Security for the NFSv4 Protocols
draft-dnoveck-nfsv4-security-02
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| Author | David Noveck | ||
| Last updated | 2021-10-13 (Latest revision 2021-08-30) | ||
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draft-dnoveck-nfsv4-security-02
NFSv4 D. Noveck, Ed.
Internet-Draft NetApp
Updates: 8881, 7530 (if approved) 13 October 2021
Intended status: Standards Track
Expires: 16 April 2022
Security for the NFSv4 Protocols
draft-dnoveck-nfsv4-security-02
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 the RPC transport.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 16 April 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 . . . . . . . . . . . . . . . . . . . 6
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 7
2.1. Keyword Definitions . . . . . . . . . . . . . . . . . . . 7
2.2. Special Considerations . . . . . . . . . . . . . . . . . 7
3. Introduction to this Update . . . . . . . . . . . . . . . . . 8
3.1. Transport-based 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
5. Structure of Access Control Lists . . . . . . . . . . . . . . 19
5.1. Access Control Entries . . . . . . . . . . . . . . . . . 20
5.2. ACE Type . . . . . . . . . . . . . . . . . . . . . . . . 20
5.3. ACE Access Mask . . . . . . . . . . . . . . . . . . . . . 22
5.4. Uses of Mask Bits . . . . . . . . . . . . . . . . . . . . 22
5.5. Requirements and Recommendations Regarding Mask
Granularity . . . . . . . . . . . . . . . . . . . . . . 32
5.6. Handling of Deletion . . . . . . . . . . . . . . . . . . 34
5.6.1. Previous Handling of Deletion . . . . . . . . . . . . 35
5.7. ACE flag bits . . . . . . . . . . . . . . . . . . . . . . 36
5.8. Details Regarding ACE Flag Bits . . . . . . . . . . . . . 38
5.9. ACE Who . . . . . . . . . . . . . . . . . . . . . . . . . 40
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5.10. Automatic Inheritance Features . . . . . . . . . . . . . 41
5.11. Attribute 13: aclsupport . . . . . . . . . . . . . . . . 44
5.12. Attribute 12: acl . . . . . . . . . . . . . . . . . . . . 45
6. Authorization in General . . . . . . . . . . . . . . . . . . 46
7. User-based File Access Authorization . . . . . . . . . . . . 46
7.1. Attributes for User-based File Access Authorization . . . 46
7.2. Handling of Multiple Parallel File Access Authorization
Models . . . . . . . . . . . . . . . . . . . . . . . . . 47
7.3. Posix Authorization Model . . . . . . . . . . . . . . . . 49
7.3.1. Attribute 33: mode . . . . . . . . . . . . . . . . . 49
7.3.2. NFSv4.1 Attribute 74: mode_set_masked . . . . . . . . 51
7.4. ACL-based Authorization Model . . . . . . . . . . . . . . 52
7.4.1. Processing Access Control Entries . . . . . . . . . . 52
7.4.2. V4.1 Attribute 58: dacl . . . . . . . . . . . . . . . 54
8. Common Considerations for Both File access Models . . . . . . 54
8.1. Server Considerations . . . . . . . . . . . . . . . . . . 54
8.2. Client Considerations . . . . . . . . . . . . . . . . . . 58
9. Combining Authorization Models . . . . . . . . . . . . . . . 59
9.1. Background for Combined Authorization Model . . . . . . . 59
9.2. Needed Attribute Coordination . . . . . . . . . . . . . . 60
9.3. Computing a Mode Attribute from an ACL . . . . . . . . . 63
9.4. Alternatives in Computing Mode Bits . . . . . . . . . . . 65
9.5. Setting Multiple ACL Attributes . . . . . . . . . . . . . 66
9.6. Setting Mode and not ACL (overall) . . . . . . . . . . . 66
9.6.1. Setting Mode and not ACL (vestigial) . . . . . . . . 66
9.6.2. Setting Mode and not ACL (Discussion) . . . . . . . . 67
9.6.3. Setting Mode and not ACL (Proposed) . . . . . . . . . 69
9.7. Setting ACL and Not Mode . . . . . . . . . . . . . . . . 73
9.8. Setting Both ACL and Mode . . . . . . . . . . . . . . . . 74
9.9. Retrieving the Mode and/or ACL Attributes . . . . . . . . 74
9.10. Creating New Objects . . . . . . . . . . . . . . . . . . 74
9.11. Use of Inherited ACL When Creating Objects . . . . . . . 76
9.12. Combined Authorization Models for NFSv4.2 . . . . . . . . 76
10. Labelled NFS Authorization Model . . . . . . . . . . . . . . 77
11. State Modification Authorization . . . . . . . . . . . . . . 77
12. Other Uses of Access Control Lists . . . . . . . . . . . . . 78
12.1. V4.1 Attribute 59: sacl . . . . . . . . . . . . . . . . 78
13. Identification and Authentication . . . . . . . . . . . . . . 78
13.1. Identification vs. Authentication . . . . . . . . . . . 79
13.2. Items to be Identified . . . . . . . . . . . . . . . . . 79
13.3. Authentication Provided by specific RPC Flavors . . . . 80
13.4. Authentication Provided by the RPC Transport . . . . . . 81
14. Security of Data in Flight . . . . . . . . . . . . . . . . . 81
14.1. Data Security Provided by the Flavor-associated
Services . . . . . . . . . . . . . . . . . . . . . . . . 81
14.2. Data Security Provided by the RPC Transport . . . . . . 81
15. Security Negotiation . . . . . . . . . . . . . . . . . . . . 81
15.1. Flavors and Pseudo-flavors . . . . . . . . . . . . . . . 82
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15.2. Negotiation of Security Flavors and Mechanisms . . . . . 83
15.3. Negotiation of RPC Transports and Characteristics . . . 84
15.4. Overall Interpretation of SECINFO Response Arrays . . . 85
15.4.1. Interpretation of SECINFO Response Arrays (Core) . . 87
15.4.2. Connection Type Transcription . . . . . . . . . . . 89
15.4.3. Flavor Transcription . . . . . . . . . . . . . . . . 89
15.5. SECINFO . . . . . . . . . . . . . . . . . . . . . . . . 89
15.5.4. SECINFO IMPLEMENTATION (general) . . . . . . . . . . 91
15.5.5. SECINFO IMPLEMENTATION (for NFSv4.0) . . . . . . . . 92
15.5.6. SECINFO IMPLEMENTATION (for NFSv4.1 and v4.2) . . . 93
16. Future Security Needs . . . . . . . . . . . . . . . . . . . . 95
17. Security Considerations . . . . . . . . . . . . . . . . . . . 96
17.1. Changes in Security Considerations . . . . . . . . . . . 96
17.1.1. Wider View of Threats . . . . . . . . . . . . . . . 96
17.1.2. Transport-layer Security Facilities . . . . . . . . 97
17.1.3. Approach to Implementation Semantic Divergences . . 98
17.1.4. Compatibility and Maturity Issues . . . . . . . . . 98
17.1.5. Discussion of AUTH_SYS . . . . . . . . . . . . . . . 99
17.2. Security Considerations Scope . . . . . . . . . . . . . 100
17.2.1. Discussion of Potential Classification of
Environments . . . . . . . . . . . . . . . . . . . . 100
17.2.2. Discussion of Environments . . . . . . . . . . . . . 100
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 . . . . . . . . . . . . . . . . . . . 101
17.3.3. Issues Regarding Valid Reasons to Bypass
Recommendations . . . . . . . . . . . . . . . . . . . 102
17.4. Data Security Threats . . . . . . . . . . . . . . . . . 102
17.5. Authentication-based threats . . . . . . . . . . . . . . 102
17.5.1. Attacks based on the use of AUTH_SYS . . . . . . . . 102
17.5.2. Attacks on Name/Userid Mapping Facilities . . . . . 103
17.6. Disruption and Denial-of-Service Attacks . . . . . . . . 103
17.6.1. Attacks Based on the Disruption of Client-Server
Shared State . . . . . . . . . . . . . . . . . . . . 103
17.6.2. Attacks Based on Forcing the Misuse of Server
Resources . . . . . . . . . . . . . . . . . . . . . . 103
18. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 103
18.1. New Authstat Values . . . . . . . . . . . . . . . . . . 103
18.2. New Authentication Pseudo-Flavors . . . . . . . . . . . 104
19. References . . . . . . . . . . . . . . . . . . . . . . . . . 105
19.1. Normative References . . . . . . . . . . . . . . . . . . 105
19.2. Informative References . . . . . . . . . . . . . . . . . 106
Appendix A. Changes Made . . . . . . . . . . . . . . . . . . . . 106
A.1. Motivating Changes . . . . . . . . . . . . . . . . . . . 107
A.2. Other Major Changes . . . . . . . . . . . . . . . . . . . 107
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Appendix B. Issues for which Consensus Needs to be
Ascertained . . . . . . . . . . . . . . . . . . . . . . . 108
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 117
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 118
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 mentioned 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
authentication when AUTH_SYS is used.
