Network File System Version 4 T. Myklebust
Internet-Draft Hammerspace
Updates: 5531 (if approved) C. Lever, Ed.
Intended status: Standards Track Oracle
Expires: May 20, 2020 November 17, 2019
Towards Remote Procedure Call Encryption By Default
draft-ietf-nfsv4-rpc-tls-04
Abstract
This document describes a mechanism that, through the use of
opportunistic Transport Layer Security (TLS), enables encryption of
in-transit Remote Procedure Call (RPC) transactions while
interoperating with ONC RPC implementations that do not support this
mechanism. This document updates RFC 5531.
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
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This Internet-Draft will expire on May 20, 2020.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. RPC-Over-TLS in Operation . . . . . . . . . . . . . . . . . . 5
4.1. Discovering Server-side TLS Support . . . . . . . . . . . 5
4.2. Authentication . . . . . . . . . . . . . . . . . . . . . 7
4.2.1. Using TLS with RPCSEC GSS . . . . . . . . . . . . . . 8
5. TLS Requirements . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Base Transport Considerations . . . . . . . . . . . . . . 8
5.1.1. Operation on TCP . . . . . . . . . . . . . . . . . . 8
5.1.2. Operation on UDP . . . . . . . . . . . . . . . . . . 9
5.1.3. Operation on Other Transports . . . . . . . . . . . . 9
5.2. TLS Peer Authentication . . . . . . . . . . . . . . . . . 9
5.2.1. X.509 Certificates Using PKIX trust . . . . . . . . . 10
5.2.2. X.509 Certificates Using Fingerprints . . . . . . . . 11
5.2.3. Pre-Shared Keys . . . . . . . . . . . . . . . . . . . 11
5.2.4. Token Binding . . . . . . . . . . . . . . . . . . . . 11
6. Implementation Status . . . . . . . . . . . . . . . . . . . . 12
6.1. DESY NFS server . . . . . . . . . . . . . . . . . . . . . 12
6.2. Hammerspace NFS server . . . . . . . . . . . . . . . . . 12
6.3. Linux NFS server and client . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7.1. Limitations of an Opportunistic Approach . . . . . . . . 13
7.1.1. STRIPTLS Attacks . . . . . . . . . . . . . . . . . . 13
7.2. Multiple User Identity Realms . . . . . . . . . . . . . . 14
7.3. Security Considerations for AUTH_SYS on TLS . . . . . . . 14
7.4. Best Security Policy Practices . . . . . . . . . . . . . 15
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. Normative References . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . 17
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Appendix A. Known Weaknesses of the AUTH_SYS Authentication
Flavor . . . . . . . . . . . . . . . . . . . . . . . 18
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
In 2014 the IETF published [RFC7258] which recognized that
unauthorized observation of network traffic had become widespread and
was a subversive threat to all who make use of the Internet at large.
It strongly recommended that newly defined Internet protocols make a
real effort to mitigate monitoring attacks. Typically this
mitigation is done by encrypting data in transit.
The Remote Procedure Call version 2 protocol has been a Proposed
Standard for three decades (see [RFC5531] and its antecedants).
Eisler et al. first introduced an in-transit encryption mechanism for
RPC with RPCSEC GSS over twenty years ago [RFC2203]. However,
experience has shown that RPCSEC GSS can be difficult to deploy:
o Per-client deployment and administrative costs are not scalable.
Keying material must be provided for each RPC client, including
transient clients.
o Parts of each RPC header remain in clear-text, and can constitute
a significant security exposure.
o Host identity management and user identity management must be
carried out in the same security realm. In certain environments,
different authorities might be responsible for provisioning client
systems versus provisioning new users.
o On-host cryptographic manipulation of data payloads can exact a
significant CPU and memory bandwidth cost on RPC peers. Offloadng
does not appear to be practical using GSS privacy since each
message is encrypted using its own key based on the issuing RPC
user.
However strong a privacy service is, it cannot provide any security
if the challenges of using it result in it not being used at all.
