draft-ietf-nfsv4-rpc-tls-02.txt   draft-ietf-nfsv4-rpc-tls-03.txt 
Network File System Version 4 T. Myklebust Network File System Version 4 T. Myklebust
Internet-Draft Hammerspace Internet-Draft Hammerspace
Updates: 5531 (if approved) C. Lever, Ed. Updates: 5531 (if approved) C. Lever, Ed.
Intended status: Standards Track Oracle Intended status: Standards Track Oracle
Expires: October 27, 2019 April 25, 2019 Expires: March 24, 2020 September 21, 2019
Remote Procedure Call Encryption By Default Remote Procedure Call Encryption By Default
draft-ietf-nfsv4-rpc-tls-02 draft-ietf-nfsv4-rpc-tls-03
Abstract Abstract
This document describes a mechanism that, through the use of This document describes a mechanism that, through the use of
opportunistic Transport Layer Security (TLS), enables encryption of opportunistic Transport Layer Security (TLS), enables encryption of
in-transit Remote Procedure Call (RPC) transactions while in-transit Remote Procedure Call (RPC) transactions while
interoperating with ONC RPC implementations that do not support this interoperating with ONC RPC implementations that do not support this
mechanism. This document updates RFC 5531. mechanism. This document updates RFC 5531.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 27, 2019. This Internet-Draft will expire on March 24, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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publication of this document. Please review these documents publication of this document. Please review these documents
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Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. RPC-Over-TLS in Operation . . . . . . . . . . . . . . . . . . 5 4. RPC-Over-TLS in Operation . . . . . . . . . . . . . . . . . . 5
4.1. Discovering Server-side TLS Support . . . . . . . . . . . 5 4.1. Discovering Server-side TLS Support . . . . . . . . . . . 5
4.2. Authentication . . . . . . . . . . . . . . . . . . . . . 7 4.2. Authentication . . . . . . . . . . . . . . . . . . . . . 7
4.2.1. Using TLS with RPCSEC GSS . . . . . . . . . . . . . . 8 4.2.1. Using TLS with RPCSEC GSS . . . . . . . . . . . . . . 8
5. TLS Requirements . . . . . . . . . . . . . . . . . . . . . . 8 5. TLS Requirements . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Base Transport Considerations . . . . . . . . . . . . . . 8 5.1. Base Transport Considerations . . . . . . . . . . . . . . 8
5.1.1. Operation on TCP . . . . . . . . . . . . . . . . . . 8 5.1.1. Operation on TCP . . . . . . . . . . . . . . . . . . 8
5.1.2. Operation on UDP . . . . . . . . . . . . . . . . . . 9 5.1.2. Operation on UDP . . . . . . . . . . . . . . . . . . 9
5.1.3. Operation on an RDMA Transport . . . . . . . . . . . 9 5.1.3. Operation on Other Transports . . . . . . . . . . . . 9
5.2. TLS Peer Authentication . . . . . . . . . . . . . . . . . 9 5.2. TLS Peer Authentication . . . . . . . . . . . . . . . . . 9
5.2.1. X.509 Certificates Using PKIX trust . . . . . . . . . 9 5.2.1. X.509 Certificates Using PKIX trust . . . . . . . . . 9
5.2.2. X.509 Certificates Using Fingerprints . . . . . . . . 11 5.2.2. X.509 Certificates Using Fingerprints . . . . . . . . 11
5.2.3. Pre-Shared Keys . . . . . . . . . . . . . . . . . . . 11 5.2.3. Pre-Shared Keys . . . . . . . . . . . . . . . . . . . 11
5.2.4. Token Binding . . . . . . . . . . . . . . . . . . . . 11 5.2.4. Token Binding . . . . . . . . . . . . . . . . . . . . 11
6. Implementation Status . . . . . . . . . . . . . . . . . . . . 11 6. Implementation Status . . . . . . . . . . . . . . . . . . . . 11
6.1. DESY NFS server . . . . . . . . . . . . . . . . . . . . . 12 6.1. DESY NFS server . . . . . . . . . . . . . . . . . . . . . 12
6.2. Hammerspace NFS server . . . . . . . . . . . . . . . . . 12 6.2. Hammerspace NFS server . . . . . . . . . . . . . . . . . 12
6.3. Linux NFS server and client . . . . . . . . . . . . . . . 12 6.3. Linux NFS server and client . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7.1. Limitations of an Opportunistic Approach . . . . . . . . 13 7.1. Limitations of an Opportunistic Approach . . . . . . . . 13
