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NFSv4                                                         W. Adamson
Internet-Draft                                                    NetApp
Intended status: Standards Track                             N. Williams
Expires: December 29, 2014                                  Cryptonector
                                                           June 27, 2014


             Remote Procedure Call (RPC) Security Version 3
                  draft-ietf-nfsv4-rpcsec-gssv3-08.txt

Abstract

   This document specifies version 3 of the Remote Procedure Call (RPC)
   security protocol (RPCSEC_GSS).  This protocol provides for multi-
   principal authentication of client hosts and user principals to
   server (constructed by generic composition), security label
   assertions for multi-level and type enforcement, structured privilege
   assertions, and channel bindings.

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 RFC 2119 [1].

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 http://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 December 29, 2014.

Copyright Notice

   Copyright (c) 2014 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



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   Provisions Relating to IETF Documents
   (http://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.


Table of Contents

   1.  Introduction and Motivation  . . . . . . . . . . . . . . . . .  3
   2.  The RPCSEC_GSSv3 Protocol  . . . . . . . . . . . . . . . . . .  4
     2.1.  Compatibility with RPCSEC_GSSv2  . . . . . . . . . . . . .  5
     2.2.  Version Negotiation  . . . . . . . . . . . . . . . . . . .  5
     2.3.  New REPLY verifier . . . . . . . . . . . . . . . . . . . .  5
     2.4.  New Version Number . . . . . . . . . . . . . . . . . . . .  6
     2.5.  New auth_stat Values . . . . . . . . . . . . . . . . . . .  8
     2.6.  New Control Procedures . . . . . . . . . . . . . . . . . .  8
       2.6.1.  New Control Procedure - RPCSEC_GSS_CREATE  . . . . . .  9
       2.6.2.  New Control Procedure - RPCSEC_GSS_LIST  . . . . . . . 15
     2.7.  Extensibility  . . . . . . . . . . . . . . . . . . . . . . 16
   3.  Operational Recommendation for Deployment  . . . . . . . . . . 17
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 18
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 18
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 19
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 19
   Appendix B.  RFC Editor Notes  . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19



















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1.  Introduction and Motivation

   The original RPCSEC_GSS protocol [2] provided for authentication of
   RPC clients and servers to each other using the Generic Security
   Services Application Programming Interface (GSS-API) [3].  The second
   version of RPCSEC_GSS [4] added support for channel bindings [5].

   We find that GSS-API mechanisms are insufficient for communicating
   certain aspects of authority to a server.  The GSS-API and its
   mechanisms certainly could be extended to address this shortcoming,
   but it seems be far simpler to address it at the application layer,
   namely, in this case, RPCSEC_GSS.

   The motivation for RPCSEC_GSSv3 is to add support for labeled
   security and server-side copy for NFSv4.

   Labeled NFS (see Section 8 of [6]) uses the subject label provided by
   the client via the RPCSEC_GSSv3 layer to enforce MAC access to
   objects owned by the server to enable server guest mode or full mode
   labeled NFS.

   A traditional inter-server file copy entails the user gaining access
   to a file on the source, reading it, and writing it to a file on the
   destination.  In secure NFSv4 inter-server server-side copy (see
   Section 3.4.1 of [6]), the user first secures access to both source
   and destination files, and then uses RPCSEC_GSSv3 multi-principal
   authentication and structured privileges to authorize the destination
   to copy the file from the source on behalf of the user.

   We therefore describe RPCSEC_GSS version 3 (RPCSEC_GSSv3).
   RPCSEC_GSSv3 is the same as RPCSEC_GSSv2 [4], except that the
   following assertions of authority have been added.

   o  Security labels for multi-level, type enforcement, and other
      labeled security models.  See [Section 46.6. Multi-Level Security (MLS) of Deployment Guide: Deployment, configuration and administration of Red Hat Enterprise Linux 5, Edition 6"">9], [10], [11], [6] and [12].

   o  Application-specific structured privileges.  For an example see
      server-side copy [6].

   o  Multi-principal authentication of the client host and user to the
      server done by binding two RPCSEC_GSS handles.  For an example see
      server-side copy [6].

   o  Simplified channel binding.

   Assertions of labels and privileges are evaluated by the server,
   which may then map the asserted values to other values, all according
   to server-side policy.



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   We add an option for enumerating server supported label format
   specifiers (LFS).  The LFS and Label Format Registry are described in
   detail in [13].

