Date/Time: May 26th 5:00-6:00 PM EST
Telecon dial-in information:
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We haven't had a telecon in a while due to various schedule reasons so I
would like to start it up this week. The proposed agenda is below with
the necessary documents for the meeting attached.
Proposed Agenda
-----------------------
+ IETF Note Well Agreement
This is a reminder that our discussions are governed by the
IETF Note Well Agreement. See:
http://www.ietf.org/NOTEWELL.html
We will start each week's meeting with this announcement.
+ Discuss RPCSEC gssv3 document (rpcsecgssv3-01.txt)
+ Label Format Specification document status update
+ Discuss possible uses of a Policy Authority field
+ Discuss possible submission topics for Linux Security Summit 2010
+ Discuss work needed for October Bake-A-Thon
NETWORK WORKING GROUP N. Williams
Internet-Draft Sun
Intended status: Standards Track January 2009
Expires: July 5, 2009
Remote Procedure Call (RPC) Security Version 3
draft-williams-rpcsecgssv3-01.txt
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 5, 2009.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents in effect on the date of
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Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
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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), channel binding, security label assertions for
multi-level and type enforcement, privilege assertions and identity
assertions.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Applications of RPCSEC_GSSv3 . . . . . . . . . . . . . . . 5
1.3. Conventions used in this document . . . . . . . . . . . . 6
2. The RPCSEC_GSSv3 protocol . . . . . . . . . . . . . . . . 7
2.1. Control messages . . . . . . . . . . . . . . . . . . . . . 10
2.1.1. New auth_stat values . . . . . . . . . . . . . . . . . . . 10
2.1.2. Create request . . . . . . . . . . . . . . . . . . . . . . 10
2.1.3. Context handle destruction . . . . . . . . . . . . . . . . 16
2.1.4. List request . . . . . . . . . . . . . . . . . . . . . . . 16
2.1.5. Extensibility . . . . . . . . . . . . . . . . . . . . . . 16
3. Privileges, auditing and identity representation for
NFSv4 . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4. Security Considerations . . . . . . . . . . . . . . . . . 21
5. IANA Considerations . . . . . . . . . . . . . . . . . . . 23
6. Normative References . . . . . . . . . . . . . . . . . . . 24
Author's Address . . . . . . . . . . . . . . . . . . . . . 25
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1. Introduction
The original RPCSEC_GSS protocol [RFC2203] provided for
authentication of RPC clients and servers to each other using the
Generic Security Services Application Programming Interface (GSS-API)
[RFC2743]. The second version of RPCSEC_GSS [add ref.] added support
for channel binding [RFC5056].
We find that GSS-API mechanisms are insufficient for communicating
certain aspects of a client's identity and authority to a server.
The GSS-API and its mechanisms certainly could be extended to address
this shortcomming, but it seems be far simpler to address it at the
application layer, namely, in this case, RPCSEC_GSS.
We therefore provide a new version of RPCSEC_GSS that allows for the
following:
o compound authentication of the client host and user to the server
(done by binding of two RPCSEC_GSS handles)
o channel binding (even though RPCSEC_GSSv2 provides this also; see
below)
o client-side assertions of authority:
* security labels (for multi-level, type enforcement, and other
labeled security models) [add refs. for labeled security]
* application-specific privileges
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
o client-side assertions of audit characteristics
* audit session ID
* audit selection mask
Assertions of labels, privilege and identity 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 also add an option for enumerating server-side domains of
interpretation (DOI), though this seems likely to be unnecessary.
RPCSEC_GSSv3 is patterned as follows:
o a client uses an existing RPCSEC_GSS context handle (of any
RPCSEC_GSS version) to protect RPCSEC_GSSv3 exchanges (this will
be termed the "parent" or "outer" handle)
o the server issues a "child" RPCSEC_GSSv3 handle, but the
underlying GSS-API security context for the parent handle is used
in all subsequent exchanges using the child handle (this works
because the RPCSEC_GSS handle is included in the integrity
protected RPCSEC_GSS auth/verifier header for all versions of
RPCSEC_GSS)
This means that RPCSEC_GSSv3 depends on RPCSEC_GSS versions 1 and/or
2 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.
