File Content Provenance for Network File System version 4
draft-ietf-nfsv4-integrity-measurement-01

Network File System Version 4                                   C. Lever
Internet-Draft                                                    Oracle
Intended status: Standards Track                      September 24, 2018
Expires: March 28, 2019

       File Content Provenance for Network File System version 4
               draft-ietf-nfsv4-integrity-measurement-01

Abstract

   This document specifies an OPTIONAL extension to NFS version 4 minor
   version 2 that enables file provenance information to be conveyed
   between NFS version 4.2 servers and clients.  File provenance
   information authenticates the creator of a file's content and helps
   guarantee the content's integrity from creation to use.

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 March 28, 2019.

Copyright Notice

   Copyright (c) 2018 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
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Protocol Extension Considerations . . . . . . . . . . . . . .   3
   4.  Managing File Provenance Metadata on NFS Files  . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   The security of software distribution systems is complex and
   challenging, especially as software distribution has become
   increasingly decentralized.  An end administrator needs to trust that
   she is running executables just as they are supplied by a software
   vendor; in other words, that they have not been modified by malicious
   actors, contracted system administration services, or broken hardware
   or software.  Software vendors want a guarantee that customer-
   installed executables that fall under support contracts have
   similarly not been modified.

   There already exist mechanisms that protect file data during certain
   portions of a file's life cycle:

   o  Whole file system checksumming can verify so-called Golden Master
      installation media before it is used to install the software it
      contains.

   o  File or block integrity mechanisms can protect data at rest on
      storage servers.

   o  For a distributed file system such as NFS, transport layer
      security or a GSS integrity service (as described in [RFC7861])
      can protect data while it traverses a network between a storage
      server and a client.

   A more extensive mechanism is needed to guarantee that no
   modification of a particular file has occurred since it was created,
   even perhaps after several generations of copies have been made of
   the file's content.

   This guarantee can be accomplished by separately preserving a keyed
   hash, such as an HMAC [RFC2104], of a file's byte stream.  This hash
   and its signature are verified as the file's content is read into
   memory just before it is used.  If verification fails, access to the

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   file's content is denied.  The hash is updated and re-signed only
   when the file is legitimately modified.

   A keyed hash authenticates the identity of the last modifier of a
   file's content and serves as a strong check of the content's
   integrity.  For the purposes of this document, we will refer to this
   as file provenance information.  The Linux Integrity Measurement
   Architecture (IMA) is an example of a mechanism for assessing file
   content provenance [IMA-WP].

   A Trusted Platform Module [TPM-SUM] can seal the key material used to
   sign and verify file content.  Distributing and protecting such key
   material is outside the scope of the NFS protocol extension specified
   in this document.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14 [RFC2119]
   [RFC8174] when, and only when, they appear in all capitals, as shown
   here.

3.  Protocol Extension Considerations

   This document specifies an OPTIONAL extension to NFS version 4 minor
   version 2 [RFC7862], hereafter referred to as NFS version 4.2.  NFS
   version 4.2 servers and clients implemented without knowledge of this
   extension will continue to interoperate with NFS version 4.2 clients
   and servers that are aware of the extension, whether or not they
   support it.

   Because [RFC7862] does not define NFS version 4.2 as non-extensible,
   [RFC8178] treats it as an extensible minor version.  Therefore this
   Standards Track RFC extends NFS version 4.2 but does not update
   [RFC7862] or [RFC7863].

3.1.  XDR Extraction

   Section 4.1 contains a description of an extension to the NFS version
   4.2 protocol, expressed in the External Data Representation (XDR)
   language [RFC4506].  This description is provided in a way that makes
   it simple to extract into ready-to-compile form.  The reader can
   apply the following sed script to this document to produce a machine-
   readable XDR description of the extension.