   This document contains the External Data Representation (XDR) ([7])
   definitions for the RPCSEC_GSSv3 protocol.  The XDR description is
   provided in this document in a way that makes it simple for the
   reader to extract into ready to compile form.  The reader can feed
   this document in the following shell script to produce the machine
   readable XDR description of RPCSEC_GSSv3:

   <CODE BEGINS>

   #!/bin/sh
   grep "^  *///" | sed 's?^  */// ??' | sed 's?^  *///$??'

   <CODE ENDS>

   I.e. if the above script is stored in a file called "extract.sh", and
   this document is in a file called "spec.txt", then the reader can do:

   <CODE BEGINS>

    sh extract.sh < spec.txt > rpcsec_gss_v3.x

   <CODE ENDS>

   The effect of the script is to remove leading white space from each
   line, plus a sentinel sequence of "///".


2.  The RPCSEC_GSSv3 Protocol

   RPCSEC_GSSv3 is the same as RPCSEC_GSSv2 [4], except that support for
   assertions has been added.  The entire RPCSEC_GSSv3 protocol is not
   presented.  Instead the differences between RPCSEC_GSSv3 and
   RPCSEC_GSSv2 are shown.

   RPCSEC_GSSv3 is patterned as follows:

   o  A client uses an existing RPCSEC_GSSv3 context handle to protect
      RPCSEC_GSSv3 exchanges, this will be termed the "parent" handle.

   o  The server issues a "child" RPCSEC_GSSv3 handle in the
      RPCSEC_GSS_CREATE response which uses the underlying GSS-API
      security context of the parent handle in all subsequent exchanges
      that uses the child handle.




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   o  An RPCSEC_GSSv3 child handle MUST NOT be used as the parent handle
      in an RPCSEC_GSS3_CREATE control message.

2.1.  Compatibility with RPCSEC_GSSv2

   The functionality of RPCSEC_GSSv2 [4] is fully supported by
   RPCSEC_GSSv3.

2.2.  Version Negotiation

   An initiator that supports version 3 of RPCSEC_GSS simply issues an
   RPCSEC_GSS request with the rgc_version field set to
   RPCSEC_GSS_VERS_3.  If the target does not recognize
   RPCSEC_GSS_VERS_3, the target will return an RPC error per Section
   5.1 of [2].

   The initiator MUST NOT attempt to use an RPCSEC_GSS handle returned
   by version 3 of a target with version 1 or version 2 of the same
   target.  The initiator MUST NOT attempt to use an RPCSEC_GSS handle
   returned by version 1 or version 2 of a target with version 3 of the
   same target.

2.3.  New REPLY verifier

   The RPCSEC_GSSv3 child handle uses the same GSS context as the parent
   handle.  Since a child and parent RPCSEC_GSSv3 handle could have the
   same RPCSEC_GSS sequence numbers, and the verifier of RPCSEC_GSS
   replies computes a MIC on just the sequence number, this provides
   opportunities for man in the middle attacks.

   This is easily addressed: RPCSEC_GSS version 3 MUST change the
   verifier of the reply to compute the verifier using the exact same
   input as that is used for verifier of the request, except for the
   mtype change from CALL to REPLY.  The new reply verifier computes a
   MIC over the following data:

     unsigned int xid;
     msg_type mtype;    /* set to REPLY */
     unsigned int rpcvers;
     unsigned int prog;
     unsigned int vers;
     unsigned int proc;
     opaque_auth  cred; /* captures the RPCSEC_GSS handle */








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2.4.  New Version Number

   <CODE BEGINS>

      ///  /*
      ///   * Copyright (c) 2013 IETF Trust and the persons
      ///   * identified as the document authors. All rights
      ///   * reserved.
      ///   *
      ///   * The document authors are identified in [RFC2203],
      ///   * [RFC5403], and [RFCxxxx].
      ///   *
      ///   * Redistribution and use in source and binary forms,
      ///   * with or without modification, are permitted
      ///   * provided that the following conditions are met:
      ///   *
      ///   * o Redistributions of source code must retain the above
      ///   *   copyright notice, this list of conditions and the
      ///   *   following disclaimer.
      ///   *
      ///   * o Redistributions in binary form must reproduce the
      ///   *   above copyright notice, this list of
      ///   *   conditions and the following disclaimer in
      ///   *   the documentation and/or other materials
      ///   *   provided with the distribution.
      ///   *
      ///   * o Neither the name of Internet Society, IETF or IETF
      ///   *   Trust, nor the names of specific contributors, may be
      ///   *   used to endorse or promote products derived from this
      ///   *   software without specific prior written permission.
      ///   *
      ///   *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS
      ///   *   AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED
      ///   *   WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
      ///   *   IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
      ///   *   FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
      ///   *   EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
      ///   *   LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
      ///   *   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
      ///   *   NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
      ///   *   SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
      ///   *   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
      ///   *   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
      ///   *   OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
      ///   *   IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
      ///   *   ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
      ///   */
      ///



