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authorSimon Wilkinson <simon@sxw.org.uk>2014-02-09 16:09:48 +0000
committerColin Watson <cjwatson@debian.org>2019-10-09 23:06:20 +0100
commit9da806e67101afdc0d3a1d304659927acf18f5c5 (patch)
tree4cb56e13b3b3b14147366a04a7ff691f76908bf7 /gss-serv.c
parent4213eec74e74de6310c27a40c3e9759a08a73996 (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. Origin: other, https://github.com/openssh-gsskex/openssh-gsskex/commits/debian/master Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=1242 Last-Updated: 2019-10-09 Patch-Name: gssapi.patch
Diffstat (limited to 'gss-serv.c')
-rw-r--r--gss-serv.c186
1 files changed, 171 insertions, 15 deletions
diff --git a/gss-serv.c b/gss-serv.c
index ab3a15f0f..1d47870e7 100644
--- a/gss-serv.c
+++ b/gss-serv.c
@@ -1,7 +1,7 @@
1/* $OpenBSD: gss-serv.c,v 1.31 2018/07/09 21:37:55 markus Exp $ */ 1/* $OpenBSD: gss-serv.c,v 1.31 2018/07/09 21:37:55 markus Exp $ */
2 2
3/* 3/*
4 * Copyright (c) 2001-2003 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
@@ -44,17 +44,19 @@
44#include "session.h" 44#include "session.h"
45#include "misc.h" 45#include "misc.h"
46#include "servconf.h" 46#include "servconf.h"
47#include "uidswap.h"
47 48
48#include "ssh-gss.h" 49#include "ssh-gss.h"
50#include "monitor_wrap.h"
49 51
50extern ServerOptions options; 52extern ServerOptions options;
51 53
52static ssh_gssapi_client gssapi_client = 54static ssh_gssapi_client gssapi_client =
53 { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER, 55 { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER, GSS_C_NO_CREDENTIAL,
54 GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}}; 56 GSS_C_NO_NAME, NULL, {NULL, NULL, NULL, NULL, NULL}, 0, 0};
55 57
56ssh_gssapi_mech gssapi_null_mech = 58ssh_gssapi_mech gssapi_null_mech =
57 { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL}; 59 { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL, NULL};
58 60
59#ifdef KRB5 61#ifdef KRB5
60extern ssh_gssapi_mech gssapi_kerberos_mech; 62extern ssh_gssapi_mech gssapi_kerberos_mech;
@@ -141,6 +143,29 @@ ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
141} 143}
142 144
143/* Unprivileged */ 145/* Unprivileged */
146char *
147ssh_gssapi_server_mechanisms(void) {
148 if (supported_oids == NULL)
149 ssh_gssapi_prepare_supported_oids();
150 return (ssh_gssapi_kex_mechs(supported_oids,
151 &ssh_gssapi_server_check_mech, NULL, NULL,
152 options.gss_kex_algorithms));
153}
154
155/* Unprivileged */
156int
157ssh_gssapi_server_check_mech(Gssctxt **dum, gss_OID oid, const char *data,
158 const char *dummy) {
159 Gssctxt *ctx = NULL;
160 int res;
161
162 res = !GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctx, oid)));
163 ssh_gssapi_delete_ctx(&ctx);
164
165 return (res);
166}
167
168/* Unprivileged */
144void 169void
145ssh_gssapi_supported_oids(gss_OID_set *oidset) 170ssh_gssapi_supported_oids(gss_OID_set *oidset)
146{ 171{
@@ -150,7 +175,9 @@ ssh_gssapi_supported_oids(gss_OID_set *oidset)
150 gss_OID_set supported; 175 gss_OID_set supported;
151 176
152 gss_create_empty_oid_set(&min_status, oidset); 177 gss_create_empty_oid_set(&min_status, oidset);
153 gss_indicate_mechs(&min_status, &supported); 178
179 if (GSS_ERROR(gss_indicate_mechs(&min_status, &supported)))
180 return;
154 181
155 while (supported_mechs[i]->name != NULL) { 182 while (supported_mechs[i]->name != NULL) {