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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.
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 should 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.
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* A paragraph headed "[Previous Treatment]:", indicates text that is
provided for context but which the author believes, should 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.
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.
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 [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.
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* The term may been used in accord with [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.
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
transport properties. 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. Transport-based Security Features
There are a number of security-related facilities that can be
provided at the transport layer eliminating the need to provide such
support to as part of RPC proper.
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These will initially be provided by RPC-with-TLS but similar
facilities might be provided by new versions of existing transports
or new RPC transports.
* The transport 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 transports, or limiting
access to those providing privacy, allowing the use of either
transport-based encryption or privacy services provided by
RPCSEC_GSS.
* The transport 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 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.
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* 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.
An exception is made regarding labelled NFS, an optional feature
within NFSv4.2, described in [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 transport level 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) provided by secure
transports such as RPC-over-TLS.
It should be noted that state protection based on RPCSEC_GSS is
treated as a version-specific feature and will continue to be
described by [8] or its successors. Also, it needs to be noted
that the use of state protection was not discussed in [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 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 pNFS optional 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
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 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 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 and RFC8881. 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 [13], 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 [13] 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 [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
filesystem.
* 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 must
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 authentication flavors and underlying transports.
[Consensus Needed, Including List (Item #1a)}: Support for multiple
authentication 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 flavors
is provided for.
This flavor provides for mutual authentication of the principal
making the request and the server performing it.
This 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 by
the underlying RPC transport, this support is useful, when the
transport 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 transport-level support.
* AUTH_NONE does not provide identification of the principal making
the request so only should 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 the RPC transport when RPC-with-TLS
is available, or when other transports provide similar services
* The transport can provide data security to all requests on the.
This is to be preferred to data security provided by the
authentication 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.
* The transport 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 transport can authenticate the client-peer 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 transport used, rather the authentication, the
process of security negotiation, described in Section 15 provides for
the negotiation of an appropriate transport at connection time if the
server's policy limits the range of transports being used and also
when use of a particular transport/flavor combination 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.
5. Structure of Access Control Lists
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.
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* 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 ACLs and discuss
ACL-related matters that apply to multiple types of ACL use,
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;
};
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;
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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.
+==============================+==============+====================+
| 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.
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5.3. ACE Access Mask
The bitmask constants used for the access mask field of the ACE are
as follows:
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 #3a.
[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.
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[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.
[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 ACLs and mode bits
are separate means of authentication, 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 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.
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* 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.
* 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
should 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 ACL case.
* 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.
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[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
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.
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ACE4_ADD_FILE
Operation(s) affected:
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.
[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
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is consulted to determine whether the operation is permitted or
whether alarm or audit activities are to be performed. If a
file has an 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
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.
ACE4_WRITE_NAMED_ATTRS
Operation(s) affected:
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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 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.
As an example, following a SETATTR of the following ACL:
nfsuser:ACE4_EXECUTE:ALLOW
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A subsequent GETATTR of ACL 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
mean that the entity can execute "ls -l" and stat. If a
READDIR operation requests attributes, this mask must be
allowed for the READDIR to succeed.
ACE4_WRITE_ATTRIBUTES
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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.
[Author Aside]: The use of "MAY" here ignores the potential for
harm which unexpected modification of the associated attributes
might cause for security/compliance.
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[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 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
Operation(s) affected:
NONE
Discussion:
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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.
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[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
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 should clearly 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.
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* 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 ACLs where the
handling for these two masks are different for any specified user
or group are to be rejected with NFS4ERR_ATTRNOTSUPP.
* [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 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 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 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 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 severs 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:
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* 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.
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".
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* 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.
* 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:
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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;
[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 support, while valid, is out-of-scope and should 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.
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]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 ACL
containing an ACE with an unsupported flag bit set the server MUST
reject the request with NFS4ERR_ATTRNOTSUPP.
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 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 should be
added to each new directory created.
If this flag is set in an ACE in an 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 should 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.
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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 ACL,
the server encounters an AUDIT or ALARM ACE that matches the
principal attempting the OPEN, the server notes that fact, and the
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.
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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.
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.
+===============+==================================================+
| Who | Description |
+===============+==================================================+
| OWNER | The owner of the file. |
+---------------+--------------------------------------------------+
| GROUP | The group associated with the file. |
+---------------+--------------------------------------------------+
| EVERYONE | The world, including the owner and owning group. |
+---------------+--------------------------------------------------+
| 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 | Accessed without any authentication. |
+---------------+--------------------------------------------------+
| AUTHENTICATED | Any authenticated user (opposite of ANONYMOUS). |
+---------------+--------------------------------------------------+
| SERVICE | Access from a system service. |
+---------------+--------------------------------------------------+
Table 2
To avoid conflict, these special identifiers are distinguished by an
appended "@" and should appear in the form "xxxx@" (with no domain
name after the "@"), for example, ANONYMOUS@.
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.
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[working group input needed]: I don't understand what might be valid
reasons to ignore this. Would "MUST" be appropriate here?
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.
[working group input needed]: Some of these require that changes be
made as discussed below:
* For "INTERACTIVE", "NETWORK", "DIALUP", "BATCH", and "SERVICE" it
needs to be specified that server's ability to make these
distinctions is limited, making their use where security is an
issue quite problematic.
* For "ANONYMOUS", clearly requests using AUTH_NONE fit but what
else?
Request by nobody and by users root-squashed to nobody are
probably OK, although you could argue about the case of a user
"nobody" authenticated by RPCSEC_GSS.
ON a more contentious note, I would argue that users
"authenticated" using AUTH_SYS, in the clear, without client-peer
authentication fit here, but we need to get to consensus on this
point.
* Issues regarding "AUTHENTICATED" will be the mirror image of those
for "ANONYMOUS".
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;
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and all other bits must be cleared. The ACE4_INHERITED_ACE flag may
be set in the ACEs of the sacl or dacl (whereas it must always 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.
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 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.
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New objects should 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 should be the union of the ACEs
reported in the dacl and sacl attributes, except that the
ACE4_INHERITED_ACE flag must 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.
When a client application queries an ACL, modifies it, and sets it
again, it should leave any ACEs marked with ACE4_INHERITED_ACE
unchanged, in their original order, at the end of the ACL. If the
application is unable to do this, it should 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 should be completely replaced by one generated
using the automatic inheritance rules.
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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.
[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 should not 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.
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[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.
[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 must appear in the same order in the acl
attribute.
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6. Authorization in General
There are three distinct methods of checking whether NFSv4 requests
are authorized:
* The most important method of authorization is used to effect user-
based file access control, as described in Section 7.
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.
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 17.6), server implementations SHOULD take
steps to prevent unauthorized state changes. This can be done by
implementing the state authorization restrictions discussed in
Section 11
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.
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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 corresponding
ACL, when using only a single ACE type. See Section 9.2 for
details.
