scope

   Because of the changes that have been made in NFSv4 security, it
   needs to be made clear that the primary goal of this threat analysis
   is to explore the threats that would be faced by implementations that
   follow the recommendations in this document.

   When the possibility is raised of implementations that do not conform
   to these recommendations, the intention is to explain why these
   recommendations were made rather that to expand the the scope of the
   threat analysis to include implementations that bypass/ignore the
   recommendations.

   The typical audience for threat analyses is client and server
   implementers, to enable implementations to be developed that are
   resistant to possible threats.  While much of the material in
   Section 17.4 is of that form, it also contains material that relates
   to threats whose success depends primarily on the ways in which the
   implementation is deployed, such as the threats discussed in Sections
   17.4.2, 17.4.4 and 17.4.3.  While it is not anticipated that those
   deploying implementations will be aware of the detail of this threat
   analysis, it is expected that implementors could use this material to
   properly set expectations and provide guidance helpful to making
   deployments secure.

17.4.2.  Threats based on Credential Compromise

   In the past, it had been assumed that a user-selected password could
   serve as a credential, the knowledge of which was adequate to
   authenticate users and provide a basis for authorization.




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   That assumption is no longer valid for a number of reasons:

   *  The inability or unwillingness of users to remember multiple
      passwords has meant that the single password they will remember
      controls access to large set of resources, increasing the value of
      this knowledge to attackers and the effort that will be expended
      to obtain it.

      In addition, the common use of a single password for applying to
      all of a user's data has resulted in a situation in which the
      client is aware of user passwords (since they are used for client
      login) that apply to data on many servers.  As will be seen later,
      this has the effect of changing the considerations appropriate to
      comparing the security of AUTH_SYS and RPCSEC_GSS.

   *  CPU developments have made exhaustive search possible for larger
      classes of passwords.

   *  The success of "phishing" attacks taking advantage of user
      gullibility provides an additional path to credential compromise
      which need to be addressed in the near-term by those deploying
      NFSv4, and will eventually need work in the security
      infrastructure on which NFSv4 is built.

   In the near term, there are a number of steps, listed below that
   those deploying NFSv4 servers can take to mitigate these weaknesses.
   These steps are outside the scope of the NFSv4 protocols and
   implementors only role with regard to them is to make it clear that
   these weaknesses exist and generally require mitigation.

   *  Limitations on password choice to eliminate weak passwords.

   *  Requirements to change passwords periodically.

   *  User education about "phishing" attacks including ways to report
      them and effective ways of replacing a compromised password.

   From a longer-term perspective, it appears that password-based
   credentials need to be either replaced or supplemented by some form
   of multi-factor authentication.  Since NFSv4's approach to security
   relies on RPC, that work would most probably be done within the RPC
   layer, limiting the work that implementations and the NFSv4 protocols
   would have to do to adapt to these changes once they are available.
   While the precise form of these changes is not predictable, the
   following points need to be kept in mind.






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   *  [Verification Needed (Item #53a)]: For those using RPCSEC_GSS
      authentication of principals, it appears that RPCSEC_GSS interface
      is flexible enough that the addition of a second credential
      element, in the form of a one-time code could be added.

      [Elaboration/Verification Needed (Item #53a)]: Enhancement of
      Kerberos is one possibility to provide multi-factor
      authentication.  However, work on this is not far enough along to
      enable deployment to be discussed now.

      If this approach were taken, rogue servers would still have access
      to user passwords but their value would be reduced since the
      second credential element would have a very limited lifetime.

   *  For those using AUTH_SYS to identify principals, the client
      operating system's authentication of user at login would need to
      be enhanced to use multi-factor authentication.

      If this were done, the client would retain responsibility for
      credential verification with the server needing to trust the
      client, as discussed in Section 17.4.6.1.

      Although there is need for protocol standardization to enable this
      approach to be commonly used, it is not likely to be widely used
      until some operating system adopts it for user login.

   *  One important variant of AUTH_SYS use concerns clients used by a
      single user, when, as recommended, client-peer authentication is
      in effect For such clients, it is possible for the authentication
      of that specific client peer to effectively become the second
      factor, in a multi-factor authentication scheme.

      Despite the fact that the the RPC-with-TLS specification [12])
      does not allow TLS to used for user authentication, this
      arrangement in which the user identity is inferred from the peer
      authentication, could be used to negate the effects of credential
      compromise since an attacker would need both the user password,
      and the physical client to gain access.

17.4.3.  Threats Based on Rouge Clients

   When client peers are not authenticated, it is possible to a node on
   the network to pretend to be a client.  In the past, in which servers
   only checked the from-IP address for correctness, address spoofing
   would allow unauthenticated request to be executed, allowing
   confidential data to be read or modified.





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   Now that such use of AUTH_SYS is recommended against, this cannot
   happen.  The recommended practice is to always authenticate client
   peers making this sort of imposture easily detectable by the server.

   Despite this protection, it is possible that an attacker, through a
   client vulnerability unrelated to NFSv4, or the installation of
   malware, could effectively control the client peer and act as
   imposter client would, effectively undercutting the authentication of
   the client.  This possibility makes it necessary, as discussed in
   Section 17.4.6.1 that those deploying NFSv4 clients using AUTH_SYS
   takes steps to limit the set of user identifications accepted by a
   server and to limit the ability of rogue code running on the server
   to present itself as a client entitled to use AUTH_SYS.

17.4.4.  Threats Based on Rouge Servers

   When server peers are not authenticated, it is possible for a node on
   the network to act as if it were an NFSv4 server, with the ability to
   save data sent to it and use it or pass it to other, rather than
   saving it in the file system, as it needs to do..

   When current recommendations are adhered to, this is be prevented as
   follows:

   *  When RPCSEC_GSS is used, the mutual authentication of the server
      and client principal provides assurance the server is not an
      imposter.

   *  When AUTH_SYS or AUTH_NONE is used, the mutual authentication of
      client and server peers provides assurance the server is not an
      imposter.

   Despite this protection, it is possible that an attacker, through a
   operating system vulnerability unrelated to NFSv4, or the
   installation of malware, could effectively control the server peer
   and act as an imposter server would, effectively undercutting the
   authentication of the server.