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      ///  /*
      ///   * This code was derived from [RFC2203]. Please
      ///   * reproduce this note if possible.
      ///   */
      ///
      ///  enum rpc_gss_service_t {
      ///          /* Note: the enumerated value for 0 is reserved. */
      ///          rpc_gss_svc_none         = 1,
      ///          rpc_gss_svc_integrity    = 2,
      ///          rpc_gss_svc_privacy      = 3,
      ///          rpc_gss_svc_channel_prot = 4
      ///  };
      ///
      ///  enum rpc_gss_proc_t {
      ///           RPCSEC_GSS_DATA          = 0,
      ///           RPCSEC_GSS_INIT          = 1,
      ///           RPCSEC_GSS_CONTINUE_INIT = 2,
      ///           RPCSEC_GSS_DESTROY       = 3,
      ///           RPCSEC_GSS_BIND_CHANNEL  = 4, /* not used */
      ///           RPCSEC_GSS_CREATE        = 5, /* new */
      ///           RPCSEC_GSS_LIST          = 6  /* new */
      ///  };
      ///
      ///  struct rpc_gss_cred_vers_1_t {
      ///          rpc_gss_proc_t    gss_proc; /* control procedure */
      ///          unsigned int      seq_num;  /* sequence number */
      ///          rpc_gss_service_t service;  /* service used */
      ///          opaque            handle<>; /* context handle */
      ///  };
      ///
      ///  const RPCSEC_GSS_VERS_1 = 1;
      ///  const RPCSEC_GSS_VERS_2 = 2;
      ///  const RPCSEC_GSS_VERS_3 = 3; /* new */
      ///
      ///  union rpc_gss_cred_t switch (unsigned int rgc_version) {
      ///  case RPCSEC_GSS_VERS_1:
      ///  case RPCSEC_GSS_VERS_2:
      ///  case RPCSEC_GSS_VERS_3: /* new */
      ///          rpc_gss_cred_vers_1_t rgc_cred_v1;
      ///  };
      ///

   <CODE ENDS>

   As seen above, the RPCSEC_GSSv3 credential has the same format as the
   RPCSEC_GSSv1 [2] and RPCSEC_GSSv2 [4] credential.  Setting the
   rgc_version field to 3 indicates that the initiator and target
   support the new RPCSEC_GSSv3 control procedures.



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2.5.  New auth_stat Values

   RPCSEC_GSSv3 requires the addition of several values to the auth_stat
   enumerated type definition.  The use of each of these new auth_stat
   values is explained later in this document.

              enum auth_stat {
                      ...
                      /*
                       * RPCSEC_GSSv3 errors
                       */
                      RPCSEC_GSS_INNER_CREDPROBLEM = 15,
                      RPCSEC_GSS_LABEL_PROBLEM = 16,
                      RPCSEC_GSS_PRIVILEGE_PROBLEM = 17,
                      RPCSEC_GSS_UNKNOWN_MESSAGE = 18
              };

2.6.  New Control Procedures

   There are two new RPCSEC_GSSv3 control procedures: RPCSEC_GSS_CREATE,
   RPCSEC_GSS_LIST.

   The RPCSEC_GSS_CREATE procedure binds any combination of assertions:
   multi-principal authentication, labels, structured privileges, or
   channel bindings to a new RPCSEC_GSSv3 context returned in the
   rgss3_create_res rcr_handle field.

   The RPCSEC_GSS_LIST procedure queries the target for supported
   assertions.