7.2. Handling of Multiple Parallel File Access Authorization Models
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 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.
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The following describe NFSv4's handling in supporting multiple
authorization models for file access.
* If a server supports the mode attribute, it should 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 should provide 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.
* On servers that support the mode attribute, if ACL attributes have
never been set on an object, via inheritance or explicitly, the
behavior should be the behavior mandated by POSIX, including the
those 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, should 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 should
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 #??.
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- [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.
* Although RFCs 7530 and 8881 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
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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.
[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 should be noted that this approach
is similar to ACL-based approach documented in Section 5.6. However
there are some semantics differences whose motivation remains unclear
and the specification does not mention RENAME, as it should.
[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.
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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 #21a)]: In the typical case, the nine low-
order bits are set such that each successive set of three bits is a
subset, not necessarily proper, of the previous three bits. Such
modes are described as forward-slope nodes because the privilege
level goes downward as you proceed forward. There are, however,
cases in which there is an increase of privilege going from owner to
group or from group to owner. Such modes are considered reverse-
slope modes. As will be seen in Sections 9.3 and 9.6, many
straightforward ways of dealing with mode that work well with
forward-slope modes need adjustment to properly deal with reverse-
slope modes.
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.
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 should be automatically modified as discussed in Sections
9.6 and 9.8.
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.
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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@".
* 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.
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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.)
[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.
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[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.
* 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.
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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.
[Previous Treatment, Including List (Item #22a)]: 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).
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* 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 [8]).
[Consensus Needed, Including List (Item #22a)]: It should 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 [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
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)]: In the following
list, the treatment used in RFC8881 is quoted, while the
corresponding text in RFC7530 is essentially identical.
* RFC8881 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
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restriction on the step that might be taken to deal with the
issue. See Section 17.1.3 for the updated treatment of this
issue.
* RFC8881 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 contains the following, which is now superseded:
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.
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Because of the effect such unrestricted access might have in
facilitating and perpetuating attacks, Section 17.1.3 will explain
that the treat analysis in Section 17, will not cover servers
which choose to allow such access.
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
should 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 "should not" would
be more appropriate.
[Consensus Needed (Item #23a)]: Clients are 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 should 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.
[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.
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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 should 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 and 5661 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.
[Author Aside]: From this point on, all unannotated paragraphs in
this section are to be assumed part of Consensus Item #25b
As a result, in this document, we will have a single treatment of
this issue, in Sections 9.2 through 9.11. In addition, an
NFSv4.2-based extension related to attribute co-ordination will be
described in Section 9.12.
The current NFSv4.0 and NFSv4.1 descriptions of this share one
unfortunate characteristic in that they both are written to give
server implementations a broad latitude in implementation choices
while neglecting entirely the need for the 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 this excessive freedom, while taking proper account of the
possibility of compatibility issues that a more tightly drawn
specification might give rise to.
[Author Aside, Including List]: The various ways in which these kinds
of issues have been dealt with are listed below:
* 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.
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* There are also cases in which no RFC2119-defined keywords are used
but it is stated that certain server implementations do a
particular, leaving the impression that that action is to be
allowed, just as if "MAY" had been used.
* There is a case in which the term "SHOULD" is clearly used
intentionally, without it being clear what the valid reasons to
ignore the guidance might be.
* There are many case in which the term "SHOULD" is used without any
clear indication why it was 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.
In order to deal with the many uses of the terms "SHOULD" and "SHOULD
NOT" 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 must 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) must be
determined entirely by the value of the ACL, so that use of the mode
is never required for anything other than setting the three high-
order bits. See Sections 9.6 through 9.8 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.
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[Author Aside]: 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 9.6 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@".
[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 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.
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{Consensus Needed (Items #26a, #28a)]: A server that supports both
mode and ACL need 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 is
relatively straightforward in the case of forward-slope modes, but
the case of reverse-slope modes need to be addressed as described in
Sections 9.3 and 9.6.
{Consensus Needed (Item #26a)]: How other ACEs are dealt with when
setting mode is described in Section 9.6. This includes ACEs with
other who value, all AUDIT and ALARM ACEs, and all ACES that affect
ACL inheritance.
[Author Aside, Including List]: The author believes that the material
now associated with Item #27, including the following paragraph and
Section 9.4 are best deleted. This is because of reasons specified
in that section and the following reasons listed below:
* Having multiple methods to map from ACL to mode undercuts the
whole purpose of Section 9, which is to co-ordinate these
attributes so that clients who use each of the attributes can use
that without interfering with those that reference others. That
cannot be accomplished if there were multiple valid ways that
servers might choose, without providing any means by which the
client might determine which mapping was being used.
* The withdrawn POSIX draft ACLs would almost certainly have been
considered in connection with an NFSv4. In any case, they were
not adopted and the current ACL model adopted. Given that fact
there is no sense in burdening the new feature with the
substantial burden of supporting the one that was rejected by the
working group
* It is very unlikely that such implementations still exist, given
that that it is over twenty years since the decision was made to
adopt the more extensive NFSv4 ACL model and over ten years since
RFC5661 was published. Even assuming this was justified as a
transition measure, the time for any such transition mechanisms is
long past.
* Despite the statement in the next section that this alternate
model is "discouraged", its continued appearance as an alternate
way of computing mode, on the same level as the one appropriate to
the NFSv4 acl model encourages this use compared to a situation in
which no alternate method of computing mode was mentioned.
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[Previous Treatment (Item #27a)]: In this section, much depends on
the method in specified Section 9.3. Many requirements refer to this
section. It should 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.
[Author Aside]: Given the mixture of RFC2219 terms, I think all of
them in Section 9 need review. Further, given the effort that has
gone into Section 9, to accommodate these implementations of a draft
that was withdrawn decades ago. The idea of trying to make mode and
acl match is undercut when there are different valid ways of
computing the mode. There shouldn't be. To specify one way to do
this is necessary to accomplish the goal here and to do so would not
"invalidate" anything. Rather, it would establish, correctly, that
such implementations are not implementations of the NFSv4 ACL model,
but of the withdrawn POSIX ACL draft.
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 valid reasons to bypass
the recommendation are limited to 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.
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[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 #28a)]: 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 #28a)]: Then translate the calculated mask
for OWNER@, GROUP@, and EVERYONE@ into mode bits for, respectively,
the user, group, and other, as follows:
[Consensus Needed, including List(Item #28a)]: 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.
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[Consensus Needed (Item #28a)]: Then translate the calculated mask
for for each set of bit into the corresponding mode bits for, user,
group, and other, 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.
9.4. Alternatives in Computing Mode Bits
[Author Aside]: For reasons explained below, the author believes this
section needs to deleted, as part of Consensus Item #27c. In order
to enable this deletion or its replacement by an alternate
formulation if the working group so decides, 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.
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.
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[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.
9.5. 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.
9.6. Setting Mode and not ACL (overall)
9.6.1. Setting Mode and not ACL (vestigial)
[Author Aside]: All unannotated paragraphs as 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.
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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.
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 9.10).
9.6.2. Setting Mode and not ACL (Discussion)
[Author Aside]: All unannotated paragraphs as 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 9.6.1, 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 9.10).
The only "requirement" which might be met by the procedure mentioned
above is the text quoted below.
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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.
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 9.6.1 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 9.6.1,
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.
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9.6.3. 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 should 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
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
and 8881, 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.
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* The security-related effects of SVTX were not addressed.
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 and 8881. 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.
9.7. 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.
9.8. 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 9.7.
9.9. 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.
9.10. 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 should 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 9.6, 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 9.7.
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 9.8.
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 should 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.
9.11. 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 should
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.
9.12. 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.
NFSv4.2 contains an OPTIONAL extension, defined in [13], 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.
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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 should 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.
Such authentication is not directly provided by any RPC
authentication flavor. However, RPC-based transports, when suitably
configured, can provide this authentication.
