1 /* $OpenBSD: gss-serv.c,v 1.37 2026/02/11 16:57:38 dtucker Exp $ */
2
3 /*
4 * Copyright (c) 2001-2003 Simon Wilkinson. All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR `AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27 #include "includes.h"
28
29 #ifdef GSSAPI
30
31 #include <sys/types.h>
32 #include <sys/param.h>
33 #include <sys/queue.h>
34
35 #include <netdb.h>
36 #include <stdarg.h>
37 #include <string.h>
38 #include <unistd.h>
39
40 #include "xmalloc.h"
41 #include "sshkey.h"
42 #include "hostfile.h"
43 #include "auth.h"
44 #include "log.h"
45 #include "channels.h"
46 #include "session.h"
47 #include "misc.h"
48 #include "servconf.h"
49
50 #include "ssh-gss.h"
51
52 extern ServerOptions options;
53
54 static ssh_gssapi_client gssapi_client =
55 { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
56 GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}};
57
58 ssh_gssapi_mech gssapi_null_mech =
59 { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
60
61 #ifdef KRB5
62 extern ssh_gssapi_mech gssapi_kerberos_mech;
63 #endif
64
65 ssh_gssapi_mech* supported_mechs[]= {
66 #ifdef KRB5
67 &gssapi_kerberos_mech,
68 #endif
69 &gssapi_null_mech,
70 };
71
72 /*
73 * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the
74 * list of supported mechanisms before privsep is set up.
75 */
76 static gss_OID_set supported_oids;
77
78 void
ssh_gssapi_prepare_supported_oids(void)79 ssh_gssapi_prepare_supported_oids(void)
80 {
81 ssh_gssapi_supported_oids(&supported_oids);
82 }
83
84 OM_uint32
ssh_gssapi_test_oid_supported(OM_uint32 * ms,gss_OID member,int * present)85 ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present)
86 {
87 if (supported_oids == NULL)
88 ssh_gssapi_prepare_supported_oids();
89 return gss_test_oid_set_member(ms, member, supported_oids, present);
90 }
91
92 /*
93 * Acquire credentials for a server running on the current host.
94 * Requires that the context structure contains a valid OID
95 */
96
97 /* Returns a GSSAPI error code */
98 /* Privileged (called from ssh_gssapi_server_ctx) */
99 static OM_uint32
ssh_gssapi_acquire_cred(Gssctxt * ctx)100 ssh_gssapi_acquire_cred(Gssctxt *ctx)
101 {
102 OM_uint32 status;
103 char lname[NI_MAXHOST];
104 gss_OID_set oidset;
105
106 if (options.gss_strict_acceptor) {
107 gss_create_empty_oid_set(&status, &oidset);
108 gss_add_oid_set_member(&status, ctx->oid, &oidset);
109
110 if (gethostname(lname, sizeof(lname))) {
111 gss_release_oid_set(&status, &oidset);
112 return (-1);
113 }
114
115 if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
116 gss_release_oid_set(&status, &oidset);
117 return (ctx->major);
118 }
119
120 if ((ctx->major = gss_acquire_cred(&ctx->minor,
121 ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds,
122 NULL, NULL)))
123 ssh_gssapi_error(ctx);
124
125 gss_release_oid_set(&status, &oidset);
126 return (ctx->major);
127 } else {
128 ctx->name = GSS_C_NO_NAME;
129 ctx->creds = GSS_C_NO_CREDENTIAL;
130 }
131 return GSS_S_COMPLETE;
132 }
133
134 /* Privileged */
135 OM_uint32
ssh_gssapi_server_ctx(Gssctxt ** ctx,gss_OID oid)136 ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
137 {
138 if (*ctx)
139 ssh_gssapi_delete_ctx(ctx);
140 ssh_gssapi_build_ctx(ctx);
141 ssh_gssapi_set_oid(*ctx, oid);
142 return (ssh_gssapi_acquire_cred(*ctx));
143 }
144
145 /* Unprivileged */
146 void
ssh_gssapi_supported_oids(gss_OID_set * oidset)147 ssh_gssapi_supported_oids(gss_OID_set *oidset)
148 {
149 int i = 0;
150 OM_uint32 min_status;
151 int present;
152 gss_OID_set supported;
153
154 gss_create_empty_oid_set(&min_status, oidset);
155 gss_indicate_mechs(&min_status, &supported);
156
157 while (supported_mechs[i]->name != NULL) {
158 if (GSS_ERROR(gss_test_oid_set_member(&min_status,
