NFSv4 W. Adamson
Internet-Draft NetApp
Intended status: Standards Track N. Williams
Expires: April 20, 2014 Cryptonector
October 17, 2013
Remote Procedure Call (RPC) Security Version 3
draft-ietf-nfsv4-rpcsec-gssv3-06.txt
Abstract
This document specifies version 3 of the Remote Procedure Call (RPC)
security protocol (RPCSEC_GSS). This protocol provides for compound
authentication of client hosts and users 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 April 20, 2014.
Copyright Notice
Copyright (c) 2013 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Applications of RPCSEC_GSSv3 . . . . . . . . . . . . . . . 4
2. The RPCSEC_GSSv3 Protocol . . . . . . . . . . . . . . . . . . 5
2.1. New auth_stat Values . . . . . . . . . . . . . . . . . . . 9
2.2. RPC Message Credential and Verifier . . . . . . . . . . . 10
2.3. Control Messages . . . . . . . . . . . . . . . . . . . . . 10
2.3.1. Create Request . . . . . . . . . . . . . . . . . . . . 11
2.3.2. Destruction Request . . . . . . . . . . . . . . . . . 15
2.3.3. List Request . . . . . . . . . . . . . . . . . . . . . 15
2.3.4. Extensibility . . . . . . . . . . . . . . . . . . . . 16
2.4. Data Messages . . . . . . . . . . . . . . . . . . . . . . 16
3. Security Considerations . . . . . . . . . . . . . . . . . . . 17
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1. Normative References . . . . . . . . . . . . . . . . . . . 18
5.2. Informative References . . . . . . . . . . . . . . . . . . 19
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 19
Appendix B. RFC Editor Notes . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
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 a client's 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 (see [6] and [9]). Both of
these features require assertions of authority from the client.
Assertions need to be verified. One party that can verify an
assertion is the client host, which can authenticate to the server
using its own credentials. We can also require users to verify an
assertion as well. This calls for compound authentication.
Because the design of RPCSEC_GSSv3 relies on either RPCSEC_GSS
version 1 (though version 2 can be used) to do the actual GSS-API
security context establishment, we add support for channel binding so
that implementors who have implemented RPCSEC_GSS version 1 but not
version 2 can provide a (simplified) channel binding implementation
using RPCSEC_GSSv3.
We therefore describe a new version of RPCSEC_GSS that allows for the
following client-side assertions of authority:
o Security labels for multi-level, type enforcement, and other
labeled security models. See [10], [11], [12], [6] and [9].
o Application-specific structured privileges. For an example see
server-side copy [6].
o Compound authentication of the client host and user to the server
done by binding two RPCSEC_GSS handles.
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.
We add an option for enumerating server supported label format
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specifiers (LFS). The LFS and Label Format Registry are described in
detail in [13].
RPCSEC_GSSv3 is patterned as follows:
o A client uses an existing RPCSEC_GSSv1 (or RPCSEC_GSSv2) context
handle to protect RPCSEC_GSSv3 exchanges (this will be termed the
"parent" handle)
o The server issues a "child" RPCSEC_GSSv3 handle which uses the
underlying GSS-API security context of the parent handle in all
subsequent exchanges that uses the child handle.
o The child handle, however, has its own sequence number space
distinct from that of the parent.
[[Comment.1: I removed the "child has a window distinct from that of
the parent" because RFC2203 states: " In a successful response, the
seq_window field is set to the sequence window length supported by
the server for this context. This window specifies the maximum
number of client requests that may be outstanding for this context."
If we want a distinct window, we will need to add that to the
rpc_gss3_create_res so that the server can set it. I see no point -
just use the parent window. --AA]]
[[Comment.2: RFC2203 states that when data integrity is used, the
seq_num in the rpc_gss_data_t must be the same as in the credential.
This means that using data integrity with GSS3 context's can not
simply construct it using the parent context as the seq_num must be
from the GSS3 context. --AA]]
This means that RPCSEC_GSSv3 depends on an existing parent
RPCSEC_GSSv1 or RPCSEC_GSSv2 context for actual GSS-API security
context establishment. This keeps the specification of RPCSEC_GSSv3
simple by avoiding the need to duplicate the core functionality of
RPCSEC_GSS version 1. This also means that an RPCSEC_GSSv3 context
MUST be destroyed prior to it's parent context being destroyed.
