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authorSimon Wilkinson <simon@sxw.org.uk>2014-02-09 16:09:48 +0000
committerColin Watson <cjwatson@debian.org>2016-01-14 15:07:15 +0000
commit6a0a4b2f79889c9b0d5e2478a6ee5f51be38dcc9 (patch)
tree2f8cd5a92310d9ed3b7020366f3030fc0d1b53a4 /gss-genr.c
parenteeff4de96f5d7365750dc56912c2c62b5c28db6b (diff)
GSSAPI key exchange support
This patch has been rejected upstream: "None of the OpenSSH developers are in favour of adding this, and this situation has not changed for several years. This is not a slight on Simon's patch, which is of fine quality, but just that a) we don't trust GSSAPI implementations that much and b) we don't like adding new KEX since they are pre-auth attack surface. This one is particularly scary, since it requires hooks out to typically root-owned system resources." However, quite a lot of people rely on this in Debian, and it's better to have it merged into the main openssh package rather than having separate -krb5 packages (as we used to have). It seems to have a generally good security history. Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=1242 Last-Updated: 2016-01-04 Patch-Name: gssapi.patch
Diffstat (limited to 'gss-genr.c')
-rw-r--r--gss-genr.c275
1 files changed, 271 insertions, 4 deletions
diff --git a/gss-genr.c b/gss-genr.c
index d617d600a..b4eca3feb 100644
--- a/gss-genr.c
+++ b/gss-genr.c
@@ -1,7 +1,7 @@
1/* $OpenBSD: gss-genr.c,v 1.23 2015/01/20 23:14:00 deraadt Exp $ */ 1/* $OpenBSD: gss-genr.c,v 1.23 2015/01/20 23:14:00 deraadt Exp $ */
2 2
3/* 3/*
4 * Copyright (c) 2001-2007 Simon Wilkinson. All rights reserved. 4 * Copyright (c) 2001-2009 Simon Wilkinson. All rights reserved.
5 * 5 *
6 * Redistribution and use in source and binary forms, with or without 6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions 7 * modification, are permitted provided that the following conditions
@@ -41,12 +41,167 @@
41#include "buffer.h" 41#include "buffer.h"
42#include "log.h" 42#include "log.h"
43#include "ssh2.h" 43#include "ssh2.h"
44#include "cipher.h"
45#include "key.h"
46#include "kex.h"
47#include <openssl/evp.h>
44 48
45#include "ssh-gss.h" 49#include "ssh-gss.h"
46 50
47extern u_char *session_id2; 51extern u_char *session_id2;
48extern u_int session_id2_len; 52extern u_int session_id2_len;
49 53
54typedef struct {
55 char *encoded;
56 gss_OID oid;
57} ssh_gss_kex_mapping;
58
59/*
60 * XXX - It would be nice to find a more elegant way of handling the
61 * XXX passing of the key exchange context to the userauth routines
62 */
63
64Gssctxt *gss_kex_context = NULL;
65
66static ssh_gss_kex_mapping *gss_enc2oid = NULL;
67
68int
69ssh_gssapi_oid_table_ok(void) {
70 return (gss_enc2oid != NULL);
71}
72
73/*
74 * Return a list of the gss-group1-sha1 mechanisms supported by this program
75 *
76 * We test mechanisms to ensure that we can use them, to avoid starting
77 * a key exchange with a bad mechanism
78 */
79
80char *
81ssh_gssapi_client_mechanisms(const char *host, const char *client) {
82 gss_OID_set gss_supported;
83 OM_uint32 min_status;
84
85 if (GSS_ERROR(gss_indicate_mechs(&min_status, &gss_supported)))