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   <CODE BEGINS>

   sed -n -e 's:^ */// ::p' -e 's:^ *///$::p'

   <CODE ENDS>

   That is, if this document is in a file called "provenance-
   extension.txt" then the reader can do the following to extract an XDR
   description file:

   <CODE BEGINS>

   sed -n -e 's:^ */// ::p' -e 's:^ *///$::p'
        < provenance-extension.txt > ima.x

   <CODE ENDS>

   Once that extraction is done, these added lines need to be inserted
   into an appropriate base XDR of the generated XDR from [RFC7863]
   together with XDR from any additional extensions to be recognized by
   the implementation.  This will result in a ready-to-compile XDR file.

4.  Managing File Provenance Metadata on NFS Files

4.1.  XDR Definition

   This section defines a new data type to encapsulate and a new
   OPTIONAL GETATTR attribute to access and update file provenance
   information associated with a particular file.

   File provenance information is opaque to the NFS protocol.  To ensure
   interoperability among accessors of this information when it is
   stored on NFS version 4.2 servers, this information MUST be self-
   describing.

   To enable a single file provenance information payload to be
   retrieved or updated via a single RPC, and to constrain the transport
   resources required for the operations defined here, the payload MUST
   NOT exceed 4096 bytes in length.

   When an NFS version 4.2 server does not recognize, or does recognize
   but does not support, this new attribute, the server responds in
   accordance with the requirements specified in Section 4.3 of
   [RFC8178].

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   <CODE BEGINS>

      /// /*
      ///  * Copyright (c) 2018 IETF Trust and the person identified
      ///  * as author of the code.  All rights reserved.
      ///  *
      ///  * The author of the code is: C. Lever
      ///  */
      ///
      /// const FILEPROV4_MAXSIZE = 4096;
      /// typedef opaque file_prov4<FILEPROV4_MAXSIZE>;
      ///
      /// %/*
      /// % * New For File Provenance Metadata
      /// % */
      /// const FATTR4_FILE_PROVENANCE = XXX;   /* to be assigned */
      ///
      /// typedef file_prov4 fattr4_file_provenance;

   <CODE ENDS>

4.2.  Storing File Provenance Metadata

   An NFS version 4.2 client stores file provenance information by
   sending a SETATTR operation that specifies the FATTR4_FILE_PROVENANCE
   attribute, targeting the file associated with the file provenance
   information to be stored.  This attribute completely replaces any
   previous one.  To remove this attribute from a file, the client sends
   a FATTR4_FILE_PROVENANCE attribute whose length is zero.

   When a SETATTR is presented to an NFS version 4.2 server with a
   credential that is unauthorized to replace the FATTR4_FILE_PROVENANCE
   attribute, the server MUST respond with NFS4ERR_ACCESS.

   When a SETATTR is presented to an NFS version 4.2 server with a
   fattr4_file_provenance field whose length is larger than
   FILEPROV4_MAXSIZE, the server MUST respond with NFS4ERR_NAMETOOLONG.

   When a SETATTR is presented to an NFS version 4.2 server that
   supports FATTR4_FILE_PROVENANCE, but the SETATTR targets an object
   which does not support this attribute, the server MUST respond with
   NFS4ERR_TYPE.

4.3.  Retrieving File Provenance Metadata

   An NFS version 4.2 client retrieves file provenance information by
   retrieving the FATTR4_FILE_PROVENANCE attribute via a GETATTR
   operation, specifying the file handle of the file associated with the

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   information to be retrieved.  This information may have been computed
   and signed previously on this client or by some other agent.

   When a GETATTR is presented to an NFS version 4.2 server that
   supports the FATTR4_FILE_PROVENANCE attribute, but the GETATTR
   targets an object which does not support this attribute, the server
   MUST respond with NFS4ERR_TYPE.  Otherwise, if no file provenance
   information is available for the targeted file handle, the server
   returns a FATTR4_FILE_PROVENANCE attribute whose length is zero.

   An NFS version 4.2 server MUST NOT prevent an NFS version 4.2 client
   from accessing a file based on provenance verification failures on
   the server.

4.4.  Performance Cost of Using File Provenance Metadata

   Computing a file checksum is typically performed on the entirety of a
   file's content.  When a file's content is first accessed, after it
   changes, or if any portion of a file is evicted from an NFS version
   4.2 client's cache, the client must retrieve any missing content
   before a fresh checksum can be computed to verify the file's content.
   This can incur a significant performance impact for large files,
   files that change frequently, or files where only a portion of the
   content is used on that client (e.g., software libraries).