1.1. Motivation
The initial motivation for RPCSEC_GSSv3 is to add support for labeled
security. Several alternatives to revising RPCSEC_GSS were
considered:
a. application-level protocol extensions, such as new operations for
the Network File System version 4 (NFSv4) protocol [RFC3530];
b. a stackable GSS-API pseudo-mechanism that could be composed with
concrete GSS-API mechanisms to provide both, authentication and
protected security label assertions;
c. per-GSS-API mechanism extensions for transporting security label
assertions;
Alternative (c) is not sufficiently general. One possible benefit of
(c) might be the ability to have per-{user, label} credentials,
though that might be difficult to manage (and, anyways, can be
emulated with regular GSS-API mechanisms through principal naming
conventions), whereas with the other approaches there is a single
credential per-user that can be used to assert multiple security
labels.
Alternative (a) is not general either, though for the purpose of the
NFSv4 community it would suffice. However, a solution at the
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RPCSEC_GSS or GSS-API layers does, or arguably should, fit more
naturally into most, if not all, NFSv4 implementations.
Alternative (b) is certainly general enough. In fact, it is more
general than the RPCSEC_GSSv3 solution in that it could be used in
non-RPC protocols that support the use of the GSS-API. However, the
RPCSEC_GSSv3 approach is attractively simple. For example, to pursue
(b) would likely entail having to specify a framework for mechanism
composition, as well as GSS-API interfaces to access assertions that
would typically be very platform-specific. (The KITTEN WG has
explored stackable pseudo-mechanisms in the past, but that work is
currently stagnant.) It is possible that stackable pseudo-mechanisms
may materialize in the future; such mechanisms would be usable
through all versions of RPCSEC_GSS so far.
As we considered these alternatives we also realized that we needed
other features that could all be packed into a single solution. For
example, the assertion of security label is conceptually equivalent,
protocol-wise, to assertions of privilege and identity.
Additionally, assertions need to be verified, and in this case the
one party that can verify an assertion is the client host, which can
authenticate to the server using its own credentials. Yet we want to
continue authenticating users as well. This calls for compound
authentication.
Finally, because the design of RPCSEC_GSSv3 relies on RPCSEC_GSSv1
(though v2 can also be used) to do the actual GSS-API security
context establishment, we add support for channel binding so that
implementors who have implemented RPCSEC_GSSv1 but not version 2 can
still provide channel binding without having to implement version 2.
Channel binding is accomplished in a more simple manner in v3 also.
1.2. Applications of RPCSEC_GSSv3
The common uses of RPCSEC_GSSv3, particularly for NFSv4, are expected
to be:
a. labeled security: client-side process label assertion [+
privilege assertion] + compound client host & user
authentication;
b. compound client host & user authentication [+ privilege
assertion];
c. client-side process credentials assertion [+ privilege assertion]
as a replacement for AUTH_SYS that is more secure than AUTH_SYS
while not requiring per-user credentials
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1.3. Conventions used in this document
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 [RFC2119].
