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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (June 14, 2011) is 4671 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: '9' is defined on line 975, but no explicit reference was found in the text -- Possible downref: Non-RFC (?) normative reference: ref. '1' ** Obsolete normative reference: RFC 1831 (ref. '4') (Obsoleted by RFC 5531) == Outdated reference: A later version (-35) exists of draft-ietf-nfsv4-rfc3530bis-09 ** Obsolete normative reference: RFC 5226 (ref. '8') (Obsoleted by RFC 8126) ** Obsolete normative reference: RFC 5661 (ref. '9') (Obsoleted by RFC 8881) Summary: 4 errors (**), 0 flaws (~~), 10 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 NFSv4 T. Haynes 3 Internet-Draft NetApp 4 Intended status: Standards Track N. Williams 5 Expires: December 16, 2011 Cryptonector 6 June 14, 2011 8 Remote Procedure Call (RPC) Security Version 3 9 draft-ietf-nfsv4-rpcsec-gssv3-00.txt 11 Abstract 13 This document specifies version 3 of the Remote Procedure Call (RPC) 14 security protocol (RPCSEC_GSS). This protocol provides for: compound 15 authentication of client hosts and users to server (constructed by 16 generic composition), channel binding, security label assertions for 17 multi-level and type enforcement, privilege assertions and identity 18 assertions. 20 Requirements Language 22 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 23 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 24 document are to be interpreted as described in RFC 2119 [1]. 26 Status of this Memo 28 This Internet-Draft is submitted to IETF in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF), its areas, and its working groups. Note that 33 other groups may also distribute working documents as Internet- 34 Drafts. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 The list of current Internet-Drafts can be accessed at 42 http://www.ietf.org/ietf/1id-abstracts.txt. 44 The list of Internet-Draft Shadow Directories can be accessed at 45 http://www.ietf.org/shadow.html. 47 This Internet-Draft will expire on December 16, 2011. 49 Copyright Notice 51 Copyright (c) 2011 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (http://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the BSD License. 64 This document may contain material from IETF Documents or IETF 65 Contributions published or made publicly available before November 66 10, 2008. The person(s) controlling the copyright in some of this 67 material may not have granted the IETF Trust the right to allow 68 modifications of such material outside the IETF Standards Process. 69 Without obtaining an adequate license from the person(s) controlling 70 the copyright in such materials, this document may not be modified 71 outside the IETF Standards Process, and derivative works of it may 72 not be created outside the IETF Standards Process, except to format 73 it for publication as an RFC or to translate it into languages other 74 than English. 76 Table of Contents 78 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 79 1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4 80 1.2. Applications of RPCSEC_GSSv3 . . . . . . . . . . . . . . . 5 81 2. The RPCSEC_GSSv3 protocol . . . . . . . . . . . . . . . . . . 5 82 2.1. Control messages . . . . . . . . . . . . . . . . . . . . . 11 83 2.1.1. New auth_stat values . . . . . . . . . . . . . . . . . 11 84 2.1.2. Create request . . . . . . . . . . . . . . . . . . . . 11 85 2.1.3. Context handle destruction . . . . . . . . . . . . . . 17 86 2.1.4. List request . . . . . . . . . . . . . . . . . . . . . 17 87 2.1.5. Extensibility . . . . . . . . . . . . . . . . . . . . 17 88 3. Privileges and identity representation for NFSv4 . . . . . . . 18 89 4. Security Considerations . . . . . . . . . . . . . . . . . . . 19 90 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 91 6. Normative References . . . . . . . . . . . . . . . . . . . . . 20 92 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 21 93 Appendix B. RFC Editor Notes . . . . . . . . . . . . . . . . . . 21 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 96 1. Introduction 98 The original RPCSEC_GSS protocol [2] provided for authentication of 99 RPC clients and servers to each other using the Generic Security 100 Services Application Programming Interface (GSS-API) [3]. The second 101 version of RPCSEC_GSS [4] added support for channel binding [5]. 103 We find that GSS-API mechanisms are insufficient for communicating 104 certain aspects of a client's identity and authority to a server. 105 The GSS-API and its mechanisms certainly could be extended to address 106 this shortcomming, but it seems be far simpler to address it at the 107 application layer, namely, in this case, RPCSEC_GSS. 109 We therefore provide a new version of RPCSEC_GSS that allows for the 110 following: 112 o compound authentication of the client host and user to the server 113 (done by binding of two RPCSEC_GSS handles) 115 o channel binding (even though RPCSEC_GSSv2 provides this also; see 116 below) 118 o client-side assertions of authority: 120 * security labels (for multi-level, type enforcement, and other 121 labeled security models) [add refs. for labeled security] 123 * application-specific privileges 125 o client-side assertions of identity: 127 * primary client/user identity 129 * supplementary group memberships of the client/user, including 130 support for specifying deltas to the membership list as seen on 131 the server 133 Assertions of labels, privilege and identity are evaluated by the 134 server, which may then map the asserted values to other values, all 135 according to server-side policy. 