   The above possibility makes it necessary, that those deploying NFSv4
   servers take the following steps, particularly in cases in cases in
   which the server has access to user credentials, including, but not
   limited to, cases in which AUTH_SYS is supported

   When an NFSv4 is implemented as part of a general-purpose operating
   system, as it often is, steps need to be taken to limit the ability
   of attackers to take advantage of operating system vulnerabilities
   that might allow the attacker to obtain privileged access and subvert
   the servers operation, turning it, effectively, into a rogue server.



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   Such steps include controls on the software installed on the machine
   acting as the server, and limitation of the network access to
   potentially dangerous sites.

17.4.5.  Data Security Threats

   When file data is transferred in the clear, it is exposed to unwanted
   exposure.  As a result, this document recommends that encryption
   always be used to transfer NFSv4 requests and responses.

   That encryption, whether done on encrypted connections, or on a per-
   request basis, using RPCSEC_GSS security services, provides the
   necessary confidentiality.  In addition, it contributes to security
   in other ways as well:

   *  The ability of an attacker to plan and execute attacks is enhanced
      by the monitoring of client-server traffic, even if none of the
      data intercepted is actually confidentiality.

      An attacker can deduce which users are allowed to read or write a
      specific file by examining the results of OPEN and ACCESS
      operations allowing later attacks to impersonate users with the
      appropriate access.

   *  All the methods on encryption used with NFS4 provide a checksum,
      to enable the detection of unwanted modifications to data being
      read or written.

17.4.6.  Authentication-based threats

17.4.6.1.  Attacks based on the use of AUTH_SYS

   Servers, when they allow access using AUTH_SYS, to a specific client
   machines using AUTH_SYS are responsible for ensuring that the
   principal identifications presented to the server can be relied upon.

   The existence of client-peer authentication as recommended in
   Section 17.1.5 means that imposter servers can be detected and not
   allowed to use AUTH_SYS.  However there are an additional number of
   issues that need to be addressed to adequately protect against use of
   AUTH_SYS enabling attacks:

   *  The server accepting requests using AUTH_SYS needs to determine
      that the authenticated client-peer can be trusted to properly
      authenticate the principals that it identifies in requests.






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      The specific standards for trustworthiness are up to the server
      but they need to take account of the controls in place to prevent
      malware from pretending to be a client and thus taking advantage
      of the fact that the request is from the expected client machine.

      This server MUST NOT accept AUTH_SYS requests from unknown clients
      or from unauthenticated clients.

   *  [Elaboration Needed (Item #54a)]: The client verification
      procedure needs to take steps to prevent code on a compromised
      client to presenting itself as the successor to a legitimate
      client, taking advantage of the fact that the machine is the same.

   *  Given the inherent vulnerabilities of client operating systems, it
      is desirable, to limit the set of users whose identification will
      be accepted.  The elimination of particular users such as "root'
      is one long-standing approach to the issue but it probably isn't
      sufficient in most environments.  More helpful would be the
      ability to exclude multiple sensitive users or group of users or
      to limit the user identifications accepted to a user group or a
      single user.

   Another important that issue that arises when AUTH_SYS is used
   concerns the storage of credentials on the clients.  While it is
   theoretically possible for these not to be of use elsewhere, the
   reluctance/inability of users to remember multiple passwords means
   that these credentials will be used by many clients and will need to
   be updated as users are added or deleted or when passwords are
   changed.  The propagation of these credentials and their storage on
   clients could be the basis for attacks if appropriate step are not
   taken to secure this data.

   While it is helpful to store a cryptographic hash of the password
   rather than the password itself, this does not dispose of the issue,
   since possession of the hash would greatly simplify an exhaustive
   search for the password, since the attacker could limit login
   attempts to guessed password whose hash value matched the value
   obtained from the files on the client.

   Although it is true that making clients responsible for
   authentication of user identities undercuts much of the original
   motivation for making RPCSEC_GSS MANDATORY to implement, it needs to
   be understood that the situation today is different from that when
   this decision was made.

   *  It has been recommended that servers not allow unauthenticated
      clients to issue requests using AUTH_SYS.




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   *  The identification of a request as issued by the user with uid
      zero, no longer provides access without file access authorization.

   *  Given that users are unaware of where their files are located and
      it is desirable that they are able to remain unaware of this, it
      is natural that they use the same password to authenticate
      themselves for local resource use as for use of files located on
      NFSv4 servers.

   Support for AUTH_SYS in NFSv4 was included for a number of reasons
   which still hold true today, despite the fact that the original
   mistake, to make no reference to the security consequences of doing
   so, is now being corrected.  Such provision is necessary for the
   following reasons, that go beyond the need to temporarily accommodate
   implementations following the older specifications, for a number of
   reasons:

   *  When considered, as NFS was to intended to be, as consistent with
      local access as possible, AUTH_SYS was the natural way of
      providing authentication, just as it had been done for local
      files.

      While use of AUTH_SYS exposes user passwords to the client
      operating system, the fact that user are unable or unwilling to
      use different passwords for different files in a multi-server
      namespace means this issue will be present even when AUTH_SYS is
      not used.

   *  [Elaboration Needed (Item #55a)]: In many important environments
      including cloud environments, important implementation constraints
      has made use of Kerberos impractical.

      [Verification Needed (Item #55a)]: In such environments, client
      credentials are maintained by the cloud customer while the cloud
      provider manages network access.

17.4.6.2.  Attacks on Name/Userid Mapping Facilities

   NFSv4 provides for the identification users and groups in two ways
   (i.e. by means of strings of the form name@domain or strings
   containing numeric uid/gid values) while file systems used on NFSv4
   servers typically use 32-bit uids and gids.









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   As a result, NFSv4 server implementations are required to have some
   means of translating between the name@domain form and the numeric
   form used internally.  While the specifics of this translation are
   not specified as part of the NFSv4 protocols, is required for server
   implementations to work, and, if it not done securely and attackers
   have the ability to interfere with this translation, it gives them
   the ability to interfere with authorization as follows:

   *  When authentication occurs using user names, as occurs when
      RPCSEC_GSS, a mistranslation might allow the numeric value used in
      authorization to allow access to a file the authenticated user
      would not be allowed to access.

