1 /* $OpenBSD: gss-serv.c,v 1.29 2015/05/22 03:50:02 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 "includes.h"
28
29 #ifdef GSSAPI
30
31 #include <sys/types.h>
32
33 #include <stdarg.h>
34 #include <string.h>
35 #include <unistd.h>
36
37 #include "openbsd-compat/sys-queue.h"
38 #include "xmalloc.h"
39 #include "buffer.h"
40 #include "key.h"
41 #include "hostfile.h"
42 #include "auth.h"
43 #include "log.h"
44 #include "channels.h"
45 #include "session.h"
46 #include "misc.h"
47 #include "servconf.h"
48
49 #include "ssh-gss.h"
50
51 extern ServerOptions options;
52
53 static ssh_gssapi_client gssapi_client =
54 { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
55 GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}};
56
57 ssh_gssapi_mech gssapi_null_mech =
58 { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
59
60 #ifdef KRB5
61 extern ssh_gssapi_mech gssapi_kerberos_mech;
62 #endif
63
64 ssh_gssapi_mech* supported_mechs[]= {
65 #ifdef KRB5
66 &gssapi_kerberos_mech,
67 #endif
68 &gssapi_null_mech,
69 };
70
71 /*
72 * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the
73 * list of supported mechanisms before privsep is set up.
74 */
75 static gss_OID_set supported_oids;
76
77 void
ssh_gssapi_prepare_supported_oids(void)78 ssh_gssapi_prepare_supported_oids(void)
79 {
80 ssh_gssapi_supported_oids(&supported_oids);
81 }
82
83 OM_uint32
ssh_gssapi_test_oid_supported(OM_uint32 * ms,gss_OID member,int * present)84 ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present)
85 {
86 if (supported_oids == NULL)
87 ssh_gssapi_prepare_supported_oids();
88 return gss_test_oid_set_member(ms, member, supported_oids, present);
89 }
90
91 /*
92 * Acquire credentials for a server running on the current host.
93 * Requires that the context structure contains a valid OID
94 */
95
96 /* Returns a GSSAPI error code */
97 /* Privileged (called from ssh_gssapi_server_ctx) */
98 static OM_uint32
ssh_gssapi_acquire_cred(Gssctxt * ctx)99 ssh_gssapi_acquire_cred(Gssctxt *ctx)
100 {
101 OM_uint32 status;
102 char lname[NI_MAXHOST];
103 gss_OID_set oidset;
104
105 if (options.gss_strict_acceptor) {
106 gss_create_empty_oid_set(&status, &oidset);
107 gss_add_oid_set_member(&status, ctx->oid, &oidset);
108
109 if (gethostname(lname, MAXHOSTNAMELEN)) {
110 gss_release_oid_set(&status, &oidset);
111 return (-1);
112 }
113
114 if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
115 gss_release_oid_set(&status, &oidset);
116 return (ctx->major);
117 }
118
119 if ((ctx->major = gss_acquire_cred(&ctx->minor,
120 ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds,
121 NULL, NULL)))
122 ssh_gssapi_error(ctx);
123
124 gss_release_oid_set(&status, &oidset);
125 return (ctx->major);
126 } else {
127 ctx->name = GSS_C_NO_NAME;
128 ctx->creds = GSS_C_NO_CREDENTIAL;
129 }
130 return GSS_S_COMPLETE;
131 }
132
133 /* Privileged */
134 OM_uint32
ssh_gssapi_server_ctx(Gssctxt ** ctx,gss_OID oid)135 ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
136 {
137 if (*ctx)