137 We also add an option for enumerating server-side domains of 138 interpretation (DOI), though this seems likely to be unnecessary. 140 RPCSEC_GSSv3 is patterned as follows: 142 o a client uses an existing RPCSEC_GSS context handle (of any 143 RPCSEC_GSS version) to protect RPCSEC_GSSv3 exchanges (this will 144 be termed the "parent" or "outer" handle) 146 o the server issues a "child" RPCSEC_GSSv3 handle, but the 147 underlying GSS-API security context for the parent handle is used 148 in all subsequent exchanges using the child handle (this works 149 because the RPCSEC_GSS handle is included in the integrity 150 protected RPCSEC_GSS auth/verifier header for all versions of 151 RPCSEC_GSS) 153 This means that RPCSEC_GSSv3 depends on RPCSEC_GSS versions 1 and/or 154 2 for actual GSS-API security context establishment. This keeps the 155 specification of RPCSEC_GSSv3 simple by avoiding the need to 156 duplicate the core functionality of RPCSEC_GSS version 1. 158 1.1. Motivation 160 The initial motivation for RPCSEC_GSSv3 is to add support for labeled 161 security. Several alternatives to revising RPCSEC_GSS were 162 considered: 164 a. application-level protocol extensions, such as new operations for 165 the Network File System version 4 (NFSv4) protocol [6]; 167 b. a stackable GSS-API pseudo-mechanism that could be composed with 168 concrete GSS-API mechanisms to provide both, authentication and 169 protected security label assertions; 171 c. per-GSS-API mechanism extensions for transporting security label 172 assertions; 174 Alternative (c) is not sufficiently general. One possible benefit of 175 (c) might be the ability to have per-{user, label} credentials, 176 though that might be difficult to manage (and, anyways, can be 177 emulated with regular GSS-API mechanisms through principal naming 178 conventions), whereas with the other approaches there is a single 179 credential per-user that can be used to assert multiple security 180 labels. 182 Alternative (a) is not general either, though for the purpose of the 183 NFSv4 community it would suffice. However, a solution at the 184 RPCSEC_GSS or GSS-API layers does, or arguably should, fit more 185 naturally into most, if not all, NFSv4 implementations. 187 Alternative (b) is certainly general enough. In fact, it is more 188 general than the RPCSEC_GSSv3 solution in that it could be used in 189 non-RPC protocols that support the use of the GSS-API. However, the 190 RPCSEC_GSSv3 approach is attractively simple. For example, to pursue 191 (b) would likely entail having to specify a framework for mechanism 192 composition, as well as GSS-API interfaces to access assertions that 193 would typically be very platform-specific. (The KITTEN WG has 194 explored stackable pseudo-mechanisms in the past, but that work is 195 currently stagnant.) It is possible that stackable pseudo-mechanisms 196 may materialize in the future; such mechanisms would be usable 197 through all versions of RPCSEC_GSS so far. 199 As we considered these alternatives we also realized that we needed 200 other features that could all be packed into a single solution. For 201 example, the assertion of security label is conceptually equivalent, 202 protocol-wise, to assertions of privilege and identity. 204 Additionally, assertions need to be verified, and in this case the 205 one party that can verify an assertion is the client host, which can 206 authenticate to the server using its own credentials. Yet we want to 207 continue authenticating users as well. This calls for compound 208 authentication. 210 Finally, because the design of RPCSEC_GSSv3 relies on RPCSEC_GSSv1 211 (though v2 can also be used) to do the actual GSS-API security 212 context establishment, we add support for channel binding so that 213 implementors who have implemented RPCSEC_GSSv1 but not version 2 can 214 still provide channel binding without having to implement version 2. 215 Channel binding is accomplished in a more simple manner in v3 also. 217 1.2. Applications of RPCSEC_GSSv3 219 The common uses of RPCSEC_GSSv3, particularly for NFSv4, are expected 220 to be: 222 a. labeled security: client-side process label assertion [+ 223 privilege assertion] + compound client host & user 224 authentication; 226 b. compound client host & user authentication [+ privilege 227 assertion]; 229 c. client-side process credentials assertion [+ privilege assertion] 230 as a replacement for AUTH_SYS that is more secure than AUTH_SYS 231 while not requiring per-user credentials 233 2. The RPCSEC_GSSv3 protocol 235 This document contains the External Data Representation (XDR) ([7]) 236 definitions for the RPCSEC_GSSv3 protocol. 