   *  When any authentication occurs on the client and the uid is
      presented to the server using AUTH_SYS a mistranslation to the
      string form could result in confusion and uncertainty about the
      users allowed to access the file.

17.4.7.  Disruption and Denial-of-Service Attacks

17.4.7.1.  Attacks Based on the Disruption of Client-Server Shared State

   When data is known to both the client and server, a rogue client can
   interfere with the correct interaction between client and server, by
   modifying that shared data, including locking state and session
   information.

   For this reason, it is recommended that client-peer authentication be
   in effect, because, it it were not, a different client could could
   easily modify data that the current client depend on, disrupting ones
   interaction with the server.

   It is still possible, if one's client is somehow compromised, as
   described in Section 17.4.3, for various forms of mischief to occur:

   *  Locks required for effective mutual exclusion can be released,
      causing application failures.

   *  Mandatory share locks can be obtained preventing those with valid
      access from opening file that they are supposed to have access to.

   *  Session slot sequence numbers may be rendered invalid if requests
      are issued on existing sessions.  As a result, the client that
      issued a request would receive unexpected sequence errors.







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17.4.7.2.  Attacks Based on Forcing the Misuse of Server Resources

   It is is also possible for attacks to be mounted, in the absence of
   the ability to obtain or modify confidential data, with the sole goal
   of the attack being to make spurious requests, with no expectation
   that the request will be authorized but with the goal of causing
   resources that would otherwise be used to service valid requests to
   be unavailable due to the burden of dealing with numerous invalid
   requests.

   The design of the NFSv4 protocols requires that clients establishing
   new connections make initial requests which establishes a shared
   context referred to by subsequent requests which might request
   substantive actions (e.g. client and session ids).  This structure
   helps mitigate the effect of such denial-of-service attacks as
   described below.

   *  The server can limit the resources devoted to connections not yet
      fully identified without unduly restricted connections which have
      identified themselves.

   *  The recommendation that client peers authenticate themselves,
      allows unknown clients to be dispensed with at an early stage
      negating their ability to make requests which could require file
      system action to obtain information needed to make authorization
      decisions (e.g.  ACLs or other authorization-related) file
      attributes.

18.  IANA Considerations

   [Author Aside]: All unannotated paragraphs in this section are to be
   considered part of Consensus Item #32c.

   Because of the shift from implementing security-related services only
   in connection with RPCSEC_GSS to one in which connection-oriented
   security has a prominent role, a number if new values need to be
   assigned.

   These include new authstat values to guide selection of a connection
   types acceptable to both client and server, presented in Section 18.1
   and new pseudo-flavors to be used in the process of security
   negotiation, presented in Section 18.2.

18.1.  New Authstat Values

   [Author Aside]: All unannotated paragraphs in this section are to be
   considered part of Consensus Item #32d.




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   The following new authstat values are necessary to enable a server to
   indicate that the server's policy does not allows requests to be made
   on the current connection because of security issues associated with
   connection type used.  In the event they are received, the client
   needs to establish a new connection.

   *  The value XP_CRYPT indicates that the server will not support
      access using unencrypted connections while the current connection
      is not encrypted.

   *  The value XP_CPAUTH indicates that the server will not support
      access using connections for which the client peer has not
      authenticated itself as part of connection while the current
      connection has not been set up in that way.

18.2.  New Authentication Pseudo-Flavors

   [Author Aside]: All unannotated paragraphs in this section are to be
   considered part of Consensus Item #32e.

   The new pseudo-flavors described in this section are to be made
   available to allow their return as part of the response to the
   SECINFO and SECINFO_NONAME operations.  How these operations are to
   used to negotiate the use of appropriate auth flavors and associated
   security-relevant connection characteristics is discussed in
   Section 15.

   The following pseodo-flavors are to be defined:

   *  FL_GSS_CRYPT is returned to indicate that subsequent secinfo
      entries indicating the auth flavor RPCSEC_GSS are to considered
      limited to use on connections for which transort-level encryption
      is provided.

      When this pseudo-flavor is used, the client constraints are
      different than they would be if the RPCSEC_GSS secinfo entry
      indicated the need for privacy/confidentiality.  That case would
      allow the encryption to be provided by either the auth-flavor or
      the by the transport layer.  When FL_GSS_CRYPT os present, only
      the latter is allowed.

   *  FL_GSS_MPA is returned to indicate that subsequent secinfo entries
      indicating the auth flavor RPCSEC_GSS are to be consdered limited
      to use on connections on which mutual peer authentication has been
      provided at connection setup.






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   These pseudo-flavors provide the same sort of facilities for
   RPCSEC_GSS as provided by [13] for AUTH_SYS and AUTH_NONE.  They
   differ in being modifiers of existing auth flavor entries rather than
   combining auth flavor and connection characteristics in a single
   entry.  This is necessary because existing XDR only allows an
   RPCSEC_GSS secinfo entry to present information in additional to the
   flavor id.

19.  References

19.1.  Normative References

   [1]        Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [2]        Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
              Specification", RFC 2203, DOI 10.17487/RFC2203, September
              1997, <https://www.rfc-editor.org/info/rfc2203>.

   [3]        Linn, J., "Generic Security Service Application Program
              Interface Version 2, Update 1", RFC 2743,
              DOI 10.17487/RFC2743, January 2000,
              <https://www.rfc-editor.org/info/rfc2743>.

   [4]        Thurlow, R., "RPC: Remote Procedure Call Protocol
              Specification Version 2", RFC 5531, DOI 10.17487/RFC5531,
              May 2009, <https://www.rfc-editor.org/info/rfc5531>.

   [5]        Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [6]        Haynes, T., Ed. and D. Noveck, Ed., "Network File System
              (NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
              March 2015, <https://www.rfc-editor.org/info/rfc7530>.

   [7]        Haynes, T., Ed. and D. Noveck, Ed., "Network File System
              (NFS) Version 4 External Data Representation Standard
              (XDR) Description", RFC 7531, DOI 10.17487/RFC7531, March
              2015, <https://www.rfc-editor.org/info/rfc7531>.

