1 /* $OpenBSD: auth2-chall.c,v 1.53 2020/02/26 13:40:09 jsg Exp $ */
2 /*
3 * Copyright (c) 2001 Markus Friedl. All rights reserved.
4 * Copyright (c) 2001 Per Allansson. 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 #include <sys/types.h>
30
31 #include <stdlib.h>
32 #include <stdio.h>
33 #include <string.h>
34 #include <stdarg.h>
35
36 #include "xmalloc.h"
37 #include "ssh2.h"
38 #include "sshkey.h"
39 #include "hostfile.h"
40 #include "auth.h"
41 #include "sshbuf.h"
42 #include "packet.h"
43 #include "dispatch.h"
44 #include "ssherr.h"
45 #include "log.h"
46 #include "misc.h"
47 #include "servconf.h"
48
49 /* import */
50 extern ServerOptions options;
51
52 static int auth2_challenge_start(struct ssh *);
53 static int send_userauth_info_request(struct ssh *);
54 static int input_userauth_info_response(int, u_int32_t, struct ssh *);
55
56 #ifdef BSD_AUTH
57 extern KbdintDevice bsdauth_device;
58 #else
59 #ifdef USE_PAM
60 extern KbdintDevice sshpam_device;
61 #endif
62 #endif
63
64 KbdintDevice *devices[] = {
65 #ifdef BSD_AUTH
66 &bsdauth_device,
67 #else
68 #ifdef USE_PAM
69 &sshpam_device,
70 #endif
71 #endif
72 NULL
73 };
74
75 typedef struct KbdintAuthctxt KbdintAuthctxt;
76 struct KbdintAuthctxt
77 {
78 char *devices;
79 void *ctxt;
80 KbdintDevice *device;
81 u_int nreq;
82 u_int devices_done;
83 };
84
85 #ifdef USE_PAM
86 void
remove_kbdint_device(const char * devname)87 remove_kbdint_device(const char *devname)
88 {
89 int i, j;
90
91 for (i = 0; devices[i] != NULL; i++)
92 if (strcmp(devices[i]->name, devname) == 0) {
93 for (j = i; devices[j] != NULL; j++)
94 devices[j] = devices[j+1];
95 i--;
96 }
97 }
98 #endif
99
100 static KbdintAuthctxt *
kbdint_alloc(const char * devs)101 kbdint_alloc(const char *devs)
102 {
103 KbdintAuthctxt *kbdintctxt;
104 struct sshbuf *b;
105 int i, r;
106
107 #ifdef USE_PAM
108 if (!options.use_pam)
109 remove_kbdint_device("pam");
110 #endif
111
112 kbdintctxt = xcalloc(1, sizeof(KbdintAuthctxt));
113 if (strcmp(devs, "") == 0) {
114 if ((b = sshbuf_new()) == NULL)
115 fatal("%s: sshbuf_new failed", __func__);
116 for (i = 0; devices[i]; i++) {
117 if ((r = sshbuf_putf(b, "%s%s",
118 sshbuf_len(b) ? "," : "", devices[i]->name)) != 0)
119 fatal("%s: buffer error: %s",
120 __func__, ssh_err(r));
121 }
122 if ((kbdintctxt->devices = sshbuf_dup_string(b)) == NULL)
123 fatal("%s: sshbuf_dup_string failed", __func__);
124 sshbuf_free(b);
125 } else {
126 kbdintctxt->devices = xstrdup(devs);
127 }
128 debug("kbdint_alloc: devices '%s'", kbdintctxt->devices);
129 kbdintctxt->ctxt = NULL;
130 kbdintctxt->device = NULL;
131 kbdintctxt->nreq = 0;
132
133 return kbdintctxt;
134 }
135 static void
kbdint_reset_device(KbdintAuthctxt * kbdintctxt)136 kbdint_reset_device(KbdintAuthctxt *kbdintctxt)
137 {
138 if (kbdintctxt->ctxt) {
139 kbdintctxt->device->free_ctx(kbdintctxt->ctxt);
140 kbdintctxt->ctxt = NULL;
141 }
142 kbdintctxt->device = NULL;
143 }
144 static void
kbdint_free(KbdintAuthctxt * kbdintctxt)145 kbdint_free(KbdintAuthctxt *kbdintctxt)
146 {
147 if (kbdintctxt->device)
148 kbdint_reset_device(kbdintctxt);
149 free(kbdintctxt->devices);
150 freezero(kbdintctxt, sizeof(*kbdintctxt));
151 }
152 /* get next device */
153 static int
kbdint_next_device(Authctxt * authctxt,KbdintAuthctxt * kbdintctxt)154 kbdint_next_device(Authctxt *authctxt, KbdintAuthctxt *kbdintctxt)
155 {
156 size_t len;
157 char *t;
158 int i;
159
160 if (kbdintctxt->device)
161 kbdint_reset_device(kbdintctxt);
162 do {
163 len = kbdintctxt->devices ?