[[Comment.3: Destruction of the parent context => first destroy child
handle. IOW fail the RPCSEC_GSS_DESTROY of parent with new
RPCSEC_GSS3_CONTEXT_EXISTS error code OR upon the destruction of the
parent context destroy any associated RPCSEC_GSSv3 contexts OR.....
--AA]]
1.1. Applications of RPCSEC_GSSv3
The common uses of RPCSEC_GSSv3, particularly for NFSv4 [6], are
expected to be:
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a. labeled security: client-side process label assertion [+
privilege assertion] + compound client host & user
authentication;
b. inter-server server-side copy: compound client host & user
authentication [+ critical structured privilege assertions]
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.
[[Comment.4: check that this language states what NFSv4.2 labeled NFS
problem we are really solving. (setting labels on the server) --AA]]
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 compound
authentication and structured privileges to authorize the destination
to copy the file from the source on behalf of the user.
2. The RPCSEC_GSSv3 Protocol
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:
#!/bin/sh
grep "^ *///" | sed 's?^ */// ??' | sed 's?^ *///$??'
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:
sh extract.sh < spec.txt > rpcsec_gss_v3.x
The effect of the script is to remove leading white space from each
line, plus a sentinel sequence of "///".
The XDR description, with the sentinel sequence follows:
/// /*
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/// * 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.
/// */
///
/// /*
/// * This code was derived from [RFC2203]. Please
/// * reproduce this note if possible.
/// */
///
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/// /*
/// * rpcsec_gss_v3.x
/// */
///
/// 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
/// };
///
/// 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 */
/// };
///
/// enum rpc_gss3_proc_t {
/// RPCSEC_GSS3_DATA = 0,
/// RPCSEC_GSS3_LIST = 5,
/// RPCSEC_GSS3_CREATE = 6,
/// RPCSEC_GSS3_DESTROY = 7
/// };
///
/// struct rpc_gss_cred_vers_3_t {
/// rpc_gss3_proc_t gss_proc;
/// unsigned int seq_num;
/// rpc_gss_service_t service;
/// opaque 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:
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/// rpc_gss_cred_vers_1_t rgc_cred_v1;
/// case RPCSEC_GSS_VERS_3: /* new */
/// rpc_gss_cred_vers_3_t rgc_cred_v3;
/// };
///
/// const MAXSEQ = 0x80000000;
///
/// struct rpc_gss3_gss_binding {
/// unsigned int vers;
/// opaque handle<>;
/// opaque nonce<>;
/// opaque mic<>;
/// };
///
/// typedef opaque rpc_gss3_chan_binding<>;
///
/// struct rpc_gss3_lfs {
/// unsigned int lfs_id;
/// unsigned int pi_id;
/// };
///
/// struct rpc_gss3_label {
/// rpc_gss3_lfs lfs;
/// opaque label<>;
/// };
///
/// struct rpc_gss3_privs {
/// string name; /* human readable */
/// opaque privilege<>;
/// };
///
/// enum rpc_gss3_assertion_type {
/// LABEL = 0,
/// PRIVS = 1
/// };
///
/// union rpc_gss3_assertion_u
/// switch (rpc_gss3_assertion_type atype) {
/// case LABEL:
/// rpc_gss3_label label;
/// case PRIVS:
/// rpc_gss3_privs privs;
/// default:
/// opaque ext<>;
/// };
///
/// struct rpc_gss3_assertion {
/// bool critical;
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/// rpc_gss3_assertion_u assertion;
/// };
///
/// struct rpc_gss3_create_args {
/// rpc_gss3_gss_binding *compound_binding;
/// rpc_gss3_chan_binding *chan_binding_mic;
/// rpc_gss3_assertion assertions<>;
/// };
///
/// struct rpc_gss3_create_res {
/// opaque handle<>;
/// rpc_gss3_chan_binding *chan_binding_mic;
/// rpc_gss3_assertion granted_assertions<>;
/// };
///
/// enum rpc_gss3_list_item {
/// LABEL = 0,
/// };
///
/// struct rpc_gss3_list_args {
/// rpc_gss3_list_item list_what<>;
/// };
///
/// union rpc_gss3_list_item_u
/// switch (rpc_gss3_list_item itype) {
/// case LABEL:
/// rpc_gss3_lable labels<>;
/// default:
/// opaque ext<>;
/// };
///
/// typedef rpc_gss3_list_item_u rpc_gss3_list_res<>;
2.1. New auth_stat Values
RPCSEC_GSSv3 requires the addition of several values to the auth_stat
enumerated type definition:
enum auth_stat {
...
