1 /* $OpenBSD: auth2-chall.c,v 1.54 2020/10/18 11:32:01 djm 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_f("sshbuf_new failed");
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_fr(r, "buffer error");
120 }
121 if ((kbdintctxt->devices = sshbuf_dup_string(b)) == NULL)
122 fatal_f("sshbuf_dup_string failed");
123 sshbuf_free(b);
124 } else {
125 kbdintctxt->devices = xstrdup(devs);
126 }
127 debug("kbdint_alloc: devices '%s'", kbdintctxt->devices);
128 kbdintctxt->ctxt = NULL;
129 kbdintctxt->device = NULL;
130 kbdintctxt->nreq = 0;
131
132 return kbdintctxt;
133 }
134 static void
kbdint_reset_device(KbdintAuthctxt * kbdintctxt)135 kbdint_reset_device(KbdintAuthctxt *kbdintctxt)
136 {
137 if (kbdintctxt->ctxt) {
138 kbdintctxt->device->free_ctx(kbdintctxt->ctxt);
139 kbdintctxt->ctxt = NULL;
140 }
141 kbdintctxt->device = NULL;
142 }
143 static void
kbdint_free(KbdintAuthctxt * kbdintctxt)144 kbdint_free(KbdintAuthctxt *kbdintctxt)
145 {
146 if (kbdintctxt->device)
147 kbdint_reset_device(kbdintctxt);
148 free(kbdintctxt->devices);
149 freezero(kbdintctxt, sizeof(*kbdintctxt));
150 }
151 /* get next device */
152 static int
kbdint_next_device(Authctxt * authctxt,KbdintAuthctxt * kbdintctxt)153 kbdint_next_device(Authctxt *authctxt, KbdintAuthctxt *kbdintctxt)
154 {
155 size_t len;
156 char *t;
157 int i;
158
159 if (kbdintctxt->device)
160 kbdint_reset_device(kbdintctxt);
161 do {
162 len = kbdintctxt->devices ?
163 strcspn(kbdintctxt->devices, ",") : 0;
164
165 if (len == 0)
166 break;
167 for (i = 0; devices[i]; i++) {
168 if ((kbdintctxt->devices_done & (1 << i)) != 0 ||
169 !auth2_method_allowed(authctxt,
170 "keyboard-interactive", devices[i]->name))
171 continue;
172 if (strncmp(kbdintctxt->devices, devices[i]->name,
173 len) == 0) {
174 kbdintctxt->device = devices[i];
175 kbdintctxt->devices_done |= 1 << i;
176 }
177 }
178 t = kbdintctxt->devices;
179 kbdintctxt->devices = t[len] ? xstrdup(t+len+1) : NULL;
180 free(t);
181 debug2("kbdint_next_device: devices %s", kbdintctxt->devices ?
182 kbdintctxt->devices : "<empty>");
183 } while (kbdintctxt->devices && !kbdintctxt->device);
184
185 return kbdintctxt->device ? 1 : 0;
186 }
187
188 /*
189 * try challenge-response, set authctxt->postponed if we have to
190 * wait for the response.
191 */
192 int
auth2_challenge(struct ssh * ssh,char * devs)193 auth2_challenge(struct ssh *ssh, char *devs)
194 {
195 Authctxt *authctxt = ssh->authctxt;
196 debug("auth2_challenge: user=%s devs=%s",
197 authctxt->user ? authctxt->user : "<nouser>",
198 devs ? devs : "<no devs>");
199
200 if (authctxt->user == NULL || !devs)
201 return 0;
202 if (authctxt->kbdintctxt == NULL)
203 authctxt->kbdintctxt = kbdint_alloc(devs);
204 return auth2_challenge_start(ssh);
205 }
206
207 /* unregister kbd-int callbacks and context */
208 void
auth2_challenge_stop(struct ssh * ssh)209 auth2_challenge_stop(struct ssh *ssh)
210 {
211 Authctxt *authctxt = ssh->authctxt;
212 /* unregister callback */
213 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_INFO_RESPONSE, NULL);
214 if (authctxt->kbdintctxt != NULL) {
215 kbdint_free(authctxt->kbdintctxt);
216 authctxt->kbdintctxt = NULL;
217 }
218 }
219
220 /* side effect: sets authctxt->postponed if a reply was sent*/
221 static int
auth2_challenge_start(struct ssh * ssh)222 auth2_challenge_start(struct ssh *ssh)
223 {
224 Authctxt *authctxt = ssh->authctxt;
225 KbdintAuthctxt *kbdintctxt = authctxt->kbdintctxt;
226
227 debug2("auth2_challenge_start: devices %s",
228 kbdintctxt->devices ? kbdintctxt->devices : "<empty>");
229
230 if (kbdint_next_device(authctxt, kbdintctxt) == 0) {
231 auth2_challenge_stop(ssh);
232 return 0;
233 }
234 debug("auth2_challenge_start: trying authentication method '%s'",
235 kbdintctxt->device->name);
236
237 if ((kbdintctxt->ctxt = kbdintctxt->device->init_ctx(authctxt)) == NULL) {
238 auth2_challenge_stop(ssh);
239 return 0;
240 }
241 if (send_userauth_info_request(ssh) == 0) {
