auth2.c revision 305476 
1/* $OpenBSD: auth2.c,v 1.135 2015/01/19 20:07:45 markus Exp $ */
2/*
3 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#include "includes.h"
27__RCSID("$FreeBSD: stable/11/crypto/openssh/auth2.c 305476 2016-09-06 14:52:14Z lidl $");
28
29#include <sys/types.h>
30#include <sys/stat.h>
31#include <sys/uio.h>
32
33#include <fcntl.h>
34#include <pwd.h>
35#include <stdarg.h>
36#include <string.h>
37#include <unistd.h>
38
39#include "atomicio.h"
40#include "xmalloc.h"
41#include "ssh2.h"
42#include "packet.h"
43#include "log.h"
44#include "buffer.h"
45#include "misc.h"
46#include "servconf.h"
47#include "compat.h"
48#include "key.h"
49#include "hostfile.h"
50#include "auth.h"
51#include "dispatch.h"
52#include "pathnames.h"
53#include "buffer.h"
54#include "canohost.h"
55#include "blacklist_client.h"
56
57#ifdef GSSAPI
58#include "ssh-gss.h"
59#endif
60#include "monitor_wrap.h"
61
62/* import */
63extern ServerOptions options;
64extern u_char *session_id2;
65extern u_int session_id2_len;
66extern Buffer loginmsg;
67
68/* methods */
69
70extern Authmethod method_none;
71extern Authmethod method_pubkey;
72extern Authmethod method_passwd;
73extern Authmethod method_kbdint;
74extern Authmethod method_hostbased;
75#ifdef GSSAPI
76extern Authmethod method_gssapi;
77#endif
78
79Authmethod *authmethods[] = {
80	&method_none,
81	&method_pubkey,
82#ifdef GSSAPI
83	&method_gssapi,
84#endif
85	&method_passwd,
86	&method_kbdint,
87	&method_hostbased,
88	NULL
89};
90
91/* protocol */
92
93static int input_service_request(int, u_int32_t, void *);
94static int input_userauth_request(int, u_int32_t, void *);
95
96/* helper */
97static Authmethod *authmethod_lookup(Authctxt *, const char *);
98static char *authmethods_get(Authctxt *authctxt);
99
100#define MATCH_NONE	0	/* method or submethod mismatch */
101#define MATCH_METHOD	1	/* method matches (no submethod specified) */
102#define MATCH_BOTH	2	/* method and submethod match */
103#define MATCH_PARTIAL	3	/* method matches, submethod can't be checked */
104static int list_starts_with(const char *, const char *, const char *);
105
106char *
107auth2_read_banner(void)
108{
109	struct stat st;
110	char *banner = NULL;
111	size_t len, n;
112	int fd;
113
114	if ((fd = open(options.banner, O_RDONLY)) == -1)
115		return (NULL);
116	if (fstat(fd, &st) == -1) {
117		close(fd);
118		return (NULL);
119	}
120	if (st.st_size <= 0 || st.st_size > 1*1024*1024) {
121		close(fd);
122		return (NULL);
123	}
124
125	len = (size_t)st.st_size;		/* truncate */
126	banner = xmalloc(len + 1);
127	n = atomicio(read, fd, banner, len);
128	close(fd);
129
130	if (n != len) {
131		free(banner);
132		return (NULL);
133	}
134	banner[n] = '\0';
135
136	return (banner);
137}
138
139void
140userauth_send_banner(const char *msg)
141{
142	if (datafellows & SSH_BUG_BANNER)
143		return;
144
145	packet_start(SSH2_MSG_USERAUTH_BANNER);
146	packet_put_cstring(msg);
147	packet_put_cstring("");		/* language, unused */
148	packet_send();
149	debug("%s: sent", __func__);
150}
151
152static void
153userauth_banner(void)
154{
155	char *banner = NULL;
156
157	if (options.banner == NULL || (datafellows & SSH_BUG_BANNER) != 0)
158		return;
159
160	if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
161		goto done;
162	userauth_send_banner(banner);
163
164done:
165	free(banner);
166}
167
168/*
169 * loop until authctxt->success == TRUE
170 */
171void
172do_authentication2(Authctxt *authctxt)
173{
174	dispatch_init(&dispatch_protocol_error);
175	dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
176	dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
177}
178
179/*ARGSUSED*/
180static int
181input_service_request(int type, u_int32_t seq, void *ctxt)
182{
183	Authctxt *authctxt = ctxt;
184	u_int len;
185	int acceptit = 0;
186	char *service = packet_get_cstring(&len);
187	packet_check_eom();
188
189	if (authctxt == NULL)
190		fatal("input_service_request: no authctxt");
191
192	if (strcmp(service, "ssh-userauth") == 0) {
193		if (!authctxt->success) {
