1 /* $NetBSD: gss-serv.c,v 1.16 2025/02/18 17:53:24 christos Exp $ */
2 /* $OpenBSD: gss-serv.c,v 1.32 2020/03/13 03:17:07 djm Exp $ */
3
4 /*
5 * Copyright (c) 2001-2003 Simon Wilkinson. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR `AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28 #include "includes.h"
29 __RCSID("$NetBSD: gss-serv.c,v 1.16 2025/02/18 17:53:24 christos Exp $");
30
31 #include <sys/param.h>
32 #include <sys/types.h>
33 #include <sys/queue.h>
34
35 #ifdef GSSAPI
36
37 #include <string.h>
38 #include <unistd.h>
39 #include <netdb.h>
40 #include <limits.h>
41 #include <stdarg.h>
42
43 #include "xmalloc.h"
44 #include "sshkey.h"
45 #include "hostfile.h"
46 #include "auth.h"
47 #include "log.h"
48 #include "channels.h"
49 #include "session.h"
50 #include "misc.h"
51 #include "servconf.h"
52
53 #include "ssh-gss.h"
54
55 extern ServerOptions options;
56
57 static ssh_gssapi_client gssapi_client =
58 { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
59 GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}};
60
61 ssh_gssapi_mech gssapi_null_mech =
62 { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
63
64 #ifdef KRB5
65 extern ssh_gssapi_mech gssapi_kerberos_mech;
66 #endif
67
68 ssh_gssapi_mech* supported_mechs[]= {
69 #ifdef KRB5
70 &gssapi_kerberos_mech,
71 #endif
72 &gssapi_null_mech,
73 };
74
75 /*
76 * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the
77 * list of supported mechanisms before privsep is set up.
78 */
79 static gss_OID_set supported_oids;
80
81 void
ssh_gssapi_prepare_supported_oids(void)82 ssh_gssapi_prepare_supported_oids(void)
83 {
84 ssh_gssapi_supported_oids(&supported_oids);
85 }
86
87 OM_uint32
ssh_gssapi_test_oid_supported(OM_uint32 * ms,gss_OID member,int * present)88 ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present)
89 {
90 if (supported_oids == NULL)
91 ssh_gssapi_prepare_supported_oids();
92 return gss_test_oid_set_member(ms, member, supported_oids, present);
93 }
94
95 /*
96 * Acquire credentials for a server running on the current host.
97 * Requires that the context structure contains a valid OID
98 */
99
100 /* Returns a GSSAPI error code */
101 /* Privileged (called from ssh_gssapi_server_ctx) */
102 static OM_uint32
ssh_gssapi_acquire_cred(Gssctxt * ctx)103 ssh_gssapi_acquire_cred(Gssctxt *ctx)
104 {
105 OM_uint32 status;
106 char lname[NI_MAXHOST];
107 gss_OID_set oidset;
108
109 if (options.gss_strict_acceptor) {
110 gss_create_empty_oid_set(&status, &oidset);
111 gss_add_oid_set_member(&status, ctx->oid, &oidset);
112
113 if (gethostname(lname, MAXHOSTNAMELEN)) {
114 gss_release_oid_set(&status, &oidset);
115 return (-1);
116 }
117
118 if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
119 gss_release_oid_set(&status, &oidset);
120 return (ctx->major);
121 }
122
123 if ((ctx->major = gss_acquire_cred(&ctx->minor,
124 ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds,
125 NULL, NULL)))
126 ssh_gssapi_error(ctx);
127
128 gss_release_oid_set(&status, &oidset);
129 return (ctx->major);
130 } else {
131 ctx->name = GSS_C_NO_NAME;
132 ctx->creds = GSS_C_NO_CREDENTIAL;
133 }
134 return GSS_S_COMPLETE;
135 }