   [8]        Noveck, D., Ed. and C. Lever, "Network File System (NFS)
              Version 4 Minor Version 1 Protocol", RFC 8881,
              DOI 10.17487/RFC8881, August 2020,
              <https://www.rfc-editor.org/info/rfc8881>.




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   [9]        Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
              "Network File System (NFS) Version 4 Minor Version 1
              External Data Representation Standard (XDR) Description",
              RFC 5662, DOI 10.17487/RFC5662, January 2010,
              <https://www.rfc-editor.org/info/rfc5662>.

   [10]       Haynes, T., "Network File System (NFS) Version 4 Minor
              Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
              November 2016, <https://www.rfc-editor.org/info/rfc7862>.

   [11]       Haynes, T., "Network File System (NFS) Version 4 Minor
              Version 2 External Data Representation Standard (XDR)
              Description", RFC 7863, DOI 10.17487/RFC7863, November
              2016, <https://www.rfc-editor.org/info/rfc7863>.

   [12]       Myklebust, T. and C. Lever, "Towards Remote Procedure Call
              Encryption By Default", Work in Progress, Internet-Draft,
              draft-ietf-nfsv4-rpc-tls-11, 23 November 2020,
              <https://datatracker.ietf.org/doc/html/draft-ietf-nfsv4-
              rpc-tls-11>.

   [13]       Lever, C., "Pseudo-flavors for Remote Procedure Calls with
              Transport Layer Security", Work in Progress, Internet-
              Draft, draft-cel-nfsv4-rpc-tls-pseudoflavors-01, 15
              December 2021, <https://datatracker.ietf.org/doc/html/
              draft-cel-nfsv4-rpc-tls-pseudoflavors-01>.

   [14]       NIST, "SP 800-209 Security Guidelines for Storage
              Infrastructure".

19.2.  Informative References

   [15]       Bensley, S., Thaler, D., Balasubramanian, P., Eggert, L.,
              and G. Judd, "Data Center TCP (DCTCP): TCP Congestion
              Control for Data Centers", RFC 8257, DOI 10.17487/RFC8257,
              October 2017, <https://www.rfc-editor.org/info/rfc8257>.

   [16]       Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
              "Network File System (NFS) Version 4 Minor Version 1
              Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
              <https://www.rfc-editor.org/info/rfc5661>.

Appendix A.  Changes Made

   This section summarizes the substantive changes between the treatment
   of security in previous minor version specification documents (i.e.
   RFCs 7530 and 8881) and the new treatment applying to NFSv4 as a
   whole.



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   This is expected to be helpful to implementers familiar with previous
   specifications but also has an important role in verifying the
   working group consensus for these changes and in guiding the search
   for potential compatibility issues.

A.1.  Motivating Changes

   A number of changes reflect the basic motivation for a new treatment
   of NFSv4 security.  These include the ability to obtain privacy and
   integrity services from RPC on a per-connection basis rather than as
   a service ancillary to a specific authentication flavor.

   This motivated a major reorganization of the treatment of security
   together with a needed emphasis on the security of data in flight.
   In addition, the security negotiation framework for NFSv4 has been
   significantly enhanced to support the combined negotiation of
   authentication-related services and connection characteristics.

   Despite these major changes there are not expected to be
   compatibility issues between peers supporting provision of security
   services on a per-connection basis and those without such support.

   Another such change was in the treatment of AUTH_SYS, previously
   described, inaccurately, as an "OPTIONAL means of authentication"
   with the unfortunate use of the RFC2119 keyword obscuring the
   negative consequences of the typical use of AUTH_SYS (in the clear;
   without client-peer authentication) for security by enabling the
   execution of unauthenticated requests.

   The new treatment avoids the inappropriate use of term
   "authentication" for all activities triggered by the use of RPC
   authentication flavors and clearly distinguishes those flavors
   providing authentication from those providing identification only or
   neither identification nor authentication.

A.2.  Other Major Changes

   The need to make the major changes discussed in Appendix A.1 has
   meant that much text dealing with security has needed to be
   significantly revised or rewritten.  As a result of the process, may
   issues involving unclear, inconsistent, or otherwise inappropriate
   text were uncovered and needed to be dealt with.

   While the author believes such changes are necessary, the fact that
   we are changing a document adopted by consensus requires the working
   group to be clear about the acceptability of the changes.  This
   applies to both the troublesome issues discussed in Section 3.4 and
   to the other changes included below.



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   Because of concurrent re-organizations, the ordering of the list
   follows the text of the current version which may differ considerably
   from that in earlier versions of the I-D.

   *  In order to deal better with the fact that ACLs have multiple uses
      some significant structural changes have been made.

      Section 5, a new top-level section describes the the structure of
      ACLs,

   *  In Section 7.2, makes clear that owner and owner group are
      essentially REQUIRED attributes.

   *  Also in Section 7.2, there is added clarity in the discussion of
      support for multiple authorization approaches by eliminating use
      of the subjective term "reasonable semantics".

      In connection with this clarification, we have switched from
      describing the needed co-ordination between modes and acls as
      "goals" to describing them as "requirements" to give clients some
      basis for expecting interoperability in handling these issues.

      As a result of this shift to a prescriptive framework applying to
      all minor versions it becomes possible to treat all minor versions
      together.  In earlier versions of this document, it had been
      assumed that NFSv4.0 was free to ignore the relevant prescriptions
      first put forth in RFC 5661 and only needed to address the "goals"
      for this co-ordination.


Appendix B.  Issues for which Consensus Needs to be Ascertained

   The section helps to keep track of specific changes which the author
   has made or intends to make to deal with issues found in RFCs 7530
   and 7881.  The changes listed here exclude those which are clearly
   editorial but includes some that the author believes are editorial
   but for which the issues are sufficiently complicated that working
   group consensus on the issue is probably necessary.

   These changes are presented in the table below, organized into a set
   of "Consensus Items" identified by the numeric code appearing in
   annotations in the proposed document text.  For each such item, a
   type code is assigned with separate sets of code define for pending
   items and for those which are no longer pending.

   The following codes are defined for pending consensus items:





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   *  "NM" denotes a change which is new material that is not purely
      editorial and thus requires Working Group consensus for eventual
      publication.

