1/*	$NetBSD: auth2-chall.c,v 1.19 2021/03/05 17:47:15 christos Exp $	*/
2/* $OpenBSD: auth2-chall.c,v 1.54 2020/10/18 11:32:01 djm Exp $ */
3
4/*
5 * Copyright (c) 2001 Markus Friedl.  All rights reserved.
6 * Copyright (c) 2001 Per Allansson.  All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 */
28
29#include "includes.h"
30__RCSID("$NetBSD: auth2-chall.c,v 1.19 2021/03/05 17:47:15 christos Exp $");
31#include <sys/types.h>
32
33#include <stdlib.h>
34#include <stdio.h>
35#include <string.h>
36#include <stdarg.h>
37
38#include "xmalloc.h"
39#include "ssh2.h"
40#include "sshkey.h"
41#include "hostfile.h"
42#include "auth.h"
43#include "sshbuf.h"
44#include "packet.h"
45#include "dispatch.h"
46#include "ssherr.h"
47#include "log.h"
48#include "misc.h"
49#include "servconf.h"
50
51/* import */
52extern ServerOptions options;
53
54static int auth2_challenge_start(struct ssh *);
55static int send_userauth_info_request(struct ssh *);
56static int input_userauth_info_response(int, u_int32_t, struct ssh *);
57
58#ifdef BSD_AUTH
59extern KbdintDevice bsdauth_device;
60#else
61#ifdef USE_PAM
62extern KbdintDevice sshpam_device;
63#endif
64#ifdef SKEY
65extern KbdintDevice skey_device;
66#endif
67#endif
68
69KbdintDevice *devices[] = {
70#ifdef BSD_AUTH
71	&bsdauth_device,
72#else
73#ifdef USE_PAM
74	&sshpam_device,
75#endif
76#ifdef SKEY
77	&skey_device,
78#endif
79#endif
80	NULL
81};
82
83typedef struct KbdintAuthctxt KbdintAuthctxt;
84struct KbdintAuthctxt
85{
86	char *devices;
87	void *ctxt;
88	KbdintDevice *device;
89	u_int nreq;
90	u_int devices_done;
91};
92
93#ifdef USE_PAM
94void remove_kbdint_device(const char *);
95void
96remove_kbdint_device(const char *xdevname)
97{
98	int i, j;
99
100	for (i = 0; devices[i] != NULL; i++)
101		if (strcmp(devices[i]->name, xdevname) == 0) {
102			for (j = i; devices[j] != NULL; j++)
103				devices[j] = devices[j+1];
104			i--;
105		}
106}
107#endif
108
109static KbdintAuthctxt *
110kbdint_alloc(const char *devs)
111{
112	KbdintAuthctxt *kbdintctxt;
113	struct sshbuf *b;
114	int i, r;
115
116#ifdef USE_PAM
117	if (!options.use_pam)
118		remove_kbdint_device("pam");
119#endif
120
121	kbdintctxt = xcalloc(1, sizeof(KbdintAuthctxt));
122	if (strcmp(devs, "") == 0) {
123		if ((b = sshbuf_new()) == NULL)
124			fatal_f("sshbuf_new failed");
125		for (i = 0; devices[i]; i++) {
126			if ((r = sshbuf_putf(b, "%s%s",
127			    sshbuf_len(b) ? "," : "", devices[i]->name)) != 0)
128				fatal_fr(r, "buffer error");
129		}
130		if ((kbdintctxt->devices = sshbuf_dup_string(b)) == NULL)
131			fatal_f("sshbuf_dup_string failed");
132		sshbuf_free(b);
133	} else {
134		kbdintctxt->devices = xstrdup(devs);
135	}
136	debug("kbdint_alloc: devices '%s'", kbdintctxt->devices);
137	kbdintctxt->ctxt = NULL;
138	kbdintctxt->device = NULL;
139	kbdintctxt->nreq = 0;
140
141	return kbdintctxt;
142}
143static void
144kbdint_reset_device(KbdintAuthctxt *kbdintctxt)
145{
146	if (kbdintctxt->ctxt) {
147		kbdintctxt->device->free_ctx(kbdintctxt->ctxt);
148		kbdintctxt->ctxt = NULL;
149	}
150	kbdintctxt->device = NULL;
151}
152static void
153kbdint_free(KbdintAuthctxt *kbdintctxt)
154{
155	if (kbdintctxt->device)
156		kbdint_reset_device(kbdintctxt);
157	free(kbdintctxt->devices);
158	freezero(kbdintctxt, sizeof(*kbdintctxt));
159}
160/* get next device */
161static int
162kbdint_next_device(Authctxt *authctxt, KbdintAuthctxt *kbdintctxt)
163{
164	size_t len;
165	char *t;
166	int i;
167
168	if (kbdintctxt->device)
169		kbdint_reset_device(kbdintctxt);
170	do {
171		len = kbdintctxt->devices ?