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2. The RPCSEC_GSSv3 protocol
The following External Data Representation (XDR) [RFC4506]
definitions are used:
#define RPCSEC_GSS_VERS_3 3
enum rpc_gss3_proc_t {
RPCSEC_GSS3_DATA = 0,
RPCSEC_GSS3_LIST = 1,
RPCSEC_GSS3_CREATE = 2,
RPCSEC_GSS3_DESTROY = 3
};
struct {
rpc_gss3_proc_t gss_proc;
unsigned int seq_num;
rpc_gss_service_t service;
unsigned int handle_version;
opaque handle<>;
} rpc_gss_cred_vers_3_t;
struct {
int type;
bool critical;
opaque data<>;
} rpc_gss3_ext;
struct {
int type;
opaque assertion_data<>;
} rpc_gss3_assext;
struct {
unsigned int version;
opaque handle<>;
opaque nonce<>;
opaque mic<>;
} rpc_gss3_gss_binding;
typedef opaque rpc_gss3_chan_binding<>;
typedef opaque rpc_gss3_doi<>;
struct {
rpc_gss3_doi doi;
opaque label<>;
} rpc_gss3_label;
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typedef opaque rpc_gss3_privs<>;
typedef opaque rpc_gss3_name<>;
struct {
rpc_gss3_name *username;
rpc_gss3_name *groups<>;
rpc_gss3_name *groups_add<>;
rpc_gss3_name *groups_remove<>;
} rpc_gss3_id;
struct {
opaque clnt_session_id<>;
string clnt_audit_mask<>;
} rpc_gss3_audit;
enum rpc_gss3_assertion_type {
LABEL = 0,
PRIVS = 1,
IDENTITY = 2,
AUDIT = 3
};
union switch (rpc_gss3_assertion_type atype) {
case LABEL:
rpc_gss3_label label;
case PRIVILEGES:
rpc_gss3_privs privs;
case IDENTITY:
rpc_gss3_id id;
case AUDIT:
rpc_gss3_audit audit;
default:
rpc_gss3_assext ext;
} rpc_gss3_assertion_u;
struct {
bool critical;
rpc_gss3_assertion_u assertion;
} rpc_gss3_assertion;
struct {
rpc_gss3_gss_binding *compound_binding;
rpc_gss3_chan_binding *chan_binding_mic;
rpc_gss3_assertion assertions<>;
rpc_gss3_ext extensions<>;
} rpc_gss3_create_args;
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struct {
opaque handle<>;
rpc_gss3_chan_binding *chan_binding_mic;
rpc_gss3_assertion granted_assertions<>;
rpc_gss3_assertion server_assertions<>;
rpc_gss3_ext extensions<>;
} rpc_gss3_create_res;
enum rpc_gss3_list_item {
DOI = 0,
PRIV = 1,
PRIV_GROUP = 2
};
struct {
rpc_gss3_list_item list_what<>;
} rpc_gss3_list_args;
union switch (rpc_gss3_list_item itype) {
case DOI:
rpc_gss3_doi dois<>;
case PRIV:
string privs;
case PRIV_GROUP:
string priv_groups;
default:
opaque ext<>;
} rpc_gss3_list_item_u;
typedef rpc_gss3_list_item_u rpc_gss3_list_res<>;
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 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 presence of a field indicating the version of
RPCSEC_GSS used to established the context handle used, if any.
RPC data messages using RPCSEC_GSSv3 context handles differ from
RPCSEC_GSSv1 only in that the version number used MUST be '3' instead
of '1' and, as described above, in that there is one more field in
the RPCSEC_GSS header to name the version of RPCSEC_GSS used to
establish the context handle used to protect this message. All other
protocol elements from RPCSEC_GSSv1-protected RPC data messages MUST
remain the same in v3 as in v1.
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RPCSEC_GSSv3 control messages are the same as RPCSEC_GSSv3 data
messages, but with a gss_proc value that indicates a control message
is contained in the data payload.
2.1. Control messages
There are two RPCSEC_GSSv3 control messages: RPCSEC_GSS3_CREATE and
RPCSEC_GSS3_LIST.
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)
o rpc_gss_svc_integrity
o rpc_gss_svc_privacy
Specifically the client MUST NOT use rpc_gss_svc_none.
2.1.1. New auth_stat values
RPCSEC_GSSv3 requires the addition of several values to the auth_stat
enumerated type definition:
enum auth_stat {
...
/*
* RPCSEC_GSS errors
*/
RPCSEC_GSS3_COMPOUND_PROBEM = <TBD>,
RPCSEC_GSS3_LABEL_PROBLEM = <TBD>,
RPCSEC_GSS3_IDENTITY_PROBLEM = <TBD>
RPCSEC_GSS3_UNKNOWN_ASSERTION = <TBD>
RPCSEC_GSS3_UNKNOWN_EXTENSION = <TBD>
RPCSEC_GSS3_UNKNOWN_MESSAGE = <TBD>
};
2.1.2. Create request
The RPCSEC_GSS3_CREATE call message consists of inputs to bind into a
new RPCSEC_GSSv3 handle. The context handle used to protect the
RPCSEC_GSS3_CREATE call message is termed the "parent" (or "outer")
handle. The reply to this message consists of either an error or a
new RPCSEC_GSSv3 handle, termed the "child" handle.