138 ssh_gssapi_delete_ctx(ctx);
139 ssh_gssapi_build_ctx(ctx);
140 ssh_gssapi_set_oid(*ctx, oid);
141 return (ssh_gssapi_acquire_cred(*ctx));
142 }
143
144 /* Unprivileged */
145 void
ssh_gssapi_supported_oids(gss_OID_set * oidset)146 ssh_gssapi_supported_oids(gss_OID_set *oidset)
147 {
148 int i = 0;
149 OM_uint32 min_status;
150 int present;
151 gss_OID_set supported;
152
153 gss_create_empty_oid_set(&min_status, oidset);
154 gss_indicate_mechs(&min_status, &supported);
155
156 while (supported_mechs[i]->name != NULL) {
157 if (GSS_ERROR(gss_test_oid_set_member(&min_status,
158 &supported_mechs[i]->oid, supported, &present)))
159 present = 0;
160 if (present)
161 gss_add_oid_set_member(&min_status,
162 &supported_mechs[i]->oid, oidset);
163 i++;
164 }
165
166 gss_release_oid_set(&min_status, &supported);
167 }
168
169
170 /* Wrapper around accept_sec_context
171 * Requires that the context contains:
172 * oid
173 * credentials (from ssh_gssapi_acquire_cred)
174 */
175 /* Privileged */
176 OM_uint32
ssh_gssapi_accept_ctx(Gssctxt * ctx,gss_buffer_desc * recv_tok,gss_buffer_desc * send_tok,OM_uint32 * flags)177 ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
178 gss_buffer_desc *send_tok, OM_uint32 *flags)
179 {
180 OM_uint32 status;
181 gss_OID mech;
182
183 ctx->major = gss_accept_sec_context(&ctx->minor,
184 &ctx->context, ctx->creds, recv_tok,
185 GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
186 send_tok, flags, NULL, &ctx->client_creds);
187
188 if (GSS_ERROR(ctx->major))
189 ssh_gssapi_error(ctx);
190
191 if (ctx->client_creds)
192 debug("Received some client credentials");
193 else
194 debug("Got no client credentials");
195
196 status = ctx->major;
197
198 /* Now, if we're complete and we have the right flags, then
199 * we flag the user as also having been authenticated
200 */
201
202 if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
203 (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
204 if (ssh_gssapi_getclient(ctx, &gssapi_client))
205 fatal("Couldn't convert client name");
206 }
207
208 return (status);
209 }
210
211 /*
212 * This parses an exported name, extracting the mechanism specific portion
213 * to use for ACL checking. It verifies that the name belongs the mechanism
214 * originally selected.
215 */
216 static OM_uint32
ssh_gssapi_parse_ename(Gssctxt * ctx,gss_buffer_t ename,gss_buffer_t name)217 ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
218 {
219 u_char *tok;
220 OM_uint32 offset;
221 OM_uint32 oidl;
222
223 tok = ename->value;
224
225 /*
226 * Check that ename is long enough for all of the fixed length
227 * header, and that the initial ID bytes are correct
228 */
229
230 if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
231 return GSS_S_FAILURE;
232
233 /*
234 * Extract the OID, and check it. Here GSSAPI breaks with tradition
235 * and does use the OID type and length bytes. To confuse things
236 * there are two lengths - the first including these, and the
237 * second without.