An alternative approach is to employ a transport layer security
mechanism that can protect the privacy of each RPC connection
transparently to RPC and Upper Layer protocols. The Transport Layer
Security protocol [RFC8446] (TLS) is a well-established Internet
building block that protects many common Internet protocols such as
the Hypertext Transport Protocol (http) [RFC2818].
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Encrypting at the RPC transport layer enables several significant
benefits.
Encryption By Default
In-transit encryption by itself may be enabled without additional
administrative actions such as identifying client systems to a
trust authority, generating additional key material, or
provisioning a secure network tunnel.
Protection of Existing Protocols
The imposition of encryption at the transport layer protects any
Upper Layer protocol that employs RPC, without alteration of that
protocol. RPC transport layer encryption can protect recent
versions of NFS such as NFS version 4.2 [RFC7862] and indeed
legacy NFS versions such as NFS version 3 [RFC1813], and NFS side-
band protocols such as the MNT protocol [RFC1813].
Decoupled User and Host Identities
TLS can be used to authenticate peer hosts while other security
mechanisms can handle user authentictation. Cryptographic
authentication of hosts can be provided while still using simpler
user authentication flavors such as AUTH_SYS.
Encryption Offload
Whereas hardware support for GSS privacy has not appeared in the
marketplace, the use of a well-established transport encryption
mechanism that is also employed by other very common network
protocols makes it likely that a hardware encryption
implementation will be available to offload encryption and
decryption.
Securing AUTH_SYS
Most critically, several security issues inherent in the current
widespread use of AUTH_SYS (i.e., acceptance of UIDs and GIDs
generated by an unauthenticated client) can be significantly
ameliorated.
This document specifies the use of RPC on a TLS-protected transport
in a fashion that is transparent to upper layer protocols based on
RPC. It provides policies in line with [RFC7435] that enable RPC-on-
TLS to be deployed opportunistically in environments with RPC
implementations that do not support TLS. Specifications for RPC-
based upper layer protocols are free to require stricter policies to
guarantee that TLS with encryption or TLS with host authentication
and encryption is used for every connection.
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Note that the protocol specification in this document assumes that
support for RPC, TLS, PKI, GSS-API, and/or DNSSEC is already
available in an implementation where RPC-on-TLS is to be added.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Terminology
This document adopts the terminology introduced in Section 3 of
[RFC6973] and assumes a working knowledge of the Remote Procedure
Call (RPC) version 2 protocol [RFC5531] and the Transport Layer
Security (TLS) version 1.3 protocol [RFC8446].
Note also that the NFS community uses the term "privacy" where other
Internet communities use "confidentiality". In this document the two
terms are synonymous.
We adhere to the convention that a "client" is a network host that
actively initiates an association, and a "server" is a network host
that passively accepts an association request.
RPC documentation historically refers to the authentication of a
connecting host as "machine authentication" or "host authentication".
TLS documentation refers to the same as "peer authentication". In
this document there is little distinction between these terms.
The term "user authentication" in this document refers specifically
to the RPC caller's credential, provided in the "cred" and "verf"
fields in each RPC Call.
4. RPC-Over-TLS in Operation
4.1. Discovering Server-side TLS Support
The mechanism described in this document interoperates fully with RPC
implementations that do not support TLS. The use of TLS is
automatically disabled in these cases.
To achieve this, we introduce a new RPC authentication flavor called
AUTH_TLS. This new flavor is used to signal that the client wants to
initiate TLS negotiation if the server supports it. Except for the
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modifications described in this section, the RPC protocol is largely
unaware of security encapsulation.
<CODE BEGINS>
enum auth_flavor {
AUTH_NONE = 0,
AUTH_SYS = 1,
AUTH_SHORT = 2,
AUTH_DH = 3,
AUTH_KERB = 4,
AUTH_RSA = 5,
RPCSEC_GSS = 6,
AUTH_TLS = 7,
/* and more to be defined */
};
<CODE ENDS>
The length of the opaque data constituting the credential sent in the
call message MUST be zero. The verifier accompanying the credential
MUST be an AUTH_NONE verifier of length zero.
The flavor value of the verifier received in the reply message from
the server MUST be AUTH_NONE. The bytes of the verifier's string
encode the fixed ASCII characters "STARTTLS".