159 &supported_mechs[i]->oid, supported, &present)))
160 present = 0;
161 if (present)
162 gss_add_oid_set_member(&min_status,
163 &supported_mechs[i]->oid, oidset);
164 i++;
165 }
166
167 gss_release_oid_set(&min_status, &supported);
168 }
169
170
171 /* Wrapper around accept_sec_context
172 * Requires that the context contains:
173 * oid
174 * credentials (from ssh_gssapi_acquire_cred)
175 */
176 /* Privileged */
177 OM_uint32
ssh_gssapi_accept_ctx(Gssctxt * ctx,gss_buffer_desc * recv_tok,gss_buffer_desc * send_tok,OM_uint32 * flags)178 ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
179 gss_buffer_desc *send_tok, OM_uint32 *flags)
180 {
181 OM_uint32 status;
182 gss_OID mech;
183
184 ctx->major = gss_accept_sec_context(&ctx->minor,
185 &ctx->context, ctx->creds, recv_tok,
186 GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
187 send_tok, flags, NULL, &ctx->client_creds);
188
189 if (GSS_ERROR(ctx->major))
190 ssh_gssapi_error(ctx);
191
192 if (ctx->client_creds)
193 debug("Received some client credentials");
194 else
195 debug("Got no client credentials");
196
197 status = ctx->major;
198
199 /* Now, if we're complete and we have the right flags, then
200 * we flag the user as also having been authenticated
201 */
202
203 if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
204 (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
205 if (ssh_gssapi_getclient(ctx, &gssapi_client))
206 fatal("Couldn't convert client name");
207 }
208
209 return (status);
210 }
211
212 /*
213 * This parses an exported name, extracting the mechanism specific portion
214 * to use for ACL checking. It verifies that the name belongs the mechanism
215 * originally selected.
216 */
217 static OM_uint32
ssh_gssapi_parse_ename(Gssctxt * ctx,gss_buffer_t ename,gss_buffer_t name)218 ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
219 {
220 u_char *tok;
221 OM_uint32 offset;
222 OM_uint32 oidl;
223
224 tok = ename->value;
225
226 /*
227 * Check that ename is long enough for all of the fixed length
228 * header, and that the initial ID bytes are correct
229 */
230
231 if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
232 return GSS_S_FAILURE;
233
234 /*
235 * Extract the OID, and check it. Here GSSAPI breaks with tradition
236 * and does use the OID type and length bytes. To confuse things
237 * there are two lengths - the first including these, and the
238 * second without.
239 */
240
241 oidl = get_u16(tok+2); /* length including next two bytes */
242 oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
243
244 /*
245 * Check the BER encoding for correct type and length, that the
246 * string is long enough and that the OID matches that in our context
247 */
248 if (tok[4] != 0x06 || tok[5] != oidl ||
249 ename->length < oidl+6 ||
250 !ssh_gssapi_check_oid(ctx, tok+6, oidl))
251 return GSS_S_FAILURE;
252
253 offset = oidl+6;
254
255 if (ename->length < offset+4)
256 return GSS_S_FAILURE;
257
258 name->length = get_u32(tok+offset);
259 offset += 4;
260
261 if (UINT_MAX - offset < name->length)
262 return GSS_S_FAILURE;
263 if (ename->length < offset+name->length)
264 return GSS_S_FAILURE;
265
266 name->value = xmalloc(name->length+1);
267 memcpy(name->value, tok+offset, name->length);
268 ((char *)name->value)[name->length] = 0;
269
270 return GSS_S_COMPLETE;
271 }
272
273 /* Extract the client details from a given context. This can only reliably
274 * be called once for a context */
275
276 /* Privileged (called from accept_secure_ctx) */
277 OM_uint32
ssh_gssapi_getclient(Gssctxt * ctx,ssh_gssapi_client * client)278 ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
279 {
280 int i = 0;
281
282 gss_buffer_desc ename;
283