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All uses of a child context handle MUST use the GSS-API security
context associated with the parent context handle of the
RPCSEC_GSS3_CREATE request that produced the child context handle.
The child context, however, has its own sequence number space and
window, distinct from that of the parent.
As described in the introduction, 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
o a channel binding
o authorization assertions (label, privileges)
o identity assertions
Servers MUST either ignore, reject or apply policy to the
authorization and identity assertions. Policies should take into
account the identity of the client and/or user as authenticated via
the GSS-API. Server implementation and policy MAY result in labels,
privileges and identities being mapped to concepts and values that
are local to the server.
2.1.2.1. Compound authentication
RPCSEC_GSSv3 allows for compound authentication of client hosts and
users to servers. This is done by using an integrity protected
RPCSEC_GSSv3 message of RPCSEC_GSS3_CREATE type which includes a
reference to the context handle to bind, a nonce and a MIC of that
nonce using the GSS-API security context associated with the named
context handle. We'll term the two context handles "parent" (or
"outer") and "inner," and the resulting context handle the "child"
handle, where the outer context handle is the context handle
providing integrity protection to the RPCSEC_GSS3_CREATE message, and
the inner context handle is the one referenced via the
compound_binding field of the RPCSEC_GSS3_CREATE arguments structure
(rpc_gss3_create_args).
All uses of a child context handle that is bound to an inner context
MUST be treated as speaking for the initiator principal (as modified
by any assertions in the RPCSEC_GSS3_CREATE message) of the inner
context handle's GSS-API security context.
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
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refuse to grant requested authority to a user acting alone (e.g., via
an unprivileged user-space program), but may grant requested
authority to a client acting on behalf of a user if the server 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 outer
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
authenticates a user. The reverse (outer 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
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 as modified by any identity assertions by
the client in the same RPCSEC_GSS3_CREATE request that the server
accepts.
2.1.2.2. Channel binding
RPCSEC_GSSv3 provides a different way to do channel binding that
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 [RFC5056], then the client calls GSS_GetMIC() to get a MIC of
resulting octet string, using the outer 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).
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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
(if the client really wanted channel binding) it MUST call
RPCSEC_GSS3_DESTROY.
As per-RPCSEC_GSSv2:
o "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".
o ...
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.
2.1.2.3. Label assertions
RPCSEC_GSSv3 clients MAY assert a security label in some DOI 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 DOI and label.
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Label encoding is specific to each DOI and not described herein. DOI
encoding is <TBD> [fill in... Solaris uses integers to name DOIs,
and there is an IANA registry of DOIs as 32-bit integers, and IPsec
(whence the IANA registry) and CALIPSO use 32-bit integers for DOIs
as well. So a 32-bit unsinged integer seems to be the way to go.
Add references... -Nico]
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.
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 don't support labeling MUST ignore non-critical label
assertions. Servers that don't support the requested DOI MUST either
ignore non-critical label assertions or map them to a suitable label
in a supported DOI. Servers that don't support labeling or don't
support the requested DOI MUST return an error if the label request
is critical. Servers that support labeling in the requested DOI MAY
map the requested label to different label as a result of server-side
policy evaluation.
2.1.2.4. Privilege assertions
Privilege assertions are similar to label assertions, except that
there is no DOI, and the privileges supported are specified by the
RPC application.
Privileges are encoded US-ASCII strings containing comma-separated
privilege names, as well as up to one privilege group name and zero
or more exclusions, where each exclusion is a privilege name or
privilege group name prefixed with an exclamation point. Two special
privilege group names are defined hereing: "all" (which represents
all possible privileges) and "basic" (which represents privileges
normally granted to all users).
RPC applications that wish to use this facility must define the set
of known privileges, and must specify which privileges are in the
"basic" privilege group. For example, NFSv4 might specify privileges
for reading, writing, chowning, linking, etcetera.
2.1.2.5. Identity assertions
Identity assertions can be used either to modify the set of groups
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assigned on the server-side to a given user (authenticated by the
GSS-API) or to implement an AUTH_SYS-like [RFC1831]. In the latter
case the client specifies at least a user-name and possibly groups
that it thinks the user belongs to.