   *  "BE" denotes a change which the author believes is editorial but
      for which the change is sufficiently complex that the judgment is
      best confirmed by the Working Group.

   *  "BC" denotes a change which is a substantive change that the
      author believes is correct.  This does not exclude the possibility
      of compatibility issues becoming an issue but is used to indicate
      that the author believes any such issues are unlikely to prevent
      its eventual acceptance.

   *  "CI" denotes a change for which the potential for compatibility
      issues is major concern with the expected result that working
      group discussion of change will focus on clarifying our knowledge
      of how existing clients and server deal with the issue and how
      they might be affected by the change or the change modified to
      accommodate them.

   *  "NS" denotes a change which represents the author's best effort to
      resolve a difficulty but for which the author is not yet confident
      that it will be adopted in its present form, principally because
      of the possibility of troublesome compatibility issues.

   *  "NE" denotes change based on an existing issue in the spec but for
      which the replacement text is incomplete and needs further
      elaboration.

   *  "WI" denotes a potential change based on an existing issue in the
      spec but for which replacement text is not yet available because
      further working group input is necessary before drafting.  It is
      expected that replacement text will be available in a later draft
      once that discussion is done.

   *  "LD" denotes a potential change based on an existing issue in the
      spec but for which replacement text is not yet available due to
      the press of time.  It is expected that replacement text will be
      available in a later draft.

   *  "EV" denote a potential change which is tentative or incomplete
      because further details need to be provide or because the author
      is unsure that he has a correct explanation of the issue.  It is
      expected that replacement text will be available in a later draft.

   The following codes are defined for consensus items which are no
   longer pending.



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   *  "RT" designates a former item which has been retired, because it
      has been merged with another one or otherwise organized out of
      existence.

      Such items no longer are referred to the document source although
      the item id is never reassigned.  They are no longer counted among
      the set of total items.

   *  "CA" designates a former item for which consensus has been
      achieved in the judgment of the author, although not by any
      official process.

      Items reaching this state are effected in the document source
      including the deletion of annotations and the elimination of
      obsoleted previous treatments.

      Items in this state are still counted among the total of item but
      are no longer considered pending

   *  "CV" designates a former item for which consensus has been
      achieved and officially verified.

      Because the author is a working group co-chair,it is probably best
      if he is not involved in this process and intends to leave it to
      the other co-chair and the Area Director.

      Items in this state are not counted among the item totals.  They
      may be kept in the table but only to indicate that the item id is
      still reserved.

   *  "DR" designates a former item which has been dropped, because it
      appears that working group acceptance of it, even with some
      modification, is unlikely.

      Such items no longer are referred to the document source although
      the item id is never reassigned.  They are no longer counted among
      the set of total items.

   When asterisk is appended to a state of "NM", "BE" or "BE" it that
   there has been adequate working group discussion leading one to
   reasonably expect it will be adopted, without major change, in a
   subsequent document revision.

   Such general acceptance is not equivalent to a formal working group
   consensus and it not expected to result in major changes to the draft
   document,





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   On the other hand, once there is a working group consensus with
   regard to a particular issue, the document will be modified to remove
   associated annotations, with the previously conditional text
   appearing just as other document text does.  The issue will remain in
   this table as a non-pendin item.  It will be mentioned in Appendices
   A.2 or A.1 to summarize the changes that have been made.

   It is is expected that these designations will change as discussion
   proceeds and new document versions are published.  It is hoped that
   most such shifts will be upward in the above list or result in the
   deletion of a pending item, by reaching a consensus to accept or
   reject it.  This would enable, once all items are dealt with, an
   eventual request for publication as an RFC, with this appendix having
   been deleted.

   +====+======+==================+===================================+
   | #  | Type | ...References... | Substance                         |
   +====+======+==================+===================================+
   | 1  | NM*  | #1a in S 4       | Outline of new approach to        |
   |    |      |                  | authetication/identification,     |
   |    |      |                  | replacing confusion about the     |
   |    |      |                  | matter in previous                |
   |    |      |                  | specifications.                   |
   +----+------+------------------+-----------------------------------+
   | 2  | NM*  | #2a in S 4       | Introduction to and outline of    |
   |    |      |                  | changes needed in negotiation     |
   |    |      |                  | framework to support provision of |
   |    |      |                  | security by RPC on a per-         |
   |    |      |                  | connection basis.                 |
   +----+------+------------------+-----------------------------------+
   | 3  | BE   | #3a in S 5.4     | Conversion of mask bit            |
   |    |      |                  | descriptions from being about     |
   |    |      |                  | "permissions" to being about the  |
   |    |      |                  | action permitted, denied, or      |
   |    |      |                  | specified as being audited or     |
   |    |      |                  | generating alarms.                |
   +----+------+------------------+-----------------------------------+
   | 4  | CI   | #4a in S 5.4     | Elimination of uses of SHOULD     |
   |    |      |                  | believed inappropriate in         |
   |    |      |                  | Section 5.4.                      |
   +----+------+------------------+-----------------------------------+
   | 5  | BE   | #5a in S 5.4     | Explicit inclusion of ACCESS as   |
   |    |      |                  | an operation affected in the mask |
   |    |      |                  | bit definitions.                  |
   +----+------+------------------+-----------------------------------+
   | 6  | CI   | #6a in S 5.4     | New/revised description of the    |
   |    |      |                  | role of the "sticky bit" for      |
   |    |      | #6b in S 5.6     | directories, both with respect to |



