Internet DRAFT - draft-cel-nfsv4-rpc-tls
draft-cel-nfsv4-rpc-tls
Network File System Version 4 T. Myklebust
Internet-Draft Hammerspace
Updates: 5531 (if approved) C. Lever, Ed.
Intended status: Standards Track Oracle
Expires: August 15, 2019 February 11, 2019
Remote Procedure Call Encryption By Default
draft-cel-nfsv4-rpc-tls-02
Abstract
This document describes a mechanism that enables encryption of in-
transit Remote Procedure Call (RPC) transactions with minimal
administrative overhead and full interoperation with 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
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 August 15, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
Myklebust & Lever Expires August 15, 2019 [Page 1]
Internet-Draft RPC-Over-TLS February 2019
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. RPC-Over-TLS in Operation . . . . . . . . . . . . . . . . . . 4
4.1. Discovering Server-side TLS Support . . . . . . . . . . . 4
4.2. Streams and Datagrams . . . . . . . . . . . . . . . . . . 6
4.3. Authentication . . . . . . . . . . . . . . . . . . . . . 6
4.3.1. No Client Authentication . . . . . . . . . . . . . . 6
4.3.2. Client Authentication . . . . . . . . . . . . . . . . 7
4.3.3. Advanced Forms of RPC Authentication . . . . . . . . 7
4.3.4. Other Forms of TLS Authentication . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5.1. Implications for AUTH_SYS . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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).
Myklebust & Lever Expires August 15, 2019 [Page 2]
Internet-Draft RPC-Over-TLS February 2019
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 is 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 the RPC header remain in clear-text, and can constitute a
significant security exposure.
o On-host cryptographic manipulation of data payloads can exact a
significant CPU cost on both clients and the server.
o Host identity management must be carried out in a security realm
that is separate from user identity management. In certain
environments, for example, different authorities might be
responsible for provisioning client systems versus provisioning
new users.
However strong a privacy service is, it can not provide any security
if the difficulties of deploying and 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].
Encrypting at the RPC transport layer enables several significant
benefits.
Encryption By Default
In-transit encryption can be enabled immediately after
installation without additional administrative actions such as
identifying the host system 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].
Myklebust & Lever Expires August 15, 2019 [Page 3]
Internet-Draft RPC-Over-TLS February 2019
Decoupled User and Host Identities
RPCSEC GSS provides a framework for cryptographically protecting
user and host identities but assumes that both are managed by the
same security authority.
Encryption Offload
The use of a well-established transport encryption mechanism that
is also employed by other very common network protocols makes it
possible to use hardware encryption implementations so that the
host CPU is not burdened with the work of encrypting and
decrypting large RPC arguments and results.
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 might use "confidentiality". In this document
the two terms are synonymous.
4. RPC-Over-TLS in Operation
In this section we cleave to the convention that a "client" is the
peer host that actively initiates a connection, and a "server" is the
peer host that passively accepts a connection request.
4.1. Discovering Server-side TLS Support
The mechanism described in this document interoperates fully with
implementations that do not support it. The use of TLS is
automatically disabled in these cases. To achieve this, we introduce
a new 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.
Myklebust & Lever Expires August 15, 2019 [Page 4]
Internet-Draft RPC-Over-TLS February 2019
<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 initiate a TLS handshake, it sends 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 MAY proceed with TLS negotiation.
If an RPC client attempts to use AUTH_TLS for anything other than the
NULL RPC procedure, the RPC server responds with a reject_stat of
AUTH_ERROR.
Myklebust & Lever Expires August 15, 2019 [Page 5]
Internet-Draft RPC-Over-TLS February 2019
Once the TLS handshake is complete, the RPC client and server will
have established a secure channel for communicating and can proceed
to use standard security flavors within that channel, presumably
after negotiating down the irrelevant 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.
4.2. Streams and Datagrams
RPC operates on several different types of transports. RPC on a
stream transport is protected by using TLS [RFC8446]; on a datagram
transport, RPC must use DTLS [RFC6347].
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.
4.3. 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.
Toward these ends, there are two main deployment modes.