156 if (GSS_ERROR(gss_test_oid_set_member(&min_status, 183 if (GSS_ERROR(gss_test_oid_set_member(&min_status,
@@ -276,8 +303,48 @@ OM_uint32
276ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client) 303ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
277{ 304{
278 int i = 0; 305 int i = 0;
306 int equal = 0;
307 gss_name_t new_name = GSS_C_NO_NAME;
308 gss_buffer_desc ename = GSS_C_EMPTY_BUFFER;
309
310 if (options.gss_store_rekey && client->used && ctx->client_creds) {
311 if (client->mech->oid.length != ctx->oid->length ||
312 (memcmp(client->mech->oid.elements,
313 ctx->oid->elements, ctx->oid->length) !=0)) {
314 debug("Rekeyed credentials have different mechanism");
315 return GSS_S_COMPLETE;
316 }
317
318 if ((ctx->major = gss_inquire_cred_by_mech(&ctx->minor,
319 ctx->client_creds, ctx->oid, &new_name,
320 NULL, NULL, NULL))) {
321 ssh_gssapi_error(ctx);
322 return (ctx->major);
323 }
324
325 ctx->major = gss_compare_name(&ctx->minor, client->name,
326 new_name, &equal);
327
328 if (GSS_ERROR(ctx->major)) {
329 ssh_gssapi_error(ctx);
330 return (ctx->major);
331 }
332
333 if (!equal) {
334 debug("Rekeyed credentials have different name");
335 return GSS_S_COMPLETE;
336 }
279 337
280 gss_buffer_desc ename; 338 debug("Marking rekeyed credentials for export");
339
340 gss_release_name(&ctx->minor, &client->name);
341 gss_release_cred(&ctx->minor, &client->creds);
342 client->name = new_name;
343 client->creds = ctx->client_creds;
344 ctx->client_creds = GSS_C_NO_CREDENTIAL;
345 client->updated = 1;
346 return GSS_S_COMPLETE;
347 }
281 348
282 client->mech = NULL; 349 client->mech = NULL;
283 350
@@ -292,6 +359,13 @@ ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
292 if (client->mech == NULL) 359 if (client->mech == NULL)
293 return GSS_S_FAILURE; 360 return GSS_S_FAILURE;
294 361
362 if (ctx->client_creds &&
363 (ctx->major = gss_inquire_cred_by_mech(&ctx->minor,
364 ctx->client_creds, ctx->oid, &client->name, NULL, NULL, NULL))) {
365 ssh_gssapi_error(ctx);
366 return (ctx->major);
367 }
368
295 if ((ctx->major = gss_display_name(&ctx->minor, ctx->client, 369 if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
296 &client->displayname, NULL))) { 370 &client->displayname, NULL))) {
297 ssh_gssapi_error(ctx); 371 ssh_gssapi_error(ctx);
@@ -309,6 +383,8 @@ ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
309 return (ctx->major); 383 return (ctx->major);
310 } 384 }
311 385
386 gss_release_buffer(&ctx->minor, &ename);
387
312 /* We can't copy this structure, so we just move the pointer to it */ 388 /* We can't copy this structure, so we just move the pointer to it */
313 client->creds = ctx->client_creds; 389 client->creds = ctx->client_creds;
314 ctx->client_creds = GSS_C_NO_CREDENTIAL; 390 ctx->client_creds = GSS_C_NO_CREDENTIAL;
@@ -356,19 +432,23 @@ ssh_gssapi_do_child(char ***envp, u_int *envsizep)
356 432
357/* Privileged */ 433/* Privileged */
358int 434int
359ssh_gssapi_userok(char *user) 435ssh_gssapi_userok(char *user, struct passwd *pw, int kex)
360{ 436{
361 OM_uint32 lmin; 437 OM_uint32 lmin;
362 438
439 (void) kex; /* used in privilege separation */
440
363 if (gssapi_client.exportedname.length == 0 || 441 if (gssapi_client.exportedname.length == 0 ||
364 gssapi_client.exportedname.value == NULL) { 442 gssapi_client.exportedname.value == NULL) {