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   |    |      |                  | ACL handling and mode handling.   |
   |    |      | #6c in S 7.3.1   |                                   |
   +----+------+------------------+-----------------------------------+
   | 7  | BE   | #7a in S 5.4     | Clarification of relationship     |
   |    |      |                  | between READ_DATA and EXECUTE.    |
   +----+------+------------------+-----------------------------------+
   | 8  | CI   | #8a in S 5.4     | Revised discussion of             |
   |    |      |                  | relationship between WRITE_DATA   |
   |    |      |                  | and APPEND_DATA.                  |
   +----+------+------------------+-----------------------------------+
   | 9  | BC   | #9a in S 5.4     | Clarification of how              |
   |    |      |                  | ADD_DIRECTORY relates to RENAME.  |
   +----+------+------------------+-----------------------------------+
   | 10 | BC   | #10a in S 5.4    | Revisions in handling of the      |
   |    |      |                  | masks WRITE_RETENTION and         |
   |    |      | #10b in S 5.5    | WRITE_RETENTION_HOLD.             |
   +----+------+------------------+-----------------------------------+
   | 11 | CI   | #11a in S 5.4    | Explicit recommendation and       |
   |    |      |                  | requirements for mask             |
   |    |      | #11b in S 5.5    | granularity, replacing the        |
   |    |      |                  | previous treatment which gave the |
   |    |      | #11c in S 5.11   | server license to ignore most of  |
   |    |      |                  | the previous section, placing     |
   |    |      |                  | clients in an unfortunate         |
   |    |      |                  | situation.                        |
   +----+------+------------------+-----------------------------------+
   | 12 | BC   | #12a in S 5.6    | Revised treatment of directory    |
   |    |      |                  | entry deletion.                   |
   |    |      | #12b in S 5.6.1  |                                   |
   +----+------+------------------+-----------------------------------+
   | 13 | BC   | #13a in 5.7      | Attempt to put some reasonable    |
   |    |      |                  | limits on possible non-support    |
   |    |      |                  | (or variations in the support     |
   |    |      |                  | provided) for the ACE flags.      |
   |    |      |                  | This is to replace a situation in |
   |    |      |                  | which the client has no real way  |
   |    |      |                  | to deal with the freedom granted  |
   |    |      |                  | to server implementations.        |
   +----+------+------------------+-----------------------------------+
   | 14 | BC   | #14a in S 5.11   | Explicit discussion of the case   |
   |    |      |                  | in which aclsupport is not        |
   |    |      |                  | supported.                        |
   +----+------+------------------+-----------------------------------+
   | 15 | BC   | #15a in S 5.11   | Handling of the proper            |
   |    |      |                  | relationship between support for  |
   |    |      | #15b in S 7.1    | ALLOW and DENY ACEs.              |
   |    |      |                  |                                   |
   |    |      | #15c in S 7.2    |                                   |



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   +----+------+------------------+-----------------------------------+
   | 16 | NM   | #16a in S 5.1    | Discussion of coherence of acl,   |
   |    |      |                  | sacl, and dacl attributes.        |
   +----+------+------------------+-----------------------------------+
   | 17 | BC   | #17a in S 7.1    | Relationship of support for ALLOW |
   |    |      |                  | and DENY ACEs                     |
   |    |      | #17b in S 7.2    |                                   |
   +----+------+------------------+-----------------------------------+
   | 18 | BC   | #18a in S 7.1    | Need for support of owner,        |
   |    |      |                  | owner_group.                      |
   |    |      | #18b in S 7.2    |                                   |
   +----+------+------------------+-----------------------------------+
   | 19 | CI   | #19a in S 7.2    | Revised discussion of             |
   |    |      |                  | coordination of mode and the ACL- |
   |    |      |                  | related attributes.               |
   +----+------+------------------+-----------------------------------+
   | 20 | WI   | #20 in S 7.3.1   | More closely align ACL_based and  |
   |    |      |                  | mode-based semantics with regard  |
   |    |      |                  | to SVTX.                          |
   +----+------+------------------+-----------------------------------+
   | 21 | BC   | #21a in S 4.1    | Introduce the concept of reverse- |
   |    |      |                  | slope modes and deal properly     |
   |    |      | #21b in S 7.3.1  | with them.  The decision as to    |
   |    |      |                  | the proper handling is addressed  |
   |    |      |                  | as Consensus Item #28.            |
   +----+------+------------------+-----------------------------------+
   | 22 | BC   | #22a in S 8.1    | Revise treatment of divergences   |
   |    |      |                  | between AC/mode authorization and |
   |    |      |                  | server behavior, dividing the     |
   |    |      |                  | treatment between cases in which  |
   |    |      |                  | something authorized is still not |
   |    |      |                  | allowed (OK), and those in which  |
   |    |      |                  | something not authorized is       |
   |    |      |                  | allowed (highly problematic from  |
   |    |      |                  | a security point of view).        |
   +----+------+------------------+-----------------------------------+
   | 23 | BC   | #23a in S 8.2    | Revise discussion of client       |
   |    |      |                  | access to of ACLs.                |
   +----+------+------------------+-----------------------------------+
   | 24 | BE   | #24a in S 8.2    | Delete bogus reference.           |
   +----+------+------------------+-----------------------------------+
   | 25 | CI   | #25a in S 3.3    | Revised description of co-        |
   |    |      |                  | ordination of acl and mode        |
   |    |      | #25b in S 9.1    | attributes to apply to NFSv4 as a |
   |    |      |                  | whole.  While this includes many  |
   |    |      | #25d in S 9.8    | aspects of the shift to be more   |
   |    |      |                  | specific about the co-ordination  |
   |    |      | #25e in S 9.10   | requirements including addressing |