NFSv4.1 defines a number of ways to provide appropriate authorization
facilities. These will not be discussed in detail here but the
following points should be noted:
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* 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 acess specified
file by specified sets of principals.
* ALARM ACEs provide a means to draw special attention to attempts
to acess 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).
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.
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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 "RPC
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.
* 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.
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* 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 Flavors
Different 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.
* When RPCSEC_GSS is used, the user making the request is
authenticated as is the server peer responding.
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13.4. Authentication Provided by the RPC Transport
Different transports differ quite considerably, as discussed below.
In contrast to the case of RPC 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 is authenticated.
* For most transports, such as TCP and RPC-over-RDMA version 1,
there is no provision for peer authentication.
As a result use of AUTH_SYS together with such transports is
inherently problematic.
* Some transports provide for the possibility of mutual peer
authentication.
14. Security of Data in Flight
14.1. Data Security Provided by the Flavor-associated Services
The only flavor providing these facilities is RPCSEC_GSS. When this
flavor is used, data security can be negotiated between client and
server as described in Section 15.2. However, when data security is
provided at the transport level, as described in Section 14.2, the
negotiation of privacy and integrity support is unnecessary,
Other flavors, such as AUTH_SYS and AUTH_NONE have no such data
security facilities. When these flavor are used, the only data
security is provided by the transport.
14.2. Data Security Provided by the RPC Transport
Some transports provide data security for all transactions performed
on them, eliminating the need for that security to be provided or
negotiated by the selection of particular flavors, mechanism, or
services.
15. Security Negotiation
[Author Aside]: All unannotated paragraphs in this section are
considered to b part of Consensus Item #32a
As previously in NFSv4, we use the term "negotiation" to characterize
the process of the server providing a set of options and the client
selecting one.
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The use of SECINFO, possibly with SECINFO_NONAME, remains the primary
means by which the security parameters are determined. The addition
of transports to flavors in providing security has resulted in the
following changes:
* Transport-related security choices are typically decided at
connection-establishment so there needs to be provision for
negotiation at this point.
* Despite the above, because the choices of flavor and transport
affect one another, SECINFO has been extended by the addition of
pseudo-flavors, while retaining the existing XDR, to allow
negotiation of transport choices and accompanying connection
establishment options, in addition to selection of flavors and
accompanying services. This allows server policies for such
matters to be different for different portions of the namespace.
15.1. Flavors and Pseudo-flavors
[Author Aside]: All unannotated paragraphs in this section are
considered to be part of Consensus Item #32b
The flavor field of the secinfo4 items returned by SECINFO and
SECINO_NONAME have always allowed pseudo flavors to be included.
However, previous treatments of these operations have not provided
information about how responses containing such pseudo-flavors are to
be interpreted.
Those pseudo-flavors now provide a means of extending the negotiation
process so it is capable of providing for the negotiation of the use
particular RPC transports and security-related options for the
connections established using those transports.
The flavors AUTH_NONE, AUTH_SYS and RPCSEC_GSS continue to indicate
the acceptability of the corresponding method of user authentication,
user identification, or user non-identification, when used with a
particular RPC transport.
The flavor AUTH_TLS, which is not used as part of issuing requests is
not included in this list and is treated as a connection-type-
specifying pseudo-flavor.
secinfo4s for the flavor RPCSEC_GSS contains additional information
describing the specific security algorithm to be used and the
ancillary services to be provided (e.g. integrity, privacy) when
these services are not provided by the transport.
Such flavors are referred to as "identification-specifying flavors"
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The classification below organizes the flavors and pseudo-flavors
used in security negotiation while Section 15.4 describes how the set
of secinfos in a response can be used by the client to select
acceptable combinations of security flavor, security mechanism,
security services, security-related transports, and security-related
connection characteristics.
* The pseudo-flavors designating a particular transport type such as
XPT_TCP or XPT_RDMA.
These pseudo-flavors are referred to as "transport- specifying
flavors".
* The pseudo-flavors designating restrictions on acceptable
connection characteristics include XPCH_ENCRYPT, XPCH_PEERAUTH,
and XPCH_SECURE.
Such pseudo-flavors are referred to as "transport-restriction
pseudo-flavors".
* The pseudo-flavors denoting sets of allowable connection types.
While many connection types are designated by a combination of a
flavor designating a transport with on designating a set of
connection characteristics, there are pseudo-flavors, called
"conection-type pseido-flavror that designate a a set of
connection types directly.
These include the flavor AUTH_TLS which is equivalent to XP_TCP
combined with XPCH_ENCRYPT, and the pseudo-flavor XP_TCP_SECURE
equivalent to XP_TCP combined with XPCH_SECURE.
* The special pseudo-flavors, XPBREAK, XPCLEAR and XPCURRENT
15.2. Negotiation of Security Flavors and Mechanisms
[Author Aside]: All unannotated paragraphs in this section are
considered to be part of Consensus Item #32c
For the current connection, this proceeds as it has previously, when
security-relevant transports were not available. Flavor entries,
including those including mechanism information are listed in order
of server preference and apply, by default, to the current
connection, which is normally is favored by the server.
When other transport-identifying pseudo-flavors appear before the
flavor entries, then the server is indicating that these transport
types are also acceptable, with the server preference following the
ordering of the entries. In this case, any flavor entries that
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follow a transport entry specify that those flavor are usable with
the transport types or connection types denoted by that transport
entry.
15.3. Negotiation of RPC Transports and Characteristics
[Author Aside]: All unannotated paragraphs in this section are
considered to be part of Consensus Item #32d
First we define some necessary terminology.
* A transport-specifying pseudo-flavor specifies one of a small set
of RPC transport types such as TCP or RDMA. There are also
pseudo-flavors that specify a set of transport types such as
XPT_ALL.
* Connection characteristics are designations of security-relevant
characteristics or sets of characteristics that connections might
have.
There are pseudo-flavors associated with connection
characteristics such as XPCH_CLPEERAUTH, denoting client-peer
authentication and XPCH_ENCRYPT, denoting the presence of an
encrypted channel. The pseudo-flavor XPCH_SECURE denotes the
presence of peer mutual authentication together with the use of an
encrypted channel.
* The combination of a transport type with a set of connection
characteristics is considered a connection type. While many
connection types are designated by a combination of a flavor
designating a transport with on designating a set of connection
characteristics, there are pseudo-flavors that designate a set of
connection types directly.
For example, the flavor AUTH_TLS is equivalent to XP_TCP combined
with XPCH_ENCRYPT and XPCH_CLPEERAUTH while the pseudo-flavor
XP_TCP_SECURE equivalent to XP_TCP combined with CONCH_SECURE.
* A flavor specification designates a specific flavor, or, in the
case of RPCSEC_GSS, a flavor combined with additional mechanism
and service information.
* A flavor assignment denotes the association of a specific flavor
specification with a connection type.
A secinfo response will designate a set of valid flavor assignments
with an implied server ordering derived from the order that the
entries appear in.
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In interpreting the response array the client is to maintain sets of
designated transport types, connection characteristics and connection
types specified individually (i.e. without separately specifying
transport types and connection characteristics). When a flavor
specification is encountered, that flavor is considered valid when
used with all currently active connection types, defined by the union
of the individually specified connection types and the Cartesian
product of the current transport types and current connection types.
The presumed ordering of these assignments is as follows:
* When one of the connection types was specified directly by a
connection type, the position of that specification is compared to
that of either the other individually-specified connection type or
the earlier of the transport-type specification and the connection
characteristics specification.
* In other cases, the position of the transport type specifications
are considered first withe the position of the connection
characteristics considered if necessary.
* If neither of the above resolve issue, the position of the flavor
specification is considered.
* The type of the current connection is considered to be specified
first, implicitly.
* There are provisions, described in Section 15.4 to modify this
ordering, as may be necessary, for example, when the current
connection, while acceptable is, of lower server preference.
15.4. Overall Interpretation of SECINFO Response Arrays
[Author Aside]: All unannotated paragraphs in this section are
considered to be part of Consensus Item #32e.