7.2. STRIPTLS Attacks . . . . . . . . . . . . . . . . . . . . 13 7.1.1. STRIPTLS Attacks . . . . . . . . . . . . . . . . . . 13
7.3. Implications for AUTH_SYS . . . . . . . . . . . . . . . . 13 7.2. Multiple User Identity Realms . . . . . . . . . . . . . . 14
7.4. Multiple User Identity Realms . . . . . . . . . . . . . . 14 7.3. Security Considerations for AUTH_SYS on TLS . . . . . . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. Normative References . . . . . . . . . . . . . . . . . . 14 9.1. Normative References . . . . . . . . . . . . . . . . . . 15
9.2. Informative References . . . . . . . . . . . . . . . . . 16 9.2. Informative References . . . . . . . . . . . . . . . . . 16
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 17 Appendix A. Known Weaknesses of the AUTH_SYS Authentication
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 Flavor . . . . . . . . . . . . . . . . . . . . . . . 18
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction 1. Introduction
In 2014 the IETF published [RFC7258] which recognized that In 2014 the IETF published [RFC7258] which recognized that
unauthorized observation of network traffic had become widespread and unauthorized observation of network traffic had become widespread and
was a subversive threat to all who make use of the Internet at large. was a subversive threat to all who make use of the Internet at large.
It strongly recommended that newly defined Internet protocols make a It strongly recommended that newly defined Internet protocols make a
real effort to mitigate monitoring attacks. Typically this real effort to mitigate monitoring attacks. Typically this
mitigation is done by encrypting data in transit. mitigation is done by encrypting data in transit.
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mechanisms can handle user authentictation. Cryptographic mechanisms can handle user authentictation. Cryptographic
authentication of hosts can be provided while still using simpler authentication of hosts can be provided while still using simpler
user authentication flavors such as AUTH_SYS. user authentication flavors such as AUTH_SYS.
Encryption Offload Encryption Offload
Whereas hardware support for GSS privacy has not appeared in the Whereas hardware support for GSS privacy has not appeared in the
marketplace, the use of a well-established transport encryption marketplace, the use of a well-established transport encryption
mechanism that is also employed by other very common network mechanism that is also employed by other very common network
protocols makes it likely that a hardware encryption protocols makes it likely that a hardware encryption
implementation will be available to offload encryption and implementation will be available to offload encryption and
decryption. A single key protects all messages associated with decryption.
one TLS session.
Securing AUTH_SYS Securing AUTH_SYS
Most critically, several security issues inherent in the current Most critically, several security issues inherent in the current
widespread use of AUTH_SYS (i.e., acceptance of UIDs and GIDs widespread use of AUTH_SYS (i.e., acceptance of UIDs and GIDs
generated by an unauthenticated client) can be significantly generated by an unauthenticated client) can be significantly
ameliorated. ameliorated.
This document proposes the use of TLS to introduce an opportunistic This document specifies the use of RPC on a TLS-protected transport
security approach, as defined by [RFC7435], to RPC. As long as there in a fashion that is transparent to upper layer protocols based on
is still a significant fleet of RPC deployments that lack support for RPC. It provides policies in line with [RFC7435] that enable RPC-on-
TLS, an opportunistic approach can help eliminate the challenges that TLS to be deployed opportunistically in environments with RPC
prevent the broad use of encryption with RPC (and its most popular implementations that do not support TLS. Specifications for RPC-
consumer, NFS) until a more thorough approach can be provided. 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.
