1 /* $OpenBSD: gss-serv.c,v 1.28 2015/01/20 23:14:00 deraadt 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
48 #include "ssh-gss.h"
49
50 static ssh_gssapi_client gssapi_client =
51 { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
52 GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}};
53
54 ssh_gssapi_mech gssapi_null_mech =
55 { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
56
57 #ifdef KRB5
58 extern ssh_gssapi_mech gssapi_kerberos_mech;
59 #endif
60
61 ssh_gssapi_mech* supported_mechs[]= {
62 #ifdef KRB5
63 &gssapi_kerberos_mech,
64 #endif
65 &gssapi_null_mech,
66 };
67
68 /*
69 * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the
70 * list of supported mechanisms before privsep is set up.
71 */
72 static gss_OID_set supported_oids;
73
74 void
ssh_gssapi_prepare_supported_oids(void)75 ssh_gssapi_prepare_supported_oids(void)
76 {
77 ssh_gssapi_supported_oids(&supported_oids);
78 }
79
80 OM_uint32
ssh_gssapi_test_oid_supported(OM_uint32 * ms,gss_OID member,int * present)81 ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present)
82 {
83 if (supported_oids == NULL)
84 ssh_gssapi_prepare_supported_oids();
85 return gss_test_oid_set_member(ms, member, supported_oids, present);
86 }
87
88 /*
89 * Acquire credentials for a server running on the current host.
90 * Requires that the context structure contains a valid OID
91 */
92
93 /* Returns a GSSAPI error code */
94 /* Privileged (called from ssh_gssapi_server_ctx) */
95 static OM_uint32
ssh_gssapi_acquire_cred(Gssctxt * ctx)96 ssh_gssapi_acquire_cred(Gssctxt *ctx)
97 {
98 OM_uint32 status;
99 char lname[NI_MAXHOST];
100 gss_OID_set oidset;
101
102 gss_create_empty_oid_set(&status, &oidset);
103 gss_add_oid_set_member(&status, ctx->oid, &oidset);
104
105 if (gethostname(lname, sizeof(lname))) {
106 gss_release_oid_set(&status, &oidset);
107 return (-1);
108 }
109
110 if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
111 gss_release_oid_set(&status, &oidset);
112 return (ctx->major);
113 }
114
115 if ((ctx->major = gss_acquire_cred(&ctx->minor,
116 ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds, NULL, NULL)))
117 ssh_gssapi_error(ctx);
118
119 gss_release_oid_set(&status, &oidset);
120 return (ctx->major);
121 }
122
123 /* Privileged */
124 OM_uint32
ssh_gssapi_server_ctx(Gssctxt ** ctx,gss_OID oid)125 ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
126 {
127 if (*ctx)
128 ssh_gssapi_delete_ctx(ctx);
129 ssh_gssapi_build_ctx(ctx);
130 ssh_gssapi_set_oid(*ctx, oid);
131 return (ssh_gssapi_acquire_cred(*ctx));
132 }
133
134 /* Unprivileged */
135 void
ssh_gssapi_supported_oids(gss_OID_set * oidset)136 ssh_gssapi_supported_oids(gss_OID_set *oidset)
137 {
138 int i = 0;
139 OM_uint32 min_status;
140 int present;
141 gss_OID_set supported;
142
143 gss_create_empty_oid_set(&min_status, oidset);
144 gss_indicate_mechs(&min_status, &supported);
145
146 while (supported_mechs[i]->name != NULL) {
147 if (GSS_ERROR(gss_test_oid_set_member(&min_status,
148 &supported_mechs[i]->oid, supported, &present)))
149 present = 0;
150 if (present)
151 gss_add_oid_set_member(&min_status,
152 &supported_mechs[i]->oid, oidset);
153 i++;
154 }
155
156 gss_release_oid_set(&min_status, &supported);
157 }
158
159
160 /* Wrapper around accept_sec_context
161 * Requires that the context contains:
162 * oid
163 * credentials (from ssh_gssapi_acquire_cred)
164 */
165 /* Privileged */
166 OM_uint32
ssh_gssapi_accept_ctx(Gssctxt * ctx,gss_buffer_desc * recv_tok,gss_buffer_desc * send_tok,OM_uint32 * flags)167 ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
168 gss_buffer_desc *send_tok, OM_uint32 *flags)
169 {
170 OM_uint32 status;
171 gss_OID mech;
172
173 ctx->major = gss_accept_sec_context(&ctx->minor,
174 &ctx->context, ctx->creds, recv_tok,
175 GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
176 send_tok, flags, NULL, &ctx->client_creds);
177
178 if (GSS_ERROR(ctx->major))
179 ssh_gssapi_error(ctx);
180
181 if (ctx->client_creds)
182 debug("Received some client credentials");
183 else
184 debug("Got no client credentials");
185
186 status = ctx->major;
187
188 /* Now, if we're complete and we have the right flags, then
189 * we flag the user as also having been authenticated
190 */
191
192 if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
193 (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
194 if (ssh_gssapi_getclient(ctx, &gssapi_client))
195 fatal("Couldn't convert client name");
196 }
197
198 return (status);
199 }
200
201 /*
202 * This parses an exported name, extracting the mechanism specific portion
203 * to use for ACL checking. It verifies that the name belongs the mechanism
204 * originally selected.