This section summarizes the processing necessary on the client to
interpret the response to a SECINFO or SECINFO_NONAME request and
determine, at the specified part of the server's namespace:
* The set of transport types acceptable to the server.
* The set of connection types acceptable to the server.
* For each acceptable connection type, the set of flavors acceptable
to the server.
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* For each acceptable connection type for which encryption is not
provided and for which the flavor RPCSEC_GSS is accepted, a set of
services to be required when using the flavor on connections of
that type.
For each of the items for which the set of acceptable elments has
more than one element, the server's preference order can be
communicated to the client.
This section provides the same information as Sections 15 through
15.3 but the presentation is in the form of an algorithm.
The algorithm needs to maintain the following information as part of
the context shared with the operations defined in Sections 15.4.2 and
15.4.3
* The ordered set of currently specified transport types.
Because of the need to retain ordering information, a mask cannot
be used to represent this.
Because duplicates are not allowed, the size of this data can be
limited, based on the number of valid transport types.
The initial value is the empty list.
* An array of sets of current transport restrictions.
Since there are three possible transport characteristics:
encryption, client-peer authentication, and server-peer
authentication, a given connection may have eight possible states
and a set of allowed characteristics represented by an eight-bit
mask of allowed combinations of chaacteristics.
The initial value is a single entry with all bits set, indicating
no current restrictions.
* The ordered set of additional connection types, beyond the
Cartesian product of the current sets of transport types and of
connection restrictions.
Each entry consists of a transport type together with a connection
characteristics mask.
The initial value is a single-entry list whose only entry consists
of the transport type of the current connection combined with a
set of transport characteristics in effect for the current
connection and no other possibilities.
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* The pseudo-flavor most previously processed.
When this is not one of the special pseudo-flavors, the pseudo-
flavor type is sufficient.
The initial value is transport-restriction pseudo-flavor type
reflecting the fact that the state of the current connection is
the initial basis for flavor specification.
* The output list showing, in order, the combinations of connection
types combined with flavors, or, in the case of RPCSEC_GSS, of
flavor triples.
15.4.1. Interpretation of SECINFO Response Arrays (Core)
[Author Aside]: This preliminary section, which is currently
incomplete, is considered Consensus Item #49a.
[Author Aside]: There are problems with the indenting in this
section. This may be due to to an xml2rfc bug or I may be using ul
incorrectly, or both. Will try to fix this for the next draft.
Processing of the response proceeds through each secinfo4 in the
response. For each such entry, the flavor value, which may be a
pseudo-flavor, controls what is to be done.
The current entry is fetched.
The pseudo-flavor for that entry controls what is done next.
If the pseudo-flavor specifies a transport type or a set of
transport types, the following is done:
If the previous pseudo-flavor was not a transport-specifying
flavor,
Connection type expansion, as described in Section 15.4.2
is performed.
If the flavor designates a single transport type,
The connection type is added to the current list, if it
is not already present in the list.
Otherwise, each included transport type is added to the
list in turn.
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If the pseudo-flavor specifies a connection restriction, the
following is done:
If the previous pseudo-flavor was not a transport-specifying
flavor, is not a restriction-specifying flavor and is not
XPBREAK,
Connection type expansion, as described in Section 15.4.2
is performed.
If the previous pseudo-favor was XPBREAK,
A new restriction entry, initialized with all bits one,
is added to the list.
In any case, the newly-specified restrictions are anded with
the last entry in the list.
If the pseudo-flavor specifies a set of connection types or is
XPCURRENT, the following is done:
Inoformation specified by the current flavor is added to the
list of additional connection types, if that same set of
connection type is not already present.
If the pseudo-flavor is XPBREAK,
Nothing specific is done at this point.
If the pseudo-flavor is XPCLEAR,
The set of data maintained by algorithm, including the
flavor output is reset to its initial state.
In addition the set of additional connection types is
cleared to empty state, i.e. information about the current
connection is removed.
If the pseudo-flavor is an authentication flavor,
Flavor expansion, as described in Section 15.4.3 is
performed to combine the current flavor or flavor triple
with each of the currently specified connection types.
Then the current pseudo-flavor is saved as the previous pseudo-
flavor.
We then move on to the next entry.
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15.4.2. Connection Type Transcription
[Author Aside]: This section will be provided in a later draft as
part of Consensus Item #48a.
15.4.3. Flavor Transcription
[Author Aside]: This section will be provided in a later draft as
part of Consensus Item #48b.
15.5. SECINFO
[Author Aside]: All unannotated paragraphs in this section are
considered to be part of Consensus Item #33a.
The description in the sub-sections below, while it adheres to the
XDR appearing [6], [7], [8], [9] and [11]. will supersede the
descriptions in [7] and [8].
This is necessary to adapt the security negotiation process to the
presence of transport-level security services such as encryption and
peer authentication.
Similar changes are necessary in the parallel SECINFO_NONAME
operation introduced in NFSv4.1. These are expected to be done as
part of the rfc5661bis effort.
15.5.1. SECINFO ARGUMENTS
[Author Aside]: All unannotated paragraphs in this section are
considered to be part of Consensus Item #33b.
struct SECINFO4args {
/* CURRENT_FH: directory */
component4 name;
};
Figure 1
15.5.2. SECINFO RESULTS
[Author Aside]: All unannotated paragraphs in this section are
considered to be part of Consensus Item #33c.
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/*
* From RFC 2203
*/
enum rpc_gss_svc_t {
RPC_GSS_SVC_NONE = 1,
RPC_GSS_SVC_INTEGRITY = 2,
RPC_GSS_SVC_PRIVACY = 3
};
struct rpcsec_gss_info {
sec_oid4 oid;
qop4 qop;
rpc_gss_svc_t service;
};
/* RPCSEC_GSS has a value of '6' - See RFC 2203 */
union secinfo4 switch (uint32_t flavor) {
case RPCSEC_GSS:
rpcsec_gss_info flavor_info;
default:
void;
};
typedef secinfo4 SECINFO4resok<>;
union SECINFO4res switch (nfsstat4 status) {
case NFS4_OK:
/* CURRENTFH: consumed */
SECINFO4resok resok4;
default:
void;
};
Figure 2
15.5.3. SECINFO DESCRIPTION
[Author Aside]: All unannotated paragraphs in this section are
considered to be part of Consensus Item #33d.
The SECINFO operation is used by the client determine the appropriate
RPC authentication flavors, security mechanisms and encrypting
transports to access a specific directory filehandle, file name pair.
SECINFO should apply the same access approach used for LOOKUP when
evaluating the name. In consequence, if the requester does not have
the appropriate access to LOOKUP the name, then SECINFO will behave
the same way and return NFS4ERR_ACCESS.
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The result will contain an array that represents the security flavor,
security mechanisms and transports available, with an order
corresponding to the server's preferences, the most preferred being
first in the array. The client is free to pick whatever security
flavors, mechanisms and transports it both desires and supports, or
to pick in the server's preference order the first one it supports.
The array entries are represented by the secinfo4 structure. The
field 'flavor' will contain one of the following sorts of values:
* a value of AUTH_NONE, AUTH_SYS (as defined in RFC 5531 [4]).
* AUTH_TLS as described in ...
* A pseudo-flavor defined in Section 18.2
* RPCSEC_GSS (as defined in RFC 2203 [2]).
* Any other security flavor or pseudo-flavor registered with IANA.
For the flavors other than RPCSEC_GSS, no additional security
information is returned. For a return value of RPCSEC_GSS, a
security triple is returned that contains the mechanism object
identifier (OID, as defined in RFC 2743 [3]), the quality of
protection (as defined in RFC 2743 [3]), and the service type (as
defined in RFC 2203 [2]). It is possible for SECINFO to return
multiple entries with flavor equal to RPCSEC_GSS with different
security triple values.
On success, the current filehandle is consumed, so that, if the
operation following SECINFO tries to use the current filehandle, that
operation will fail with the status NFS4ERR_NOFILEHANDLE.