365 debug("No suitable client data"); 443 debug("No suitable client data");
366 return 0; 444 return 0;
367 } 445 }
368 if (gssapi_client.mech && gssapi_client.mech->userok) 446 if (gssapi_client.mech && gssapi_client.mech->userok)
369 if ((*gssapi_client.mech->userok)(&gssapi_client, user)) 447 if ((*gssapi_client.mech->userok)(&gssapi_client, user)) {
448 gssapi_client.used = 1;
449 gssapi_client.store.owner = pw;
370 return 1; 450 return 1;
371 else { 451 } else {
372 /* Destroy delegated credentials if userok fails */ 452 /* Destroy delegated credentials if userok fails */
373 gss_release_buffer(&lmin, &gssapi_client.displayname); 453 gss_release_buffer(&lmin, &gssapi_client.displayname);
374 gss_release_buffer(&lmin, &gssapi_client.exportedname); 454 gss_release_buffer(&lmin, &gssapi_client.exportedname);
@@ -382,14 +462,90 @@ ssh_gssapi_userok(char *user)
382 return (0); 462 return (0);
383} 463}
384 464
385/* Privileged */ 465/* These bits are only used for rekeying. The unpriviledged child is running
386OM_uint32 466 * as the user, the monitor is root.
387ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic) 467 *
468 * In the child, we want to :
469 * *) Ask the monitor to store our credentials into the store we specify
470 * *) If it succeeds, maybe do a PAM update
471 */
472
473/* Stuff for PAM */
474
475#ifdef USE_PAM
476static int ssh_gssapi_simple_conv(int n, const struct pam_message **msg,
477 struct pam_response **resp, void *data)
388{ 478{
389 ctx->major = gss_verify_mic(&ctx->minor, ctx->context, 479 return (PAM_CONV_ERR);
390 gssbuf, gssmic, NULL); 480}
481#endif
391 482
392 return (ctx->major); 483void
484ssh_gssapi_rekey_creds(void) {
485 int ok;
486#ifdef USE_PAM
487 int ret;
488 pam_handle_t *pamh = NULL;
489 struct pam_conv pamconv = {ssh_gssapi_simple_conv, NULL};
490 char *envstr;
491#endif
492
493 if (gssapi_client.store.filename == NULL &&
494 gssapi_client.store.envval == NULL &&
495 gssapi_client.store.envvar == NULL)
496 return;
497
498 ok = PRIVSEP(ssh_gssapi_update_creds(&gssapi_client.store));
499
500 if (!ok)
501 return;
502
503 debug("Rekeyed credentials stored successfully");
504
505 /* Actually managing to play with the ssh pam stack from here will
506 * be next to impossible. In any case, we may want different options
507 * for rekeying. So, use our own :)
508 */
509#ifdef USE_PAM
510 if (!use_privsep) {
511 debug("Not even going to try and do PAM with privsep disabled");
512 return;
513 }
514
515 ret = pam_start("sshd-rekey", gssapi_client.store.owner->pw_name,
516 &pamconv, &pamh);
517 if (ret)
518 return;
519
520 xasprintf(&envstr, "%s=%s", gssapi_client.store.envvar,
521 gssapi_client.store.envval);
522
523 ret = pam_putenv(pamh, envstr);
524 if (!ret)
525 pam_setcred(pamh, PAM_REINITIALIZE_CRED);
526 pam_end(pamh, PAM_SUCCESS);
527#endif
528}
529
530int
531ssh_gssapi_update_creds(ssh_gssapi_ccache *store) {
532 int ok = 0;
533
534 /* Check we've got credentials to store */
535 if (!gssapi_client.updated)
536 return 0;
537
538 gssapi_client.updated = 0;
539
540 temporarily_use_uid(gssapi_client.store.owner);
541 if (gssapi_client.mech && gssapi_client.mech->updatecreds)
542 ok = (*gssapi_client.mech->updatecreds)(store, &gssapi_client);
543 else
544 debug("No update function for this mechanism");
545
546 restore_uid();
547
548 return ok;
393} 549}
394 550
395/* Privileged */ 551/* Privileged */