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