238 The XDR description is provided in this document in a way that makes 239 it simple for the reader to extract into ready to compile form. The 240 reader can feed this document in the following shell script to 241 produce the machine readable XDR description of RPCSEC_GSSv3: 243 #!/bin/sh 244 grep "^ *///" | sed 's?^ */// ??' | sed 's?^ *///$??' 246 I.e. if the above script is stored in a file called "extract.sh", and 247 this document is in a file called "spec.txt", then the reader can do: 249 sh extract.sh < spec.txt > rpcsec_gss_v3.x 251 The effect of the script is to remove leading white space from each 252 line, plus a sentinel sequence of "///". 254 The XDR description, with the sentinel sequence follows: 256 /// /* 257 /// * Copyright (c) 2011 IETF Trust and the persons 258 /// * identified as the document authors. All rights 259 /// * reserved. 260 /// * 261 /// * The document authors are identified in [RFC2203], 262 /// * [RFC5403], and [RFCxxxx]. 263 /// * 264 /// * Redistribution and use in source and binary forms, 265 /// * with or without modification, are permitted 266 /// * provided that the following conditions are met: 267 /// * 268 /// * o Redistributions of source code must retain the above 269 /// * copyright notice, this list of conditions and the 270 /// * following disclaimer. 271 /// * 272 /// * o Redistributions in binary form must reproduce the 273 /// * above copyright notice, this list of 274 /// * conditions and the following disclaimer in 275 /// * the documentation and/or other materials 276 /// * provided with the distribution. 277 /// * 278 /// * o Neither the name of Internet Society, IETF or IETF 279 /// * Trust, nor the names of specific contributors, may be 280 /// * used to endorse or promote products derived from this 281 /// * software without specific prior written permission. 282 /// * 283 /// * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 284 /// * AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED 285 /// * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 286 /// * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 287 /// * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO 288 /// * EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 289 /// * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 290 /// * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 291 /// * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 292 /// * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 293 /// * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 294 /// * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 295 /// * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING 296 /// * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 297 /// * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 298 /// */ 299 /// 300 /// /* 301 /// * This code was derived from [RFC2203]. Please 302 /// * reproduce this note if possible. 303 /// */ 304 /// 305 /// /* 306 /// * rpcsec_gss_v3.x 307 /// */ 308 /// 309 /// enum rpc_gss_service_t { 310 /// /* Note: the enumerated value for 0 is reserved. */ 311 /// rpc_gss_svc_none = 1, 312 /// rpc_gss_svc_integrity = 2, 313 /// rpc_gss_svc_privacy = 3, 314 /// rpc_gss_svc_channel_prot = 4 315 /// }; 316 /// 317 /// enum rpc_gss_proc_t { 318 /// RPCSEC_GSS_DATA = 0, 319 /// RPCSEC_GSS_INIT = 1, 320 /// RPCSEC_GSS_CONTINUE_INIT = 2, 321 /// RPCSEC_GSS_DESTROY = 3, 322 /// RPCSEC_GSS_BIND_CHANNEL = 4 323 /// }; 324 /// 325 /// struct rpc_gss_cred_vers_1_t { 326 /// rpc_gss_proc_t gss_proc; /* control procedure */ 327 /// unsigned int seq_num; /* sequence number */ 328 /// rpc_gss_service_t service; /* service used */ 329 /// opaque handle<>; /* context handle */ 330 /// }; 331 /// 332 /// enum rpc_gss3_proc_t { 333 /// RPCSEC_GSS3_DATA = 0, 334 /// RPCSEC_GSS3_LIST = 5, 335 /// RPCSEC_GSS3_CREATE = 6, 336 /// RPCSEC_GSS3_DESTROY = 7 337 /// }; 338 /// 339 /// struct rpc_gss_cred_vers_3_t { 340 /// rpc_gss3_proc_t gss_proc; 341 /// unsigned int seq_num; 342 /// rpc_gss_service_t service; 343 /// opaque handle<>; 344 /// unsigned int handle_version; 345 /// }; 346 /// 347 /// const RPCSEC_GSS_VERS_1 = 1; 348 /// const RPCSEC_GSS_VERS_2 = 2; 349 /// const RPCSEC_GSS_VERS_3 = 3; /* new */ 350 /// 351 /// union rpc_gss_cred_t switch (unsigned int rgc_version) { 352 /// case RPCSEC_GSS_VERS_1: 353 /// case RPCSEC_GSS_VERS_2: 354 /// rpc_gss_cred_vers_1_t rgc_cred_v1; 355 /// case RPCSEC_GSS_VERS_3: /* new */ 356 /// rpc_gss_cred_vers_3_t rgc_cred_v3; 357 /// }; 358 /// 359 /// const MAXSEQ = 0x80000000; 360 /// 361 /// struct rpc_gss3_extension { 362 /// int type; 363 /// bool critical; 364 /// opaque data<>; 365 /// }; 366 /// 367 /// struct rpc_gss3_gss_binding { 368 /// unsigned int vers; 369 /// opaque handle<>; 370 /// opaque nonce<>; 371 /// opaque mic<>; 372 /// }; 373 /// 374 /// typedef opaque rpc_gss3_chan_binding<>; 375 /// 376 /// typedef opaque rpc_gss3_doi<>; 377 /// struct rpc_gss3_label { 378 /// rpc_gss3_doi doi; 379 /// opaque label<>; 380 /// }; 381 /// 382 /// typedef opaque rpc_gss3_privs<>; 383 /// 384 /// typedef opaque rpc_gss3_name<>; 385 /// 386 /// typedef rpc_gss3_name rpc_gss3_group_list<>; 387 /// struct rpc_gss3_id { 388 /// rpc_gss3_name *username; 389 /// rpc_gss3_group_list *groups; 390 /// rpc_gss3_group_list groups_add; 391 /// rpc_gss3_group_list groups_remove; 392 /// }; 393 /// 394 /// enum rpc_gss3_assertion_type { 395 /// LABEL = 0, 396 /// PRIVS = 1, 397 /// IDENTITY = 2 398 /// }; 399 /// 400 /// union rpc_gss3_assertion_u 401 /// switch (rpc_gss3_assertion_type atype) { 402 /// case LABEL: 403 /// rpc_gss3_label label; 404 /// case PRIVILEGES: 405 /// rpc_gss3_privs privs; 406 /// case IDENTITY: 407 /// rpc_gss3_id id; 408 /// default: 409 /// opaque ext<>; 410 /// }; 411 /// 412 /// struct rpc_gss3_assertion { 413 /// bool critical; 414 /// rpc_gss3_assertion_u assertion; 415 /// }; 416 /// 417 /// struct rpc_gss3_create_args { 418 /// rpc_gss3_gss_binding *compound_binding; 419 /// rpc_gss3_chan_binding *chan_binding_mic; 420 /// rpc_gss3_assertion assertions<>; 421 /// rpc_gss3_extension extensions<>; 422 /// }; 423 /// 424 /// struct rpc_gss3_create_res { 425 /// opaque handle<>; 426 /// rpc_gss3_chan_binding *chan_binding_mic; 427 /// rpc_gss3_assertion granted_assertions<>; 428 /// rpc_gss3_assertion assertions_denied<>; 429 /// rpc_gss3_assertion assertions_not_understood<>; 430 /// rpc_gss3_assertion server_assertions<>; 431 /// rpc_gss3_extension extensions<>; 432 /// }; 433 /// 434 /// enum rpc_gss3_list_item { 435 /// DOI = 0, 436 /// PRIV = 1, 437 /// PRIV_GROUP = 2 438 /// }; 439 /// 440 /// struct rpc_gss3_list_args { 441 /// rpc_gss3_list_item list_what<>; 442 /// }; 443 /// 444 /// union rpc_gss3_list_item_u 445 /// switch (rpc_gss3_list_item itype) { 446 /// case DOI: 447 /// rpc_gss3_doi dois<>; 448 /// case PRIV: 449 /// string privs<>; 450 /// case PRIV_GROUP: 451 /// string priv_groups<>; 452 /// default: 453 /// opaque ext<>; 454 /// }; 455 /// 456 /// typedef rpc_gss3_list_item_u rpc_gss3_list_res<>; 458 The rpc_gss_cred_vers_3_t type is used in much the same way that 459 rpc_gss_cred_vers_1_t is used in RPCSEC_GSSv1, that is: as the arm of 460 the rpc_gss_cred_t discriminated union corresponding to version 3 461 (RPCSEC_GSS_VERS_3). It differs from rpc_gss_cred_vers_1_t in that: 463 a. the values for gss_proc corresponding to control messages are 464 different, 466 b. the presence of a field indicating the version of RPCSEC_GSS used 467 to established the context handle used, if any. 469 RPC data messages using RPCSEC_GSSv3 context handles differ from 470 RPCSEC_GSSv1 only in that the version number used MUST be '3' instead 471 of '1' and, as described above, in that there is one more field in 472 the RPCSEC_GSS header to name the version of RPCSEC_GSS used to 473 establish the context handle used to protect this message. All other 474 protocol elements from RPCSEC_GSSv1-protected RPC data messages MUST 475 remain the same in v3 as in v1. 477 RPCSEC_GSSv3 control messages are the same as RPCSEC_GSSv3 data 478 messages, but with a gss_proc value that indicates a control message 479 is contained in the data payload. 481 2.1. Control messages 483 There are two RPCSEC_GSSv3 control messages: RPCSEC_GSS3_CREATE and 484 RPCSEC_GSS3_LIST. 486 The client MUST use one of the following security services to protect 487 any RPCSEC_GSSv3 control message: 489 o rpc_gss_svc_channel_prot (see RPCSEC_GSSv2) 491 o rpc_gss_svc_integrity 493 o rpc_gss_svc_privacy 495 Specifically the client MUST NOT use rpc_gss_svc_none. 497 2.1.1. New auth_stat values 499 RPCSEC_GSSv3 requires the addition of several values to the auth_stat 500 enumerated type definition: 502 enum auth_stat { 503 ... 504 /* 505 * RPCSEC_GSS errors 506 */ 507 RPCSEC_GSS3_COMPOUND_PROBEM = <>, 508 RPCSEC_GSS3_LABEL_PROBLEM = <>, 509 RPCSEC_GSS3_IDENTITY_PROBLEM = <> 510 RPCSEC_GSS3_UNKNOWN_ASSERTION = <> 511 RPCSEC_GSS3_UNKNOWN_EXTENSION = <> 512 RPCSEC_GSS3_UNKNOWN_MESSAGE = <> 513 }; 515 XXX: fix above into YYY. All the entries are TBD... 517 2.1.2. Create request 519 The RPCSEC_GSS3_CREATE call message consists of inputs to bind into a 520 new RPCSEC_GSSv3 handle. The context handle used to protect the 521 RPCSEC_GSS3_CREATE call message is termed the "parent" (or "outer") 522 handle. The reply to this message consists of either an error or a 523 new RPCSEC_GSSv3 handle, termed the "child" handle. 525 All uses of a child context handle MUST use the GSS-API security 526 context associated with the parent context handle of the 527 RPCSEC_GSS3_CREATE request that produced the child context handle. 528 The child context, however, has its own sequence number space and 529 window, distinct from that of the parent. 531 As described in the introduction, the RPCSEC_GSS3_CREATE call message 532 binds one or more items of several kinds into a new RPCSEC_GSSv3 533 context handle: 535 o another RPCSEC_GSS (version 1, 2, or 3) context handle 537 o a channel binding 539 o authorization assertions (label, privileges) 541 o identity assertions 543 Servers MUST either ignore, reject or apply policy to the 544 authorization and identity assertions. Policies should take into 545 account the identity of the client and/or user as authenticated via 546 the GSS-API. Server implementation and policy MAY result in labels, 547 privileges and identities being mapped to concepts and values that 548 are local to the server. 