   RPCSEC_GSS version 3 control messages are similar to the RPCSEC_GSS
   version 1 and version2 RPCSEC_GSS_DESTROY control message (see
   section 5.4 [2]) in that the sequence number in the request must be
   valid, and the header checksum in the verifier must be valid.  As in
   RPCSEC_GSS version 1 and version 2, the RPCSEC_GSSv version 3 control
   messages may contain call data following the verifier in the body of
   the NULLPROC procedure.  In other words, they look a lot like an
   RPCSEC_GSS data message with the header procedure set to NULLPROC.

   The client MUST use one of the following security services to protect
   the RPCSEC_GSS_CREATE or RPCSEC_GSS_LIST control message:

   o  rpc_gss_svc_channel_prot (see RPCSEC_GSSv2 [4])

   o  rpc_gss_svc_integrity

   o  rpc_gss_svc_privacy




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   Specifically the client MUST NOT use rpc_gss_svc_none.

2.6.1.  New Control Procedure - RPCSEC_GSS_CREATE

   <CODE BEGINS>

      ///  struct rgss3_create_args {
      ///          rgss3_gss_mp_auth    *rca_mp_auth;
      ///          rgss3_chan_binding   *rca_chan_bind_mic;
      ///          rgss3_assertion      rca_assertions<>;
      ///  };
      ///
      ///  struct rgss3_create_res {
      ///          opaque               rcr_handle<>;
      ///          rgss3_gss_mp_auth    *rcr_mp_auth;
      ///          rgss3_chan_binding   *rcr_chan_bind_mic;
      ///          rgss3_assertion      rcr_assertions<>;
      ///  };
      ///
      ///  enum rgss3_assertion_type {
      ///          LABEL = 0,
      ///          PRIVS = 1
      ///  };
      ///
      ///  union rgss3_assertion_u
      ///        switch (rgss3_assertion_type atype) {
      ///  case LABEL:
      ///          rgss3_label  rau_label;
      ///  case PRIVS:
      ///          rgss3_privs  rau_privs;
      ///  default:
      ///          opaque       rau_ext<>;
      ///  };
      ///
      ///  struct rgss3_assertion {
      ///          bool                 ra_critical;
      ///          rgss3_assertion_u    ra_assertion;
      ///  };
      ///

   <CODE ENDS>

   The call data for an RPCSEC_GSS_CREATE request consists of an
   rgss3_create_args which binds one or more items of several kinds to
   the returned rcr_handle RPCSEC_GSSv3 context handle called the
   "child" handle:





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   o  Multi-principal authentication: another RPCSEC_GSS context handle

   o  Authorization assertions: labels and or privileges

   o  A channel binding

   The reply to this message consists of either an error or an
   rgss3_create_res structure.

   Upon successful RPCSEC_GSS_CREATE, both the client and the server
   SHOULD associate the resultant child rcr_handle context handle with
   the parent context handle in their GSS context caches so as to be
   able to reference the parent context given the child context handle.

   RPCSEC_GSSv3 child handles MUST be destroyed upon the destruction of
   the associated parent handle.

   Server implementation and policy MAY result in labels, privileges,
   and identities being mapped to concepts and values that are local to
   the server.  Server policies should take into account the identity of
   the client and/or user as authenticated via the GSS-API.

2.6.1.1.  Multi-principal Authentication

   <CODE BEGINS>

      ///
      ///  struct rgss3_gss_mp_auth {
      ///          opaque          rgmp_handle<>; /* inner handle */
      ///          opaque          rgmp_nonce<>;
      ///          opaque          rgmp_nounc_mic<>;
      ///  };
      ///

   <CODE ENDS>

   RPCSEC_GSSv3 clients MAY assert a multi-principal authentication of
   the client host principal and a user principal.  This feature is
   needed, for example, when a client wishes to use authority assertions
   that the server may only grant if a user and a client are
   authenticated together to the server.  Thus a server may refuse to
   grant requested authority to a user acting alone (e.g., via an
   unprivileged user-space program), or to a client acting alone (e.g.
   when a client is acting on behalf of a user) but may grant requested
   authority to a client acting on behalf of a user if the server
   identifies the user and trusts the client.

   It is assumed that an unprivileged user-space program would not have



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   access to client host credentials needed to establish a GSS-API
   security context authenticating the client to the server, therefore
   an unprivileged user-space program could not create an RPCSEC_GSSv3
   RPCSEC_GSS_CREATE message that successfully binds a client and a user
   security context.