If the name has a length of zero, or if the name does not obey the
UTF-8 definition in circumstances in which UTF-8 names are required,
the error NFS4ERR_INVAL will be returned.
See Sections 15.2 through 15.4 for additional information on the use
of SECINFO.
15.5.4. SECINFO IMPLEMENTATION (general)
[Author Aside]: All unannotated paragraphs in this section are
considered to be part of Consensus Item #33e.
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The SECINFO operation is expected to be used by the NFS client when
the error value of NFS4ERR_WRONGSEC is returned from another NFS
operation. This signifies to the client that the server's security
policy is different from what the client is currently using. At this
point, the client is expected to obtain a list of possible security
flavors and choose what best suits its policies.
15.5.5. SECINFO IMPLEMENTATION (for NFSv4.0)
[Author Aside]: All unannotated paragraphs in this section are
considered to be part of Consensus Item #34a.
The server's security policies will determine when a client request
receives NFS4ERR_WRONGSEC. The operations that may receive this
error are LINK, LOOKUP, LOOKUPP, OPEN, PUTFH, PUTPUBFH, PUTROOTFH,
RENAME, RESTOREFH, and, indirectly, READDIR. LINK and RENAME will
only receive this error if the security used for the operation is
inappropriate for the saved filehandle. With the exception of
READDIR, these operations represent the point at which the client can
instantiate a filehandle into the current filehandle at the server.
The filehandle is either provided by the client (PUTFH, PUTPUBFH,
PUTROOTFH) or generated as a result of a name-to-filehandle
translation (LOOKUP and OPEN). RESTOREFH is treated differently
because the filehandle is a result of a previous SAVEFH. Even though
the filehandle, for RESTOREFH, might have previously passed the
server's inspection for a security match, the server will check it
again on RESTOREFH to ensure that the security policy has not
changed.
If the client is to resolve an error return of NFS4ERR_WRONGSEC, the
following will occur:
* For LOOKUP and OPEN, the client will use SECINFO with the same
current filehandle and name as provided in the original LOOKUP or
OPEN to determine the acceptable combinations of transport types,
transport restrictions, and flavor-based triple use to make
requests directed at the specified portion of the server
namespace.
* For LINK, PUTFH, RENAME, and RESTOREFH, the client will use
SECINFO and provide the parent directory filehandle and the object
name that corresponds to the filehandle originally provided by the
PUTFH or RESTOREFH, or, for LINK and RENAME, the SAVEFH.
* For LOOKUPP, PUTROOTFH, and PUTPUBFH, the client will be unable to
use the SECINFO operation since SECINFO requires a current
filehandle and none exist for these three operations. Therefore,
the client must iterate through the security triples expected to
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be available at the client for use by the current connection (i.e,
because they are REQUIRED and attempt the PUTROOTFH or PUTPUBFH
operation repeatedly, once for each possible triple. In the
unfortunate event that none of the MANDATORY security triples are
supported by the client and server, the client should try using
others that are believed to be available. It is desirable to do
so in a manner which provides encryption or at least integrity
support integrity. Often his will be possible if the connection
is encrypted. In other cases. the client can try using AUTH_NONE,
but because such forms lack integrity checks, there is an element
of risk in doing so. However the risk can be made small if the
server returns NFS4ERR_WRONGSEC when entering any subdirectory of
the root or public filehandle.
The READDIR operation will not directly return the NFS4ERR_WRONGSEC
error. However, if the READDIR request included a request for
attributes, it is possible that the READDIR request's security triple
does not match that of a directory entry. If this is the case and
the client has requested the rdattr_error attribute, the server will
return the NFS4ERR_WRONGSEC error in rdattr_error for the entry.
This will allow SECINFO to be issued for that entry with the same
current file handle as used for the READDIR and a name derived from
the entry for which the error was noted.
[Author Aside]: The following paragraph seems dubious since it would
best if the server tells the client to use, rather than leaving him
to guess, and the server will know what he supports. Would like to
delete this as part of Consensus Item #47a, unless compatibility
issues make that impossible.
[Previous Treatment (Item #47a)]: Note that a server MAY use the
AUTH_NONE flavor to signify that the client is allowed to attempt to
use authentication flavors that are not explicitly listed in the
SECINFO results. Instead of using a listed flavor, the client might
then, for instance, opt to use an otherwise unlisted RPCSEC_GSS
mechanism instead of AUTH_NONE. It may wish to do so in order to
meet an application requirement for data integrity or privacy. In
choosing to use an unlisted flavor, the client SHOULD always be
prepared to handle a failure by falling back to using AUTH_NONE or
another listed flavor. It cannot assume that identity mapping is
supported and should be prepared for the fact that its identity is
squashed.
15.5.6. SECINFO IMPLEMENTATION (for NFSv4.1 and v4.2)
[Author Aside]: All unannotated paragraphs in this section are
considered to be part of Consensus Item #33f.
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As mentioned, the server's security policies will determine when a
client request receives NFS4ERR_WRONGSEC.
See Table 14 of [8] for a list of operations that can return
NFS4ERR_WRONGSEC. in the case of v4.2, there might be extensions
allowed to return NFS4ERR_WRONGSEC. In addition, when READDIR
returns attributes, the rdattr_error (Section 5.8.1.12 of [8]) can
contain NFS4ERR_WRONGSEC.
Note that CREATE and REMOVE MUST NOT return NFS4ERR_WRONGSEC. The
rationale for CREATE is that unless the target name exists, it cannot
have a separate security policy from the parent directory, and the
security policy of the parent was checked when its filehandle was
injected into the COMPOUND request's operations stream (for similar
reasons, an OPEN operation that creates the target MUST NOT return
NFS4ERR_WRONGSEC). If the target name exists, while it might have a
separate security policy, that is irrelevant because CREATE MUST
return NFS4ERR_EXIST. The rationale for REMOVE is that while that
target might have a separate security policy, the target is going to
be removed, and so the security policy of the parent trumps that of
the object being removed. RENAME and LINK MAY return
NFS4ERR_WRONGSEC, but the NFS4ERR_WRONGSEC error applies only to the
saved filehandle (see Section 2.6.3.1.2 of [8]). Any
NFS4ERR_WRONGSEC error on the current filehandle used by LINK and
RENAME MUST be returned by the PUTFH, PUTPUBFH, PUTROOTFH, or
RESTOREFH operation that injected the current filehandle.
With the exception of LINK and RENAME, the set of operations that can
return NFS4ERR_WRONGSEC represents the point at which the client can
inject a filehandle into the "current filehandle" at the server. The
filehandle is either provided by the client (PUTFH, PUTPUBFH,
PUTROOTFH), generated as a result of a name-to-filehandle translation
(LOOKUP and OPEN), or generated from the saved filehandle via
RESTOREFH. As Section 2.6.3.1.1.1 of [8] states, a put filehandle
operation followed by SAVEFH MUST NOT return NFS4ERR_WRONGSEC. Thus,
the RESTOREFH operation, under certain conditions (see
Section 2.6.3.1.1 of [8]), is permitted to return NFS4ERR_WRONGSEC so
that security policies can be honored.
The READDIR operation will not directly return the NFS4ERR_WRONGSEC
error. However, if the READDIR request included a request for
attributes, it is possible that the READDIR request's security triple
did not match that of a directory entry. If this is the case and the
client has requested the rdattr_error attribute, the server will
return the NFS4ERR_WRONGSEC error in rdattr_error for the entry.
To resolve an error return of NFS4ERR_WRONGSEC, the client does the
following:
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* For LOOKUP and OPEN, the client will use SECINFO with the same
current filehandle and name as provided in the original LOOKUP or
OPEN to enumerate the available security triples.
* For the rdattr_error, the client will use SECINFO with the same
current filehandle as provided in the original READDIR. The name
passed to SECINFO will be that of the directory entry (as returned
from READDIR) that had the NFS4ERR_WRONGSEC error in the
rdattr_error attribute.
