xref: /openssh-portable/auth2-chall.c (revision 816036f1)
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