1 /* $OpenBSD: auth2-gss.c,v 1.32 2021/01/27 10:15:08 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 extern ServerOptions options;
52
53 static int input_gssapi_token(int type, u_int32_t plen, struct ssh *ssh);
54 static int input_gssapi_mic(int type, u_int32_t plen, struct ssh *ssh);
55 static int input_gssapi_exchange_complete(int type, u_int32_t plen, struct ssh *ssh);
56 static int input_gssapi_errtok(int, u_int32_t, struct ssh *);
57
58 /*
59 * We only support those mechanisms that we know about (ie ones that we know
60 * how to check local user kuserok and the like)
61 */
62 static int
userauth_gssapi(struct ssh * ssh)63 userauth_gssapi(struct ssh *ssh)
64 {
65 Authctxt *authctxt = ssh->authctxt;
66 gss_OID_desc goid = {0, NULL};
67 Gssctxt *ctxt = NULL;
68 int r, present;
69 u_int mechs;
70 OM_uint32 ms;
71 size_t len;
72 u_char *doid = NULL;
73
74 if ((r = sshpkt_get_u32(ssh, &mechs)) != 0)
75 fatal_fr(r, "parse packet");
76
77 if (mechs == 0) {
78 debug("Mechanism negotiation is not supported");
79 return (0);
80 }
81
82 do {
83 mechs--;
84
85 free(doid);
86
87 present = 0;
88 if ((r = sshpkt_get_string(ssh, &doid, &len)) != 0)
89 fatal_fr(r, "parse oid");
90
91 if (len > 2 && doid[0] == SSH_GSS_OIDTYPE &&
92 doid[1] == len - 2) {
93 goid.elements = doid + 2;
94 goid.length = len - 2;
95 ssh_gssapi_test_oid_supported(&ms, &goid, &present);
96 } else {
97 logit("Badly formed OID received");
98 }
99 } while (mechs > 0 && !present);
100
101 if (!present) {
102 free(doid);
103 authctxt->server_caused_failure = 1;
104 return (0);
105 }
106
107 if (!authctxt->valid || authctxt->user == NULL) {
108 debug2_f("disabled because of invalid user");
109 free(doid);
110 return (0);
111 }
112
113 if (GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctxt, &goid)))) {
114 if (ctxt != NULL)
115 ssh_gssapi_delete_ctx(&ctxt);
116 free(doid);
117 authctxt->server_caused_failure = 1;
118 return (0);
119 }
120
121 authctxt->methoddata = (void *)ctxt;
122
123 /* Return the OID that we received */
124 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_GSSAPI_RESPONSE)) != 0 ||
125 (r = sshpkt_put_string(ssh, doid, len)) != 0 ||
126 (r = sshpkt_send(ssh)) != 0)
127 fatal_fr(r, "send packet");
128
129 free(doid);
130
131 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, &input_gssapi_token);
132 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, &input_gssapi_errtok);
133 authctxt->postponed = 1;
134
135 return (0);
136 }
137
138 static int
input_gssapi_token(int type,u_int32_t plen,struct ssh * ssh)139 input_gssapi_token(int type, u_int32_t plen, struct ssh *ssh)
140 {
141 Authctxt *authctxt = ssh->authctxt;
142 Gssctxt *gssctxt;
143 gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
144 gss_buffer_desc recv_tok;
145 OM_uint32 maj_status, min_status, flags;
146 u_char *p;
147 size_t len;
148 int r;
149
150 if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
151 fatal("No authentication or GSSAPI context");
152
153 gssctxt = authctxt->methoddata;
154 if ((r = sshpkt_get_string(ssh, &p, &len)) != 0 ||
155 (r = sshpkt_get_end(ssh)) != 0)
156 fatal_fr(r, "parse packet");
157
158 recv_tok.value = p;
159 recv_tok.length = len;
160 maj_status = PRIVSEP(ssh_gssapi_accept_ctx(gssctxt, &recv_tok,
161 &send_tok, &flags));
162
163 free(p);
164
165 if (GSS_ERROR(maj_status)) {
166 if (send_tok.length != 0) {
167 if ((r = sshpkt_start(ssh,
168 SSH2_MSG_USERAUTH_GSSAPI_ERRTOK)) != 0 ||
169 (r = sshpkt_put_string(ssh, send_tok.value,
170 send_tok.length)) != 0 ||
171 (r = sshpkt_send(ssh)) != 0)
172 fatal_fr(r, "send ERRTOK packet");
173 }
174 authctxt->postponed = 0;
175 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
176 userauth_finish(ssh, 0, "gssapi-with-mic", NULL);
177 } else {
178 if (send_tok.length != 0) {
179 if ((r = sshpkt_start(ssh,
180 SSH2_MSG_USERAUTH_GSSAPI_TOKEN)) != 0 ||
181 (r = sshpkt_put_string(ssh, send_tok.value,
182 send_tok.length)) != 0 ||