242 auth2_challenge_stop(ssh);
243 return 0;
244 }
245 ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_INFO_RESPONSE,
246 &input_userauth_info_response);
247
248 authctxt->postponed = 1;
249 return 0;
250 }
251
252 static int
send_userauth_info_request(struct ssh * ssh)253 send_userauth_info_request(struct ssh *ssh)
254 {
255 Authctxt *authctxt = ssh->authctxt;
256 KbdintAuthctxt *kbdintctxt;
257 char *name, *instr, **prompts;
258 u_int r, i, *echo_on;
259
260 kbdintctxt = authctxt->kbdintctxt;
261 if (kbdintctxt->device->query(kbdintctxt->ctxt,
262 &name, &instr, &kbdintctxt->nreq, &prompts, &echo_on))
263 return 0;
264
265 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_INFO_REQUEST)) != 0 ||
266 (r = sshpkt_put_cstring(ssh, name)) != 0 ||
267 (r = sshpkt_put_cstring(ssh, instr)) != 0 ||
268 (r = sshpkt_put_cstring(ssh, "")) != 0 || /* language not used */
269 (r = sshpkt_put_u32(ssh, kbdintctxt->nreq)) != 0)
270 fatal_fr(r, "start packet");
271 for (i = 0; i < kbdintctxt->nreq; i++) {
272 if ((r = sshpkt_put_cstring(ssh, prompts[i])) != 0 ||
273 (r = sshpkt_put_u8(ssh, echo_on[i])) != 0)
274 fatal_fr(r, "assemble packet");
275 }
276 if ((r = sshpkt_send(ssh)) != 0 ||
277 (r = ssh_packet_write_wait(ssh)) != 0)
278 fatal_fr(r, "send packet");
279
280 for (i = 0; i < kbdintctxt->nreq; i++)
281 free(prompts[i]);
282 free(prompts);
283 free(echo_on);
284 free(name);
285 free(instr);
286 return 1;
287 }
288
289 static int
input_userauth_info_response(int type,u_int32_t seq,struct ssh * ssh)290 input_userauth_info_response(int type, u_int32_t seq, struct ssh *ssh)
291 {
292 Authctxt *authctxt = ssh->authctxt;
293 KbdintAuthctxt *kbdintctxt;
294 int authenticated = 0, res;
295 int r;
296 u_int i, nresp;
297 const char *devicename = NULL;
298 char **response = NULL;
299
300 if (authctxt == NULL)
301 fatal_f("no authctxt");
302 kbdintctxt = authctxt->kbdintctxt;
303 if (kbdintctxt == NULL || kbdintctxt->ctxt == NULL)
304 fatal_f("no kbdintctxt");
305 if (kbdintctxt->device == NULL)
306 fatal_f("no device");
307
308 authctxt->postponed = 0; /* reset */
309 if ((r = sshpkt_get_u32(ssh, &nresp)) != 0)
310 fatal_fr(r, "parse packet");
311 if (nresp != kbdintctxt->nreq)
312 fatal_f("wrong number of replies");
313 if (nresp > 100)
314 fatal_f("too many replies");
315 if (nresp > 0) {
316 response = xcalloc(nresp, sizeof(char *));
317 for (i = 0; i < nresp; i++) {
318 if ((r = sshpkt_get_cstring(ssh, &response[i], NULL)) != 0)
319 fatal_fr(r, "parse response");
320 }
321 }
322 if ((r = sshpkt_get_end(ssh)) != 0)
323 fatal_fr(r, "parse packet");
324
325 res = kbdintctxt->device->respond(kbdintctxt->ctxt, nresp, response);
326
327 for (i = 0; i < nresp; i++) {
328 explicit_bzero(response[i], strlen(response[i]));
329 free(response[i]);
330 }
331 free(response);
332
333 switch (res) {
334 case 0:
335 /* Success! */
336 authenticated = authctxt->valid ? 1 : 0;
337 break;
338 case 1:
339 /* Authentication needs further interaction */
340 if (send_userauth_info_request(ssh) == 1)
341 authctxt->postponed = 1;
342 break;
343 default:
344 /* Failure! */
345 break;
346 }
347 devicename = kbdintctxt->device->name;
348 if (!authctxt->postponed) {
349 if (authenticated) {
350 auth2_challenge_stop(ssh);
351 } else {
352 /* start next device */
353 /* may set authctxt->postponed */
354 auth2_challenge_start(ssh);
355 }
356 }
357 userauth_finish(ssh, authenticated, "keyboard-interactive",
358 devicename);
359 return 0;
360 }
361
362 void
privsep_challenge_enable(void)363 privsep_challenge_enable(void)
364 {
365 #if defined(BSD_AUTH) || defined(USE_PAM)
366 int n = 0;
367 #endif
368 #ifdef BSD_AUTH
369 extern KbdintDevice mm_bsdauth_device;
370 #endif
371 #ifdef USE_PAM
372 extern KbdintDevice mm_sshpam_device;
373 #endif
374
375 #ifdef BSD_AUTH
376 devices[n++] = &mm_bsdauth_device;
377 #else
378 #ifdef USE_PAM
379 devices[n++] = &mm_sshpam_device;
380 #endif
381 #endif
382 }
383