* For PUTFH, PUTROOTFH, PUTPUBFH, RESTOREFH, LINK, and RENAME, the
client will use SECINFO_NO_NAME { style =
SECINFO_STYLE4_CURRENT_FH }. The client will prefix the
SECINFO_NO_NAME operation with the appropriate PUTFH, PUTPUBFH, or
PUTROOTFH operation that provides the filehandle originally
provided by the PUTFH, PUTPUBFH, PUTROOTFH, or RESTOREFH
operation.
NOTE: In NFSv4.0, the client was required to use SECINFO, and had
to reconstruct the parent of the original filehandle and the
component name of the original filehandle. The introduction in
NFSv4.1 of SECINFO_NO_NAME obviates the need for reconstruction.
* For LOOKUPP, the client will use SECINFO_NO_NAME { style =
SECINFO_STYLE4_PARENT } and provide the filehandle that equals the
filehandle originally provided to LOOKUPP.
16. Future Security Needs
[Author Aside]: All unannotated paragraphs in this section are
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.
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* 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 RPC-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.
17. Security Considerations
17.1. Changes in Security Considerations
Beyond the needed inclusion of a threat analysis and the fact that
all minor versions are dealt with together, there are a number of
substantive changes in the approach to NFSv4 security presented in
RFCs 7530 and 8881 and that appearing in this document.
This document will not seek to speculate how the previous treatment,
now viewed as incorrect, came to be written, approved, and published.
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 available at the RPC transport level can be used to
deal with security issues, as described in Section 17.1.2
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.
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.
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With regard to specific threats, there is no mention in existing
security consideration 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.
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. Transport-layer Security Facilities
Such transport-level RPC facilities as RPC-over-TLS provide important
ways of proving better security for all the NFSv4 minor versions.
In particular:
* The presence of encryption by default will deal with security
issue regarding data-in-flight, for both RPCSEC_GSS and AUTH_SYS.
* Peer authentication provided by the server eliminates the
possibility of a server-impersonation attack, even when using
AUTH_SYS.
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* When mutual authentication is part of connection establishment,
there is a possibility, where an appropriate trust relationship
exists, of treating the userid's presented in AUTH_SYS, as
effectively authenticated, based on the authentication of the
client peer.
17.1.3. Approach to Implementation Semantic Divergences
[Consensus Needed (Items #36a, #37a)]: For a variety of reasons,
there are many cases in which one approach to security is preferred
where others are allowed, if only to give time for implementers to
adapt to the preferred approach. In such cases the word "SHOULD is
used to introduce the preferred while others are allowed to allow
compatibility 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 the RPC transport, allowance has
been made for implementations for which these new transport are
not available and for which, based on previous standards-track
guidance, AUTH_SYS us used, in the clear, without client-peer
authentication.
* [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 now
clearly defining the recommended behavior in dealing with these
issues, allowance has been made to give times 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 transport- level security facilities such as RPC-over-
TLS.
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* 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
support from the transport layer.
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 server 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.
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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
network separately from the internet per se.
* 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
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.
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This 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.
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.
17.3. 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 #41a.
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 by the RPC
transport, 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.
17.3.2. Recommendations Regarding Client Peer Authentication
[Author Aside]: All unannotated paragraphs within this section are
considered part of Consensus Item #41b.
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.
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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 are allowed to be executed.
17.3.3. Issues Regarding Valid Reasons to Bypass Recommendations
[Author Aside]: All unannotated paragraphs within this section are
considered part of Consensus Item #41c.
Clearly, the maturity and compatibility issues mentioned in
Section 17.1.4 are valid reasons to bypass the above recommendations,
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 encrypted transports constitutes, in
itself, a valid reason to ignore the above recommendations.
[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 these issues it needs to be understood that the
transport-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. Data Security Threats
Will be addressed in a later draft as part of Consensus Item #42a.
17.5. Authentication-based threats
17.5.1. Attacks based on the use of AUTH_SYS
Will be addressed in a later draft as part of Consensus Item #43a.
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17.5.2. Attacks on Name/Userid Mapping Facilities
Will be addressed in a later draft as part of Consensus Item #44a.
17.6. Disruption and Denial-of-Service Attacks
17.6.1. Attacks Based on the Disruption of Client-Server Shared State
Will be addressed in a later draft as part of Consensus Item #45a.
17.6.2. Attacks Based on Forcing the Misuse of Server Resources
Will be addressed in a later draft as part of Consensus Item #46a.
18. IANA Considerations
[Author Aside]: All unannotated paragraphs in this section are to be
considered part of Consensus Item #33f.
Because of the shift from implementing security-related services only
in connection with RPCSEC_GSS to one in which transport-level
security has a prominent role, a number if new values need to be
assigned.
These include new authstat values to guide selection of a Transports
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 #33g.
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
the rpc transport. 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.
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18.2. New Authentication Pseudo-Flavors
[Author Aside]: All unannotated paragraphs in this section are to be
considered part of Consensus Item #33h.
The new pseudo-flavors described in this section are to be made
available to allow their return as part of the response to SECINFO
operation described in Section 15.5 and for similar operations.
The following transport-specifying flavors are to be defined:
* XPT_TCP denotes use of a TCP transport to support to RPC. The use
of TLS as provided by RPC-with-TLS is orthogonal to the transport
type, as is the use of optional authentication features. Such
facilities are treated as transport characteristics.
When RDMA support is layered on TCP, that fact is not relevant to
the transport type, which is still XPT_RDMA.
* XPT_RDMA denotes use of any version of RPC-over-RDMA to support
RPC. Although Version 1 has no security-support, future version
may have such facilities.
In any case, the specification of the presence or need for such
facilities are handled as transport characteristics.
* XPT_ALL is currently equivalent to XPT_TCP followed by XPT_RDMA.
When new transport types are made available for use wit NFSv4, it
is intended that
The following transport-restricting flavors are to be defined:
* XPCH_ENCRYPT restrict connections to those providing encryption.
* XPCH_SVRAUTH restricts connections allowed to those that provide,
at connection time authentication of the server peer.
* XPCH_CLAUTH restricts connections allowed to those that provide,
at connection time authentication of the server peer.
* XPCH_PEERAUTH is equivalent to XPCH_SVRAUTH combined with
XPCH_CLAUTH.
* XPCH_SECURE is equivalent to XPCH_ENCRYPT combined with
XPCH_PEERAUTH.
The follow connection-specifying flavors are to be defined:
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* AUTH_TLS is equivalent to XP_TCP combined with XPCH_ENCRYPT and
XPCH_CLPEERAUTH
* XP_TCP_SECURE is equivalent to XP_TCP combined with XPCH_SECURE.
The following special flavors are to be defined:
* XPCLEAR reset the state of processing to an empty state. This is
useful if the current connection type is not usable for the
specified region of the namespace or if it is of lower server
preference.
* XPBREAK forces the use of a new set transport restrictions,
separate from previous ones and applying to the same set of
transport types.
* XPCURRENT specifies that the type of the current connection is
usable for access, with the preference derived from its location
in the SECINFO response array.
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>.
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[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>.
[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>.
19.2. Informative References
[13] 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>.
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 the RPC transport 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 transport characteristics.
Despite these major changes there are not expected to be
compatibility issues between peers supporting secure transport
characteristics 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 interopherability 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 the following codes defined:
* "NM" denotes a change which is new material that is not purely
editorial and thus requires Working Group consensus for eventual
publication.
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* "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.
When the document is promoted to a working group document, there
should be very few issues in this state and, for each such issue,
a clear plan to address the possibility of any compatibility
problems, enabling resolution of the issue to be reasonably
anticipated.
* "NE" denotes change based on an existing issue in the spec but for
which the replacement text is incomplete and needs further
elaboration.
There will be no changes in this state when promotion to a working
group document is requested.
* "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.
There will be no changes in this state when promotion to a working
group document is requested.
* "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.