2. Requirements Language 2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Terminology 3. Terminology
This document adopts the terminology introduced in Section 3 of This document adopts the terminology introduced in Section 3 of
[RFC6973] and assumes a working knowledge of the Remote Procedure [RFC6973] and assumes a working knowledge of the Remote Procedure
Call (RPC) version 2 protocol [RFC5531] and the Transport Layer Call (RPC) version 2 protocol [RFC5531] and the Transport Layer
Security (TLS) version 1.3 protocol [RFC8446]. Security (TLS) version 1.3 protocol [RFC8446].
Note also that the NFS community uses the term "privacy" where other Note also that the NFS community uses the term "privacy" where other
Internet communities use "confidentiality". In this document the two Internet communities use "confidentiality". In this document the two
terms are synonymous. terms are synonymous.
We cleave to the convention that a "client" is a network host that We adhere to the convention that a "client" is a network host that
actively initiates an association, and a "server" is a network host actively initiates an association, and a "server" is a network host
that passively accepts an association request. that passively accepts an association request.
RPC documentation historically refers to the authentication of a RPC documentation historically refers to the authentication of a
connecting host as "machine authentication" or "host authentication". connecting host as "machine authentication" or "host authentication".
TLS documentation refers to the same as "peer authentication". In TLS documentation refers to the same as "peer authentication". In
this document there is little distinction between these terms. this document there is little distinction between these terms.
The term "user authentication" in this document refers specifically The term "user authentication" in this document refers specifically
to the RPC caller's credential, provided in the "cred" and "verf" to the RPC caller's credential, provided in the "cred" and "verf"
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4.2. Authentication 4.2. Authentication
Both RPC and TLS have their own variants of authentication, and there Both RPC and TLS have their own variants of authentication, and there
is some overlap in capability. The goal of interoperability with is some overlap in capability. The goal of interoperability with
implementations that do not support TLS requires that we limit the implementations that do not support TLS requires that we limit the
combinations that are allowed and precisely specify the role that combinations that are allowed and precisely specify the role that
each layer plays. We also want to handle TLS such that an RPC each layer plays. We also want to handle TLS such that an RPC
implementation can make the use of TLS invisible to existing RPC implementation can make the use of TLS invisible to existing RPC
consumer applications. consumer applications.
Depending on its configuration, an RPC server MAY request a TLS peer Each RPC server that supports RPC-over-TLS MUST possess a unique
identity from each client upon first contact. This permits two global identity (e.g., a certificate that is signed by a well-known
different modes of deployment: 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 Server-only Host Authentication
A server possesses a unique global identity (e.g., a certificate In this type of deployment, RPC-over-TLS clients are essentially
that is signed by a well-known trust anchor) while its clients are anonymous; i.e., they present no globally unique identifier to the
anonymous (i.e., present no identifier). In this situation, the server peer. In this situation, the client can authenticate the
client SHOULD authenticate the server host using the presented TLS server host using the presented server peer TLS identity, but the
identity, but the server cannot authenticate clients. server cannot authenticate the client.
Mutual Host Authentication Mutual Host Authentication
In this type of deployment, both the server and its clients In this type of deployment, the client possesses a unique global
possess unique identities (e.g., certificates). As part of the identity (e.g., a certificate). As part of the TLS handshake,
TLS handshake, both peers SHOULD authenticate using the presented both peers authenticate using the presented TLS identities. If
TLS identities. Should authentication of either peer fail, or authentication of either peer fails, or if authorization based on
should authorization based on those identities block access to the those identities blocks access to the server, the client
server, the client association MAY be rejected. association SHOULD be rejected.