When an RPC client is ready to begin sending traffic to a server, it
starts with a NULL RPC request with an auth_flavor of AUTH_TLS. The
NULL request is made to the same port as if TLS were not in use.
The RPC server can respond in one of three ways:
o If the RPC server does not recognise the AUTH_TLS authentication
flavor, it responds with a reject_stat of AUTH_ERROR. The RPC
client then knows that this server does not support TLS.
o If the RPC server accepts the NULL RPC procedure, but fails to
return an AUTH_NONE verifier containing the string "STARTTLS", the
RPC client knows that this server does not support TLS.
o If the RPC server accepts the NULL RPC procedure, and returns an
AUTH_NONE verifier containing the string "STARTTLS", the RPC
client SHOULD send a STARTTLS.
Once the TLS handshake is complete, the RPC client and server will
have established a secure channel for communicating. The client MUST
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switch to a security flavor other than AUTH_TLS within that channel,
presumably after negotiating down redundant RPCSEC_GSS privacy and
integrity services and applying channel binding [RFC7861].
If TLS negotiation fails for any reason -- say, the RPC server
rejects the certificate presented by the RPC client, or the RPC
client fails to authenticate the RPC server -- the RPC client reports
this failure to the calling application the same way it would report
an AUTH_ERROR rejection from the RPC server.
If an RPC client attempts to use AUTH_TLS for anything other than the
NULL RPC procedure, the RPC server MUST respond with a reject_stat of
AUTH_ERROR. If the client sends a STARTTLS after it has sent other
non-encrypted RPC traffic or after a TLS session has already been
negotiated, the server MUST silently discard it.
4.2. Authentication
Both RPC and TLS have their own variants of authentication, and there
is some overlap in capability. The goal of interoperability with
implementations that do not support TLS requires that we limit the
combinations that are allowed and precisely specify the role that
each layer plays. We also want to handle TLS such that an RPC
implementation can make the use of TLS invisible to existing RPC
consumer applications.
Each RPC server that supports RPC-over-TLS MUST possess a unique
global identity (e.g., a certificate that is signed by a well-known
trust anchor). Such an RPC server MUST request a TLS peer identity
from each client upon first contact. There are two different modes
of client deployment:
Server-only Host Authentication
In this type of deployment, RPC-over-TLS clients are essentially
anonymous; i.e., they present no globally unique identifier to the
server peer. In this situation, the client can authenticate the
server host using the presented server peer TLS identity, but the
server cannot authenticate the client.
Mutual Host Authentication
In this type of deployment, the client possesses a unique global
identity (e.g., a certificate). As part of the TLS handshake,
both peers authenticate using the presented TLS identities. If
authentication of either peer fails, or if authorization based on
those identities blocks access to the server, the client
association MUST be rejected.
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In either of these modes, RPC user authentication is not affected by
the use of transport layer security. Once a TLS session is
established, the server MUST NOT substitute RPC_AUTH_TLS, or the
remote identity used for TLS peer authentication, for existing forms
of per-request RPC user authentication specified by [RFC5531].
4.2.1. Using TLS with RPCSEC GSS
RPCSEC GSS can provide per-request integrity or privacy (also known
as confidentiality) services. When operating over a TLS session,
these services become redundant. A TLS-capable RPC implementation
uses GSS channel binding for detecting when GSS integrity or privacy
is unnecessary and can therefore be avoided. See Section 2.5 of
[RFC7861] for details.
When employing GSS above TLS, a GSS service principal is still
required on the server, and mutual GSS authentication of server and
client still occurs after the TLS session is established.
5. TLS Requirements
When a TLS session is negotiated for the purpose of transporting RPC,
the following restrictions apply:
o Implementations MUST NOT negotiate TLS versions prior to v1.3
[RFC8446]. Support for mandatory-to-implement ciphersuites for
the negotiated TLS version is REQUIRED.
o Implementations MUST support certificate-based mutual
authentication. Support for TLS-PSK mutual authentication
[RFC4279] is OPTIONAL. See Section 4.2 for further details.
o Negotiation of a ciphersuite providing for confidentiality as well
as integrity protection is REQUIRED. Support for and negotiation
of compression is OPTIONAL.