284 client->mech = NULL;
285
286 while (supported_mechs[i]->name != NULL) {
287 if (supported_mechs[i]->oid.length == ctx->oid->length &&
288 (memcmp(supported_mechs[i]->oid.elements,
289 ctx->oid->elements, ctx->oid->length) == 0))
290 client->mech = supported_mechs[i];
291 i++;
292 }
293
294 if (client->mech == NULL)
295 return GSS_S_FAILURE;
296
297 if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
298 &client->displayname, NULL))) {
299 ssh_gssapi_error(ctx);
300 return (ctx->major);
301 }
302
303 if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
304 &ename))) {
305 ssh_gssapi_error(ctx);
306 return (ctx->major);
307 }
308
309 if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
310 &client->exportedname))) {
311 return (ctx->major);
312 }
313
314 /* We can't copy this structure, so we just move the pointer to it */
315 client->creds = ctx->client_creds;
316 ctx->client_creds = GSS_C_NO_CREDENTIAL;
317 return (ctx->major);
318 }
319
320 /* As user - called on fatal/exit */
321 void
ssh_gssapi_cleanup_creds(void)322 ssh_gssapi_cleanup_creds(void)
323 {
324 if (gssapi_client.store.filename != NULL) {
325 /* Unlink probably isn't sufficient */
326 debug("removing gssapi cred file\"%s\"",
327 gssapi_client.store.filename);
328 unlink(gssapi_client.store.filename);
329 }
330 }
331
332 /* As user */
333 void
ssh_gssapi_storecreds(void)334 ssh_gssapi_storecreds(void)
335 {
336 if (options.gss_deleg_creds == 0) {
337 debug_f("delegate credential is disabled, doing nothing");
338 return;
339 }
340
341 if (gssapi_client.mech && gssapi_client.mech->storecreds) {
342 (*gssapi_client.mech->storecreds)(&gssapi_client);
343 } else
344 debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
345 }
346
347 /* This allows GSSAPI methods to do things to the child's environment based
348 * on the passed authentication process and credentials.
349 */
350 /* As user */
351 void
ssh_gssapi_do_child(char *** envp,u_int * envsizep)352 ssh_gssapi_do_child(char ***envp, u_int *envsizep)
353 {
354
355 if (gssapi_client.store.envvar != NULL &&
356 gssapi_client.store.envval != NULL) {
357 debug("Setting %s to %s", gssapi_client.store.envvar,
358 gssapi_client.store.envval);
359 child_set_env(envp, envsizep, gssapi_client.store.envvar,
360 gssapi_client.store.envval);
361 }
362 }
363
364 /* Privileged */
365 int
ssh_gssapi_userok(char * user)366 ssh_gssapi_userok(char *user)
367 {
368 OM_uint32 lmin;
369
370 if (gssapi_client.exportedname.length == 0 ||
371 gssapi_client.exportedname.value == NULL) {
372 debug("No suitable client data");
373 return 0;
374 }
375 if (gssapi_client.mech && gssapi_client.mech->userok)
376 if ((*gssapi_client.mech->userok)(&gssapi_client, user))
377 return 1;
378 else {
379 /* Destroy delegated credentials if userok fails */
380 gss_release_buffer(&lmin, &gssapi_client.displayname);
381 gss_release_buffer(&lmin, &gssapi_client.exportedname);
382 gss_release_cred(&lmin, &gssapi_client.creds);
383 explicit_bzero(&gssapi_client,
384 sizeof(ssh_gssapi_client));
385 return 0;
386 }
387 else
388 debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
389 return (0);
390 }
391
392 /* Privileged */
393 OM_uint32
ssh_gssapi_checkmic(Gssctxt * ctx,gss_buffer_t gssbuf,gss_buffer_t gssmic)394 ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
395 {
396 ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
397 gssbuf, gssmic, NULL);
398
399 return (ctx->major);
400 }
401
402 /* Privileged */
ssh_gssapi_displayname(void)403 const char *ssh_gssapi_displayname(void)
404 {
405 if (gssapi_client.displayname.length == 0 ||
406 gssapi_client.displayname.value == NULL)
407 return NULL;
408 return (char *)gssapi_client.displayname.value;
409 }
410
411 #endif
412