86 return NULL;
87
88 return(ssh_gssapi_kex_mechs(gss_supported, ssh_gssapi_check_mechanism,
89 host, client));
90}
91
92char *
93ssh_gssapi_kex_mechs(gss_OID_set gss_supported, ssh_gssapi_check_fn *check,
94 const char *host, const char *client) {
95 Buffer buf;
96 size_t i;
97 int oidpos, enclen;
98 char *mechs, *encoded;
99 u_char digest[EVP_MAX_MD_SIZE];
100 char deroid[2];
101 const EVP_MD *evp_md = EVP_md5();
102 EVP_MD_CTX md;
103
104 if (gss_enc2oid != NULL) {
105 for (i = 0; gss_enc2oid[i].encoded != NULL; i++)
106 free(gss_enc2oid[i].encoded);
107 free(gss_enc2oid);
108 }
109
110 gss_enc2oid = xmalloc(sizeof(ssh_gss_kex_mapping) *
111 (gss_supported->count + 1));
112
113 buffer_init(&buf);
114
115 oidpos = 0;
116 for (i = 0; i < gss_supported->count; i++) {
117 if (gss_supported->elements[i].length < 128 &&
118 (*check)(NULL, &(gss_supported->elements[i]), host, client)) {
119
120 deroid[0] = SSH_GSS_OIDTYPE;
121 deroid[1] = gss_supported->elements[i].length;
122
123 EVP_DigestInit(&md, evp_md);
124 EVP_DigestUpdate(&md, deroid, 2);
125 EVP_DigestUpdate(&md,
126 gss_supported->elements[i].elements,
127 gss_supported->elements[i].length);
128 EVP_DigestFinal(&md, digest, NULL);
129
130 encoded = xmalloc(EVP_MD_size(evp_md) * 2);
131 enclen = __b64_ntop(digest, EVP_MD_size(evp_md),
132 encoded, EVP_MD_size(evp_md) * 2);
133
134 if (oidpos != 0)
135 buffer_put_char(&buf, ',');
136
137 buffer_append(&buf, KEX_GSS_GEX_SHA1_ID,
138 sizeof(KEX_GSS_GEX_SHA1_ID) - 1);
139 buffer_append(&buf, encoded, enclen);
140 buffer_put_char(&buf, ',');
141 buffer_append(&buf, KEX_GSS_GRP1_SHA1_ID,
142 sizeof(KEX_GSS_GRP1_SHA1_ID) - 1);
143 buffer_append(&buf, encoded, enclen);
144 buffer_put_char(&buf, ',');
145 buffer_append(&buf, KEX_GSS_GRP14_SHA1_ID,
146 sizeof(KEX_GSS_GRP14_SHA1_ID) - 1);
147 buffer_append(&buf, encoded, enclen);
148
149 gss_enc2oid[oidpos].oid = &(gss_supported->elements[i]);
150 gss_enc2oid[oidpos].encoded = encoded;
151 oidpos++;
152 }
153 }
154 gss_enc2oid[oidpos].oid = NULL;
155 gss_enc2oid[oidpos].encoded = NULL;
156
157 buffer_put_char(&buf, '\0');
158
159 mechs = xmalloc(buffer_len(&buf));
160 buffer_get(&buf, mechs, buffer_len(&buf));
161 buffer_free(&buf);
162
163 if (strlen(mechs) == 0) {
164 free(mechs);
165 mechs = NULL;
166 }
167
168 return (mechs);
169}
170
171gss_OID
172ssh_gssapi_id_kex(Gssctxt *ctx, char *name, int kex_type) {
173 int i = 0;
174
175 switch (kex_type) {
176 case KEX_GSS_GRP1_SHA1:
177 if (strlen(name) < sizeof(KEX_GSS_GRP1_SHA1_ID))
178 return GSS_C_NO_OID;
179 name += sizeof(KEX_GSS_GRP1_SHA1_ID) - 1;
180 break;
181 case KEX_GSS_GRP14_SHA1:
182 if (strlen(name) < sizeof(KEX_GSS_GRP14_SHA1_ID))
183 return GSS_C_NO_OID;
184 name += sizeof(KEX_GSS_GRP14_SHA1_ID) - 1;
185 break;
186 case KEX_GSS_GEX_SHA1:
187 if (strlen(name) < sizeof(KEX_GSS_GEX_SHA1_ID))
188 return GSS_C_NO_OID;
189 name += sizeof(KEX_GSS_GEX_SHA1_ID) - 1;
190 break;
191 default:
192 return GSS_C_NO_OID;
193 }
194
195 while (gss_enc2oid[i].encoded != NULL &&
196 strcmp(name, gss_enc2oid[i].encoded) != 0)
197 i++;
198