550 2.1.2.1. Compound authentication 552 RPCSEC_GSSv3 allows for compound authentication of client hosts and 553 users to servers. This is done by using an integrity protected 554 RPCSEC_GSSv3 message of RPCSEC_GSS3_CREATE type which includes a 555 reference to the context handle to bind, a nonce and a MIC of that 556 nonce using the GSS-API security context associated with the named 557 context handle. We'll term the two context handles "parent" (or 558 "outer") and "inner," and the resulting context handle the "child" 559 handle, where the outer context handle is the context handle 560 providing integrity protection to the RPCSEC_GSS3_CREATE message, and 561 the inner context handle is the one referenced via the 562 compound_binding field of the RPCSEC_GSS3_CREATE arguments structure 563 (rpc_gss3_create_args). 565 All uses of a child context handle that is bound to an inner context 566 MUST be treated as speaking for the initiator principal (as modified 567 by any assertions in the RPCSEC_GSS3_CREATE message) of the inner 568 context handle's GSS-API security context. 570 This feature is needed, for example, when a client wishes to use 571 authority assertions that the server may only grant if a user and a 572 client are authenticated together to the server. Thus a server may 573 refuse to grant requested authority to a user acting alone (e.g., via 574 an unprivileged user-space program), but may grant requested 575 authority to a client acting on behalf of a user if the server trusts 576 the client. 578 It is assumed that an unprivileged user-space program would not have 579 access to client host credentials needed to establish a GSS-API 580 security context authenticating the client to the server, therefore 581 an unprivileged user-space program could not create an RPCSEC_GSSv3 582 RPCSEC_GSS3_CREATE message that successfully binds a client and a 583 user security context. 585 Clients using RPCSEC_GSS context binding MUST use, as the outer 586 context handle, an RPCSEC_GSS context handle that corresponds to a 587 GSS-API security context that authenticates the client host, and for 588 the inner context handle it SHOULD use a context handle to 589 authenticates a user. The reverse (outer handle authenticates user, 590 inner authenticates client) MUST NOT be used. Other compounds might 591 eventually make sense. 593 An RPCSEC_GSSv3 context handle that is bound to another RPCSEC_GSS 594 context MUST be treated by servers as authenticating the GSS-API 595 initiator principal authenticated by the inner context handle's GSS- 596 API security context. This principal may be mapped to a server-side 597 notion of user or principal as modified by any identity assertions by 598 the client in the same RPCSEC_GSS3_CREATE request that the server 599 accepts. 601 2.1.2.2. Channel binding 603 RPCSEC_GSSv3 provides a different way to do channel binding than 604 RPCSEC_GSSv2. Specifically: 606 a. RPCSEC_GSSv3 builds on RPCSEC_GSSv1 by reusing existing, 607 established context handles rather than providing a different RPC 608 security flavor for establishing context handles, 610 b. channel bindings data are not hashed because the community now 611 agrees that it is the secure channel's responsibility to produce 612 channel bindings data of manageable size. 614 (a) is useful in keeping RPCSEC_GSSv3 simple in general, not just for 615 channel binding. (b) is useful in keeping RPCSEC_GSSv3 simple 616 specifically for channel binding. 618 Channel binding is accomplished as follows. The client prefixes the 619 channel bindings data octet string with the channel type as described 620 in [5], then the client calls GSS_GetMIC() to get a MIC of resulting 621 octet string, using the outer RPCSEC_GSS context handle's GSS-API 622 security context. The MIC is then placed in the chan_binding_mic 623 field of RPCSEC_GSS3_CREATE arguments (rpc_gss3_create_args). 625 If the chan_binding_mic field of the arguments of a 626 RPCSEC_GSS3_CREATE control message is set, then the server MUST 627 verify the client's channel binding MIC if the server supports this 628 feature. If channel binding verification succeeds then the server 629 MUST generate a new MIC of the same channel bindings and place it in 630 the chan_binding_mic field of the RPCSEC_GSS3_CREATE results. If 631 channel binding verification fails or the server doesn't support 632 channel binding then the server MUST indicate this in its reply by 633 not including a chan_binding_mic value (chan_binding_mic is an 634 optional field). 636 The client MUST verify the result's chan_binding_mic value, if the 637 server included it, by calling GSS_VerifyMIC() with the given MIC and 638 the channel bindings data (including the channel type prefix). If 639 client-side channel binding verification fails then the client MUST 640 call RPCSEC_GSS3_DESTROY. If the client requested channel binding 641 but the server did not include a chan_binding_mic field in the 642 results, then the client MAY continue to use the resulting context 643 handle as though channel binding had never been requested, otherwise 644 (if the client really wanted channel binding) it MUST call 645 RPCSEC_GSS3_DESTROY. 