1 /* $OpenBSD: auth2-gss.c,v 1.36 2024/05/17 04:42:13 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, u_int32_t plen, struct ssh *ssh);
57 static int input_gssapi_mic(int type, u_int32_t plen, struct ssh *ssh);
58 static int input_gssapi_exchange_complete(int type, u_int32_t plen, struct ssh *ssh);
59 static int input_gssapi_errtok(int, u_int32_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 (!authctxt->valid || authctxt->user == NULL) {
115 debug2_f("disabled because of invalid user");
116 free(doid);
117 return (0);
118 }
119
120 if (GSS_ERROR(mm_ssh_gssapi_server_ctx(&ctxt, &goid))) {
121 if (ctxt != NULL)
122 ssh_gssapi_delete_ctx(&ctxt);
123 free(doid);
124 authctxt->server_caused_failure = 1;
125 return (0);
126 }
127
128 authctxt->methoddata = (void *)ctxt;
129
130 /* Return the OID that we received */
131 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_GSSAPI_RESPONSE)) != 0 ||
132 (r = sshpkt_put_string(ssh, doid, len)) != 0 ||
133 (r = sshpkt_send(ssh)) != 0)
134 fatal_fr(r, "send packet");
135
136 free(doid);
137
138 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, &input_gssapi_token);
139 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, &input_gssapi_errtok);
140 authctxt->postponed = 1;
141
142 return (0);
143 }
144
145 static int
input_gssapi_token(int type,u_int32_t plen,struct ssh * ssh)146 input_gssapi_token(int type, u_int32_t plen, struct ssh *ssh)
147 {
148 Authctxt *authctxt = ssh->authctxt;
149 Gssctxt *gssctxt;
150 gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
151 gss_buffer_desc recv_tok;
152 OM_uint32 maj_status, min_status, flags;
153 u_char *p;
154 size_t len;
155 int r;
156
157 if (authctxt == NULL)
158 fatal("No authentication or GSSAPI context");
159
160 gssctxt = authctxt->methoddata;
161 if ((r = sshpkt_get_string(ssh, &p, &len)) != 0 ||
162 (r = sshpkt_get_end(ssh)) != 0)
163 fatal_fr(r, "parse packet");
164
165 recv_tok.value = p;
166 recv_tok.length = len;
167 maj_status = mm_ssh_gssapi_accept_ctx(gssctxt, &recv_tok,
168 &send_tok, &flags);
169
170 free(p);
171
172 if (GSS_ERROR(maj_status)) {
173 if (send_tok.length != 0) {
174 if ((r = sshpkt_start(ssh,
175 SSH2_MSG_USERAUTH_GSSAPI_ERRTOK)) != 0 ||
176 (r = sshpkt_put_string(ssh, send_tok.value,
177 send_tok.length)) != 0 ||
178 (r = sshpkt_send(ssh)) != 0)
179 fatal_fr(r, "send ERRTOK packet");
180 }
181 authctxt->postponed = 0;
182 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, 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, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
195 if (flags & GSS_C_INTEG_FLAG)
196 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_MIC,
197 &input_gssapi_mic);
198 else
199 ssh_dispatch_set(ssh,
200 SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE,
201 &input_gssapi_exchange_complete);
202 }
203 }
204
205 gss_release_buffer(&min_status, &send_tok);
206 return 0;
207 }
208
209 static int
input_gssapi_errtok(int type,u_int32_t plen,struct ssh * ssh)210 input_gssapi_errtok(int type, u_int32_t plen, struct ssh *ssh)
211 {
212 Authctxt *authctxt = ssh->authctxt;
213 Gssctxt *gssctxt;
214 gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
215 gss_buffer_desc recv_tok;
216 OM_uint32 maj_status;
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 gssctxt = authctxt->methoddata;
225 if ((r = sshpkt_get_string(ssh, &p, &len)) != 0 ||
226 (r = sshpkt_get_end(ssh)) != 0)
227 fatal_fr(r, "parse packet");
228 recv_tok.value = p;
229 recv_tok.length = len;
230
231 /* Push the error token into GSSAPI to see what it says */
232 maj_status = mm_ssh_gssapi_accept_ctx(gssctxt, &recv_tok,
233 &send_tok, NULL);
234
235 free(recv_tok.value);
236
237 /* We can't return anything to the client, even if we wanted to */
238 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
239 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
240
241 /* The client will have already moved on to the next auth */
242
243 gss_release_buffer(&maj_status, &send_tok);
244 return 0;
245 }
246
247 /*
248 * This is called when the client thinks we've completed authentication.
249 * It should only be enabled in the dispatch handler by the function above,
250 * which only enables it once the GSSAPI exchange is complete.
251 */
252
253 static int
input_gssapi_exchange_complete(int type,u_int32_t plen,struct ssh * ssh)254 input_gssapi_exchange_complete(int type, u_int32_t plen, struct ssh *ssh)
255 {
256 Authctxt *authctxt = ssh->authctxt;
257 int r, authenticated;
258
259 if (authctxt == NULL)
260 fatal("No authentication or GSSAPI context");
261
262 /*
263 * We don't need to check the status, because we're only enabled in
264 * the dispatcher once the exchange is complete
265 */
266
267 if ((r = sshpkt_get_end(ssh)) != 0)
268 fatal_fr(r, "parse packet");
269
270 authenticated = mm_ssh_gssapi_userok(authctxt->user);
271
272 authctxt->postponed = 0;
273 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
274 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
275 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_MIC, NULL);
276 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
277 userauth_finish(ssh, authenticated, "gssapi-with-mic", NULL);
278 return 0;
279 }
280
281 static int
input_gssapi_mic(int type,u_int32_t plen,struct ssh * ssh)282 input_gssapi_mic(int type, u_int32_t plen, struct ssh *ssh)
283 {
284 Authctxt *authctxt = ssh->authctxt;
285 Gssctxt *gssctxt;
286 int r, authenticated = 0;
287 struct sshbuf *b;
288 gss_buffer_desc mic, gssbuf;
289 u_char *p;
290 size_t len;
291
292 if (authctxt == NULL)
293 fatal("No authentication or GSSAPI context");
294
295 gssctxt = authctxt->methoddata;
296
297 if ((r = sshpkt_get_string(ssh, &p, &len)) != 0)
298 fatal_fr(r, "parse packet");
299 if ((b = sshbuf_new()) == NULL)
300 fatal_f("sshbuf_new failed");
301 mic.value = p;
302 mic.length = len;
303 ssh_gssapi_buildmic(b, authctxt->user, authctxt->service,
304 "gssapi-with-mic", ssh->kex->session_id);
305
306 if ((gssbuf.value = sshbuf_mutable_ptr(b)) == NULL)
307 fatal_f("sshbuf_mutable_ptr failed");
308 gssbuf.length = sshbuf_len(b);
309
310 if (!GSS_ERROR(mm_ssh_gssapi_checkmic(gssctxt, &gssbuf, &mic)))
311 authenticated = mm_ssh_gssapi_userok(authctxt->user);
312 else
313 logit("GSSAPI MIC check failed");
314
315 sshbuf_free(b);
316 free(mic.value);
317
318 authctxt->postponed = 0;
319 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
320 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
321 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_MIC, NULL);
322 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
323 userauth_finish(ssh, authenticated, "gssapi-with-mic", NULL);
324 return 0;
325 }
326
327 Authmethod method_gssapi = {
328 &methodcfg_gssapi,
329 userauth_gssapi,
330 };
331
332 #endif /* GSSAPI */
333