5.1. Base Transport Considerations
5.1.1. Operation on TCP
RPC over TCP is protected by using TLS [RFC8446]. As soon as a
client completes the TCP handshake, it uses the mechanism described
in Section 4.1 to discover TLS support and then negotiate a TLS
session.
After the TLS session is established, all traffic on the connection
is encapsulated and protected until the TLS session is terminated.
This includes reverse-direction operations (i.e., RPC requests
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initiated on the server-end of the connection). An RPC client
receiving a reverse-direction operation on a connection outside of an
existing TLS session MUST reject the request with a reject_stat of
AUTH_ERROR.
An RPC peer terminates a TLS session by sending a TLS closure alert,
or by closing the underlying TCP socket. After TLS session
termination, a recipient MUST reject any subsequent RPC requests over
the same connection with a reject_stat of AUTH_ERROR.
5.1.2. Operation on UDP
RPC over UDP is protected using DTLS [RFC6347]. As soon as a client
initializes a socket for use with an unfamiliar server, it uses the
mechanism described in Section 4.1 to discover DTLS support and then
negotiate a DTLS session. Connected operation is RECOMMENDED.
Using a DTLS transport does not introduce reliable or in-order
semantics to RPC on UDP. Also, DTLS does not support fragmentation
of RPC messages. One RPC message fits in a single DTLS datagram.
DTLS encapsulation has overhead which reduces the effective Path MTU
(PMTU) and thus the maximum RPC payload size.
DTLS does not detect STARTTLS replay. A DTLS session can be
terminated by sending a TLS closure alert. Subsequent RPC messages
passing between the client and server will no longer be protected
until a new TLS session is established.
5.1.3. Operation on Other Transports
RPC-over-RDMA can make use of Transport Layer Security below the RDMA
transport layer [RFC8166]. The exact mechanism is not within the
scope of this document. Because there might not be provisions to
exchange client and server certificates, authentication material
could be provided by facilites within a future RPC-over-RDMA
transport.
Transports that provide intrinsic TLS-level security (e.g., QUIC)
would need to be accommodated separately from the current document.
In such cases, use of TLS might not be opportunitic as it is for TCP
or UDP.
5.2. TLS Peer Authentication
Peer authentication can be performed by TLS using any of the
following mechanisms:
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5.2.1. X.509 Certificates Using PKIX trust
Implementations are REQUIRED to support this mechanism. In this
mode, an RPC peer is uniquely identified by the tuple (serial number
of presented certificate;Issuer).
o Implementations MUST allow the configuration of a list of trusted
Certification Authorities for incoming connections.
o Certificate validation MUST include the verification rules as per
[RFC5280].
o Implementations SHOULD indicate their trusted Certification
Authorities (CAs).
o Peer validation always includes a check on whether the locally
configured expected DNS name or IP address of the server that is
contacted matches its presented certificate. DNS names and IP
addresses can be contained in the Common Name (CN) or
subjectAltName entries. For verification, only one of these
entries is to be considered. The following precedence applies:
for DNS name validation, subjectAltName:DNS has precedence over
CN; for IP address validation, subjectAltName:iPAddr has
precedence over CN. Implementors of this specification are
advised to read Section 6 of [RFC6125] for more details on DNS
name validation.
o Implementations MAY allow the configuration of a set of additional
properties of the certificate to check for a peer's authorization
to communicate (e.g., a set of allowed values in
subjectAltName:URI or a set of allowed X509v3 Certificate
Policies).
o When the configured trust base changes (e.g., removal of a CA from
the list of trusted CAs; issuance of a new CRL for a given CA),
implementations MAY renegotiate the TLS session to reassess the
connecting peer's continued authorization.
Authenticating a connecting entity does not mean the RPC server
necessarily wants to communicate with that client. For example, if
the Issuer is not in a trusted set of Issuers, the RPC server may
decline to perform RPC transactions with this client.