4.3.1. No Client Authentication
In a basic deployment, a server possesses a certificate that is self-
signed or signed by a well-known trust anchor, while its clients
might not possess a certificate. In this situation, the client MAY
authenticate the server host, but the server cannot authenticate
connecting clients. Here, encryption of the transport connection is
established and the RPC requests in transit carry user and group
identities according to the conventions of the ONC RPC protocol.
Myklebust & Lever Expires August 15, 2019 [Page 6]
Internet-Draft RPC-Over-TLS February 2019
4.3.2. Client Authentication
In this type of deployment, both the server and its clients possess
valid certificates. As part of the TLS handshake, both peers MAY
authenticate. Should authentication of either peer fail, or should
authorization based on those identities block access to the server,
the connection can be rejected. However, once encryption of the
transport connection is established, the server MUST NOT utilize TLS
identity for the purpose of authorizing RPC requests.
In some cases, a client might choose to present a certificate that
represents a user rather than one that is bound to the client host.
As above, the server MUST NOT utilize this identity for the purpose
of authorizing RPC requests.
4.3.3. Advanced Forms of RPC Authentication
RPCSEC GSS can provide integrity or privacy (also known as
confidentiality) services. When operating over an encrypted TLS
session, these services become redundant. Each RPC implementation is
responsible for using channel binding for detecting when GSS
integrity or privacy is unnecessary and can therefore be disabled See
Section 2.5 of [RFC7861] for details.
Note that a GSS service principal is still required on the server,
and mutual authentication of server and client still occurs after the
TLS session is established.
4.3.4. Other Forms of TLS Authentication
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]. When such versions
of TLS are used to encrypted RPC traffic, token binding may replace
the use of certificates, but the restrictions specified earlier in
this section still apply.
5. 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.
Myklebust & Lever Expires August 15, 2019 [Page 7]
Internet-Draft RPC-Over-TLS February 2019
The NFS version 4 protocol permits more than one user to use an NFS
client at the same time [RFC7862]. Typically that NFS client will
conserve connection resources by routing RPC transactions from all of
its users over a few or a single connection. In circumstances where
the users on that NFS client belong to multiple distinct security
domains, it may be necessary to establish separate TLS-protected
connections that do not share the same encryption parameters.
5.1. Implications for AUTH_SYS
Ever since the IETF NFSV4 Working Group took over the maintenance of
the NFSv4 family of protocols (currently specified in [RFC7530],
[RFC5661], and [RFC7863], among others), it has encouraged the use of
RPCSEC GSS over AUTH_SYS. For various reasons, unfortunately
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
the shortcomings of AUTH_SYS so that, where it has been impractical
to deploy RPCSEC GSS, better NFSv4 security can nevertheless be
achieved.
When AUTH_SYS is used with TLS and no client certificate is
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 both servers and
clients have certificate material available so that servers can have
a degree of trust that clients are acting responsibly.
6. 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:
Myklebust & Lever Expires August 15, 2019 [Page 8]
Internet-Draft RPC-Over-TLS February 2019
RFC-TBD
7. References
7.1. 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>.
[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>.
[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>.
[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>.
7.2. Informative References
[LJNL] Fisher, C., "Encrypting NFSv4 with Stunnel TLS", August
2018, <https://www.linuxjournal.com/content/
encrypting-nfsv4-stunnel-tls>.
Myklebust & Lever Expires August 15, 2019 [Page 9]
Internet-Draft RPC-Over-TLS February 2019
[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>.
[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>.
[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>.
Myklebust & Lever Expires August 15, 2019 [Page 10]
Internet-Draft RPC-Over-TLS February 2019
[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>.
Acknowledgments
Special mention goes to Charles Fisher, author of "Encrypting NFSv4
with Stunnel TLS" [LJNL]. His article inspired the mechanism
described in this document.
The authors are grateful to Bill Baker, David Black, Lars Eggert,
Benjamin Kaduk Greg Marsden, Alex McDonald, David Noveck, Justin
Mazzola Paluska, and Tom Talpey for their input and support of this
work.
Special thanks go to Transport Area Director Spencer Dawkins, 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
Myklebust & Lever Expires August 15, 2019 [Page 11]