In either of these modes, RPC user authentication is not affected by In either of these modes, RPC user authentication is not affected by
the use of transport layer security. Once a TLS session is the use of transport layer security. Once a TLS session is
established, the server MUST NOT utilize the client peer's TLS established, the server MUST NOT utilize the client peer's TLS
identity for the purpose of authorizing individual RPC requests. identity for the purpose of authorizing individual RPC requests.
4.2.1. Using TLS with RPCSEC GSS 4.2.1. Using TLS with RPCSEC GSS
RPCSEC GSS can provide per-request integrity or privacy (also known RPCSEC GSS can provide per-request integrity or privacy (also known
as confidentiality) services. When operating over a TLS session, as confidentiality) services. When operating over a TLS session,
these services become redundant. Each RPC implementation is these services become redundant. A TLS-capable RPC implementation
responsible for using channel binding for detecting when GSS uses GSS channel binding for detecting when GSS integrity or privacy
integrity or privacy is unnecessary and can therefore be disabled. is unnecessary and can therefore be avoided. See Section 2.5 of
See Section 2.5 of [RFC7861] for details. [RFC7861] for details.
Note that a GSS service principal is still required on the server, When employing GSS above TLS, a GSS service principal is still
and mutual GSS authentication of server and client still occurs after required on the server, and mutual GSS authentication of server and
the TLS session is established. client still occurs after the TLS session is established.
5. TLS Requirements 5. TLS Requirements
When a TLS session is negotiated for the purpose of transporting RPC, When a TLS session is negotiated for the purpose of transporting RPC,
the following restrictions apply: the following restrictions apply:
o Implementations MUST NOT negotiate TLS versions prior to v1.3 o Implementations MUST NOT negotiate TLS versions prior to v1.3
[RFC8446]. Support for mandatory-to-implement ciphersuites for [RFC8446]. Support for mandatory-to-implement ciphersuites for
the negotiated TLS version is REQUIRED. the negotiated TLS version is REQUIRED.
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5.1.1. Operation on TCP 5.1.1. Operation on TCP
RPC over TCP is protected by using TLS [RFC8446]. As soon as a RPC over TCP is protected by using TLS [RFC8446]. As soon as a
client completes the TCP handshake, it uses the mechanism described client completes the TCP handshake, it uses the mechanism described
in Section 4.1 to discover TLS support and then negotiate a TLS in Section 4.1 to discover TLS support and then negotiate a TLS
session. session.
After the TLS session is established, all traffic on the connection After the TLS session is established, all traffic on the connection
is encapsulated and protected until the TLS session is terminated. is encapsulated and protected until the TLS session is terminated.
This includes reverse-direction operations (i.e., RPC requests This includes reverse-direction operations (i.e., RPC requests
initiated on the server-end of the connection). A reverse-direction initiated on the server-end of the connection). An RPC client
operation sent on a connection outside of its existing TLS session receiving a reverse-direction operation on a connection outside of an
MUST fail with a reject_stat of AUTH_ERROR. 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, An RPC peer terminates a TLS session by sending a TLS closure alert,
or by closing the underlying TCP socket. After TLS session or by closing the underlying TCP socket. After TLS session
termination, any subsequent RPC request over the same connection MUST termination, a recipient MUST reject any subsequent RPC requests over
fail with a reject_stat of AUTH_ERROR. the same connection with a reject_stat of AUTH_ERROR.
5.1.2. Operation on UDP 5.1.2. Operation on UDP
RPC over UDP is protected using DTLS [RFC6347]. As soon as a client 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 initializes a socket for use with an unfamiliar server, it uses the
mechanism described in Section 4.1 to discover DTLS support and then mechanism described in Section 4.1 to discover DTLS support and then
negotiate a DTLS session. Connected operation is RECOMMENDED. negotiate a DTLS session. Connected operation is RECOMMENDED.
Using a DTLS transport does not introduce reliable or in-order Using a DTLS transport does not introduce reliable or in-order
semantics to RPC on UDP. Also, DTLS does not support fragmentation semantics to RPC on UDP. Also, DTLS does not support fragmentation
of RPC messages. One RPC message fits in a single DTLS datagram. of RPC messages. One RPC message fits in a single DTLS datagram.
