1 /* $OpenBSD: gss-serv.c,v 1.32 2020/03/13 03:17:07 djm 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 <sys/types.h>
28 #include <sys/queue.h>
29
30 #ifdef GSSAPI
31
32 #include <string.h>
33
34 #include "xmalloc.h"
35 #include "sshkey.h"
36 #include "hostfile.h"
37 #include "auth.h"
38 #include "log.h"
39 #include "channels.h"
40 #include "session.h"
41 #include "misc.h"
42 #include "servconf.h"
43
44 #include "ssh-gss.h"
45
46 extern ServerOptions options;
47
48 static ssh_gssapi_client gssapi_client =
49 { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
50 GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}};
51
52 ssh_gssapi_mech gssapi_null_mech =
53 { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
54
55 #ifdef KRB5
56 extern ssh_gssapi_mech gssapi_kerberos_mech;
57 #endif
58
59 ssh_gssapi_mech* supported_mechs[]= {
60 #ifdef KRB5
61 &gssapi_kerberos_mech,
62 #endif
63 &gssapi_null_mech,
64 };
65
66 /*
67 * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the
68 * list of supported mechanisms before privsep is set up.
69 */
70 static gss_OID_set supported_oids;
71
72 void
ssh_gssapi_prepare_supported_oids(void)73 ssh_gssapi_prepare_supported_oids(void)
74 {
75 ssh_gssapi_supported_oids(&supported_oids);
76 }
77
78 OM_uint32
ssh_gssapi_test_oid_supported(OM_uint32 * ms,gss_OID member,int * present)79 ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present)
80 {
81 if (supported_oids == NULL)
82 ssh_gssapi_prepare_supported_oids();
83 return gss_test_oid_set_member(ms, member, supported_oids, present);
84 }
85
86 /*
87 * Acquire credentials for a server running on the current host.
88 * Requires that the context structure contains a valid OID
89 */
90
91 /* Returns a GSSAPI error code */
92 /* Privileged (called from ssh_gssapi_server_ctx) */
93 static OM_uint32
ssh_gssapi_acquire_cred(Gssctxt * ctx)94 ssh_gssapi_acquire_cred(Gssctxt *ctx)
95 {
96 OM_uint32 status;
97 char lname[NI_MAXHOST];
98 gss_OID_set oidset;
99
100 if (options.gss_strict_acceptor) {
101 gss_create_empty_oid_set(&status, &oidset);
102 gss_add_oid_set_member(&status, ctx->oid, &oidset);
103
104 if (gethostname(lname, MAXHOSTNAMELEN)) {
105 gss_release_oid_set(&status, &oidset);
106 return (-1);
107 }
108
109 if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
110 gss_release_oid_set(&status, &oidset);
111 return (ctx->major);
112 }
113
114 if ((ctx->major = gss_acquire_cred(&ctx->minor,
115 ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds,
116 NULL, NULL)))
117 ssh_gssapi_error(ctx);
118
119 gss_release_oid_set(&status, &oidset);
120 return (ctx->major);
121 } else {
122 ctx->name = GSS_C_NO_NAME;
123 ctx->creds = GSS_C_NO_CREDENTIAL;
124 }
125 return GSS_S_COMPLETE;
126 }
127
128 /* Privileged */
129 OM_uint32
ssh_gssapi_server_ctx(Gssctxt ** ctx,gss_OID oid)130 ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
131 {
132 if (*ctx)
133 ssh_gssapi_delete_ctx(ctx);
134 ssh_gssapi_build_ctx(ctx);
135 ssh_gssapi_set_oid(*ctx, oid);
136 return (ssh_gssapi_acquire_cred(*ctx));
137 }
138
139 /* Unprivileged */
140 void
ssh_gssapi_supported_oids(gss_OID_set * oidset)141 ssh_gssapi_supported_oids(gss_OID_set *oidset)
142 {
143 int i = 0;
144 OM_uint32 min_status;
145 int present;
146 gss_OID_set supported;
147
148 gss_create_empty_oid_set(&min_status, oidset);
149 gss_indicate_mechs(&min_status, &supported);
150
151 while (supported_mechs[i]->name != NULL) {
152 if (GSS_ERROR(gss_test_oid_set_member(&min_status,
153 &supported_mechs[i]->oid, supported, &present)))
154 present = 0;
155 if (present)
156 gss_add_oid_set_member(&min_status,