136
137 /* Privileged */
138 OM_uint32
ssh_gssapi_server_ctx(Gssctxt ** ctx,gss_OID oid)139 ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
140 {
141 if (*ctx)
142 ssh_gssapi_delete_ctx(ctx);
143 ssh_gssapi_build_ctx(ctx);
144 ssh_gssapi_set_oid(*ctx, oid);
145 return (ssh_gssapi_acquire_cred(*ctx));
146 }
147
148 /* Unprivileged */
149 void
ssh_gssapi_supported_oids(gss_OID_set * oidset)150 ssh_gssapi_supported_oids(gss_OID_set *oidset)
151 {
152 int i = 0;
153 OM_uint32 min_status;
154 int present;
155 gss_OID_set supported;
156
157 gss_create_empty_oid_set(&min_status, oidset);
158 gss_indicate_mechs(&min_status, &supported);
159
160 while (supported_mechs[i]->name != NULL) {
161 if (GSS_ERROR(gss_test_oid_set_member(&min_status,
162 &supported_mechs[i]->oid, supported, &present)))
163 present = 0;
164 if (present)
165 gss_add_oid_set_member(&min_status,
166 &supported_mechs[i]->oid, oidset);
167 i++;
168 }
169
170 gss_release_oid_set(&min_status, &supported);
171 }
172
173
174 /* Wrapper around accept_sec_context
175 * Requires that the context contains:
176 * oid
177 * credentials (from ssh_gssapi_acquire_cred)
178 */
179 /* Privileged */
180 OM_uint32
ssh_gssapi_accept_ctx(Gssctxt * ctx,gss_buffer_desc * recv_tok,gss_buffer_desc * send_tok,OM_uint32 * flags)181 ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
182 gss_buffer_desc *send_tok, OM_uint32 *flags)
183 {
184 OM_uint32 status;
185 gss_OID mech;
186
187 ctx->major = gss_accept_sec_context(&ctx->minor,
188 &ctx->context, ctx->creds, recv_tok,
189 GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
190 send_tok, flags, NULL, &ctx->client_creds);
191
192 if (GSS_ERROR(ctx->major))
193 ssh_gssapi_error(ctx);
194
195 if (ctx->client_creds)
196 debug("Received some client credentials");
197 else
198 debug("Got no client credentials");
199
200 status = ctx->major;
201
202 /* Now, if we're complete and we have the right flags, then
203 * we flag the user as also having been authenticated
204 */
205
206 if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
207 (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
208 if (ssh_gssapi_getclient(ctx, &gssapi_client))
209 fatal("Couldn't convert client name");
210 }
211
212 return (status);
213 }
214
215 /*
216 * This parses an exported name, extracting the mechanism specific portion
217 * to use for ACL checking. It verifies that the name belongs the mechanism
218 * originally selected.
219 */
220 static OM_uint32
ssh_gssapi_parse_ename(Gssctxt * ctx,gss_buffer_t ename,gss_buffer_t name)221 ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
222 {
223 u_char *tok;
224 OM_uint32 offset;
225 OM_uint32 oidl;
226
227 tok = ename->value;
228
229 /*
230 * Check that ename is long enough for all of the fixed length
231 * header, and that the initial ID bytes are correct
232 */
233
234 if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
235 return GSS_S_FAILURE;
236
237 /*
238 * Extract the OID, and check it. Here GSSAPI breaks with tradition
239 * and does use the OID type and length bytes. To confuse things
240 * there are two lengths - the first including these, and the
241 * second without.