647 As per-RPCSEC_GSSv2: 649 o "Once a successful [channel binding] procedure has been performed 650 on an [RPCSEC_GSSv3] context handle, the initiator's 651 implementation may map application requests for rpc_gss_svc_none 652 and rpc_gss_svc_integrity to rpc_gss_svc_channel_prot credentials. 653 And if the secure channel has privacy enabled, requests for 654 rpc_gss_svc_privacy can also be mapped to 655 rpc_gss_svc_channel_prot." 657 o ... 659 Any RPCSEC_GSSv3 context handle that has been bound to a secure 660 channel in this way SHOULD be used only with the 661 rpc_gss_svc_channel_prot, and SHOULD NOT be used with 662 rpc_gss_svc_none nor rpc_gss_svc_integrity -- if the secure channel 663 does not provide privacy protection then the client MAY use 664 rpc_gss_svc_privacy where privacy protection is needed or desired. 666 2.1.2.3. Label assertions 668 RPCSEC_GSSv3 clients MAY assert a security label in some DOI by 669 binding this assertion into an RPCSEC_GSSv3 context handle. This is 670 done by including an assertion of type rpc_gss3_label in the 671 'assertions' field (discriminant: 'LABEL') of the RPCSEC_GSS3_CREATE 672 arguments to the desired DOI and label. 674 Label encoding is specific to each DOI and not described herein. DOI 675 encoding is TBD [fill in... Solaris uses integers to name DOIs, and 676 there is an IANA registry of DOIs as 32-bit integers, and IPsec 677 (whence the IANA registry) and CALIPSO use 32-bit integers for DOIs 678 as well. So a 32-bit unsinged integer seems to be the way to go. 679 Add references... -Nico] 681 If a label itself requires privacy protection (i.e., that the user 682 can assert that label is a secret) then the client MUST use the 683 rpc_gss_svc_privacy protection service for the RPCSEC_GSS3_CREATE 684 request or, if the parent handle is bound to a secure channel that 685 provides privacy protection, rpc_gss_svc_channel_prot. 687 If a client wants to ensure that the server understands the asserted 688 label then it MUST set the 'critical' field of the label assertion to 689 TRUE, otherwise it MUST set it to FALSE. 691 Servers that don't support labeling MUST ignore non-critical label 692 assertions. Servers that don't support the requested DOI MUST either 693 ignore non-critical label assertions or map them to a suitable label 694 in a supported DOI. Servers that don't support labeling or don't 695 support the requested DOI MUST return an error if the label request 696 is critical. Servers that support labeling in the requested DOI MAY 697 map the requested label to different label as a result of server-side 698 policy evaluation. 700 2.1.2.4. Privilege assertions 702 Privilege assertions are similar to label assertions, except that 703 there is no DOI, and the privileges supported are specified by the 704 RPC application. 706 Privileges are encoded US-ASCII strings containing comma-separated 707 privilege names, as well as up to one privilege group name and zero 708 or more exclusions, where each exclusion is a privilege name or 709 privilege group name prefixed with an exclamation point. Two special 710 privilege group names are defined here: "all" (which represents all 711 possible privileges) and "basic" (which represents privileges 712 normally granted to all users). 714 RPC applications that wish to use this facility must define the set 715 of known privileges, and must specify which privileges are in the 716 "basic" privilege group. For example, NFSv4 might specify privileges 717 for reading, writing, chowning, linking, etcetera. 719 2.1.2.5. Identity assertions 721 Identity assertions can be used either to modify the set of groups 722 assigned on the server-side to a given user (authenticated by the 723 GSS-API) or to implement an AUTH_SYS-like [4]. In the latter case 724 the client specifies at least a user-name and possibly groups that it 725 thinks the user belongs to. 727 Clients may set a username, a group list, and/or lists of groups to 728 be added or removed from the group list that the server would 729 normally use for the given user. 731 The server MUST decide whether to accept identity assertions by 732 applying local policy. Such policies is not described herein. 733 Example policies: 735 o "always accept identity assertions" 737 o "always accept identity assertions where the identities are 738 understood" 740 o "accept identity assertions ... only from trusted clients" (where 741 the identity of the client is taken from the initiator principal 742 of the outer context handle's GSS-API security context, or from 743 the network address of the client...) 