183 (r = sshpkt_send(ssh)) != 0)
184 fatal_fr(r, "send TOKEN packet");
185 }
186 if (maj_status == GSS_S_COMPLETE) {
187 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
188 if (flags & GSS_C_INTEG_FLAG)
189 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_MIC,
190 &input_gssapi_mic);
191 else
192 ssh_dispatch_set(ssh,
193 SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE,
194 &input_gssapi_exchange_complete);
195 }
196 }
197
198 gss_release_buffer(&min_status, &send_tok);
199 return 0;
200 }
201
202 static int
input_gssapi_errtok(int type,u_int32_t plen,struct ssh * ssh)203 input_gssapi_errtok(int type, u_int32_t plen, struct ssh *ssh)
204 {
205 Authctxt *authctxt = ssh->authctxt;
206 Gssctxt *gssctxt;
207 gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
208 gss_buffer_desc recv_tok;
209 OM_uint32 maj_status;
210 int r;
211 u_char *p;
212 size_t len;
213
214 if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
215 fatal("No authentication or GSSAPI context");
216
217 gssctxt = authctxt->methoddata;
218 if ((r = sshpkt_get_string(ssh, &p, &len)) != 0 ||
219 (r = sshpkt_get_end(ssh)) != 0)
220 fatal_fr(r, "parse packet");
221 recv_tok.value = p;
222 recv_tok.length = len;
223
224 /* Push the error token into GSSAPI to see what it says */
225 maj_status = PRIVSEP(ssh_gssapi_accept_ctx(gssctxt, &recv_tok,
226 &send_tok, NULL));
227
228 free(recv_tok.value);
229
230 /* We can't return anything to the client, even if we wanted to */
231 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
232 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
233
234 /* The client will have already moved on to the next auth */
235
236 gss_release_buffer(&maj_status, &send_tok);
237 return 0;
238 }
239
240 /*
241 * This is called when the client thinks we've completed authentication.
242 * It should only be enabled in the dispatch handler by the function above,
243 * which only enables it once the GSSAPI exchange is complete.
244 */
245
246 static int
input_gssapi_exchange_complete(int type,u_int32_t plen,struct ssh * ssh)247 input_gssapi_exchange_complete(int type, u_int32_t plen, struct ssh *ssh)
248 {
249 Authctxt *authctxt = ssh->authctxt;
250 int r, authenticated;
251 const char *displayname;
252
253 if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
254 fatal("No authentication or GSSAPI context");
255
256 /*
257 * We don't need to check the status, because we're only enabled in
258 * the dispatcher once the exchange is complete
259 */
260
261 if ((r = sshpkt_get_end(ssh)) != 0)
262 fatal_fr(r, "parse packet");
263
264 authenticated = PRIVSEP(ssh_gssapi_userok(authctxt->user));
265
266 if ((!use_privsep || mm_is_monitor()) &&
267 (displayname = ssh_gssapi_displayname()) != NULL)
268 auth2_record_info(authctxt, "%s", displayname);
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,u_int32_t plen,struct ssh * ssh)280 input_gssapi_mic(int type, u_int32_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 const char *displayname;
288 u_char *p;
289 size_t len;
290
291 if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
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(PRIVSEP(ssh_gssapi_checkmic(gssctxt, &gssbuf, &mic))))
310 authenticated = PRIVSEP(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 ((!use_privsep || mm_is_monitor()) &&
318 (displayname = ssh_gssapi_displayname()) != NULL)
319 auth2_record_info(authctxt, "%s", displayname);
320
321 authctxt->postponed = 0;
322 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
323 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
324 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_MIC, NULL);
325 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
326 userauth_finish(ssh, authenticated, "gssapi-with-mic", NULL);
327 return 0;
328 }
329
330 Authmethod method_gssapi = {
331 "gssapi-with-mic",
332 userauth_gssapi,
333 &options.gss_authentication
334 };
335
336 #endif /* GSSAPI */
337