   In addition to the parent handle (Section 2), the multi-principal
   authentication call data has an RPCSEC_GSS version 3 handle
   referenced via the rgmp_handle field termed the "inner" handle.
   Clients using RPCSEC_GSSv3 multi-principal authentication MUST use an
   RPCSEC_GSSv3 context handle that corresponds to a GSS-API security
   context that authenticates the client host for the parent handle.
   The inner context handle it SHOULD use a context handle to
   authenticate a user.  The reverse (parent handle authenticates user,
   inner authenticates client) MUST NOT be used.  Other multi-principal
   parent and inner context handle uses might eventually make sense.

   An inner RPCSEC_GSSv3 context handle that is bound to a parent
   RPCSEC_GSS context through multi-principal authentication MUST be
   treated by servers as authenticating the GSS-API initiator principal
   authenticated by the inner context handle's GSS-API security context.
   This principal may be mapped to a server-side notion of user or
   principal.

   Multi-principal binding is done by including an assertion of type
   rgss3_gss_mp_auth in the RPCSEC_GSS_CREATE rgss3_create_args call
   data.  The inner context handle is place in the rbmp_handle field.  A
   nonce and a MIC of that nounce created using the GSS-API security
   context associated with the inner handle is also provided.

   The target verifies the multi-principal authentication by verifying
   the rgmp_nouce_mic.  On a successful reply, the rgss3_gss_mp_auth
   field in the rgss3_create_res reply uses the parent RPCSEC_GSSv3
   context as the rgmp_handle, the same rgmp_nounce as was sent in the
   call data with the rgmp_nounce_mic created using the GSS-API security
   context associate with the parent handle.  Verification of the
   rbg_nounce_mic by the initiator demonstrates that the target agrees
   to the multi-principal authentication.

   On failure, the rgss3_gss_mp_auth field is not sent
   (rgss3_gss_mp_auth is an optional field).  A MSG_DENIED reply to an
   RPCSEC_GSS_CREATE formulated as usual.  A new value,
   RPCSEC_GSS_INNER_CREDPROBLEM, has been added to the auth_stat type.
   As described in Section 5.3.3.3 of [2] the server maintains a list of
   contexts for the clients that are currently in session with it.  When
   a client request comes in, there may not be a context corresponding
   to its handle.  When this occurs on an RPCSEC_GSS3_CREATE request
   processing of the parent handle, the server rejects the request with



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   a reply status of MSG_DENIED with the reject_stat of AUTH_ERROR and
   with an auth_stat value of RPCSEC_GSS_CREDPROBLEM.

   With a multi-pricipal authorization request, the server must also
   have a context corresponding to the inner context handle.  When the
   server does not have a context handle corresponding to the inner
   context handle of a multi-pricipal authorization request, the server
   send a reply status of MSG_DENIED with the reject_stat of AUTH_ERROR
   and with an auth_stat value of RPCSEC_GSS_INNER_CREDPROBLEM.

   When processing the multi-principal authentication request, if the
   GSS_VerifyMIC() call on the inner handle nouce fails to return
   GSS_S_COMPLETE, the server sends a reply status of MSG_DENIED with
   the reject_stat of AUTH_ERROR and with an auth_stat value of
   RPCSEC_GSS_INNER_CREDPROBLEM.

2.6.1.2.  Label Assertions

   <CODE BEGINS>

      ///  struct rgss3_label {
      ///          rgss3_lfs       rl_lfs;
      ///          opaque          rl_label<>;
      ///  };
      ///
      ///  struct rgss3_lfs {
      ///          unsigned int rlf_lfs_id;
      ///          unsigned int rlf_pi_id;
      ///  };
      ///

   <CODE ENDS>

   The client discovers which labels the server supports via the
   RPCSEC_GSS_LIST control message.

   RPCSEC_GSSv3 clients MAY assert a server security label in some LSF
   by binding a label assertion to the RPCSEC_GSSv3 context handle.
   This is done by including an assertion of type rgss3_label in the
   RPCSEC_GSS_CREATE rgss3_create_args rca_assertions call data.

   The labels that are accepted by the target and bound to the
   RPCSEC_GSSv3 context will be enumerated in the rcr_assertions field
   of the rgss3_create_res RPCSEC_GSS_CREATE reply.

   Label encoding is specified to mirror the NFSv4.2 sec_label attribute
   described in Section 12.2.2 of [6].  The label format specifier (LFS)
   is an identifier used by the client to establish the syntactic format



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   of the security label and the semantic meaning of its components.
   The policy identifier (PI) is an optional part of the definition of
   an LFS which allows for clients and server to identify specific
   security policies.  The opaque label field of rgss3_label is
   dependent on the MAC model to interpret and enforce.

