1 /* $OpenBSD: auth2-gss.c,v 1.41 2026/07/06 07:53:30 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
35 #include "xmalloc.h"
36 #include "sshkey.h"
37 #include "hostfile.h"
38 #include "auth.h"
39 #include "ssh2.h"
40 #include "log.h"
41 #include "dispatch.h"
42 #include "sshbuf.h"
43 #include "ssherr.h"
44 #include "misc.h"
45 #include "servconf.h"
46 #include "packet.h"
47 #include "kex.h"
48 #include "ssh-gss.h"
49 #include "monitor_wrap.h"
50
51 #define SSH_GSSAPI_MAX_MECHS 2048
52
53 extern ServerOptions options;
54 extern struct authmethod_cfg methodcfg_gssapi;
55
56 static int input_gssapi_token(int type, uint32_t plen, struct ssh *ssh);
57 static int input_gssapi_mic(int type, uint32_t plen, struct ssh *ssh);
58 static int input_gssapi_exchange_complete(int type, uint32_t plen, struct ssh *ssh);
59 static int input_gssapi_errtok(int, uint32_t, struct ssh *);
60
61 /*
62 * We only support those mechanisms that we know about (ie ones that we know
63 * how to check local user kuserok and the like)
64 */
65 static int
userauth_gssapi(struct ssh * ssh,const char * method)66 userauth_gssapi(struct ssh *ssh, const char *method)
67 {
68 Authctxt *authctxt = ssh->authctxt;
69 gss_OID_desc goid = {0, NULL};
70 Gssctxt *ctxt = NULL;
71 int r, present;
72 u_int mechs;
73 OM_uint32 ms;
74 size_t len;
75 u_char *doid = NULL;
76
77 if ((r = sshpkt_get_u32(ssh, &mechs)) != 0)
78 fatal_fr(r, "parse packet");
79
80 if (mechs == 0) {
81 logit_f("mechanism negotiation is not supported");
82 return (0);
83 } else if (mechs > SSH_GSSAPI_MAX_MECHS) {
84 logit_f("too many mechanisms requested %u > %u", mechs,
85 SSH_GSSAPI_MAX_MECHS);
86 return (0);
87 }
88
89 do {
90 mechs--;
91
92 free(doid);
93
94 present = 0;
95 if ((r = sshpkt_get_string(ssh, &doid, &len)) != 0)
96 fatal_fr(r, "parse oid");
97
98 if (len > 2 && doid[0] == SSH_GSS_OIDTYPE &&
99 doid[1] == len - 2) {
100 goid.elements = doid + 2;
101 goid.length = len - 2;
102 ssh_gssapi_test_oid_supported(&ms, &goid, &present);
103 } else {
104 logit_f("badly formed OID received");
105 }
106 } while (mechs > 0 && !present);
107
108 if (!present) {
109 free(doid);
110 authctxt->server_caused_failure = 1;
111 return (0);
112 }
113
114 if (GSS_ERROR(mm_ssh_gssapi_server_ctx(&ctxt, &goid))) {
115 if (ctxt != NULL)
116 ssh_gssapi_delete_ctx(&ctxt);
117 free(doid);
118 authctxt->server_caused_failure = 1;
119 return (0);
120 }
121
122 authctxt->methoddata = (void *)ctxt;
123
124 /* Return the OID that we received */
125 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_GSSAPI_RESPONSE)) != 0 ||
126 (r = sshpkt_put_string(ssh, doid, len)) != 0 ||
127 (r = sshpkt_send(ssh)) != 0)
128 fatal_fr(r, "send packet");
129
130 free(doid);
131
132 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, &input_gssapi_token);
133 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, &input_gssapi_errtok);
134 authctxt->postponed = 1;
135
136 return (0);
137 }
138
139 static int
input_gssapi_token(int type,uint32_t plen,struct ssh * ssh)140 input_gssapi_token(int type, uint32_t plen, struct ssh *ssh)
141 {
142 Authctxt *authctxt = ssh->authctxt;
143 Gssctxt *gssctxt;
144 gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
145 gss_buffer_desc recv_tok;
146 OM_uint32 maj_status, min_status, flags;
147 u_char *p;
148 size_t len;
149 int r;
150
151 if (authctxt == NULL)
152 fatal("No authentication or GSSAPI context");
153
154 gssctxt = authctxt->methoddata;
155 if ((r = sshpkt_get_string(ssh, &p, &len)) != 0 ||
156 (r = sshpkt_get_end(ssh)) != 0)
157 fatal_fr(r, "parse packet");
158
159 recv_tok.value = p;
160 recv_tok.length = len;
161 maj_status = mm_ssh_gssapi_accept_ctx(gssctxt, &recv_tok,
162 &send_tok, &flags);
163
164 free(p);
165
166 if (GSS_ERROR(maj_status)) {
167 if (send_tok.length != 0) {
168 if ((r = sshpkt_start(ssh,
169 SSH2_MSG_USERAUTH_GSSAPI_ERRTOK)) != 0 ||
170 (r = sshpkt_put_string(ssh, send_tok.value,
171 send_tok.length)) != 0 ||
172 (r = sshpkt_send(ssh)) != 0)
173 fatal_fr(r, "send ERRTOK packet");
174 }
175 logit("Failed gssapi-with-mic for %s%.100s "
176 "from %.200s port %d ssh2",
177 authctxt->valid ? "" : "invalid user ",
178 authctxt->user,
179 ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
180 authctxt->postponed = 0;
181 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
182 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
183 userauth_finish(ssh, 0, "gssapi-with-mic", NULL);
184 } else {
185 if (send_tok.length != 0) {
186 if ((r = sshpkt_start(ssh,
187 SSH2_MSG_USERAUTH_GSSAPI_TOKEN)) != 0 ||
188 (r = sshpkt_put_string(ssh, send_tok.value,
189 send_tok.length)) != 0 ||