164 strcspn(kbdintctxt->devices, ",") : 0;
165
166 if (len == 0)
167 break;
168 for (i = 0; devices[i]; i++) {
169 if ((kbdintctxt->devices_done & (1 << i)) != 0 ||
170 !auth2_method_allowed(authctxt,
171 "keyboard-interactive", devices[i]->name))
172 continue;
173 if (strncmp(kbdintctxt->devices, devices[i]->name,
174 len) == 0) {
175 kbdintctxt->device = devices[i];
176 kbdintctxt->devices_done |= 1 << i;
177 }
178 }
179 t = kbdintctxt->devices;
180 kbdintctxt->devices = t[len] ? xstrdup(t+len+1) : NULL;
181 free(t);
182 debug2("kbdint_next_device: devices %s", kbdintctxt->devices ?
183 kbdintctxt->devices : "<empty>");
184 } while (kbdintctxt->devices && !kbdintctxt->device);
185
186 return kbdintctxt->device ? 1 : 0;
187 }
188
189 /*
190 * try challenge-response, set authctxt->postponed if we have to
191 * wait for the response.
192 */
193 int
auth2_challenge(struct ssh * ssh,char * devs)194 auth2_challenge(struct ssh *ssh, char *devs)
195 {
196 Authctxt *authctxt = ssh->authctxt;
197 debug("auth2_challenge: user=%s devs=%s",
198 authctxt->user ? authctxt->user : "<nouser>",
199 devs ? devs : "<no devs>");
200
201 if (authctxt->user == NULL || !devs)
202 return 0;
203 if (authctxt->kbdintctxt == NULL)
204 authctxt->kbdintctxt = kbdint_alloc(devs);
205 return auth2_challenge_start(ssh);
206 }
207
208 /* unregister kbd-int callbacks and context */
209 void
auth2_challenge_stop(struct ssh * ssh)210 auth2_challenge_stop(struct ssh *ssh)
211 {
212 Authctxt *authctxt = ssh->authctxt;
213 /* unregister callback */
214 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_INFO_RESPONSE, NULL);
215 if (authctxt->kbdintctxt != NULL) {
216 kbdint_free(authctxt->kbdintctxt);
217 authctxt->kbdintctxt = NULL;
218 }
219 }
220
221 /* side effect: sets authctxt->postponed if a reply was sent*/
222 static int
auth2_challenge_start(struct ssh * ssh)223 auth2_challenge_start(struct ssh *ssh)
224 {
225 Authctxt *authctxt = ssh->authctxt;
226 KbdintAuthctxt *kbdintctxt = authctxt->kbdintctxt;
227
228 debug2("auth2_challenge_start: devices %s",
229 kbdintctxt->devices ? kbdintctxt->devices : "<empty>");
230
231 if (kbdint_next_device(authctxt, kbdintctxt) == 0) {
232 auth2_challenge_stop(ssh);
233 return 0;
234 }
235 debug("auth2_challenge_start: trying authentication method '%s'",
236 kbdintctxt->device->name);
237
238 if ((kbdintctxt->ctxt = kbdintctxt->device->init_ctx(authctxt)) == NULL) {
239 auth2_challenge_stop(ssh);
240 return 0;
241 }
242 if (send_userauth_info_request(ssh) == 0) {
243 auth2_challenge_stop(ssh);
244 return 0;
245 }
246 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_INFO_RESPONSE,
247 &input_userauth_info_response);
248
249 authctxt->postponed = 1;
250 return 0;
251 }
252
253 static int
send_userauth_info_request(struct ssh * ssh)254 send_userauth_info_request(struct ssh *ssh)
255 {
256 Authctxt *authctxt = ssh->authctxt;
257 KbdintAuthctxt *kbdintctxt;
258 char *name, *instr, **prompts;
259 u_int r, i, *echo_on;
260
261 kbdintctxt = authctxt->kbdintctxt;
262 if (kbdintctxt->device->query(kbdintctxt->ctxt,
263 &name, &instr, &kbdintctxt->nreq, &prompts, &echo_on))
264 return 0;
265
266 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_INFO_REQUEST)) != 0 ||
267 (r = sshpkt_put_cstring(ssh, name)) != 0 ||
268 (r = sshpkt_put_cstring(ssh, instr)) != 0 ||