/*
* RPCSEC_GSSv3 errors
*/
RPCSEC_GSS3_COMPOUND_PROBEM = <>,
RPCSEC_GSS3_LABEL_PROBLEM = <>,
RPCSEC_GSS3_UNKNOWN_PRIVILEGE = <>
RPCSEC_GSS3_UNKNOWN_MESSAGE = <>
};
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[[Comment.5: fix above into YYY. All the entries are TBD... --NW]]
[[Comment.6: The compound authentication problems are: can't find the
handle plus handle version on the target, or the MIC of the nounce
does not match. Both of these errors already have auth_stat entries:
RPCSEC_GSS_CREDPROBLEM for the first and "reply status of
MSG_ACCEPTED, and an acceptance status of GARBAGE_ARGS." --AA]]
2.2. RPC Message Credential and Verifier
The rpc_gss_cred_vers_3_t type is used in much the same way that
rpc_gss_cred_vers_1_t is used in RPCSEC_GSSv1, that is: as the arm of
the rpc_gss_cred_t discriminated union in the RPC message header
opaque_auth structure corresponding to version 3 (RPCSEC_GSS_VERS_3).
It differs from rpc_gss_cred_vers_1_t in that:
a. the values for gss_proc corresponding to control messages are
different.
b. the handle field is the RPCSEC_GSSv3 (child) handle, except for
the RPCSEC_GSS3_CREATE and RPCSEC_GSS3_LIST control messages
where it is set to the parent context handle.
For all RPCSEC_GSSv3 data and control messages, the verifier field in
the RPC message header is constructed in the RPCSEC_GSSv1 manner
using the parent GSS-API security context.
2.3. Control Messages
There are three RPCSEC_GSSv3 control messages: RPCSEC_GSS3_CREATE,
RPCSEC_GSS3_DESTROY, and RPCSEC_GSS3_LIST.
RPCSEC_GSSv3 control messages are similar to the RPCSEC_GSSv1
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. In other words, they look a lot like
an RPCSEC_GSSv3 data message with the header procedure set to
NULLPROC.
As in RPCSEC_GSSv1, the RPCSEC_GSSv3 control messages may contain
information following the verifier in the body of the NULLPROC
procedure.
The client MUST use one of the following security services to protect
any RPCSEC_GSSv3 control message:
o rpc_gss_svc_channel_prot (see RPCSEC_GSSv2)
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o rpc_gss_svc_integrity
o rpc_gss_svc_privacy
Specifically the client MUST NOT use rpc_gss_svc_none.
For RPCSEC_GSSv3 control messages the rpc_gss_cred_vers_3_t in the
RPC message opaque_auth structure is encoded as follows:
o the union rpc_gss_cred_t version is set to 3 with the value being
of type rpc_gss_cred_vers_3_t instead of rpc_gss_cred_vers_1_t.
o the gss_proc is set to one of RPCSEC_GSS3_CREATE,
RPCSEC_GSS3_DESTROY, or RPCSEC_GSS3_LIST.
o the seq_num is a valid sequence number for the context in the
handle field.
o the rpc_gss_service_t is one of rpc_gss_svc_integrity,
rpc_gss_svc_privacy, or rpc_gss_svc_channel_prot.
o the rpc_gss_cred_vers_3_t handle field is either set to the parent
context handle for RPCSEC_GSS3_CREATE and RPCSEC_GSS3_LIST, or to
the GSS3 child handle for RPCSEC_GSS3_DESTROY.