   Asserting a server supported label via RPCSEC_GSS_CREATE enables
   server guest mode labels.  Full mode is enabled when an
   RPCSEC_GSS_CREATE label assertion is combined with asserting the same
   label with the NFSv4.2 sec_label attribute.

   If a label itself requires privacy protection (i.e., that the user
   can assert that label is a secret) then the client MUST use the
   rpc_gss_svc_privacy protection service for the RPCSEC_GSS_CREATE
   request or, if the parent handle is bound to a secure channel that
   provides privacy protection, rpc_gss_svc_channel_prot.

   If a client wants to ensure that the server understands the asserted
   label then it MUST set the 'critical' field of the label assertion to
   TRUE, otherwise it MUST set it to FALSE.

   Servers that do not support labeling MUST ignore non-critical label
   assertions.  Servers that do not support the requested LFS MUST
   either ignore non-critical label assertions or map them to a suitable
   label in a supported LFS.  Servers that do not support labeling or do
   not support the requested LFS MUST return an error if the label
   request is critical.  Servers that support labeling in the requested
   LFS MAY map the requested label to different label as a result of
   server-side policy evaluation.

2.6.1.3.  Structured Privilege Assertions

   <CODE BEGINS>

      ///
      ///  struct rgss3_privs {
      ///          string          rp_name<>; /* human readable */
      ///          opaque          rp_privilege<>;
      ///  };

   <CODE ENDS>

   A structured privilege is an RPC application defined privilege.
   RPCSEC_GSSv3 clients MAY assert a structured privilege by binding the
   privilege to the RPCSEC_GSSv3 context handle.  This is done by
   including an assertion of type rgss3_privs in the RPCSEC_GSS_CREATE
   rgss3_create_args rca_assertions call data.  Encoding, server
   verification and any policies for structured privileges are described



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   by the RPC application definition.

   A successful structured privilege assertion will be enumerated in the
   rcr_assertions field of the rgss3_create_res RPCSEC_GSS_CREATE reply.

   If a server receives a structured privilege assertion that it does
   not recognize the assertion is rejected with MSG_DENIED, a
   reject_status of AUTH_ERROR, and an auth_stat of
   RPCSEC_GSS_UNKNOWN_MESSAGE.  If the server fails the RPC application
   defined server verification for a structured privilege, the assertion
   is rejected with MSG_DENIED, a reject_status of AUTH_ERROR, and an
   auth_stat of RPCSEC_GSS_PRIVILEGE_PROBLEM.

   Section 3.4.1.2.  "Inter-Server Copy with RPCSEC_GSSv3" of [6] shows
   an example of structured privilege definition and use.

2.6.1.4.  Channel Binding

   <CODE BEGINS>

      ///
      ///  typedef opaque rgss3_chan_binding<>;
      ///

   <CODE ENDS>

   RPCSEC_GSSv3 provides a different way to do channel binding than
   RPCSEC_GSSv2 [4].  Specifically:

   a.  RPCSEC_GSSv3 builds on RPCSEC_GSSv1 by reusing existing,
       established context handles rather than providing a different RPC
       security flavor for establishing context handles,

   b.  channel bindings data are not hashed because the community now
       agrees that it is the secure channel's responsibility to produce
       channel bindings data of manageable size.

   (a) is useful in keeping RPCSEC_GSSv3 simple in general, not just for
   channel binding. (b) is useful in keeping RPCSEC_GSSv3 simple
   specifically for channel binding.

   Channel binding is accomplished as follows.  The client prefixes the
   channel bindings data octet string with the channel type as described
   in [5], then the client calls GSS_GetMIC() to get a MIC of resulting
   octet string, using the RPCSEC_GSSv3 context handle's GSS-API
   security context.  The MIC is then placed in the rca_chan_bind_mic
   field of RPCSEC_GSS_CREATE arguments (rgss3_create_args).




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   If the rca_chan_bind_mic field of the arguments of a
   RPCSEC_GSS_CREATE control message is set, then the server MUST verify
   the client's channel binding MIC if the server supports this feature.
   If channel binding verification succeeds then the server MUST
   generate a new MIC of the same channel bindings and place it in the
   rcr_chan_bind_mic field of the RPCSEC_GSS_CREATE rgss3_create_res
   results.  If channel binding verification fails or the server doesn't
   support channel binding then the server MUST indicate this in its
   reply by not including a rgss3_chan_binding value in rgss3_create_res
   (rgss3_chan_binding is an optional field).

