1 /* $OpenBSD: gss-serv.c,v 1.26 2014/02/26 20:28:44 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 #include <sys/param.h>
33
34 #include <stdarg.h>
35 #include <string.h>
36 #include <unistd.h>
37
38 #include "openbsd-compat/sys-queue.h"
39 #include "xmalloc.h"
40 #include "buffer.h"
41 #include "key.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
49 #include "ssh-gss.h"
50
51 static ssh_gssapi_client gssapi_client =
52 { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
53 GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}};
54
55 ssh_gssapi_mech gssapi_null_mech =
56 { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
57
58 #ifdef KRB5
59 extern ssh_gssapi_mech gssapi_kerberos_mech;
60 #endif
61
62 ssh_gssapi_mech* supported_mechs[]= {
63 #ifdef KRB5
64 &gssapi_kerberos_mech,
65 #endif
66 &gssapi_null_mech,
67 };
68
69 /*
70 * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the
71 * list of supported mechanisms before privsep is set up.
72 */
73 static gss_OID_set supported_oids;
74
75 void
ssh_gssapi_prepare_supported_oids(void)76 ssh_gssapi_prepare_supported_oids(void)
77 {
78 ssh_gssapi_supported_oids(&supported_oids);
79 }
80
81 OM_uint32
ssh_gssapi_test_oid_supported(OM_uint32 * ms,gss_OID member,int * present)82 ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present)
83 {
84 if (supported_oids == NULL)
85 ssh_gssapi_prepare_supported_oids();
86 return gss_test_oid_set_member(ms, member, supported_oids, present);
87 }
88
89 /*
90 * Acquire credentials for a server running on the current host.
91 * Requires that the context structure contains a valid OID
92 */
93
94 /* Returns a GSSAPI error code */
95 /* Privileged (called from ssh_gssapi_server_ctx) */
96 static OM_uint32
ssh_gssapi_acquire_cred(Gssctxt * ctx)97 ssh_gssapi_acquire_cred(Gssctxt *ctx)
98 {
99 OM_uint32 status;
100 char lname[MAXHOSTNAMELEN];
101 gss_OID_set oidset;
102
103 gss_create_empty_oid_set(&status, &oidset);
104 gss_add_oid_set_member(&status, ctx->oid, &oidset);
105
106 if (gethostname(lname, MAXHOSTNAMELEN)) {
107 gss_release_oid_set(&status, &oidset);
108 return (-1);
109 }
110
111 if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
112 gss_release_oid_set(&status, &oidset);
113 return (ctx->major);
114 }
115
116 if ((ctx->major = gss_acquire_cred(&ctx->minor,
117 ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds, NULL, NULL)))
118 ssh_gssapi_error(ctx);
119
120 gss_release_oid_set(&status, &oidset);
121 return (ctx->major);
122 }
123
124 /* Privileged */
125 OM_uint32
ssh_gssapi_server_ctx(Gssctxt ** ctx,gss_OID oid)126 ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
127 {
128 if (*ctx)
129 ssh_gssapi_delete_ctx(ctx);
130 ssh_gssapi_build_ctx(ctx);
131 ssh_gssapi_set_oid(*ctx, oid);
132 return (ssh_gssapi_acquire_cred(*ctx));
133 }
134
135 /* Unprivileged */
136 void
ssh_gssapi_supported_oids(gss_OID_set * oidset)137 ssh_gssapi_supported_oids(gss_OID_set *oidset)
138 {
139 int i = 0;
140 OM_uint32 min_status;
141 int present;
142 gss_OID_set supported;
143
144 gss_create_empty_oid_set(&min_status, oidset);
145 gss_indicate_mechs(&min_status, &supported);
146
147 while (supported_mechs[i]->name != NULL) {
148 if (GSS_ERROR(gss_test_oid_set_member(&min_status,
149 &supported_mechs[i]->oid, supported, &present)))
150 present = 0;
151 if (present)
152 gss_add_oid_set_member(&min_status,
153 &supported_mechs[i]->oid, oidset);
154 i++;
155 }
156
157 gss_release_oid_set(&min_status, &supported);
158 }
159
160
161 /* Wrapper around accept_sec_context
162 * Requires that the context contains:
163 * oid
164 * credentials (from ssh_gssapi_acquire_cred)
165 */
166 /* Privileged */
167 OM_uint32
ssh_gssapi_accept_ctx(Gssctxt * ctx,gss_buffer_desc * recv_tok,gss_buffer_desc * send_tok,OM_uint32 * flags)168 ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
169 gss_buffer_desc *send_tok, OM_uint32 *flags)
170 {
171 OM_uint32 status;
172 gss_OID mech;
173
174 ctx->major = gss_accept_sec_context(&ctx->minor,
175 &ctx->context, ctx->creds, recv_tok,
176 GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
177 send_tok, flags, NULL, &ctx->client_creds);
178
179 if (GSS_ERROR(ctx->major))
180 ssh_gssapi_error(ctx);
181
182 if (ctx->client_creds)
183 debug("Received some client credentials");
184 else
185 debug("Got no client credentials");
186
187 status = ctx->major;
188
189 /* Now, if we're complete and we have the right flags, then
190 * we flag the user as also having been authenticated
191 */
192
193 if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
194 (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
195 if (ssh_gssapi_getclient(ctx, &gssapi_client))
196 fatal("Couldn't convert client name");
197 }
198
199 return (status);
200 }
201
202 /*
203 * This parses an exported name, extracting the mechanism specific portion
204 * to use for ACL checking. It verifies that the name belongs the mechanism
205 * originally selected.