Implementations that want to support a wide variety of trust models
should expose as many details of the presented certificate to the
administrator as possible so that the trust model can be implemented
by the administrator. As a suggestion, at least the following
parameters of the X.509 client certificate SHOULD be exposed:
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o Originating IP address
o Certificate Fingerprint
o Issuer
o Subject
o all X509v3 Extended Key Usage
o all X509v3 Subject Alternative Name
o all X509v3 Certificate Policies
5.2.2. X.509 Certificates Using Fingerprints
This mechanism is OPTIONAL to implement. In this mode, an RPC peer
is uniquely identified by the fingerprint of the presented
certificate.
Implementations SHOULD allow the configuration of a list of trusted
certificates, identified via fingerprint of the DER encoded
certificate octets. Implementations MUST support SHA-256 or newer as
the hash algorithm for the fingerprint.
5.2.3. Pre-Shared Keys
This mechanism is OPTIONAL to implement. In this mode, an RPC peer
is uniquely identified by key material that has been shared out-of-
band or by a previous TLS-protected connection (see [RFC8446]
Section 2.2). At least the following parameters of the TLS
connection SHOULD be exposed:
o Originating IP address
o TLS Identifier
5.2.4. Token Binding
This mechanism is OPTIONAL to implement. In this mode, an RPC peer
is uniquely identified by a token.
Versions of TLS subsequent to TLS 1.2 feature a token binding
mechanism which is nominally more secure than using certificates.
This is discussed in further detail in [RFC8471].
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6. Implementation Status
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs.
Please note that the listing of any individual implementation here
does not imply endorsement by the IETF. Furthermore, no effort has
been spent to verify the information presented here that was supplied
by IETF contributors. This is not intended as, and must not be
construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
6.1. DESY NFS server
Organization: DESY
URL: https://desy.de
Maturity: Prototype software based on early versions of this
document.
Coverage: The bulk of this specification is implemented. The use of
DTLS functionality is not implemented.
Licensing: LGPL
Implementation experience: No comments from implementors.
6.2. Hammerspace NFS server
Organization: Hammerspace
URL: https://hammerspace.com
Maturity: Prototype software based on early versions of this
document.
Coverage: The bulk of this specification is implemented. The use of
DTLS functionality is not implemented.
Licensing: Proprietary
Implementation experience: No comments from implementors.
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6.3. Linux NFS server and client
Organization: The Linux Foundation
URL: https://www.kernel.org
Maturity: Prototype software based on early versions of this
document.
Coverage: The bulk of this specification is implemented. The use of
DTLS functionality is not implemented.
Licensing: GPLv2
Implementation experience: No comments from implementors.
7. Security Considerations
One purpose of the mechanism described in this document is to protect
RPC-based applications against threats to the privacy of RPC
transactions and RPC user identities. A taxonomy of these threats
appears in Section 5 of [RFC6973]. In addition, Section 6 of
[RFC7525] contains a detailed discussion of technologies used in
conjunction with TLS. Implementers should familiarize themselves
with these materials.
7.1. Limitations of an Opportunistic Approach
The purpose of using an explicitly opportunistic approach is to
enable interoperation with implementations that do not support RPC-
over-TLS. A range of options is allowed by this approach, from "no
peer authentication or encryption" to "server-only authentication
with encryption" to "mutual authentication with encryption". The
actual security level may indeed be selected based on a policy and
without user intervention.
In cases where interoperability is a priority, the security benefits
of TLS are partially or entirely waived. Implementations of the
mechanism described in this document must take care to accurately
represent to all RPC consumers the level of security that is actually
in effect. In addition, implementations are REQUIRED to provide an
audit log of RPC-over-TLS security mode selection.
7.1.1. STRIPTLS Attacks
A classic form of attack on network protocols that initiate an
association in plain-text to discover support for TLS is a man-in-
the-middle that alters the plain-text handshake to make it appear as
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though TLS support is not available on one or both peers. Clients
implementers can choose from the following to mitigate STRIPTLS
attacks:
o A TLSA record [RFC6698] can alert clients that TLS is expected to
work, and provides a binding of hostname to x.509 identity. If
TLS cannot be negotiated or authentication fails, the client
disconnects and reports the problem.
o Client security policy can be configured to require that a TLS
session is established on every connection. If an attacker spoofs
the handshake, the client disconnects and reports the problem. If
TLSA records are not available, this approach is strongly
encouraged.