DTLS encapsulation has overhead which reduces the effective Path MTU DTLS encapsulation has overhead which reduces the effective Path MTU
(PMTU) and thus the maximum RPC payload size. (PMTU) and thus the maximum RPC payload size.
DTLS does not detect STARTTLS replay. A DTLS session can be DTLS does not detect STARTTLS replay. A DTLS session can be
terminated by sending a TLS closure alert. Subsequent RPC messages terminated by sending a TLS closure alert. Subsequent RPC messages
passing between the client and server will no longer be protected passing between the client and server will no longer be protected
until a new TLS session is established. until a new TLS session is established.
5.1.3. Operation on an RDMA Transport 5.1.3. Operation on Other Transports
RPC-over-RDMA can make use of Transport Layer Security below the RDMA RPC-over-RDMA can make use of Transport Layer Security below the RDMA
transport layer [RFC8166]. The exact mechanism is not within the transport layer [RFC8166]. The exact mechanism is not within the
scope of this document. 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 5.2. TLS Peer Authentication
Peer authentication can be performed by TLS using any of the Peer authentication can be performed by TLS using any of the
following mechanisms: following mechanisms:
5.2.1. X.509 Certificates Using PKIX trust 5.2.1. X.509 Certificates Using PKIX trust
Implementations are REQUIRED to support this mechanism. In this Implementations are REQUIRED to support this mechanism. In this
mode, an RPC peer is uniquely identified by the tuple (serial number mode, an RPC peer is uniquely identified by the tuple (serial number
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Organization: DESY Organization: DESY
URL: https://desy.de URL: https://desy.de
Maturity: Prototype software based on early versions of this Maturity: Prototype software based on early versions of this
document. document.
Coverage: The bulk of this specification is implemented. The use of Coverage: The bulk of this specification is implemented. The use of
DTLS functionality is not implemented. DTLS functionality is not implemented.
Licensing: Freely distributable with acknowledgment. Licensing: LGPL
Implementation experience: No comments from implementors. Implementation experience: No comments from implementors.
6.2. Hammerspace NFS server 6.2. Hammerspace NFS server
Organization: Hammerspace Organization: Hammerspace
URL: https://hammerspace.com URL: https://hammerspace.com
Maturity: Prototype software based on early versions of this Maturity: Prototype software based on early versions of this
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7.1. Limitations of an Opportunistic Approach 7.1. Limitations of an Opportunistic Approach
A range of options is allowed by the opportunistic approach described A range of options is allowed by the opportunistic approach described
in this document, from "no peer authentication or encryption" to in this document, from "no peer authentication or encryption" to
"server-only authentication with encryption" to "mutual "server-only authentication with encryption" to "mutual
authentication with encryption". The security level may indeed be authentication with encryption". The security level may indeed be
selected without user intervention based on a policy. selected without user intervention based on a policy.
Implementations must take care to accurately represent to all RPC Implementations must take care to accurately represent to all RPC
consumers the level of security that is actually in effect. consumers the level of security that is actually in effect.
7.2. STRIPTLS Attacks 7.1.1. STRIPTLS Attacks
A classic form of attack on network protocols that initiate an A classic form of attack on network protocols that initiate an
association in plain-text to discover support for TLS is a man-in- 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 the-middle that alters the plain-text handshake to make it appear as
though TLS support is not available on one or both peers. Clients though TLS support is not available on one or both peers. Clients
implementers can choose from the following to mitigate STRIPTLS implementers can choose from the following to mitigate STRIPTLS
attacks: attacks:
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.
This approach is RECOMMENDED.
o A TLSA record [RFC6698] can alert clients that TLS is expected to 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 work, and provides a binding of hostname to x.509 identity. If
TLS cannot be negotiated or authentication fails, the client TLS cannot be negotiated or authentication fails, the client
disconnects and reports the problem. disconnects and reports the problem.