172		    strcspn(kbdintctxt->devices, ",") : 0;
173
174		if (len == 0)
175			break;
176		for (i = 0; devices[i]; i++) {
177			if ((kbdintctxt->devices_done & (1 << i)) != 0 ||
178			    !auth2_method_allowed(authctxt,
179			    "keyboard-interactive", devices[i]->name))
180				continue;
181			if (strncmp(kbdintctxt->devices, devices[i]->name,
182			    len) == 0) {
183				kbdintctxt->device = devices[i];
184				kbdintctxt->devices_done |= 1 << i;
185			}
186		}
187		t = kbdintctxt->devices;
188		kbdintctxt->devices = t[len] ? xstrdup(t+len+1) : NULL;
189		free(t);
190		debug2("kbdint_next_device: devices %s", kbdintctxt->devices ?
191		    kbdintctxt->devices : "<empty>");
192	} while (kbdintctxt->devices && !kbdintctxt->device);
193
194	return kbdintctxt->device ? 1 : 0;
195}
196
197/*
198 * try challenge-response, set authctxt->postponed if we have to
199 * wait for the response.
200 */
201int
202auth2_challenge(struct ssh *ssh, char *devs)
203{
204	Authctxt *authctxt = ssh->authctxt;
205	debug("auth2_challenge: user=%s devs=%s",
206	    authctxt->user ? authctxt->user : "<nouser>",
207	    devs ? devs : "<no devs>");
208
209	if (authctxt->user == NULL || !devs)
210		return 0;
211	if (authctxt->kbdintctxt == NULL)
212		authctxt->kbdintctxt = kbdint_alloc(devs);
213	return auth2_challenge_start(ssh);
214}
215
216/* unregister kbd-int callbacks and context */
217void
218auth2_challenge_stop(struct ssh *ssh)
219{
220	Authctxt *authctxt = ssh->authctxt;
221	/* unregister callback */
222	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_INFO_RESPONSE, NULL);
223	if (authctxt->kbdintctxt != NULL) {
224		kbdint_free(authctxt->kbdintctxt);
225		authctxt->kbdintctxt = NULL;
226	}
227}
228
229/* side effect: sets authctxt->postponed if a reply was sent*/
230static int
231auth2_challenge_start(struct ssh *ssh)
232{
233	Authctxt *authctxt = ssh->authctxt;
234	KbdintAuthctxt *kbdintctxt = authctxt->kbdintctxt;
235
236	debug2("auth2_challenge_start: devices %s",
237	    kbdintctxt->devices ?  kbdintctxt->devices : "<empty>");
238
239	if (kbdint_next_device(authctxt, kbdintctxt) == 0) {
240		auth2_challenge_stop(ssh);
241		return 0;
242	}
243	debug("auth2_challenge_start: trying authentication method '%s'",
244	    kbdintctxt->device->name);
245
246	if ((kbdintctxt->ctxt = kbdintctxt->device->init_ctx(authctxt)) == NULL) {
247		auth2_challenge_stop(ssh);
248		return 0;
249	}
250	if (send_userauth_info_request(ssh) == 0) {
251		auth2_challenge_stop(ssh);
252		return 0;
253	}
254	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_INFO_RESPONSE,
255	    &input_userauth_info_response);
256
257	authctxt->postponed = 1;
258	return 0;
259}
260
261static int
262send_userauth_info_request(struct ssh *ssh)
263{
264	Authctxt *authctxt = ssh->authctxt;
265	KbdintAuthctxt *kbdintctxt;
266	char *name, *instr, **prompts;
267	int r;
268	u_int i, *echo_on;
269
270	kbdintctxt = authctxt->kbdintctxt;
271	if (kbdintctxt->device->query(kbdintctxt->ctxt,
272	    &name, &instr, &kbdintctxt->nreq, &prompts, &echo_on))
273		return 0;
274
275	if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_INFO_REQUEST)) != 0 ||
276	    (r = sshpkt_put_cstring(ssh, name)) != 0 ||
277	    (r = sshpkt_put_cstring(ssh, instr)) != 0 ||