238 */
239
240 oidl = get_u16(tok+2); /* length including next two bytes */
241 oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
242
243 /*
244 * Check the BER encoding for correct type and length, that the
245 * string is long enough and that the OID matches that in our context
246 */
247 if (tok[4] != 0x06 || tok[5] != oidl ||
248 ename->length < oidl+6 ||
249 !ssh_gssapi_check_oid(ctx, tok+6, oidl))
250 return GSS_S_FAILURE;
251
252 offset = oidl+6;
253
254 if (ename->length < offset+4)
255 return GSS_S_FAILURE;
256
257 name->length = get_u32(tok+offset);
258 offset += 4;
259
260 if (UINT_MAX - offset < name->length)
261 return GSS_S_FAILURE;
262 if (ename->length < offset+name->length)
263 return GSS_S_FAILURE;
264
265 name->value = xmalloc(name->length+1);
266 memcpy(name->value, tok+offset, name->length);
267 ((char *)name->value)[name->length] = 0;
268
269 return GSS_S_COMPLETE;
270 }
271
272 /* Extract the client details from a given context. This can only reliably
273 * be called once for a context */
274
275 /* Privileged (called from accept_secure_ctx) */
276 OM_uint32
ssh_gssapi_getclient(Gssctxt * ctx,ssh_gssapi_client * client)277 ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
278 {
279 int i = 0;
280
281 gss_buffer_desc ename;
282
283 client->mech = NULL;
284
285 while (supported_mechs[i]->name != NULL) {
286 if (supported_mechs[i]->oid.length == ctx->oid->length &&
287 (memcmp(supported_mechs[i]->oid.elements,
288 ctx->oid->elements, ctx->oid->length) == 0))
289 client->mech = supported_mechs[i];
290 i++;
291 }
292
293 if (client->mech == NULL)
294 return GSS_S_FAILURE;
295
296 if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
297 &client->displayname, NULL))) {
298 ssh_gssapi_error(ctx);
299 return (ctx->major);
300 }
301
302 if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
303 &ename))) {
304 ssh_gssapi_error(ctx);
305 return (ctx->major);
306 }
307
308 if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
309 &client->exportedname))) {
310 return (ctx->major);
311 }
312
313 /* We can't copy this structure, so we just move the pointer to it */
314 client->creds = ctx->client_creds;
315 ctx->client_creds = GSS_C_NO_CREDENTIAL;
316 return (ctx->major);
317 }
318
319 /* As user - called on fatal/exit */
320 void
ssh_gssapi_cleanup_creds(void)321 ssh_gssapi_cleanup_creds(void)
322 {
323 if (gssapi_client.store.filename != NULL) {
324 /* Unlink probably isn't sufficient */
325 debug("removing gssapi cred file\"%s\"",
326 gssapi_client.store.filename);
327 unlink(gssapi_client.store.filename);
328 }
329 }
330
331 /* As user */
332 void
ssh_gssapi_storecreds(void)333 ssh_gssapi_storecreds(void)
334 {
335 if (gssapi_client.mech && gssapi_client.mech->storecreds) {
336 (*gssapi_client.mech->storecreds)(&gssapi_client);
337 } else
338 debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
339 }
340
341 /* This allows GSSAPI methods to do things to the childs environment based
342 * on the passed authentication process and credentials.
343 */
344 /* As user */
345 void
ssh_gssapi_do_child(char *** envp,u_int * envsizep)346 ssh_gssapi_do_child(char ***envp, u_int *envsizep)
347 {
348
349 if (gssapi_client.store.envvar != NULL &&
350 gssapi_client.store.envval != NULL) {
351 debug("Setting %s to %s", gssapi_client.store.envvar,
352 gssapi_client.store.envval);
353 child_set_env(envp, envsizep, gssapi_client.store.envvar,
354 gssapi_client.store.envval);
355 }
356 }
357
358 /* Privileged */
359 int
ssh_gssapi_userok(char * user)360 ssh_gssapi_userok(char *user)
361 {
362 OM_uint32 lmin;
363
364 if (gssapi_client.exportedname.length == 0 ||
365 gssapi_client.exportedname.value == NULL) {
366 debug("No suitable client data");
367 return 0;
368 }
369 if (gssapi_client.mech && gssapi_client.mech->userok)
370 if ((*gssapi_client.mech->userok)(&gssapi_client, user))
371 return 1;
372 else {
373 /* Destroy delegated credentials if userok fails */
374 gss_release_buffer(&lmin, &gssapi_client.displayname);
375 gss_release_buffer(&lmin, &gssapi_client.exportedname);
376 gss_release_cred(&lmin, &gssapi_client.creds);
377 explicit_bzero(&gssapi_client,
378 sizeof(ssh_gssapi_client));
379 return 0;
380 }
381 else
382 debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
383 return (0);
384 }
385
386 /* Privileged */
387 OM_uint32
ssh_gssapi_checkmic(Gssctxt * ctx,gss_buffer_t gssbuf,gss_buffer_t gssmic)388 ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
389 {
390 ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
391 gssbuf, gssmic, NULL);
392
393 return (ctx->major);
394 }
395
396 #endif
397