745 o "accept identity assertions ... only from trusted clients where 746 IPsec policy protects this application's packet flows between the 747 clients and this server" 749 o "accept only removals of groups from a user's group membership 750 list as determined by the server" 752 o "never accept identity assertions" 754 o etcetera 756 Clients may mark an identity assertion as being critical, in which 757 case the server MUST respond with an error if the server does not 758 accept the identity assertion as-is. 760 The representation of users and groups is not given here, but is left 761 to the application. It is expected that RPCSEC_GSSv3 identity 762 assertions in the context of the NFSv4 application would consist of 763 NFSv4 user and group representations as used on the wire in NFSv4 764 access control lists (ACLs). 766 2.1.2.6. Server assertions 768 Servers MAY inform clients of assertions were granted by setting the 769 'granted_assertions' field of the RPCSEC_GSS3_CREATE reply. 771 The protocol provides a field ('server_assertions') for servers to 772 make assertions about themselves. At this time there is not much use 773 for this field, though servers MAY assert a single security label, 774 indicating that all contents on the server is at that label. The 775 client MUST, of course, either evaluate or ignore any server-side 776 assertions. 778 2.1.3. Context handle destruction 780 The RPCSEC_GSS3_DESTROY procedure is the same as for RPCSEC_GSSv1, 781 but with the version 3 header. 783 2.1.4. List request 785 The RPCSEC_GSS3_LIST call message consists of a single integer 786 indicating what should be listed, and the reply consists of an error 787 or the requested list. 789 The client may list DOIs, privilege names, or privilege group names. 791 The result is an opaque octet string containing a list of DOIs 792 [encoding TBD] or a US-ASCII string containing a comma-separated list 793 of privilege names or privilege group names. 795 2.1.5. Extensibility 797 Assertion types may be added in the future by adding arms to the 798 'rpc_gss3_assertion_u' union. Every assertion has a 'critical' flag 799 that can be used to indicate criticality. 801 New fields may be added through the 'extensions' typed hole. All 802 such extensions have a 'critical' flag. 804 New message types may be added. 806 Clients receiving unknown critical server assertions MUST destroy the 807 established RPCSEC_GSSv3 context handle. Servers receiving unknown 808 critical client assertions or unknown RPCSEC_GSS_v3 extensions MUST 809 return an error. 811 There is no IANA or other registry for RPCSEC_GSSv3 extensions. All 812 extensions MUST be done by IETF Protocol Action. 814 3. Privileges and identity representation for NFSv4 816 The representation of users and groups for use in identity assertions 817 in RPCSEC_GSSv3 SHALL be the same as the user and group 818 representations used by NFSv4 for access control list subjects on the 819 wire, cast as an octet string ("opaque"). 821 The following privileges are defined for use with the NFSv4 protocol: 823 file_chown Generally allows the caller to change a file's owner 824 regardless of who owns the file. 826 file_chown_self Generally allows the caller to change the owner of a 827 file it owns. 829 file_dac_execute Generally allows the caller to read any file for 830 execution. 832 file_dac_read Generally allows the caller to read any file or 833 directory. 835 file_dac_search Generally allows the caller to search any directory. 837 file_dac_write Generally allows the caller to write to any file (or 838 create/delete/link objects in directories). 840 file_link_any Generally allows the caller to create hardlinks to 841 files not owned by the caller. 843 file_owner Generally allows the caller to modify the access, 844 modification and other timestamps of a filesystem object, as well 845 as its permissions and ACL. 847 file_setid Generally allows the caller to set the set-user-ID and 848 set-group-ID bits of a file. 850 file_downgrade_sl Generally allows the caller to downgrade the 851 security label of a filesystem object. 853 file_update_sl Generally allows the caller to upgrade the security 854 label of a filesystem object. 856 [What about NFSv3? The representation of privs would be the same for 857 v3 as for v4, though there'd be no privs for dealing with labels 858 (file_downgrade_sl and file_update_sl). And the representation of 859 users/groups would NFSv3's representation thereof. But should we 860 bother to specify this? -Nico] 862 [Also, this is derived from Solaris' notion of privileges. We should 863 look at how well this scheme relates to other operating systems as 864 NFSv4 clients and servers. -Nico] 866 The contents of the 'basic' privilege set is not defined herein. 867 Note that 'file_link_any' and 'file_chown_self' may be present in the 868 server's notion of the basic privilege set. 870 The NFSv4-specific privileges may be limited by the server in ways 871 not specified above. For example, the server may deny access for 872 certain operations that would normally be granted given the granted 873 assertion of a given privilege (e.g., "no one may write to files 874 owned by such and such user"), or the server may require that all 875 privileges be asserted (and granted, of course) in order to allow 876 certain operations (e.g., "all privileges are required in order to 877 write to files owned by such and such user, not just 878 file_dac_write"). 