190 (r = sshpkt_send(ssh)) != 0)
191 fatal_fr(r, "send TOKEN packet");
192 }
193 if (maj_status == GSS_S_COMPLETE) {
194 ssh_dispatch_set(ssh,
195 SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
196 /* note: keep ERRTOK handler as per RFC 4462 s3.4 */
197 if (flags & GSS_C_INTEG_FLAG) {
198 ssh_dispatch_set(ssh,
199 SSH2_MSG_USERAUTH_GSSAPI_MIC,
200 &input_gssapi_mic);
201 } else {
202 ssh_dispatch_set(ssh,
203 SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE,
204 &input_gssapi_exchange_complete);
205 }
206 }
207 }
208
209 gss_release_buffer(&min_status, &send_tok);
210 return 0;
211 }
212
213 static int
input_gssapi_errtok(int type,uint32_t plen,struct ssh * ssh)214 input_gssapi_errtok(int type, uint32_t plen, struct ssh *ssh)
215 {
216 Authctxt *authctxt = ssh->authctxt;
217 int r;
218 u_char *p;
219 size_t len;
220
221 if (authctxt == NULL)
222 fatal("No authentication or GSSAPI context");
223
224 /* Minimal error handling - just cancel auth and return FAILURE */
225 if ((r = sshpkt_get_string_direct(ssh, NULL, NULL)) != 0 ||
226 (r = sshpkt_get_end(ssh)) != 0)
227 fatal_fr(r, "parse packet");
228
229 logit("Failed gssapi-with-mic for %s%.100s from %.200s port %d ssh2",
230 authctxt->valid ? "" : "invalid user ",
231 authctxt->user,
232 ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
233 authctxt->postponed = 0;
234 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
235 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
236 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_MIC, NULL);
237 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
238 userauth_finish(ssh, 0, "gssapi-with-mic", NULL);
239 return 0;
240 }
241
242 /*
243 * This is called when the client thinks we've completed authentication.
244 * It should only be enabled in the dispatch handler by the function above,
245 * which only enables it once the GSSAPI exchange is complete.
246 */
247
248 static int
input_gssapi_exchange_complete(int type,uint32_t plen,struct ssh * ssh)249 input_gssapi_exchange_complete(int type, uint32_t plen, struct ssh *ssh)
250 {
251 Authctxt *authctxt = ssh->authctxt;
252 int r, authenticated;
253 double tstart = monotime_double();
254
255 if (authctxt == NULL)
256 fatal("No authentication or GSSAPI context");
257
258 /*
259 * We don't need to check the status, because we're only enabled in
260 * the dispatcher once the exchange is complete
261 */
262
263 if ((r = sshpkt_get_end(ssh)) != 0)
264 fatal_fr(r, "parse packet");
265
266 authenticated = mm_ssh_gssapi_userok(authctxt->user);
267 if (!authenticated)
268 auth_failure_delay(authctxt, tstart);
269
270 authctxt->postponed = 0;
271 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
272 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
273 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_MIC, NULL);
274 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
275 userauth_finish(ssh, authenticated, "gssapi-with-mic", NULL);
276 return 0;
277 }
278
279 static int
input_gssapi_mic(int type,uint32_t plen,struct ssh * ssh)280 input_gssapi_mic(int type, uint32_t plen, struct ssh *ssh)
281 {
282 Authctxt *authctxt = ssh->authctxt;
283 Gssctxt *gssctxt;
284 int r, authenticated = 0;
285 struct sshbuf *b;
286 gss_buffer_desc mic, gssbuf;
287 u_char *p;
288 size_t len;
289 double tstart = monotime_double();
290
291 if (authctxt == NULL)
292 fatal("No authentication or GSSAPI context");
293
294 gssctxt = authctxt->methoddata;
295
296 if ((r = sshpkt_get_string(ssh, &p, &len)) != 0)
297 fatal_fr(r, "parse packet");
298 if ((b = sshbuf_new()) == NULL)
299 fatal_f("sshbuf_new failed");
300 mic.value = p;
301 mic.length = len;
302 ssh_gssapi_buildmic(b, authctxt->user, authctxt->service,
303 "gssapi-with-mic", ssh->kex->session_id);
304
305 if ((gssbuf.value = sshbuf_mutable_ptr(b)) == NULL)
306 fatal_f("sshbuf_mutable_ptr failed");
307 gssbuf.length = sshbuf_len(b);
308
309 if (!GSS_ERROR(mm_ssh_gssapi_checkmic(gssctxt, &gssbuf, &mic)))
310 authenticated = mm_ssh_gssapi_userok(authctxt->user);
311 else
312 logit("GSSAPI MIC check failed");
313
314 sshbuf_free(b);
315 free(mic.value);
316
317 if (!authenticated)
318 auth_failure_delay(authctxt, tstart);
319
320 authctxt->postponed = 0;
321 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
322 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
323 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_MIC, NULL);
324 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
325 userauth_finish(ssh, authenticated, "gssapi-with-mic", NULL);
326 return 0;
327 }
328
329 Authmethod method_gssapi = {
330 &methodcfg_gssapi,
331 userauth_gssapi,
332 };
333 #endif
334