199 if (gss_enc2oid[i].oid != NULL && ctx != NULL)
200 ssh_gssapi_set_oid(ctx, gss_enc2oid[i].oid);
201
202 return gss_enc2oid[i].oid;
203}
204
50/* Check that the OID in a data stream matches that in the context */ 205/* Check that the OID in a data stream matches that in the context */
51int 206int
52ssh_gssapi_check_oid(Gssctxt *ctx, void *data, size_t len) 207ssh_gssapi_check_oid(Gssctxt *ctx, void *data, size_t len)
@@ -199,7 +354,7 @@ ssh_gssapi_init_ctx(Gssctxt *ctx, int deleg_creds, gss_buffer_desc *recv_tok,
199 } 354 }
200 355
201 ctx->major = gss_init_sec_context(&ctx->minor, 356 ctx->major = gss_init_sec_context(&ctx->minor,
202 GSS_C_NO_CREDENTIAL, &ctx->context, ctx->name, ctx->oid, 357 ctx->client_creds, &ctx->context, ctx->name, ctx->oid,
203 GSS_C_MUTUAL_FLAG | GSS_C_INTEG_FLAG | deleg_flag, 358 GSS_C_MUTUAL_FLAG | GSS_C_INTEG_FLAG | deleg_flag,
204 0, NULL, recv_tok, NULL, send_tok, flags, NULL); 359 0, NULL, recv_tok, NULL, send_tok, flags, NULL);
205 360
@@ -229,8 +384,42 @@ ssh_gssapi_import_name(Gssctxt *ctx, const char *host)
229} 384}
230 385
231OM_uint32 386OM_uint32
387ssh_gssapi_client_identity(Gssctxt *ctx, const char *name)
388{
389 gss_buffer_desc gssbuf;
390 gss_name_t gssname;
391 OM_uint32 status;
392 gss_OID_set oidset;
393
394 gssbuf.value = (void *) name;
395 gssbuf.length = strlen(gssbuf.value);
396
397 gss_create_empty_oid_set(&status, &oidset);
398 gss_add_oid_set_member(&status, ctx->oid, &oidset);
399
400 ctx->major = gss_import_name(&ctx->minor, &gssbuf,
401 GSS_C_NT_USER_NAME, &gssname);
402
403 if (!ctx->major)
404 ctx->major = gss_acquire_cred(&ctx->minor,
405 gssname, 0, oidset, GSS_C_INITIATE,
406 &ctx->client_creds, NULL, NULL);
407
408 gss_release_name(&status, &gssname);
409 gss_release_oid_set(&status, &oidset);
410
411 if (ctx->major)
412 ssh_gssapi_error(ctx);
413
414 return(ctx->major);
415}
416
417OM_uint32
232ssh_gssapi_sign(Gssctxt *ctx, gss_buffer_t buffer, gss_buffer_t hash) 418ssh_gssapi_sign(Gssctxt *ctx, gss_buffer_t buffer, gss_buffer_t hash)
233{ 419{
420 if (ctx == NULL)
421 return -1;
422
234 if ((ctx->major = gss_get_mic(&ctx->minor, ctx->context, 423 if ((ctx->major = gss_get_mic(&ctx->minor, ctx->context,
235 GSS_C_QOP_DEFAULT, buffer, hash))) 424 GSS_C_QOP_DEFAULT, buffer, hash)))
236 ssh_gssapi_error(ctx); 425 ssh_gssapi_error(ctx);
@@ -238,6 +427,19 @@ ssh_gssapi_sign(Gssctxt *ctx, gss_buffer_t buffer, gss_buffer_t hash)
238 return (ctx->major); 427 return (ctx->major);
239} 428}
240 429
430/* Priviledged when used by server */
431OM_uint32
432ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
433{
434 if (ctx == NULL)
435 return -1;
436
437 ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
438 gssbuf, gssmic, NULL);
439
440 return (ctx->major);
441}
442
241void 443void
242ssh_gssapi_buildmic(Buffer *b, const char *user, const char *service, 444ssh_gssapi_buildmic(Buffer *b, const char *user, const char *service,
243 const char *context) 445 const char *context)
@@ -251,11 +453,16 @@ ssh_gssapi_buildmic(Buffer *b, const char *user, const char *service,
251} 453}
252 454
253int 455int