   The client MUST verify the result's rcr_chan_bind_mic value by
   calling GSS_VerifyMIC() with the given MIC and the channel bindings
   data (including the channel type prefix).  If client-side channel
   binding verification fails then the client MUST call
   RPCSEC_GSS_DESTROY.  If the client requested channel binding but the
   server did not include an rcr_chan_binding_mic field in the results,
   then the client MAY continue to use the resulting context handle as
   though channel binding had never been requested, otherwise (if the
   client really wanted channel binding) it MUST call
   RPCSEC_GSS_DESTROY.

   As per-RPCSEC_GSSv2 [4]:

      "Once a successful [channel binding] procedure has been performed
      on an [RPCSEC_GSSv3] context handle, the initiator's
      implementation may map application requests for rpc_gss_svc_none
      and rpc_gss_svc_integrity to rpc_gss_svc_channel_prot credentials.
      And if the secure channel has privacy enabled, requests for
      rpc_gss_svc_privacy can also be mapped to
      rpc_gss_svc_channel_prot."

   Any RPCSEC_GSSv3 context handle that has been bound to a secure
   channel in this way SHOULD be used only with the
   rpc_gss_svc_channel_prot, and SHOULD NOT be used with
   rpc_gss_svc_none nor rpc_gss_svc_integrity -- if the secure channel
   does not provide privacy protection then the client MAY use
   rpc_gss_svc_privacy where privacy protection is needed or desired.

2.6.2.  New Control Procedure - RPCSEC_GSS_LIST

   <CODE BEGINS>









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      ///  enum rgss3_list_item {
      ///          LABEL = 0,
      ///          PRIVS = 1
      ///  };
      ///
      ///  struct rgss3_list_args {
      ///          rgss3_list_item      rla_list_what<>;
      ///  };
      ///
      ///  union rgss3_list_item_u
      ///        switch (rgss3_list_item itype) {
      ///  case LABEL:
      ///          rgss3_label          rli_labels<>;
      ///  case PRIVS:
      ///          rgss3_privs          rli_privs<>;
      ///  default:
      ///          opaque               rli_ext<>;
      ///  };
      ///
      ///  typedef rgss3_list_item_u rgss3_list_res<>;
      ///

   <CODE ENDS>

   The call data for an RPCSEC_GSS_LIST request consists of a list of
   integers (rla_list_what<>) indicating what assertions to be listed,
   and the reply consists of an error or the requested list.

   [[Comment.1: What good is the rli_ext field?  How should we describe
   it's use? --AA]]

   The result of requesting a list of rgss3_list_item LABEL is a list of
   LFSs supported by the server.  The client can then use the LFS list
   to assert labels via the RPCSEC_GSS_CREATE label assertions.  See
   Section 2.6.1.2.

2.7.  Extensibility

   Assertion types may be added in the future by adding arms to the
   'rgss3_assertion_u' union.  Every assertion has a 'critical' flag
   that can be used to indicate criticality.  Other assertion types are
   described elsewhere and include:

   o  Client-side assertions of identity:

      *  Primary client/user identity





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      *  Supplementary group memberships of the client/user, including
         support for specifying deltas to the membership list as seen on
         the server.

   New control message types may be added.

   Servers receiving unknown critical client assertions MUST return an
   error.


3.  Operational Recommendation for Deployment

   RPCSEC_GSSv3 is a superset of RPCSEC_GSSv2 [4] which in turn is a
   superset of RPCSEC_GSSv1 [2], and so can be used in all situations
   where RPCSEC_GSSv1 or RPCSEC_GSSv2 is used.  RPCSEC_GSSv3 should be
   used when the new functionality is needed.


4.  Security Considerations

   This entire document deals with security issues.

   The RPCSEC_GSSv3 protocol allows for client-side assertions of data
   that is relevant to server-side authorization decisions.  These
   assertions must be evaludated by the server in the context of whether
   the client and/or user are authenticated, whether multi-principal
   authentication was used, whether the client is trusted, what ranges
   of assertions are allowed for the client and the user (separately or
   together), and any relevant server-side policy.