7.2. Multiple User Identity Realms
To maintain the privacy of RPC users on a single client belonging to
multiple distinct security realms, the client MUST establish an
independent TLS session for each user identity domain, each using a
distinct globally unique identity. The purpose of this separation is
to prevent even privileged users in each security realm from
monitoring RPC traffic emitted on behalf of users in other security
realms on the same peer.
7.3. Security Considerations for AUTH_SYS on TLS
The use of a TLS-protected transport when the AUTH_SYS authentication
flavor is in use addresses a number of longstanding weaknesses (as
detailed in Appendix A). TLS augments AUTH_SYS by providing both
integrity protection and a privacy service that AUTH_SYS lacks. This
protects data payloads, RPC headers, and user identities against
monitoring or alteration while in transit. TLS guards against the
insertion or deletion of messages, thus also ensuring the integrity
of the message stream between RPC client and server.
The use of TLS enables strong authentication of the communicating RPC
peers, providing a degree of non-repudiation. When AUTH_SYS is used
with TLS but the RPC client is unauthenticated, the RPC server is
still acting on RPC requests for which there is no trustworthy
authentication. In-transit traffic is protected, but the RPC client
itself can still misrepresent user identity without server detection.
This is an improvement from AUTH_SYS without encryption, but it
leaves a critical security exposure.
In light of the above, it is RECOMMENDED that when AUTH_SYS is used,
RPC clients present authentication material necessary for RPC servers
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they contact to have a degree of trust that the clients are acting
responsibly.
The use of TLS does not enable detection of compromise on RPC clients
that leads to impersonation of RPC users. In addition, there
continues to be a requirement that the mapping of 32-bit user and
group ID values to user identities is the same on both the RPC client
and server.
7.4. Best Security Policy Practices
To achieve the strongest possible security with RPC-over-TLS, RPC-
over-TLS implementations and deployments are strongly encouraged to
adhere to these policies:
When using AUTH_NULL or AUTH_SYS:
Both peers are required to have DNS TLSA records and certificate
material; a policy that requires mutual peer authentication and
rejection of a connection when host authentication fails.
When using RPCSEC_GSS:
GSS/Kerberos provides adequate host authentication already; a
policy that requires GSS mutual authentication and rejection of a
connection when host authentication fails. GSS integrity and
privacy services should be disabled in favor of TLS encryption
without peer authentication.
8. IANA Considerations
In accordance with Section 6 of [RFC7301], the authors request that
IANA allocate the following value in the "Application-Layer Protocol
Negotiation (ALPN) Protocol IDs" registry. The "sunrpc" string
identifies SunRPC when used over TLS.
Protocol:
SunRPC
Identification Sequence:
0x73 0x75 0x6e 0x72 0x70 0x63 ("sunrpc")
Reference:
RFC-TBD
9. References
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9.1. Normative References
[RFC2119] 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>.
[RFC4279] Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
Ciphersuites for Transport Layer Security (TLS)",
RFC 4279, DOI 10.17487/RFC4279, December 2005,
<https://www.rfc-editor.org/info/rfc4279>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC5531] 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>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/info/rfc7301>.
[RFC7861] Adamson, A. and N. Williams, "Remote Procedure Call (RPC)
Security Version 3", RFC 7861, DOI 10.17487/RFC7861,
November 2016, <https://www.rfc-editor.org/info/rfc7861>.
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[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
[RFC8174] 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>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
9.2. Informative References
[RFC1813] Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
Version 3 Protocol Specification", RFC 1813,
DOI 10.17487/RFC1813, June 1995,
<https://www.rfc-editor.org/info/rfc1813>.
[RFC2203] 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>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>.
[RFC5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1
Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
<https://www.rfc-editor.org/info/rfc5661>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
2012, <https://www.rfc-editor.org/info/rfc6698>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <https://www.rfc-editor.org/info/rfc7435>.
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[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
[RFC7530] 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>.
[RFC7862] 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>.