7.3. Implications for AUTH_SYS 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.
Ever since the IETF NFSV4 Working Group took over the maintenance of 7.2. Multiple User Identity Realms
the NFSv4 family of protocols (currently specified in [RFC7530],
[RFC5661], and [RFC7863], among others), it has encouraged the use of
RPCSEC GSS rather than AUTH_SYS. For various reasons, AUTH_SYS
continues to be the primary authentication mechanism deployed by NFS
administrators. As a result, NFS security remains in an
unsatisfactory state.
A deeper purpose of this document is to attempt to address some of To maintain the privacy of RPC users on a single client belonging to
the shortcomings of AUTH_SYS so that, where it has been impractical multiple distinct security realms, the client MUST establish an
to deploy RPCSEC GSS, better NFSv4 security can nevertheless be independent TLS session for each user identity domain, each using a
achieved. 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.
When AUTH_SYS is used with TLS and no client certificate is 7.3. Security Considerations for AUTH_SYS on TLS
available, the RPC server is still acting on RPC requests for which
there is no trustworthy authentication. In-transit traffic is
protected, but the client itself can still misrepresent user identity
without detection. This is an improvement from AUTH_SYS without
encryption, but it leaves a critical security exposure.
Therefore, the RECOMMENDED deployment mode is that clients have The use of a TLS-protected transport when the AUTH_SYS authentication
certificate material configured and used so that servers can have a flavor is in use addresses a number of longstanding weaknesses (as
degree of trust that clients are acting responsibly. 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.
7.4. Multiple User Identity Realms 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 circumstances where the RPC users on a single client belong to In light of the above, it is RECOMMENDED that when AUTH_SYS is used,
multiple distinct security realms, the client MUST establish an RPC clients present authentication material necessary for RPC servers
independent TLS session for each user identity realm. 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.
8. IANA Considerations 8. IANA Considerations
In accordance with Section 6 of [RFC7301], the authors request that In accordance with Section 6 of [RFC7301], the authors request that
IANA allocate the following value in the "Application-Layer Protocol IANA allocate the following value in the "Application-Layer Protocol
Negotiation (ALPN) Protocol IDs" registry. The "sunrpc" string Negotiation (ALPN) Protocol IDs" registry. The "sunrpc" string
identifies SunRPC when used over TLS. identifies SunRPC when used over TLS.
Protocol: Protocol:
SunRPC SunRPC
skipping to change at page 17, line 32 skipping to change at page 18, line 9
[RFC8471] Popov, A., Ed., Nystroem, M., Balfanz, D., and J. Hodges, [RFC8471] Popov, A., Ed., Nystroem, M., Balfanz, D., and J. Hodges,
"The Token Binding Protocol Version 1.0", RFC 8471, "The Token Binding Protocol Version 1.0", RFC 8471,
DOI 10.17487/RFC8471, October 2018, DOI 10.17487/RFC8471, October 2018,
<https://www.rfc-editor.org/info/rfc8471>. <https://www.rfc-editor.org/info/rfc8471>.
9.3. URIs 9.3. URIs
[1] https://www.linuxjournal.com/content/encrypting-nfsv4-stunnel-tls [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
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 Acknowledgments
Special mention goes to Charles Fisher, author of "Encrypting NFSv4 Special mention goes to Charles Fisher, author of "Encrypting NFSv4
with Stunnel TLS" [1]. His article inspired the mechanism described with Stunnel TLS" [1]. His article inspired the mechanism described
in this document. in this document.
Many thanks to Tigran Mkrtchyan for his work on the DESY prototype Many thanks to Tigran Mkrtchyan for his work on the DESY prototype
and resulting feedback to this document. and resulting feedback to this document.
The authors are grateful to Bill Baker, David Black, Alan DeKok, Lars The authors are grateful to Bill Baker, David Black, Alan DeKok, Lars
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