2.3.1. Create Request
As noted in the introduction, RPCSEC_GSSv3 relies on the RPCSEC_GSS
version 1 parent context (though version 2 can be used) secure
connection to do the actual GSS-API GSS3 security context
establishment. As such, for the RPCSEC_GSS3_CREATE request, the
rpc_gss_cred_vers_3_t fields in the RPC Call opaque_auth use the
parent context handle and seq_num stream.
The RPCSEC_GSS3_CREATE call message binds one or more items of
several kinds into a new RPCSEC_GSSv3 context handle:
o another RPCSEC_GSS (version 1, 2, or 3) context handle (compound
authentication)
o a channel binding
o authorization assertions (labels, privileges)
The reply to this message consists of either an error or an
rpc_gss3_create_res structure which includes a new RPCSEC_GSSv3
handle, termed the "child" which is used for subsequent control and
data messages.
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Upon successful RPCSEC_GSS3_CREATE, both the client and the server
should associate the resultant GSSv3 child 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.
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.
2.3.1.1. Compound Authentication
RPCSEC_GSSv3 allows for compound authentication of client hosts and
users to servers. As in non-compound authentication, there is a
parent handle used to protect the RPCSEC_GSS3_CREATE call message and
a resultant RPCSEC_GSSv3 child handle. In addition to the parent
handle, the compound authentication create control message has a
handle referenced via the compound_binding field of the
RPCSEC_GSS3_CREATE arguments structure (rpc_gss3_create_args) termed
the "inner" handle, as well as a nonce and a MIC of that nounce
created using the GSS-API security context associated with the
"inner" handle.
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
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_GSS3_CREATE message that successfully binds a client and a
user security context.
Clients using RPCSEC_GSS context binding MUST use, as the parent
context handle, an RPCSEC_GSS context handle that corresponds to a
GSS-API security context that authenticates the client host, and for
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 compounds might
eventually make sense.
An RPCSEC_GSSv3 context handle that is bound to another RPCSEC_GSS
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context 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.
2.3.1.2. Channel Binding
RPCSEC_GSSv3 provides a different way to do channel binding than
RPCSEC_GSSv2. 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 parent RPCSEC_GSS context handle's GSS-API
security context. The MIC is then placed in the chan_binding_mic
field of RPCSEC_GSS3_CREATE arguments (rpc_gss3_create_args).
If the chan_binding_mic field of the arguments of a
RPCSEC_GSS3_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 chan_binding_mic field of the RPCSEC_GSS3_CREATE 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 chan_binding_mic value (chan_binding_mic is an
optional field).
The client MUST verify the result's chan_binding_mic value, if the
server included it, 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_GSS3_DESTROY. If the client requested channel binding
but the server did not include a 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
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(if the client really wanted channel binding) it MUST call
RPCSEC_GSS3_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.
2.3.1.3. Label Assertions
RPCSEC_GSSv3 clients MAY assert a security label in some LSF by
binding this assertion into an RPCSEC_GSSv3 context handle. This is
done by including an assertion of type rpc_gss3_label in the
'assertions' field (discriminant: 'LABEL') of the RPCSEC_GSS3_CREATE
arguments to the desired LSF and label.
Label encoding is specified to mirror the NFSv4 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
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 rpc_gss3_label is
dependent on the MAC model to interpret and enforce.
[[Comment.7: Check that this Label definition provides all the
required pieces to enable full mode when combined with NFSv4.2 LNFS.
Specifically, how does the client find out and respond if a server
has changed a label. --AA]]
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_GSS3_CREATE
request or, if the parent handle is bound to a secure channel that
provides privacy protection, rpc_gss_svc_channel_prot.
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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.
2.3.1.4. Structured Privilege Assertions
A structured privilege is an RPC application defined structure that
is opaque, and is encoded in the rpc_gss3_privs privilege field.
Encoding, server verification and any server policies for structured
privileges are described by the RPC application definition.
A successful structured privilege assertion RPCSEC_GSS3_CREATE call
must return all granted privileges in the rpc_gss3_privs
granted_assertions field.
Section 3.4.1.2. "Inter-Server Copy with RPCSEC_GSSv3" of [6] shows
an example of structured privilege definition and use.