157 &supported_mechs[i]->oid, oidset);
158 i++;
159 }
160
161 gss_release_oid_set(&min_status, &supported);
162 }
163
164
165 /* Wrapper around accept_sec_context
166 * Requires that the context contains:
167 * oid
168 * credentials (from ssh_gssapi_acquire_cred)
169 */
170 /* Privileged */
171 OM_uint32
ssh_gssapi_accept_ctx(Gssctxt * ctx,gss_buffer_desc * recv_tok,gss_buffer_desc * send_tok,OM_uint32 * flags)172 ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
173 gss_buffer_desc *send_tok, OM_uint32 *flags)
174 {
175 OM_uint32 status;
176 gss_OID mech;
177
178 ctx->major = gss_accept_sec_context(&ctx->minor,
179 &ctx->context, ctx->creds, recv_tok,
180 GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
181 send_tok, flags, NULL, &ctx->client_creds);
182
183 if (GSS_ERROR(ctx->major))
184 ssh_gssapi_error(ctx);
185
186 if (ctx->client_creds)
187 debug("Received some client credentials");
188 else
189 debug("Got no client credentials");
190
191 status = ctx->major;
192
193 /* Now, if we're complete and we have the right flags, then
194 * we flag the user as also having been authenticated
195 */
196
197 if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
198 (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
199 if (ssh_gssapi_getclient(ctx, &gssapi_client))
200 fatal("Couldn't convert client name");
201 }
202
203 return (status);
204 }
205
206 /*
207 * This parses an exported name, extracting the mechanism specific portion
208 * to use for ACL checking. It verifies that the name belongs the mechanism
209 * originally selected.
210 */
211 static OM_uint32
ssh_gssapi_parse_ename(Gssctxt * ctx,gss_buffer_t ename,gss_buffer_t name)212 ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
213 {
214 u_char *tok;
215 OM_uint32 offset;
216 OM_uint32 oidl;
217
218 tok = ename->value;
219
220 /*
221 * Check that ename is long enough for all of the fixed length
222 * header, and that the initial ID bytes are correct
223 */
224
225 if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
226 return GSS_S_FAILURE;
227
228 /*
229 * Extract the OID, and check it. Here GSSAPI breaks with tradition
230 * and does use the OID type and length bytes. To confuse things
231 * there are two lengths - the first including these, and the
232 * second without.
233 */
234
235 oidl = get_u16(tok+2); /* length including next two bytes */
236 oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
237
238 /*
239 * Check the BER encoding for correct type and length, that the
240 * string is long enough and that the OID matches that in our context
241 */
242 if (tok[4] != 0x06 || tok[5] != oidl ||
243 ename->length < oidl+6 ||
244 !ssh_gssapi_check_oid(ctx, tok+6, oidl))
245 return GSS_S_FAILURE;
246
247 offset = oidl+6;
248
249 if (ename->length < offset+4)
250 return GSS_S_FAILURE;
251
252 name->length = get_u32(tok+offset);
253 offset += 4;
254
255 if (UINT_MAX - offset < name->length)
256 return GSS_S_FAILURE;
257 if (ename->length < offset+name->length)
258 return GSS_S_FAILURE;
259
260 name->value = xmalloc(name->length+1);
261 memcpy(name->value, tok+offset, name->length);
262 ((char *)name->value)[name->length] = 0;
263
264 return GSS_S_COMPLETE;
265 }
266
267 /* Extract the client details from a given context. This can only reliably
268 * be called once for a context */
269
270 /* Privileged (called from accept_secure_ctx) */
271 OM_uint32
ssh_gssapi_getclient(Gssctxt * ctx,ssh_gssapi_client * client)272 ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
273 {
274 int i = 0;
275
276 gss_buffer_desc ename;
277