206 */
207 static OM_uint32
ssh_gssapi_parse_ename(Gssctxt * ctx,gss_buffer_t ename,gss_buffer_t name)208 ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
209 {
210 u_char *tok;
211 OM_uint32 offset;
212 OM_uint32 oidl;
213
214 tok = ename->value;
215
216 /*
217 * Check that ename is long enough for all of the fixed length
218 * header, and that the initial ID bytes are correct
219 */
220
221 if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
222 return GSS_S_FAILURE;
223
224 /*
225 * Extract the OID, and check it. Here GSSAPI breaks with tradition
226 * and does use the OID type and length bytes. To confuse things
227 * there are two lengths - the first including these, and the
228 * second without.
229 */
230
231 oidl = get_u16(tok+2); /* length including next two bytes */
232 oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
233
234 /*
235 * Check the BER encoding for correct type and length, that the
236 * string is long enough and that the OID matches that in our context
237 */
238 if (tok[4] != 0x06 || tok[5] != oidl ||
239 ename->length < oidl+6 ||
240 !ssh_gssapi_check_oid(ctx, tok+6, oidl))
241 return GSS_S_FAILURE;
242
243 offset = oidl+6;
244
245 if (ename->length < offset+4)
246 return GSS_S_FAILURE;
247
248 name->length = get_u32(tok+offset);
249 offset += 4;
250
251 if (UINT_MAX - offset < name->length)
252 return GSS_S_FAILURE;
253 if (ename->length < offset+name->length)
254 return GSS_S_FAILURE;
255
256 name->value = xmalloc(name->length+1);
257 memcpy(name->value, tok+offset, name->length);
258 ((char *)name->value)[name->length] = 0;
259
260 return GSS_S_COMPLETE;
261 }
262
263 /* Extract the client details from a given context. This can only reliably
264 * be called once for a context */
265
266 /* Privileged (called from accept_secure_ctx) */
267 OM_uint32
ssh_gssapi_getclient(Gssctxt * ctx,ssh_gssapi_client * client)268 ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
269 {
270 int i = 0;
271
272 gss_buffer_desc ename;
273
274 client->mech = NULL;
275
276 while (supported_mechs[i]->name != NULL) {
277 if (supported_mechs[i]->oid.length == ctx->oid->length &&
278 (memcmp(supported_mechs[i]->oid.elements,
279 ctx->oid->elements, ctx->oid->length) == 0))
280 client->mech = supported_mechs[i];
281 i++;
282 }
283
284 if (client->mech == NULL)
285 return GSS_S_FAILURE;
286
287 if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
288 &client->displayname, NULL))) {
289 ssh_gssapi_error(ctx);
290 return (ctx->major);
291 }
292
293 if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
294 &ename))) {
295 ssh_gssapi_error(ctx);
296 return (ctx->major);
297 }
298
299 if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
300 &client->exportedname))) {
301 return (ctx->major);
302 }
303
304 /* We can't copy this structure, so we just move the pointer to it */
305 client->creds = ctx->client_creds;
306 ctx->client_creds = GSS_C_NO_CREDENTIAL;
307 return (ctx->major);
308 }
309
310 /* As user - called on fatal/exit */
311 void
ssh_gssapi_cleanup_creds(void)312 ssh_gssapi_cleanup_creds(void)
313 {
314 if (gssapi_client.store.filename != NULL) {
315 /* Unlink probably isn't sufficient */
316 debug("removing gssapi cred file\"%s\"",
317 gssapi_client.store.filename);
318 unlink(gssapi_client.store.filename);
319 }
320 }
321
322 /* As user */
323 void
ssh_gssapi_storecreds(void)324 ssh_gssapi_storecreds(void)
325 {
326 if (gssapi_client.mech && gssapi_client.mech->storecreds) {
327 (*gssapi_client.mech->storecreds)(&gssapi_client);
328 } else
329 debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
330 }
331
332 /* This allows GSSAPI methods to do things to the childs environment based
333 * on the passed authentication process and credentials.
334 */
335 /* As user */
336 void
ssh_gssapi_do_child(char *** envp,u_int * envsizep)337 ssh_gssapi_do_child(char ***envp, u_int *envsizep)
338 {
339
340 if (gssapi_client.store.envvar != NULL &&
341 gssapi_client.store.envval != NULL) {
342 debug("Setting %s to %s", gssapi_client.store.envvar,
343 gssapi_client.store.envval);
344 child_set_env(envp, envsizep, gssapi_client.store.envvar,
345 gssapi_client.store.envval);
346 }
347 }
348
349 /* Privileged */
350 int
ssh_gssapi_userok(char * user)351 ssh_gssapi_userok(char *user)
352 {
353 OM_uint32 lmin;
354
355 if (gssapi_client.exportedname.length == 0 ||
356 gssapi_client.exportedname.value == NULL) {
357 debug("No suitable client data");
358 return 0;
359 }
360 if (gssapi_client.mech && gssapi_client.mech->userok)
361 if ((*gssapi_client.mech->userok)(&gssapi_client, user))
362 return 1;
363 else {
364 /* Destroy delegated credentials if userok fails */
365 gss_release_buffer(&lmin, &gssapi_client.displayname);
366 gss_release_buffer(&lmin, &gssapi_client.exportedname);
367 gss_release_cred(&lmin, &gssapi_client.creds);
368 explicit_bzero(&gssapi_client,
369 sizeof(ssh_gssapi_client));
370 return 0;
371 }
372 else
373 debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
374 return (0);
375 }
376
377 /* Privileged */
378 OM_uint32
ssh_gssapi_checkmic(Gssctxt * ctx,gss_buffer_t gssbuf,gss_buffer_t gssmic)379 ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
380 {
381 ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
382 gssbuf, gssmic, NULL);
383
384 return (ctx->major);
385 }
386
387 #endif
388