2.3.2. Destruction Request
The RPCSEC_GSS3_DESTROY control message is the same as the
RPCSEC_GSSv1 RPCSEC_GSS_DESTROY control message, but with the version
3 header. Specifically, the rpc_gss_cred_vers_3_t fields in the RPC
Call opaque_auth use the GSS3 context handle and seq_num stream. As
with all RPCSEC_GSSv3 messages, the header checksum uses the parent
context, and needs to be valid.
The server sends a response as it would to a data request. The
client and server must then destroy the context for the session.
2.3.3. List Request
The RPCSEC_GSS3_LIST control message is similar to RPCSEC_GSS3_CREATE
message. Specifically, the rpc_gss_cred_vers_3_t fields in the RPC
Call opaque_auth use the parent context handle and seq_num stream.
As with all RPCSEC_GSSv3 messages, the header checksum uses the
parent context, and needs to be valid.
The RPCSEC_GSS3_LIST control message consists of a single integer
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indicating what should be listed, and the reply consists of an error
or the requested list. The client may query the server to list
available LFSs.
The result is an opaque octet string containing a list of LFSs
[encoding TBD].
2.3.4. Extensibility
Assertion types may be added in the future by adding arms to the
'rpc_gss3_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
* 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.
2.4. Data Messages
RPCSEC_GSS3_DATA messages differ from from RPCSEC_GSSv1 data messages
in that the version number used MUST be '3' instead of '1'. As noted
in Section 2.2 the RPCSEC_GSSv3 context handle is used along with
it's sequence number stream.
For RPCSEC_GSSv3 data messages the rpc_gss_cred_vers_3_t in the RPC
message opaque_auth structure is encoded as follows:
1. the union rpc_gss_cred_t version is set to 3 with the value being
of type rpc_gss_cred_vers_3_t instead of rpc_gss_cred_vers_1_t.
2. the gss_proc is set to RPCSEC_GSS3_DATA
3. the seq_num is a valid GSS3 context (child context) sequence
number.
4. just as in RPCSEC_GSSv1, the rpc_gss_service_t is one of
rpc_gss_svc_none, rpc_gss_svc_integrity, rpc_gss_svc_privacy, or
rpc_gss_svc_channel_prot.
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5. the handle field is set to the (child) RPCSEC_GSSv3 context
handle
3. 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 compound
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
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.8: [Add text about interaction with GSS-SSV...] --NW]]
[[Comment.9: I see no reason to use RPCSEC_GSSv3 contexts for NFSv4.x
back channel. --AA]]
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[[Comment.10: Since GSS3 requires an RPCSEC_GSSv1 or v2 context
handle to establish a GSS3 context, SSV can not be used as this draft
is written.]]
[[Comment.11: AFAICS the reason to use SSV is to avoid using a client
machine credential which means compound authentication can not be
used. Since GSS3 requires an RPCSEC_GSSv1 or v2 context handle to
establish a GSS3 context, SSV can not be used as the parent context
for GSSv3. --AA]]
4. 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).
5. References
5.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", 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] Srinivasan, R., "RPC: Remote Procedure Call Protocol
Specification Version 2", RFC 1831, August 1995.
[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-minorversion2-19 (Work In Progress),
March 2013.
[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.
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5.2. Informative References
[9] Haynes, T., "Requirements for Labeled NFS",
draft-ietf-nfsv4-labreqs-03 (work in progress).
[10] "Section 46.6. Multi-Level Security (MLS) of Deployment Guide:
Deployment, configuration and administration of Red Hat
Enterprise Linux 5, Edition 6", 2011.
[11] Smalley, S., "The Distributed Trusted Operating System (DTOS)
Home Page",
<http://www.cs.utah.edu/flux/fluke/html/dtos/HTML/dtos.html>.
[12] Carter, J., "Implementing SELinux Support for NFS",
<http://www.nsa.gov/research/_files/selinux/papers/nfsv3.pdf>.
[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
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]
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
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Nico Williams
cryptonector.com
13115 Tamayo Dr
Austin, TX 78729
USA
Email: nico@cryptonector.com
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