880 4. Security Considerations 882 This entire document deals with security issues. 884 The RPCSEC_GSSv3 protocol allows for client-side assertions of data 885 that is relevant to server-side authorization decisions. These 886 assertions must be evaludated by the server in the context of whether 887 the client and/or user are authenticated, whether compound 888 authentication was used, whether the client is trusted, what ranges 889 of assertions are allowed for the client and the user (separately or 890 together), and any relevant server-side policy. 892 The security semantics of assertions carried by RPCSEC_GSSv3 are 893 application protocol-specific. 895 RPCSEC_GSSv3 supports a notion of critical assertions (and 896 extensions), but there's no need for peers to tell each other what 897 assertions were granted, or what they were mapped to. 899 Note that RPSEC_GSSv3 is not a complete solution for labeling: it 900 conveys the labels of actors, but not the labels of objects. RPC 901 application protocols may require extending in order to carry object 902 label information. 904 The RPCSEC_GSSv3 protocol also provides for a replacement of the old 905 AUTH_SYS RPC authentication flavor. AUTH_SYS relies on "privileged 906 port numbers" for "authentication," and was quite limited in what 907 assertions it supported and incompatible with NFSv4 representations 908 of identity. To replace AUTH_SYS with RPCSEC_GSSv3 simply use a GSS- 909 API mechanism to authenticate the client (but not the user) and let 910 the client assert the user's identity. This is more secure than 911 AUTH_SYS in that at least the client can be strongly authenticated 912 using GSS-API mechanisms, and it is more functional than AUTH_SYS in 913 that identity representations are defined by the application layer. 915 It is possible that a GSS-API mechanism that does not provide any 916 security services could be created so as to make it possible to 917 replace AUTH_SYS with RPCSEC_GSSv3 while retaining the same 918 privileged port semantics. Such a mechanism is out of scope for this 919 document and would have its own security considerations. 921 There may be interactions with NFSv4's callback security scheme and 922 NFSv4.1's GSS-API "SSV" mechanisms. Specifically, the NFSv4 callback 923 scheme requires that the server initiate GSS-API security contexts, 924 which does not work well in practice, and in the context of client- 925 side processes running as the same user but with different privileges 926 and security labels the NFSv4 callback security scheme seems 927 particularly unlikely to work well. NFSv4.1 has the server use an 928 existing, client-initiated RPCSEC_GSS context handle to protect 929 server-initiated callback RPCs. The NFSv4.1 callback security scheme 930 lacks all the problems of the NFSv4 scheme, however, it is important 931 that the server pick an appropriate RPCSEC_GSS context handle to 932 protect any callbacks. Specifically, it is important that the server 933 use RPCSEC_GSS context handles which authenticate the client to 934 protect any callbacks relating to server state initiated by RPCs 935 protected by RPCSEC_GSSv3 contexts. [Add text about interaction with 936 GSS-SSV...] 938 [Anything else?] 940 5. IANA Considerations 942 This section uses terms that are defined in [8]. 944 There are no IANA considerations in this document. TBDs in this 945 document will be assigned by the ONC RPC registrart (which is not 946 IANA, XXX: verify). 948 6. Normative References 950 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 951 Levels", March 1997. 953 [2] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol 954 Specification", RFC 2203, September 1997. 956 [3] Linn, J., "Generic Security Service Application Program 957 Interface Version 2, Update 1", RFC 2743, January 2000. 959 [4] Srinivasan, R., "RPC: Remote Procedure Call Protocol 960 Specification Version 2", RFC 1831, August 1995. 962 [5] Williams, N., "On the Use of Channel Bindings to Secure 963 Channels", RFC 5056, November 2007. 965 [6] Haynes, T. and D. Noveck, "Network File System (NFS) version 4 966 Protocol", draft-ietf-nfsv4-rfc3530bis-09 (Work In Progress), 967 March 2011. 969 [7] Eisler, M., "XDR: External Data Representation Standard", 970 RFC 4506, May 2006. 972 [8] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA 973 Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. 975 [9] Shepler, S., Eisler, M., and D. Noveck, "Network File System 976 (NFS) Version 4 Minor Version 1 Protocol", RFC 5661, 977 January 2010. 979 Appendix A. Acknowledgments 981 Appendix B. RFC Editor Notes 983 [RFC Editor: please remove this section prior to publishing this 984 document as an RFC] 986 [RFC Editor: prior to publishing this document as an RFC, please 987 replace all occurrences of RFCTBD10 with RFCxxxx where xxxx is the 988 RFC number of this document] 990 Authors' Addresses 992 Thomas Haynes 993 NetApp 994 9110 E 66th St 995 Tulsa, OK 74133 996 USA 998 Phone: +1 918 307 1415 999 Email: thomas@netapp.com 1000 Nico Williams 1001 cryptonector.com 1002 13115 Tamayo Dr 1003 Austin, TX 78729 1004 USA 1006 Email: nico@cryptonector.com