Clients may set a username, a group list, and/or lists of groups to
be added or removed from the group list that the server would
normally use for the given user.
The server MUST decide whether to accept identity assertions by
applying local policy. Such policies is not described herein.
Example policies:
o "always accept identity assertions"
o "always accept identity assertions where the identities are
understood"
o "accept identity assertions ... only from trusted clients" (where
the identity of the client is taken from the initiator principal
of the outer context handle's GSS-API security context, or from
the network address of the client...)
o "accept identity assertions ... only from trusted clients where
IPsec policy protects this application's packet flows between the
clients and this server"
o "accept only removals of groups from a user's group membership
list as determined by the server"
o "never accept identity assertions"
o etcetera
Clients may mark an identity assertion as being critical, in which
case the server MUST respond with an error if the server does not
accept the identity assertion as-is.
The representation of users and groups is not given here, but is left
to the application. It is expected that RPCSEC_GSSv3 identity
assertions in the context of the NFSv4 application would consist of
NFSv4 user and group representations as used on the wire in NFSv4
access control lists (ACLs).
2.1.2.6. Audit assertions
Audit characteristics assertions allow a client to inform the server
what the client-side audit ID of a users' processes is, and what
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operations are being audited on the client-side. The audit ID is
opaque. The operations to be audited as specified as a set of
application protocol specific operations, encoded as a comma-
separated list of operations, as with privileges -- this is called an
"auditing mask".
Servers that support auditing MUST work out an appropriate "auditing
mask" for a given client/user or else MUST have a global mask, and
servers SHOULD add to that mask any operations in the client-asserted
mask that are not in the server's.
2.1.2.7. Server assertions
Servers MAY inform clients of assertions were granted by setting the
'granted_assertions' field of the RPCSEC_GSS3_CREATE reply.
The protocol provides a field ('server_assertions') for servers to
make assertions about themselves. At this time there is not much use
for this field, though servers MAY assert a single security label,
indicating that all contents on the server is at that label. The
client MUST, of course, either evaluate or ignore any server-side
assertions.
2.1.3. Context handle destruction
The RPCSEC_GSS3_DESTROY procedure is the same as for RPCSEC_GSSv1,
but with the version 3 header.
2.1.4. List request
The RPCSEC_GSS3_LIST call message consists of a single integer
indicating what should be listed, and the reply consists of an error
or the requested list.
The client may list DOIs, privilege names, or privilege group names.
The result is an opaque octet string containing a list of DOIs
[encoding <TBD>] or a US-ASCII string containing a comma-separated
list of privilege names or privilege group names.
2.1.5. 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.
New fields may be added through the 'extensions' typed hole. All
such extensions have a 'critical' flag.
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New message types may be added.
Clients receiving unknown critical server assertions MUST destroy the
established RPCSEC_GSSv3 context handle. Servers receiving unknown
critical client assertions or unknown RPCSEC_GSS_v3 extensions MUST
return an error.
There is no IANA or other registry for RPCSEC_GSSv3 extensions. All
extensions MUST be done by IETF Protocol Action.
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3. Privileges, auditing and identity representation for NFSv4
The representation of users and groups for use in identity assertions
in RPCSEC_GSSv3 SHALL be the same as the user and group
representations used by NFSv4 for access control list subjects on the
wire, cast as an octet string ("opaque").
The following privileges are defined for use with the NFSv4 protocol:
file_chown Generally allows the caller to change a file's owner
regardless of who owns the file.
file_chown_self Generally allows the caller to change the owner of a
file it owns.
file_dac_execute Generally allows the caller to read any file for
execution. There's little difference between file_dac_execute and
file_dac_read from the server's perspective.
file_dac_read Generally allows the caller to read any file or
directory.
file_dac_search Generally allows the caller to search any directory.
file_dac_write Generally allows the caller to write to any file (or
create/delete/link objects in directories).
file_link_any Generally allows the caller to create hardlinks to
files not owned by the caller.
file_owner Generally allows the caller to modify the access,
modification and other timestamps of a filesystem object, as well
as its permissions and ACL.
file_setid Generally allows the caller to set the set-user-ID and
set-group-ID bits of a file.
file_downgrade_sl Generally allows the caller to downgrade the
security label of a filesystem object.
file_update_sl Generally allows the caller to upgrade the security
label of a filesystem object.