254ssh_gssapi_check_mechanism(Gssctxt **ctx, gss_OID oid, const char *host) 456ssh_gssapi_check_mechanism(Gssctxt **ctx, gss_OID oid, const char *host,
457 const char *client)
255{ 458{
256 gss_buffer_desc token = GSS_C_EMPTY_BUFFER; 459 gss_buffer_desc token = GSS_C_EMPTY_BUFFER;
257 OM_uint32 major, minor; 460 OM_uint32 major, minor;
258 gss_OID_desc spnego_oid = {6, (void *)"\x2B\x06\x01\x05\x05\x02"}; 461 gss_OID_desc spnego_oid = {6, (void *)"\x2B\x06\x01\x05\x05\x02"};
462 Gssctxt *intctx = NULL;
463
464 if (ctx == NULL)
465 ctx = &intctx;
259 466
260 /* RFC 4462 says we MUST NOT do SPNEGO */ 467 /* RFC 4462 says we MUST NOT do SPNEGO */
261 if (oid->length == spnego_oid.length && 468 if (oid->length == spnego_oid.length &&
@@ -265,6 +472,10 @@ ssh_gssapi_check_mechanism(Gssctxt **ctx, gss_OID oid, const char *host)
265 ssh_gssapi_build_ctx(ctx); 472 ssh_gssapi_build_ctx(ctx);
266 ssh_gssapi_set_oid(*ctx, oid); 473 ssh_gssapi_set_oid(*ctx, oid);
267 major = ssh_gssapi_import_name(*ctx, host); 474 major = ssh_gssapi_import_name(*ctx, host);
475
476 if (!GSS_ERROR(major) && client)
477 major = ssh_gssapi_client_identity(*ctx, client);
478
268 if (!GSS_ERROR(major)) { 479 if (!GSS_ERROR(major)) {
269 major = ssh_gssapi_init_ctx(*ctx, 0, GSS_C_NO_BUFFER, &token, 480 major = ssh_gssapi_init_ctx(*ctx, 0, GSS_C_NO_BUFFER, &token,
270 NULL); 481 NULL);
@@ -274,10 +485,66 @@ ssh_gssapi_check_mechanism(Gssctxt **ctx, gss_OID oid, const char *host)
274 GSS_C_NO_BUFFER); 485 GSS_C_NO_BUFFER);
275 } 486 }
276 487
277 if (GSS_ERROR(major)) 488 if (GSS_ERROR(major) || intctx != NULL)
278 ssh_gssapi_delete_ctx(ctx); 489 ssh_gssapi_delete_ctx(ctx);
279 490
280 return (!GSS_ERROR(major)); 491 return (!GSS_ERROR(major));
281} 492}
282 493
494int
495ssh_gssapi_credentials_updated(Gssctxt *ctxt) {
496 static gss_name_t saved_name = GSS_C_NO_NAME;
497 static OM_uint32 saved_lifetime = 0;
498 static gss_OID saved_mech = GSS_C_NO_OID;
499 static gss_name_t name;
500 static OM_uint32 last_call = 0;
501 OM_uint32 lifetime, now, major, minor;
502 int equal;
503
504 now = time(NULL);
505
506 if (ctxt) {
507 debug("Rekey has happened - updating saved versions");
508
509 if (saved_name != GSS_C_NO_NAME)
510 gss_release_name(&minor, &saved_name);
511
512 major = gss_inquire_cred(&minor, GSS_C_NO_CREDENTIAL,
513 &saved_name, &saved_lifetime, NULL, NULL);
514
515 if (!GSS_ERROR(major)) {
516 saved_mech = ctxt->oid;
517 saved_lifetime+= now;
518 } else {
519 /* Handle the error */
520 }
521 return 0;
522 }
523
524 if (now - last_call < 10)
525 return 0;
526
527 last_call = now;
528
529 if (saved_mech == GSS_C_NO_OID)
530 return 0;
531
532 major = gss_inquire_cred(&minor, GSS_C_NO_CREDENTIAL,
533 &name, &lifetime, NULL, NULL);
534 if (major == GSS_S_CREDENTIALS_EXPIRED)
535 return 0;
536 else if (GSS_ERROR(major))
537 return 0;
538
539 major = gss_compare_name(&minor, saved_name, name, &equal);
540 gss_release_name(&minor, &name);
541 if (GSS_ERROR(major))
542 return 0;
543
544 if (equal && (saved_lifetime < lifetime + now - 10))
545 return 1;
546
547 return 0;
548}
549
283#endif /* GSSAPI */ 550#endif /* GSSAPI */