242 */
243
244 oidl = get_u16(tok+2); /* length including next two bytes */
245 oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
246
247 /*
248 * Check the BER encoding for correct type and length, that the
249 * string is long enough and that the OID matches that in our context
250 */
251 if (tok[4] != 0x06 || tok[5] != oidl ||
252 ename->length < oidl+6 ||
253 !ssh_gssapi_check_oid(ctx, tok+6, oidl))
254 return GSS_S_FAILURE;
255
256 offset = oidl+6;
257
258 if (ename->length < offset+4)
259 return GSS_S_FAILURE;
260
261 name->length = get_u32(tok+offset);
262 offset += 4;
263
264 if (UINT_MAX - offset < name->length)
265 return GSS_S_FAILURE;
266 if (ename->length < offset+name->length)
267 return GSS_S_FAILURE;
268
269 name->value = xmalloc(name->length+1);
270 memcpy(name->value, tok+offset, name->length);
271 ((char *)name->value)[name->length] = 0;
272
273 return GSS_S_COMPLETE;
274 }
275
276 /* Extract the client details from a given context. This can only reliably
277 * be called once for a context */
278
279 /* Privileged (called from accept_secure_ctx) */
280 OM_uint32
ssh_gssapi_getclient(Gssctxt * ctx,ssh_gssapi_client * client)281 ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
282 {
283 int i = 0;
284
285 gss_buffer_desc ename;
286
287 client->mech = NULL;
288
289 while (supported_mechs[i]->name != NULL) {
290 if (supported_mechs[i]->oid.length == ctx->oid->length &&
291 (memcmp(supported_mechs[i]->oid.elements,
292 ctx->oid->elements, ctx->oid->length) == 0))
293 client->mech = supported_mechs[i];
294 i++;
295 }
296
297 if (client->mech == NULL)
298 return GSS_S_FAILURE;
299
300 if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
301 &client->displayname, NULL))) {
302 ssh_gssapi_error(ctx);
303 return (ctx->major);
304 }
305
306 if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
307 &ename))) {
308 ssh_gssapi_error(ctx);
309 return (ctx->major);
310 }
311
312 if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
313 &client->exportedname))) {
314 return (ctx->major);
315 }
316
317 /* We can't copy this structure, so we just move the pointer to it */
318 client->creds = ctx->client_creds;
319 ctx->client_creds = GSS_C_NO_CREDENTIAL;
320 return (ctx->major);
321 }
322
323 /* As user - called on fatal/exit */
324 void
ssh_gssapi_cleanup_creds(void)325 ssh_gssapi_cleanup_creds(void)
326 {
327 if (gssapi_client.store.filename != NULL) {
328 /* Unlink probably isn't sufficient */
329 debug("removing gssapi cred file\"%s\"",
330 gssapi_client.store.filename);
331 unlink(gssapi_client.store.filename);
332 }
333 }
334
335 /* As user */
336 void
ssh_gssapi_storecreds(void)337 ssh_gssapi_storecreds(void)
338 {
339 if (gssapi_client.mech && gssapi_client.mech->storecreds) {
340 (*gssapi_client.mech->storecreds)(&gssapi_client);
341 } else
342 debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
343 }
344
345 /* This allows GSSAPI methods to do things to the child's environment based
346 * on the passed authentication process and credentials.
347 */
348 /* As user */
349 void
ssh_gssapi_do_child(char *** envp,u_int * envsizep)350 ssh_gssapi_do_child(char ***envp, u_int *envsizep)
351 {
352
353 if (gssapi_client.store.envvar != NULL &&
354 gssapi_client.store.envval != NULL) {
355 debug("Setting %s to %s", gssapi_client.store.envvar,
356 gssapi_client.store.envval);
357 child_set_env(envp, envsizep, gssapi_client.store.envvar,
358 gssapi_client.store.envval);
359 }
360 }
361
362 /* Privileged */
363 int
ssh_gssapi_userok(char * user)364 ssh_gssapi_userok(char *user)
365 {
366 OM_uint32 lmin;
367
368 if (gssapi_client.exportedname.length == 0 ||
369 gssapi_client.exportedname.value == NULL) {
370 debug("No suitable client data");
371 return 0;
372 }
373 if (gssapi_client.mech && gssapi_client.mech->userok)
374 if ((*gssapi_client.mech->userok)(&gssapi_client, user))
375 return 1;
376 else {
377 /* Destroy delegated credentials if userok fails */
378 gss_release_buffer(&lmin, &gssapi_client.displayname);
379 gss_release_buffer(&lmin, &gssapi_client.exportedname);
380 gss_release_cred(&lmin, &gssapi_client.creds);
381 explicit_bzero(&gssapi_client,
382 sizeof(ssh_gssapi_client));
383 return 0;
384 }
385 else
386 debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
387 return (0);
388 }
389
390 /* Privileged */
391 OM_uint32
ssh_gssapi_checkmic(Gssctxt * ctx,gss_buffer_t gssbuf,gss_buffer_t gssmic)392 ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
393 {
394 ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
395 gssbuf, gssmic, NULL);
396
397 return (ctx->major);
398 }
399
400 /* Privileged */
ssh_gssapi_displayname(void)401 const char *ssh_gssapi_displayname(void)
402 {
403 if (gssapi_client.displayname.length == 0 ||
404 gssapi_client.displayname.value == NULL)
405 return NULL;
406 return (char *)gssapi_client.displayname.value;
407 }
408
409 #endif
410