The operations that may appear in an auditing mask for NFSv4 are:
lookup [To be described as it relates to NFSv4 ops.]
open [To be described as it relates to NFSv4 ops.]
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create [To be described as it relates to NFSv4 ops.]
mkdir [To be described as it relates to NFSv4 ops.]
rmdir [To be described as it relates to NFSv4 ops.]
link [To be described as it relates to NFSv4 ops.]
unlink [To be described as it relates to NFSv4 ops.]
symlink [To be described as it relates to NFSv4 ops.]
rename [To be described as it relates to NFSv4 ops.]
truncate [To be described as it relates to NFSv4 ops.]
read [To be described as it relates to NFSv4 ops.]
readdir [To be described as it relates to NFSv4 ops.]
write [To be described as it relates to NFSv4 ops.]
setattr [To be described as it relates to NFSv4 ops.]
getattr [To be described as it relates to NFSv4 ops.]
... ...
[What about NFSv3? The representation of privs would be the same for
v3 as for v4, though there'd be no privs for dealing with labels
(file_downgrade_sl and file_update_sl). And the representation of
users/groups would NFSv3's representation thereof. But should we
bother to specify this? -Nico]
[Also, this is derived from Solaris' notion of privileges. We should
look at how well this scheme relates to other operating systems as
NFSv4 clients and servers. -Nico]
The contents of the 'basic' privilege set is not defined herein.
Note that 'file_link_any' and 'file_chown_self' may be present in the
server's notion of the basic privilege set.
The NFSv4-specific privileges may be limited by the server in ways
not specified above. For example, the server may deny access for
certain operations that would normally be granted given the granted
assertion of a given privilege (e.g., "no one may write to files
owned by such and such user"), or the server may require that all
privileges be asserted (and granted, of course) in order to allow
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certain operations (e.g., "all privileges are required in order to
write to files owned by such and such user, not just
file_dac_write").
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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 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 (and
extensions), 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.
The RPCSEC_GSSv3 protocol also provides for a replacement of the old
AUTH_SYS RPC authentication flavor. AUTH_SYS relies on "privileged
port numbers" for "authentication," and was quite limited in what
assertions it supported and incompatible with NFSv4 representations
of identity. To replace AUTH_SYS with RPCSEC_GSSv3 simply use a GSS-
API mechanism to authenticate the client (but not the user) and let
the client assert the user's identity. This is more secure than
AUTH_SYS in that at least the client can be strongly authenticated
using GSS-API mechanisms, and it is more functional than AUTH_SYS in
that identity representations are defined by the application layer.
It is possible that a GSS-API mechanism that does not provide any
security services could be created so as to make it possible to
replace AUTH_SYS with RPCSEC_GSSv3 while retaining the same
privileged port semantics. Such a mechanism is out of scope for this
document and would have its own security considerations.
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
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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. [Add text about interaction with
GSS-SSV...]
[Anything else?]
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5. IANA Considerations
There are no IANA considerations in this document.
TBDs in this document will be assigned by the ONC RPC registrart
(which is not IANA, as I recall).
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6. Normative References
[RFC1831] Srinivasan, R., "RPC: Remote Procedure Call Protocol
Specification Version 2", RFC 1831, August 1995.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2203] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
Specification", RFC 2203, September 1997.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC3530] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
Beame, C., Eisler, M., and D. Noveck, "Network File System
(NFS) version 4 Protocol", RFC 3530, April 2003.
[RFC4506] Eisler, M., "XDR: External Data Representation Standard",
STD 67, RFC 4506, May 2006.
[RFC5056] Williams, N., "On the Use of Channel Bindings to Secure
Channels", RFC 5056, November 2007.
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Author's Address
Nicolas Williams
Sun Microsystems
5300 Riata Trace Ct
Austin, TX 78727
US
Email: [email protected]
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