1/* $OpenBSD: auth2-chall.c,v 1.50 2018/07/11 18:55:11 markus 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 <stdarg.h>
32#include <stdio.h>
33#include <string.h>
34
35#include "xmalloc.h"
36#include "ssh2.h"
37#include "sshkey.h"
38#include "hostfile.h"
39#include "auth.h"
40#include "sshbuf.h"
41#include "packet.h"
42#include "dispatch.h"
43#include "ssherr.h"
44#include "log.h"
45#include "misc.h"
46#include "servconf.h"
47
48/* import */
49extern ServerOptions options;
50
51static int auth2_challenge_start(struct ssh *);
52static int send_userauth_info_request(struct ssh *);
53static int input_userauth_info_response(int, u_int32_t, struct ssh *);
54
55#ifdef BSD_AUTH
56extern KbdintDevice bsdauth_device;
57#else
58#ifdef USE_PAM
59extern KbdintDevice sshpam_device;
60#endif
61#endif
62
63KbdintDevice *devices[] = {
64#ifdef BSD_AUTH
65	&bsdauth_device,
66#else
67#ifdef USE_PAM
68	&sshpam_device,
69#endif
70#endif
71	NULL
72};
73
74typedef struct KbdintAuthctxt KbdintAuthctxt;
75struct KbdintAuthctxt
76{
77	char *devices;
78	void *ctxt;
79	KbdintDevice *device;
80	u_int nreq;
81	u_int devices_done;
82};
83
84#ifdef USE_PAM
85void
86remove_kbdint_device(const char *devname)
87{
88	int i, j;
89
90	for (i = 0; devices[i] != NULL; i++)
91		if (strcmp(devices[i]->name, devname) == 0) {
92			for (j = i; devices[j] != NULL; j++)
93				devices[j] = devices[j+1];
94			i--;
95		}
96}
97#endif
98
99static KbdintAuthctxt *
100kbdint_alloc(const char *devs)
101{
102	KbdintAuthctxt *kbdintctxt;
103	struct sshbuf *b;
104	int i, r;
105
106#ifdef USE_PAM
107	if (!options.use_pam)
108		remove_kbdint_device("pam");
109#endif
110
111	kbdintctxt = xcalloc(1, sizeof(KbdintAuthctxt));
112	if (strcmp(devs, "") == 0) {
113		if ((b = sshbuf_new()) == NULL)
114			fatal("%s: sshbuf_new failed", __func__);
115		for (i = 0; devices[i]; i++) {
116			if ((r = sshbuf_putf(b, "%s%s",
117			    sshbuf_len(b) ? "," : "", devices[i]->name)) != 0)
118				fatal("%s: buffer error: %s",
119				    __func__, ssh_err(r));
120		}
121		if ((kbdintctxt->devices = sshbuf_dup_string(b)) == NULL)
122			fatal("%s: sshbuf_dup_string failed", __func__);
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}
134static void
135kbdint_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}
143static void
144kbdint_free(KbdintAuthctxt *kbdintctxt)
145{
146	if (kbdintctxt->device)
147		kbdint_reset_device(kbdintctxt);
148	free(kbdintctxt->devices);
149	explicit_bzero(kbdintctxt, sizeof(*kbdintctxt));
150	free(kbdintctxt);
151}
152/* get next device */
153static int
154kbdint_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 */
193int
194auth2_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 */
209void
210auth2_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*/
222static int
223auth2_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
253static int
254send_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
290static int
291input_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
363void
364privsep_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