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   |    |      |                  | apparently unmotivated uses of    |
   |    |      | #25f in S 9.11   | the terms "SHOULD" and "SHOULD    |
   |    |      |                  | NOT", it excludes some arguably   |
   |    |      | #25g in S 9.12   | related matters dealt with as     |
   |    |      |                  | Consensus Items #26 and #27.      |
   +----+------+------------------+-----------------------------------+
   | 26 | CI   | #26a in S 9.2    | Decide how ACEs with who values   |
   |    |      |                  | other than OWNER@, Group, or      |
   |    |      | #26 in S 9.7.3   | EVERYONE@ are be dealt with when  |
   |    |      |                  | setting mode.                     |
   +----+------+------------------+-----------------------------------+
   | 27 | CI   | #27a in S 9.2    | Concerns the possible existence   |
   |    |      |                  | of multiple methods of computing  |
   |    |      | #27b in S 9.3    | a mode from an acl that clients   |
   |    |      |                  | can depend on, and the proper     |
   |    |      | #27c in S 9.4    | elationship among these methods.  |
   +----+------+------------------+-----------------------------------+
   | 28 | WI   | #28a in S 9.2    | Decide how to address flaws in    |
   |    |      |                  | mapping to/from reverse- slope    |
   |    |      | #28b in S 9.3    | modes.                            |
   |    |      |                  |                                   |
   |    |      | #28 in S 9.7.3   |                                   |
   +----+------+------------------+-----------------------------------+
   | 29 | BC   | #29 in S 9.7.3   | Address the coordination of mode  |
   |    |      |                  | and ACL-based attributes in       |
   |    |      |                  | unified way for all minor         |
   |    |      |                  | versions.                         |
   +----+------+------------------+-----------------------------------+
   | 30 | CI   | #30a in S 9.7.1  | New proposed treatment of setting |
   |    |      |                  | mode incorporating some           |
   |    |      | #30b in S 9.7.2  | consequences of anticipated       |
   |    |      |                  | decisions regarding other         |
   |    |      | #30c in S 9.7.3  | consensus items (#26, #28, #29)   |
   +----+------+------------------+-----------------------------------+
   | 31 | WI   | #31a in S 9.7.3  | Need to deal with mask bits       |
   |    |      |                  | ACE4_READ_ATTRIBUTES,             |
   |    |      |                  | ACE4_WRITE_RETENTION,             |
   |    |      |                  | ACE4_WRITE_RETENTION_HOLD,        |
   |    |      |                  | ACE4_READ_ACL to reflect the      |
   |    |      |                  | semantics of the mode attribute.  |
   +----+------+------------------+-----------------------------------+
   | 32 | BC   | #32a in S 15     | Expanded negotiation framework to |
   |    |      |                  | accommodate multiple transport    |
   |    |      | #32b in S 15.1   | types and security services       |
   |    |      |                  | provided on a per-connection      |
   |    |      | #32c in S 18     | basis, i.e. encryption and peer   |
   |    |      |                  | authentication.                   |
   |    |      | #32d in S 18.1   |                                   |



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   |    |      |                  |                                   |
   |    |      | #32e in S 18.2   |                                   |
   +----+------+------------------+-----------------------------------+
   | 33 | RJ   | Material         | Reorganization of description of  |
   |    |      | formerly here    | SECINFO op to apply to all minor  |
   |    |      | moved to #32.    | versions.  (Dropped)              |
   +----+------+------------------+-----------------------------------+
   | 34 | RJ   | Superseded by    | Revision to NFSv4.0 SECINFO       |
   |    |      | simpler          | implementation section (Dropped.  |
   |    |      | treatment.       |                                   |
   +----+------+------------------+-----------------------------------+
   | 35 | NE   | #35a in S 16     | Now has preliminary work on       |
   |    |      |                  | future security needs.            |
   +----+------+------------------+-----------------------------------+
   | 36 | CI   | #36a in S 17.1.3 | Threat analysis only dealing with |
   |    |      |                  | RECOMMENDED behavior regarding    |
   |    |      |                  | use of per-connection security    |
   |    |      |                  | facilities and handling of        |
   |    |      |                  | AUTH_SYS.                         |
   +----+------+------------------+-----------------------------------+
   | 37 | CI   | #37a in S 17.1.3 | Threat analysis only dealing with |
   |    |      |                  | RECOMMENDED behavior with regard  |
   |    |      |                  | to acl support including ACL/mode |
   |    |      |                  | coordination.                     |
   +----+------+------------------+-----------------------------------+
   | 38 | CI   | #38a in S 17.1.4 | Address the need to temporarily   |
   |    |      |                  | allow unsafe behavior mistakenly  |
   |    |      |                  | allowed by previous               |
   |    |      |                  | specifications                    |
   +----+------+------------------+-----------------------------------+
   | 39 | CI   | #39a in S 17.1.5 | Define new approach to AUTH_SYS.  |
   +----+------+------------------+-----------------------------------+
   | 40 | CI   | #40a in S 17.2.1 | Discussion of scope for security  |
   |    |      |                  | considerations and the            |
   |    |      | #40a in S 17.2.2 | corresponding threat analysis.    |
   +----+------+------------------+-----------------------------------+
   | 41 | CI   | #41a in S 8.1    | Discuss major new security        |
   |    |      |                  | recommendations regarding         |
   |    |      | #41b in S 17.3.1 | protection of data in flight and  |
   |    |      |                  | client peer authentication.       |
   |    |      | #41c in S 17.3.2 | Also, covers the circumstances    |
   |    |      |                  | under which such recommendations  |
   |    |      | #41d in S 17.3.4 | can be bypassed.                  |
   |    |      |                  |                                   |
   +----+------+------------------+-----------------------------------+
   | 42 | RT   | #42a in S 17.4.5 | Former placeholders for threat    |
   +----+------+------------------+ analysis subsections have now     |
   | 43 | RT   | #43a in S        | been superseded by new proposed   |