[RFC7863] 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>.
[RFC8166] Lever, C., Ed., Simpson, W., and T. Talpey, "Remote Direct
Memory Access Transport for Remote Procedure Call Version
1", RFC 8166, DOI 10.17487/RFC8166, June 2017,
<https://www.rfc-editor.org/info/rfc8166>.
[RFC8471] Popov, A., Ed., Nystroem, M., Balfanz, D., and J. Hodges,
"The Token Binding Protocol Version 1.0", RFC 8471,
DOI 10.17487/RFC8471, October 2018,
<https://www.rfc-editor.org/info/rfc8471>.
9.3. URIs
[1] https://www.linuxjournal.com/content/encrypting-nfsv4-stunnel-tls
Appendix A. Known Weaknesses of the AUTH_SYS Authentication Flavor
The ONC RPC protocol as specified in [RFC5531] provides several modes
of security, traditionally referred to as "authentication flavors",
though some of these flavors provide much more than an authentication
service. We will refer to these as authentication flavors, security
flavors, or simply, flavors. One of the earliest and most basic
flavor is AUTH_SYS, also known as AUTH_UNIX. AUTH_SYS is currently
specified in Appendix A of [RFC5531].
AUTH_SYS assumes that both the RPC client and server use POSIX-style
user and group identifiers (each user and group can be distinctly
represented as a 32-bit unsigned integer), and that both client and
server use the same mapping of user and group to integer. One user
ID, one main group ID, and up to 16 supplemental group IDs are
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associated with each RPC request. The combination of these identify
the entity on the client that is making the request.
Peers are identified by a string in each RPC request. RFC 5531 does
not specify any requirements for this string other than that is no
longer than 255 octets. It does not have to be the same from request
to request, nor does it have to match the name of the sending host.
For these reasons, though most implementations do fill in their
hostname in this field, receivers typically ignore its content.
RFC 5531 Appendix A contains a brief explanation of security
considerations:
It should be noted that use of this flavor of authentication does
not guarantee any security for the users or providers of a
service, in itself. The authentication provided by this scheme
can be considered legitimate only when applications using this
scheme and the network can be secured externally, and privileged
transport addresses are used for the communicating end-points (an
example of this is the use of privileged TCP/UDP ports in UNIX
systems -- note that not all systems enforce privileged transport
address mechanisms).
It should be clear, therefore, that AUTH_SYS by itself offers little
to no communication security:
1. It does not protect the privacy or integrity of RPC requests,
users, or payloads, relying instead on "external" security.
2. It also does not provide actual authentication of RPC peer
machines, other than an unprotected domain name.
3. The use of 32-bit unsigned integers as user and group identifiers
is problematic because these simple data types are not signed or
otherwise verified by any authority.
4. Because the user and group ID fields are not integrity-protected,
AUTH_SYS does not offer non-repudiation.
Acknowledgments
Special mention goes to Charles Fisher, author of "Encrypting NFSv4
with Stunnel TLS" [1]. His article inspired the mechanism described
in this document.
Many thanks to Tigran Mkrtchyan for his work on the DESY prototype
and resulting feedback to this document.
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Thanks to Derrell Piper for numerous suggestions that improved both
the security of this simple mechanism and the security-related
discussion in this document.
The authors are grateful to Bill Baker, David Black, Alan DeKok, Lars
Eggert, Benjamin Kaduk, Olga Kornievskaia, Greg Marsden, Alex
McDonald, David Noveck, Justin Mazzola Paluska, Tom Talpey, and
Martin Thomson for their input and support of this work.
Lastly, special thanks go to Transport Area Director Magnus
Westerlund, NFSV4 Working Group Chairs Spencer Shepler and Brian
Pawlowski, and NFSV4 Working Group Secretary Thomas Haynes for their
guidance and oversight.
Authors' Addresses
Trond Myklebust
Hammerspace Inc
4300 El Camino Real Ste 105
Los Altos, CA 94022
United States of America
Email: trond.myklebust@hammerspace.com
Charles Lever (editor)
Oracle Corporation
United States of America
Email: chuck.lever@oracle.com
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