205 */
206 static OM_uint32
ssh_gssapi_parse_ename(Gssctxt * ctx,gss_buffer_t ename,gss_buffer_t name)207 ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
208 {
209 u_char *tok;
210 OM_uint32 offset;
211 OM_uint32 oidl;
212
213 tok = ename->value;
214
215 /*
216 * Check that ename is long enough for all of the fixed length
217 * header, and that the initial ID bytes are correct
218 */
219
220 if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
221 return GSS_S_FAILURE;
222
223 /*
224 * Extract the OID, and check it. Here GSSAPI breaks with tradition
225 * and does use the OID type and length bytes. To confuse things
226 * there are two lengths - the first including these, and the
227 * second without.
228 */
229
230 oidl = get_u16(tok+2); /* length including next two bytes */
231 oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
232
233 /*
234 * Check the BER encoding for correct type and length, that the
235 * string is long enough and that the OID matches that in our context
236 */
237 if (tok[4] != 0x06 || tok[5] != oidl ||
238 ename->length < oidl+6 ||
239 !ssh_gssapi_check_oid(ctx, tok+6, oidl))
240 return GSS_S_FAILURE;
241
242 offset = oidl+6;
243
244 if (ename->length < offset+4)
245 return GSS_S_FAILURE;
246
247 name->length = get_u32(tok+offset);
248 offset += 4;
249
250 if (UINT_MAX - offset < name->length)
251 return GSS_S_FAILURE;
252 if (ename->length < offset+name->length)
253 return GSS_S_FAILURE;
254
255 name->value = xmalloc(name->length+1);
256 memcpy(name->value, tok+offset, name->length);
257 ((char *)name->value)[name->length] = 0;
258
259 return GSS_S_COMPLETE;
260 }
261
262 /* Extract the client details from a given context. This can only reliably
263 * be called once for a context */
264
265 /* Privileged (called from accept_secure_ctx) */
266 OM_uint32
ssh_gssapi_getclient(Gssctxt * ctx,ssh_gssapi_client * client)267 ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
268 {
269 int i = 0;
270
271 gss_buffer_desc ename;
272
273 client->mech = NULL;
274
275 while (supported_mechs[i]->name != NULL) {
276 if (supported_mechs[i]->oid.length == ctx->oid->length &&
277 (memcmp(supported_mechs[i]->oid.elements,
278 ctx->oid->elements, ctx->oid->length) == 0))
279 client->mech = supported_mechs[i];
280 i++;
281 }
282
283 if (client->mech == NULL)
284 return GSS_S_FAILURE;
285
286 if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
287 &client->displayname, NULL))) {
288 ssh_gssapi_error(ctx);
289 return (ctx->major);
290 }
291
292 if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
293 &ename))) {
294 ssh_gssapi_error(ctx);
295 return (ctx->major);
296 }
297
298 if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
299 &client->exportedname))) {
300 return (ctx->major);
301 }
302
303 /* We can't copy this structure, so we just move the pointer to it */
304 client->creds = ctx->client_creds;
305 ctx->client_creds = GSS_C_NO_CREDENTIAL;
306 return (ctx->major);
307 }
308
309 /* As user - called on fatal/exit */
310 void
ssh_gssapi_cleanup_creds(void)311 ssh_gssapi_cleanup_creds(void)
312 {
313 if (gssapi_client.store.filename != NULL) {
314 /* Unlink probably isn't sufficient */
315 debug("removing gssapi cred file\"%s\"",
316 gssapi_client.store.filename);
317 unlink(gssapi_client.store.filename);
318 }
319 }
320
321 /* As user */
322 void
ssh_gssapi_storecreds(void)323 ssh_gssapi_storecreds(void)
324 {
325 if (gssapi_client.mech && gssapi_client.mech->storecreds) {
326 (*gssapi_client.mech->storecreds)(&gssapi_client);
327 } else
328 debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
329 }
330
331 /* This allows GSSAPI methods to do things to the childs environment based
332 * on the passed authentication process and credentials.
333 */
334 /* As user */
335 void
ssh_gssapi_do_child(char *** envp,u_int * envsizep)336 ssh_gssapi_do_child(char ***envp, u_int *envsizep)
337 {
338
339 if (gssapi_client.store.envvar != NULL &&
340 gssapi_client.store.envval != NULL) {
341 debug("Setting %s to %s", gssapi_client.store.envvar,
342 gssapi_client.store.envval);
343 child_set_env(envp, envsizep, gssapi_client.store.envvar,
344 gssapi_client.store.envval);
345 }
346 }
347
348 /* Privileged */
349 int
ssh_gssapi_userok(char * user)350 ssh_gssapi_userok(char *user)
351 {
352 OM_uint32 lmin;
353
354 if (gssapi_client.exportedname.length == 0 ||
355 gssapi_client.exportedname.value == NULL) {
356 debug("No suitable client data");
357 return 0;
358 }
359 if (gssapi_client.mech && gssapi_client.mech->userok)
360 if ((*gssapi_client.mech->userok)(&gssapi_client, user))
361 return 1;
362 else {
363 /* Destroy delegated credentials if userok fails */
364 gss_release_buffer(&lmin, &gssapi_client.displayname);
365 gss_release_buffer(&lmin, &gssapi_client.exportedname);
366 gss_release_cred(&lmin, &gssapi_client.creds);
367 explicit_bzero(&gssapi_client,
368 sizeof(ssh_gssapi_client));
369 return 0;
370 }
371 else
372 debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
373 return (0);
374 }
375
376 /* Privileged */
377 OM_uint32
ssh_gssapi_checkmic(Gssctxt * ctx,gss_buffer_t gssbuf,gss_buffer_t gssmic)378 ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
379 {
380 ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
381 gssbuf, gssmic, NULL);
382
383 return (ctx->major);
384 }
385
386 #endif
387