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   |    |      | 17.4.6.1         | subsections.                      |
   +----+------+------------------+                                   |
   | 44 | RT   | #44a in S        |                                   |
   |    |      | 17.4.6.2         |                                   |
   +----+------+------------------+                                   |
   | 45 | RT   | #45a in S        |                                   |
   |    |      | 17.4.7.1         |                                   |
   +----+------+------------------+                                   |
   | 46 | RT   | #46a in S        |                                   |
   |    |      | 17.4.7.2         |                                   |
   +----+------+------------------+-----------------------------------+
   | 47 | CI   | gone fir now.    | Dubious paragraph regarding       |
   |    |      |                  | AUTH_NONe is SECINFO response     |
   |    |      |                  | which should be deleted if there  |
   |    |      |                  | are no compatibility issues that  |
   |    |      |                  | make that impossible.             |
   +----+------+------------------+-----------------------------------+
   | 48 | RJ   | Superseded by    | Missing pieces of secinfo         |
   |    |      | simpler          | processing algorithm that didn't  |
   |    |      | treatment.       | get done in -02.                  |
   +----+------+------------------+-----------------------------------+
   | 49 | RJ   | perseded by      | Secinfo processing algorithm that |
   |    |      | simpler          | needs to finished in -04.         |
   |    |      | treatment.       |                                   |
   +----+------+------------------+-----------------------------------+
   | 50 | BC   | #50a in S 5.9    | Revise handling of "special" who  |
   |    |      |                  | values, making it clear for which |
   |    |      |                  | ones "special" is a euphemism for |
   |    |      |                  | "semantics-challenged".           |
   +----+------+------------------+-----------------------------------+
   | 51 | BC   | #51a in S 5.9    | Clarify the handling of the group |
   |    |      |                  | bit for the special who values.   |
   +----+------+------------------+-----------------------------------+
   | 52 | BC   | #52a in S 8.1    | Eliminate superuser semantics as  |
   |    |      |                  | it had been, as valid by          |
   |    |      | #52b in S 17.3.3 | implication.  Also, deal with the |
   |    |      |                  | security consequences of its      |
   |    |      |                  | inclusion appropriately.          |
   +----+------+------------------+-----------------------------------+
   | 53 | EV   | #53a in S 17.4.2 | Discussion of possible adaptation |
   |    |      |                  | of RPCSEC_GSS/Kerberos to multi-  |
   |    |      |                  | factor authentication.            |
   +----+------+------------------+-----------------------------------+
   | 54 | EV   | #54a in S        | Discussion of prevention of code  |
   |    |      | 17.4.6.1         | on a compromised client from      |
   |    |      |                  | hijacking the client machine's    |
   |    |      |                  | peer authentication.              |
   +----+------+------------------+-----------------------------------+



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   | 55 | EV   | #55a in S        | Discussion of issues with         |
   |    |      | 17.4.6.1         | potential use of Kerberos in      |
   |    |      |                  | cloud environments                |
   +----+------+------------------+-----------------------------------+
   | 56 | WI   | #56a in S 4.1    | Discussion of issues related to   |
   |    |      |                  | the handling of UNIX ACLs.        |
   |    |      | #56b in S 9.5    |                                   |
   |    |      |                  |                                   |
   |    |      | #56c in S 16     |                                   |
   +----+------+------------------+-----------------------------------+

                                 Table 3

   The following table summarizes the issues in each particular pending
   state, dividing them into those associated with the motivating
   changes for this new document and those that derive from other
   issues, that were uncovered later, once work on a new treatment of
   NFSv4 security had begun.

































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               +========+=====+============================+
               | Type   | Cnt | Issues                     |
               +========+=====+============================+
               | NM*(M) | 2   | 1, 2                       |
               +--------+-----+----------------------------+
               | BC(M)  | 2   | 32, 52                     |
               +--------+-----+----------------------------+
               | CI(M)  | 5   | 36, 38, 39, 40, 41         |
               +--------+-----+----------------------------+
               | WI(M)  | 1   | 47                         |
               +--------+-----+----------------------------+
               | NE(M)  | 1   | 35                         |
               +--------+-----+----------------------------+
               | EV(M)  | 3   | 53, 54, 55                 |
               +--------+-----+----------------------------+
               | All(M) | 14  | As listed above.           |
               +--------+-----+----------------------------+
               | NM(O)  | 1   | 16                         |
               +--------+-----+----------------------------+
               | BE(O)  | 4   | 3, 5, 7, 24                |
               +--------+-----+----------------------------+
               | BC(O)  | 14  | 9, 10, 12, 13, 14, 15, 17, |
               |        |     | 18, 21, 22, 23, 29, 50, 51 |
               +--------+-----+----------------------------+
               | CI(O)  | 10  | 4, 6, 8, 11, 19, 25, 26,   |
               |        |     | 27, 30, 37                 |
               +--------+-----+----------------------------+
               | WI(O)  | 4   | 20, 28, 31, 56             |
               +--------+-----+----------------------------+
               | All(O) | 33  | As described above         |
               +--------+-----+----------------------------+
               | *All*  | 47  | Grand total for above      |
               |        |     | table.                     |
               +--------+-----+----------------------------+

                                  Table 4

   The following table summarizes the issues in each particular non-
   pending state, dividing them into those associated with the
   motivating changes for this new document and those that derive from
   other issues, that were uncovered later, once work on a new treatment
   of NFSv4 security had begun.









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              +========+=====+==============================+
              | Type   | Cnt | Issues                       |
              +========+=====+==============================+
              | RT(M)  | 5   | 42, 43, 44, 45, 46           |
              +--------+-----+------------------------------+
              | RJ(M)  | 4   | 33, 34, 48, 49               |
              +--------+-----+------------------------------+
              | All(M) | 9   | As listed above.             |
              +--------+-----+------------------------------+
              | All(O) | 0   | Nothing yet.                 |
              +--------+-----+------------------------------+
              | *All*  | 9   | Grand total for above table. |
              +--------+-----+------------------------------+

                                  Table 5

Acknowledgments

   The author wishes to thank Tom Haynes for his helpful suggestion to
   deal with security for all NFSv4 minor versions in the same document.

   The author wishes to draw people's attention to Nico Williams' remark
   that NFSv4 security was not so bad, except that there was no
   provision for authentication of the client peer.  This perceptive
   remark, which now seems like common sense, did not seem so when made,
   but it has served as a beacon for those working on putting NFSv4
   security on a firmer footing.  We appreciate this perceptive
   guidance.

   The author wishes to thank Bruce Fields for his helpful comments
   regarding ACL support which had a major role in the evolution of this
   document.

   The author wishes to acknowledge the important role of the authors of
   RPC-with-TLS, Chuck Lever and Trond Myklebust, in moving the NFS
   security agenda forward and thank them for all their efforts to
   improve NFS security.

   The author wishes to thank Chuck Lever for his many helpful comments
   about nfsv4 security issues, his explanation of many unclear points,
   and and much important guidance he provided that is reflected in this
   document.

   The author wishes to thank Rick Macklem for his role in clarifying
   possible server policies regarding RPC-with-TLS and in bringing the
   to the Working Group's attention the possibility of deriving limited
   principal identification from client peer authentication while still
   staying within the boundaries of RPC-with-TLS.



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Author's Address

   David Noveck (editor)
   NetApp
   1601 Trapelo Road, Suite 16
   Waltham, MA 02451
   United States of America

   Phone: +1-781-572-8038
   Email: davenoveck@gmail.com









































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