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There will be no changes in this state when promotion to a working
group document is requested.
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,
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 be
removed from this table although it will be mentioned in Appendices
A.2 or A.1
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 the RPC transport. |
+----+------+------------------+-------------------------------+
| 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. |
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+----+------+------------------+-------------------------------+
| 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" |
| | | #6b in S 5.6 | for directories, both with |
| | | | respect to ACL handling and |
| | | #6c in S 7.3.1 | mode handling. |
+----+------+------------------+-------------------------------+
| 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 |
| | | #11c in S 5.11 | the 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 |
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| | | | 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 |
| | | #15b in S 7.1 | for ALLOW and DENY ACEs. |
| | | | |
| | | #15c in S 7.2 | |
+----+------+------------------+-------------------------------+
| 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 7.3.1 | Introduce the concept of |
| | | | reverse-slope modes and deal |
| | | #21b in S 9.3 | properly with them. The |
| | | | decision as to the proper |
| | | #21c in S 9.6 | 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 |
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| | | | 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 |
| | | #25d in S 9.7 | includes many aspects of the |
| | | | shift to be more specific |
| | | #25e in S 9.9 | about the co-ordination |
| | | | requirements including |
| | | #25f in S 9.10 | addressing apparently |
| | | | unmotivated uses of the terms |
| | | #25g in S 9.11 | "SHOULD" and "SHOULD NOT", it |
| | | | excludes some arguably |
| | | | 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@, |
| | | #26 in S 9.6.3 | Group, or EVERYONE@ are be |
| | | | dealt with when setting mode. |
+----+------+------------------+-------------------------------+
| 27 | CI | #27a in S 9.2 | Concerns the possibility of |
| | | | establishing one way of |
| | | #27b in S 9.3 | computing a mode from an acl |
| | | | that clients can depend on, |
| | | #27c in S 9.4 | rather than two or an |
| | | | unbounded number. |
+----+------+------------------+-------------------------------+
| 28 | WI | #28a in S 9.3 | Decide how to address flaws |
| | | | in mapping to/from reverse- |
| | | #28 in S 9.6.3 | slope modes. |
+----+------+------------------+-------------------------------+
| 29 | BC | #29 in S 9.6.3 | Address the coordination of |
| | | | mode and ACL-based attributes |
| | | | in unified way for all minor |
| | | | versions. |
+----+------+------------------+-------------------------------+
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| 30 | CI | #30a in S 9.6.1 | New proposed treatment of |
| | | | setting mode incorporating |
| | | #30b in S 9.6.2 | some consequences of |
| | | | anticipated decisions |
| | | #30c in S 9.6.3 | regarding other consensus |
| | | | items (#26, #28, #29) |
+----+------+------------------+-------------------------------+
| 31 | WI | #31a in S 9.6.3 | 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 accomodate |
| | | #32b in S 15.1 | multiple transport types and |
| | | | services derivable from |
| | | #32c in S 15.2 | transport characteristics, |
| | | | i.e. encryption and peer |
| | | #32d in S 15.3 | authentication. |
| | | | |
| | | #32e in S 15.4 | |
+----+------+------------------+-------------------------------+
| 33 | BE | #33a in S 15.5 | Reorganization of description |
| | | | of SECINFO op to apply to all |
| | | #33b in S 15.5.1 | minor versions. Assumes |
| | | | basics of proposal for Item |
| | | #33c in S 15.5.2 | #32. |
| | | | |
| | | #33d in S 15.5.3 | |
| | | | |
| | | #33e in S 15.5.4 | |
| | | | |
| | | #33f in S 18 | |
| | | | |
| | | #33g in S 18.1 | |
| | | | |
| | | #33h in S 18.2 | |
+----+------+------------------+-------------------------------+
| 34 | BC | #34a in S 15.5.6 | Revision to NFSv4.0 SECINFO |
| | | | implementation section to be |
| | | | compatible with expanded |
| | | | approach to negotiation. |
| | | | Assumes basics of proposals |
| | | | for Items #32 and #33. |
+----+------+------------------+-------------------------------+
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| 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 transport |
| | | | 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 |
| | | #40a in S 17.2.2 | the corresponding threat |
| | | | analysis. |
+----+------+------------------+-------------------------------+
| 41 | CI | #41a in S 17.3.1 | Discuss major new security |
| | | | recommendations regarding |
| | | #41b in S 17.3.2 | protection of data in flight |
| | | | and client peer |
| | | #41c in S 17.3.3 | authentication. Also, covers |
| | | | the circumstances under which |
| | | | such recommendations can be |
| | | | bypassed. |
+----+------+------------------+-------------------------------+
| 42 | LD | #42a in S 17.4 | Placeholder for threat |
| | | | analysis section regarding |
| | | | security of data in flight. |
+----+------+------------------+-------------------------------+
| 43 | LD | #43a in S 17.5.1 | Placeholder for threat |
| | | | analysis section dealing with |
| | | | the use of AUTH_SYS. |
+----+------+------------------+-------------------------------+
| 44 | LD | #44a in S 17.5.2 | Placeholder for threat |
| | | | analysis section dealing with |
| | | | attacks on userid/name |
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| | | | mapping. |
+----+------+------------------+-------------------------------+
| 45 | LD | #45a in S 17.6.1 | Placeholder for threat |
| | | | analysis section dealing with |
| | | | disruption attacks based on |
| | | | attacks on shared state. |
+----+------+------------------+-------------------------------+
| 46 | LD | #46a in S 17.6.2 | Placeholder for threat |
| | | | analysis section dealing with |
| | | | attacks on shared state |
| | | | design to cause misuse of |
| | | | resources. |
+----+------+------------------+-------------------------------+
| 47 | CI | #47a in S 15.5.5 | Dubious paragraph which |
| | | | should be deleted if there |
| | | | are no compatibility issues |
| | | | that make that impossible. |
+----+------+------------------+-------------------------------+
| 48 | CI | #48a in S 15.4.2 | Missing pieces of secinfo |
| | | | processing algorithm that |
| | | #48b in S 15.4.3 | didn't get done in -02. |
+----+------+------------------+-------------------------------+
| 49 | NE | #49a in S 15.4.1 | Main secinfo processing |
| | | | algorithm that needs to |
| | | | finished in -02. |
+----+------+------------------+-------------------------------+
Table 3
The following table summarizes the issues in each particular 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 |
+--------+-----+-----------------------------------------------+
| BE(M) | 1 | 33 |
+--------+-----+-----------------------------------------------+
| BC(M) | 2 | 32, 34 |
+--------+-----+-----------------------------------------------+
| CI(M) | 7 | 36, 38, 39, 40, 41, 47, 48 |
+--------+-----+-----------------------------------------------+
| NE(M) | 2 | 35, 49 |
+--------+-----+-----------------------------------------------+
| LD(M) | 5 | 42, 43, 44, 45, 46 |
+--------+-----+-----------------------------------------------+
| All(M) | 19 | As listed above. |
+--------+-----+-----------------------------------------------+
| NM(O) | 1 | 16 |
+--------+-----+-----------------------------------------------+
| BE(O) | 4 | 3, 5, 7, 24 |
+--------+-----+-----------------------------------------------+
| BC(O) | 12 | 9, 10, 12, 13, 14, 15, 17, 18, 21, 22, 23, 29 |
+--------+-----+-----------------------------------------------+
| CI(O) | 11 | 4, 6, 8, 11, 19, 25, 26, 27, 28, 30, 37 |
+--------+-----+-----------------------------------------------+
| WI(O) | 2 | 20, 31 |
+--------+-----+-----------------------------------------------+
| All(O) | 30 | As described above |
+--------+-----+-----------------------------------------------+
| *All* | 49 | Grand total for above table. |
+--------+-----+-----------------------------------------------+
Table 4
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 putting NFSv4 security on a
firmer footing. We appreciate this perceptive guidance.
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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-over-TLS and bringing possible
approaches to the attention of the working group.
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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