   An NFS version 4.2 client can employ mechanisms not specified here to
   reduce this impact.  For example, instead of signing a hash of the
   file's byte stream, a Merkle tree can be constructed that allows
   clients to verify the integrity of smaller portions of a large file
   [MERKLE].  The root hash of that tree, being of sufficiently limited
   size, can be signed and stored as file provenance information.  The
   Merkle tree, which is stored elsewhere, can be used to verify
   portions of the file's content without the need to read the whole
   file.

5.  Security Considerations

   An NFS version 4.2 server is REQUIRED to enforce a suitable level of
   privilege before permitting a local or remote agent to alter file
   provenance information.  This document does not specify a policy for
   authorizing modification of this information.

   When file provenance information for a file exists, the content of a
   file is protected from creation to use.  Receivers can reliably
   detect unintentional or malicious alteration of file content by
   verifying its content using file provenance information.  Additional
   protection of file content while at rest or in transit on an
   untrusted network is unnecessary.

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   Likewise, receivers can also reliably detect unintentional or
   malicious alteration of file provenance information that is
   cryptographically signed, simply by verifying its signature.
   Additional protection of signed file provenance information while at
   rest or in transit on an untrusted network is unnecessary.

   In the rare cases when file provenance information is not
   cryptographically self-protected, the information MUST be protected
   while in transit on an untrusted network using a cryptographically
   strong transport layer security service that can detect tampering,
   such as RPCSEC with an integrity-protecting service [RFC7861].

   Like other mechanisms that protect data integrity during transit, A
   malicious agent or a network malfunction can create a denial-of-
   service condition by repeatedly triggering integrity verification
   failures on NFS version 4.2 clients.

6.  IANA Considerations

   This document does not require any actions by IANA.

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>.

   [RFC4506]  Eisler, M., Ed., "XDR: External Data Representation
              Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506, May
              2006, <https://www.rfc-editor.org/info/rfc4506>.

   [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>.

   [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>.

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   [RFC8178]  Noveck, D., "Rules for NFSv4 Extensions and Minor
              Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017,
              <https://www.rfc-editor.org/info/rfc8178>.

7.2.  Informative References

   [IMA-WP]   Safford, D., "An Overview of The Linux Integrity
              Subsystem", <http://downloads.sf.net/project/linux-ima/
              linux-ima/Integrity_overview.pdf>.

   [MERKLE]   Merkle, R., ""A Digital Signature Based on a Conventional
              Encryption Function" Advances in Cryptology - CRYPTO '87",
              DOI 10.1007/3-540-48184-2_32, 1988.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              DOI 10.17487/RFC2104, February 1997,
              <https://www.rfc-editor.org/info/rfc2104>.

   [RFC5662]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
              "Network File System (NFS) Version 4 Minor Version 1
              External Data Representation Standard (XDR) Description",
              RFC 5662, DOI 10.17487/RFC5662, January 2010,
              <https://www.rfc-editor.org/info/rfc5662>.

   [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>.

   [TPM-SUM]  Trusted Computing Group, "Trusted Platform Module (TPM)
              Summary", April 2008, <https://trustedcomputinggroup.org/
              wp-content/uploads/
              Trusted-Platform-Module-Summary_04292008.pdf>.

Acknowledgments

   The author wishes to thank Mimi Zohar and James Morris for their
   early review of the concepts in this document, Wim Coekaerts for his
   encouragement of this work, and Dave Noveck for his work on NFS
   version 4 extensibility.

   The XDR extraction conventions were first described by the authors of
   the NFS version 4.1 XDR specification [RFC5662].  Herbert van den
   Bergh suggested the replacement sed script used in this document.

   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 support.

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Author's Address

   Charles Lever
   Oracle Corporation
   1015 Granger Avenue
   Ann Arbor, MI  48104
   United States of America

   Phone: +1 248 816 6463
   Email: chuck.lever@oracle.com

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