269 (r = sshpkt_put_cstring(ssh, "")) != 0 || /* language not used */
270 (r = sshpkt_put_u32(ssh, kbdintctxt->nreq)) != 0)
271 fatal("%s: %s", __func__, ssh_err(r));
272 for (i = 0; i < kbdintctxt->nreq; i++) {
273 if ((r = sshpkt_put_cstring(ssh, prompts[i])) != 0 ||
274 (r = sshpkt_put_u8(ssh, echo_on[i])) != 0)
275 fatal("%s: %s", __func__, ssh_err(r));
276 }
277 if ((r = sshpkt_send(ssh)) != 0 ||
278 (r = ssh_packet_write_wait(ssh)) != 0)
279 fatal("%s: %s", __func__, ssh_err(r));
280
281 for (i = 0; i < kbdintctxt->nreq; i++)
282 free(prompts[i]);
283 free(prompts);
284 free(echo_on);
285 free(name);
286 free(instr);
287 return 1;
288 }
289
290 static int
input_userauth_info_response(int type,u_int32_t seq,struct ssh * ssh)291 input_userauth_info_response(int type, u_int32_t seq, struct ssh *ssh)
292 {
293 Authctxt *authctxt = ssh->authctxt;
294 KbdintAuthctxt *kbdintctxt;
295 int authenticated = 0, res;
296 int r;
297 u_int i, nresp;
298 const char *devicename = NULL;
299 char **response = NULL;
300
301 if (authctxt == NULL)
302 fatal("input_userauth_info_response: no authctxt");
303 kbdintctxt = authctxt->kbdintctxt;
304 if (kbdintctxt == NULL || kbdintctxt->ctxt == NULL)
305 fatal("input_userauth_info_response: no kbdintctxt");
306 if (kbdintctxt->device == NULL)
307 fatal("input_userauth_info_response: no device");
308
309 authctxt->postponed = 0; /* reset */
310 if ((r = sshpkt_get_u32(ssh, &nresp)) != 0)
311 fatal("%s: %s", __func__, ssh_err(r));
312 if (nresp != kbdintctxt->nreq)
313 fatal("input_userauth_info_response: wrong number of replies");
314 if (nresp > 100)
315 fatal("input_userauth_info_response: too many replies");
316 if (nresp > 0) {
317 response = xcalloc(nresp, sizeof(char *));
318 for (i = 0; i < nresp; i++)
319 if ((r = sshpkt_get_cstring(ssh, &response[i],
320 NULL)) != 0)
321 fatal("%s: %s", __func__, ssh_err(r));
322 }
323 if ((r = sshpkt_get_end(ssh)) != 0)
324 fatal("%s: %s", __func__, ssh_err(r));
325
326 res = kbdintctxt->device->respond(kbdintctxt->ctxt, nresp, response);
327
328 for (i = 0; i < nresp; i++) {
329 explicit_bzero(response[i], strlen(response[i]));
330 free(response[i]);
331 }
332 free(response);
333
334 switch (res) {
335 case 0:
336 /* Success! */
337 authenticated = authctxt->valid ? 1 : 0;
338 break;
339 case 1:
340 /* Authentication needs further interaction */
341 if (send_userauth_info_request(ssh) == 1)
342 authctxt->postponed = 1;
343 break;
344 default:
345 /* Failure! */
346 break;
347 }
348 devicename = kbdintctxt->device->name;
349 if (!authctxt->postponed) {
350 if (authenticated) {
351 auth2_challenge_stop(ssh);
352 } else {
353 /* start next device */
354 /* may set authctxt->postponed */
355 auth2_challenge_start(ssh);
356 }
357 }
358 userauth_finish(ssh, authenticated, "keyboard-interactive",
359 devicename);
360 return 0;
361 }
362
363 void
privsep_challenge_enable(void)364 privsep_challenge_enable(void)
365 {
366 #if defined(BSD_AUTH) || defined(USE_PAM)
367 int n = 0;
368 #endif
369 #ifdef BSD_AUTH
370 extern KbdintDevice mm_bsdauth_device;
371 #endif
372 #ifdef USE_PAM
373 extern KbdintDevice mm_sshpam_device;
374 #endif
375
376 #ifdef BSD_AUTH
377 devices[n++] = &mm_bsdauth_device;
378 #else
379 #ifdef USE_PAM
380 devices[n++] = &mm_sshpam_device;
381 #endif
382 #endif
383 }
384