278 client->mech = NULL;
279
280 while (supported_mechs[i]->name != NULL) {
281 if (supported_mechs[i]->oid.length == ctx->oid->length &&
282 (memcmp(supported_mechs[i]->oid.elements,
283 ctx->oid->elements, ctx->oid->length) == 0))
284 client->mech = supported_mechs[i];
285 i++;
286 }
287
288 if (client->mech == NULL)
289 return GSS_S_FAILURE;
290
291 if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
292 &client->displayname, NULL))) {
293 ssh_gssapi_error(ctx);
294 return (ctx->major);
295 }
296
297 if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
298 &ename))) {
299 ssh_gssapi_error(ctx);
300 return (ctx->major);
301 }
302
303 if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
304 &client->exportedname))) {
305 return (ctx->major);
306 }
307
308 /* We can't copy this structure, so we just move the pointer to it */
309 client->creds = ctx->client_creds;
310 ctx->client_creds = GSS_C_NO_CREDENTIAL;
311 return (ctx->major);
312 }
313
314 /* As user - called on fatal/exit */
315 void
ssh_gssapi_cleanup_creds(void)316 ssh_gssapi_cleanup_creds(void)
317 {
318 if (gssapi_client.store.filename != NULL) {
319 /* Unlink probably isn't sufficient */
320 debug("removing gssapi cred file\"%s\"",
321 gssapi_client.store.filename);
322 unlink(gssapi_client.store.filename);
323 }
324 }
325
326 /* As user */
327 void
ssh_gssapi_storecreds(void)328 ssh_gssapi_storecreds(void)
329 {
330 if (gssapi_client.mech && gssapi_client.mech->storecreds) {
331 (*gssapi_client.mech->storecreds)(&gssapi_client);
332 } else
333 debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
334 }
335
336 /* This allows GSSAPI methods to do things to the child's environment based
337 * on the passed authentication process and credentials.
338 */
339 /* As user */
340 void
ssh_gssapi_do_child(char *** envp,u_int * envsizep)341 ssh_gssapi_do_child(char ***envp, u_int *envsizep)
342 {
343
344 if (gssapi_client.store.envvar != NULL &&
345 gssapi_client.store.envval != NULL) {
346 debug("Setting %s to %s", gssapi_client.store.envvar,
347 gssapi_client.store.envval);
348 child_set_env(envp, envsizep, gssapi_client.store.envvar,
349 gssapi_client.store.envval);
350 }
351 }
352
353 /* Privileged */
354 int
ssh_gssapi_userok(char * user)355 ssh_gssapi_userok(char *user)
356 {
357 OM_uint32 lmin;
358
359 if (gssapi_client.exportedname.length == 0 ||
360 gssapi_client.exportedname.value == NULL) {
361 debug("No suitable client data");
362 return 0;
363 }
364 if (gssapi_client.mech && gssapi_client.mech->userok)
365 if ((*gssapi_client.mech->userok)(&gssapi_client, user))
366 return 1;
367 else {
368 /* Destroy delegated credentials if userok fails */
369 gss_release_buffer(&lmin, &gssapi_client.displayname);
370 gss_release_buffer(&lmin, &gssapi_client.exportedname);
371 gss_release_cred(&lmin, &gssapi_client.creds);
372 explicit_bzero(&gssapi_client,
373 sizeof(ssh_gssapi_client));
374 return 0;
375 }
376 else
377 debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
378 return (0);
379 }
380
381 /* Privileged */
382 OM_uint32
ssh_gssapi_checkmic(Gssctxt * ctx,gss_buffer_t gssbuf,gss_buffer_t gssmic)383 ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
384 {
385 ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
386 gssbuf, gssmic, NULL);
387
388 return (ctx->major);
389 }
390
391 /* Privileged */
ssh_gssapi_displayname(void)392 const char *ssh_gssapi_displayname(void)
393 {
394 if (gssapi_client.displayname.length == 0 ||
395 gssapi_client.displayname.value == NULL)
396 return NULL;
397 return (char *)gssapi_client.displayname.value;
398 }
399
400 #endif
401