   The security semantics of assertions carried by RPCSEC_GSSv3 are
   application protocol-specific.

   RPCSEC_GSSv3 supports a notion of critical assertions but there's no
   need for peers to tell each other what assertions were granted, or
   what they were mapped to.

   Note that RPSEC_GSSv3 is not a complete solution for labeling: it
   conveys the labels of actors, but not the labels of objects.  RPC
   application protocols may require extending in order to carry object
   label information.

   There may be interactions with NFSv4's callback security scheme and
   NFSv4.1's GSS-API "SSV" mechanisms.  Specifically, the NFSv4 callback
   scheme requires that the server initiate GSS-API security contexts,
   which does not work well in practice, and in the context of client-
   side processes running as the same user but with different privileges
   and security labels the NFSv4 callback security scheme seems



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   particularly unlikely to work well.  NFSv4.1 has the server use an
   existing, client-initiated RPCSEC_GSS context handle to protect
   server-initiated callback RPCs.  The NFSv4.1 callback security scheme
   lacks all the problems of the NFSv4 scheme, however, it is important
   that the server pick an appropriate RPCSEC_GSS context handle to
   protect any callbacks.  Specifically, it is important that the server
   use RPCSEC_GSS context handles which authenticate the client to
   protect any callbacks relating to server state initiated by RPCs
   protected by RPCSEC_GSSv3 contexts.

   [[Comment.2: [Add text about interaction with GSS-SSV...] --NW]]

   [[Comment.3: AFAICS the reason to use SSV is to avoid using a client
   machine credential which means multi-principal authentication can not
   be used. --AA]]


5.  IANA Considerations

   This section uses terms that are defined in [8].

   There are no IANA considerations in this document.  TBDs in this
   document will be assigned by the ONC RPC registrar (which is not
   IANA, XXX: verify).


6.  References

6.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", RFC 2119, March 1997.

   [2]   Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
         Specification", RFC 2203, September 1997.

   [3]   Linn, J., "Generic Security Service Application Program
         Interface Version 2, Update 1", RFC 2743, January 2000.

   [4]   Eisler, M., "RPCSEC_GSS Version 2", RFC 5403, February 2009.

   [5]   Williams, N., "On the Use of Channel Bindings to Secure
         Channels", RFC 5056, November 2007.

   [6]   Haynes, T., "NFS Version 4 Minor Version 2",
         draft-ietf-nfsv4-minorversion2-27 (Work In Progress),
         June 2014.




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   [7]   Eisler, M., "XDR: External Data Representation Standard",
         RFC 4506, May 2006.

   [8]   Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
         Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.

6.2.  Informative References

   [9]   "Section 46.6. Multi-Level Security (MLS) of Deployment Guide:
         Deployment, configuration and administration of Red Hat
         Enterprise Linux 5, Edition 6", 2011.

   [10]  Smalley, S., "The Distributed Trusted Operating System (DTOS)
         Home Page",
         <http://www.cs.utah.edu/flux/fluke/html/dtos/HTML/dtos.html>.

   [11]  Carter, J., "Implementing SELinux Support for NFS",
         <http://www.nsa.gov/research/_files/selinux/papers/nfsv3.pdf>.

   [12]  Haynes, T., "Requirements for Labeled NFS",
         draft-ietf-nfsv4-labreqs-05 (work in progress).

   [13]  Quigley, D. and J. Lu, "Registry Specification for MAC Security
         Label Formats", draft-quigley-label-format-registry (work in
         progress), 2011.


Appendix A.  Acknowledgments

   Andy Adamson would like to thank NetApp, Inc. for its funding of his
   time on this project.

   Lars Eggert and Mike Eisler for their most helpful reviews.


Appendix B.  RFC Editor Notes

   [RFC Editor: please remove this section prior to publishing this
   document as an RFC]

   [RFC Editor: prior to publishing this document as an RFC, please
   replace all occurrences of RFCTBD10 with RFCxxxx where xxxx is the
   RFC number of this document]








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Authors' Addresses

   William A. (Andy) Adamson
   NetApp
   3629 Wagner Ridge Ctt
   Ann Arbor, MI  48103
   USA

   Phone: +1 734 665 1204
   Email: andros@netapp.com


   Nico Williams
   cryptonector.com
   13115 Tamayo Dr
   Austin, TX  78729
   USA

   Email: nico@cryptonector.com
































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