278	    (r = sshpkt_put_cstring(ssh, "")) != 0 ||	/* language not used */
279	    (r = sshpkt_put_u32(ssh, kbdintctxt->nreq)) != 0)
280		fatal_fr(r, "start packet");
281	for (i = 0; i < kbdintctxt->nreq; i++) {
282		if ((r = sshpkt_put_cstring(ssh, prompts[i])) != 0 ||
283		    (r = sshpkt_put_u8(ssh, echo_on[i])) != 0)
284			fatal_fr(r, "assemble packet");
285	}
286	if ((r = sshpkt_send(ssh)) != 0 ||
287	    (r = ssh_packet_write_wait(ssh)) < 0)
288		fatal_fr(r, "send packet");
289
290	for (i = 0; i < kbdintctxt->nreq; i++)
291		free(prompts[i]);
292	free(prompts);
293	free(echo_on);
294	free(name);
295	free(instr);
296	return 1;
297}
298
299static int
300input_userauth_info_response(int type, u_int32_t seq, struct ssh *ssh)
301{
302	Authctxt *authctxt = ssh->authctxt;
303	KbdintAuthctxt *kbdintctxt;
304	int authenticated = 0, res;
305	int r;
306	u_int i, nresp;
307	const char *devicename = NULL;
308	char **response = NULL;
309
310	if (authctxt == NULL)
311		fatal_f("no authctxt");
312	kbdintctxt = authctxt->kbdintctxt;
313	if (kbdintctxt == NULL || kbdintctxt->ctxt == NULL)
314		fatal_f("no kbdintctxt");
315	if (kbdintctxt->device == NULL)
316		fatal_f("no device");
317
318	authctxt->postponed = 0;	/* reset */
319	if ((r = sshpkt_get_u32(ssh, &nresp)) != 0)
320		fatal_fr(r, "parse packet");
321	if (nresp != kbdintctxt->nreq)
322		fatal_f("wrong number of replies");
323	if (nresp > 100)
324		fatal_f("too many replies");
325	if (nresp > 0) {
326		response = xcalloc(nresp, sizeof(char *));
327		for (i = 0; i < nresp; i++) {
328			if ((r = sshpkt_get_cstring(ssh, &response[i], NULL)) != 0)
329				fatal_fr(r, "parse response");
330		}
331	}
332	if ((r = sshpkt_get_end(ssh)) != 0)
333		fatal_fr(r, "parse packet");
334
335	res = kbdintctxt->device->respond(kbdintctxt->ctxt, nresp, response);
336
337	for (i = 0; i < nresp; i++) {
338		explicit_bzero(response[i], strlen(response[i]));
339		free(response[i]);
340	}
341	free(response);
342
343	switch (res) {
344	case 0:
345		/* Success! */
346		authenticated = authctxt->valid ? 1 : 0;
347		break;
348	case 1:
349		/* Authentication needs further interaction */
350		if (send_userauth_info_request(ssh) == 1)
351			authctxt->postponed = 1;
352		break;
353	default:
354		/* Failure! */
355		break;
356	}
357	devicename = kbdintctxt->device->name;
358	if (!authctxt->postponed) {
359		if (authenticated) {
360			auth2_challenge_stop(ssh);
361		} else {
362			/* start next device */
363			/* may set authctxt->postponed */
364			auth2_challenge_start(ssh);
365		}
366	}
367	userauth_finish(ssh, authenticated, "keyboard-interactive",
368	    devicename);
369	return 0;
370}
371
372void
373privsep_challenge_enable(void)
374{
375#if defined(BSD_AUTH) || defined(USE_PAM) || defined(SKEY)
376	int n = 0;
377#endif
378#ifdef BSD_AUTH
379	extern KbdintDevice mm_bsdauth_device;
380#endif
381#ifdef USE_PAM
382	extern KbdintDevice mm_sshpam_device;
383#endif
384#ifdef SKEY
385	extern KbdintDevice mm_skey_device;
386#endif
387	/* As long as SSHv1 has devices[0] hard coded this is fine */
388#ifdef BSD_AUTH
389	devices[n++] = &mm_bsdauth_device;
390#endif
391#ifdef USE_PAM
392	devices[n++] = &mm_sshpam_device;
393#endif
394#ifdef SKEY
395	devices[n++] = &mm_skey_device;
396#endif
397}
398