194			acceptit = 1;
195			/* now we can handle user-auth requests */
196			dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
197		}
198	}
199	/* XXX all other service requests are denied */
200
201	if (acceptit) {
202		packet_start(SSH2_MSG_SERVICE_ACCEPT);
203		packet_put_cstring(service);
204		packet_send();
205		packet_write_wait();
206	} else {
207		debug("bad service request %s", service);
208		packet_disconnect("bad service request %s", service);
209	}
210	free(service);
211	return 0;
212}
213
214/*ARGSUSED*/
215static int
216input_userauth_request(int type, u_int32_t seq, void *ctxt)
217{
218	Authctxt *authctxt = ctxt;
219	Authmethod *m = NULL;
220	char *user, *service, *method, *style = NULL;
221	int authenticated = 0;
222#ifdef HAVE_LOGIN_CAP
223	login_cap_t *lc;
224	const char *from_host, *from_ip;
225
226	from_host = get_canonical_hostname(options.use_dns);
227	from_ip = get_remote_ipaddr();
228#endif
229
230	if (authctxt == NULL)
231		fatal("input_userauth_request: no authctxt");
232
233	user = packet_get_cstring(NULL);
234	service = packet_get_cstring(NULL);
235	method = packet_get_cstring(NULL);
236	debug("userauth-request for user %s service %s method %s", user, service, method);
237	debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
238
239	if ((style = strchr(user, ':')) != NULL)
240		*style++ = 0;
241
242	if (authctxt->attempt++ == 0) {
243		/* setup auth context */
244		authctxt->pw = PRIVSEP(getpwnamallow(user));
245		authctxt->user = xstrdup(user);
246		if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
247			authctxt->valid = 1;
248			debug2("input_userauth_request: setting up authctxt for %s", user);
249		} else {
250			logit("input_userauth_request: invalid user %s", user);
251			authctxt->pw = fakepw();
252			BLACKLIST_NOTIFY(BLACKLIST_AUTH_FAIL);
253#ifdef SSH_AUDIT_EVENTS
254			PRIVSEP(audit_event(SSH_INVALID_USER));
255#endif
256		}
257#ifdef USE_PAM
258		if (options.use_pam)
259			PRIVSEP(start_pam(authctxt));
260#endif
261		setproctitle("%s%s", authctxt->valid ? user : "unknown",
262		    use_privsep ? " [net]" : "");
263		authctxt->service = xstrdup(service);
264		authctxt->style = style ? xstrdup(style) : NULL;
265		if (use_privsep)
266			mm_inform_authserv(service, style);
267		userauth_banner();
268		if (auth2_setup_methods_lists(authctxt) != 0)
269			packet_disconnect("no authentication methods enabled");
270	} else if (strcmp(user, authctxt->user) != 0 ||
271	    strcmp(service, authctxt->service) != 0) {
272		packet_disconnect("Change of username or service not allowed: "
273		    "(%s,%s) -> (%s,%s)",
274		    authctxt->user, authctxt->service, user, service);
275	}
276
277#ifdef HAVE_LOGIN_CAP
278	if (authctxt->pw != NULL) {
279		lc = login_getpwclass(authctxt->pw);
280		if (lc == NULL)
281			lc = login_getclassbyname(NULL, authctxt->pw);
282		if (!auth_hostok(lc, from_host, from_ip)) {
283			logit("Denied connection for %.200s from %.200s [%.200s].",
284			    authctxt->pw->pw_name, from_host, from_ip);
285			packet_disconnect("Sorry, you are not allowed to connect.");
286		}
287		if (!auth_timeok(lc, time(NULL))) {
288			logit("LOGIN %.200s REFUSED (TIME) FROM %.200s",
289			    authctxt->pw->pw_name, from_host);
290			packet_disconnect("Logins not available right now.");
291		}
292		login_close(lc);
293		lc = NULL;
294	}
295#endif  /* HAVE_LOGIN_CAP */
296
297	/* reset state */
298	auth2_challenge_stop(authctxt);
299
300#ifdef GSSAPI
301	/* XXX move to auth2_gssapi_stop() */
302	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
303	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
304#endif
305
306	authctxt->postponed = 0;
307	authctxt->server_caused_failure = 0;
308
309	/* try to authenticate user */
310	m = authmethod_lookup(authctxt, method);
311	if (m != NULL && authctxt->failures < options.max_authtries) {
312		debug2("input_userauth_request: try method %s", method);
313		authenticated =	m->userauth(authctxt);
314	}
315	userauth_finish(authctxt, authenticated, method, NULL);
316
317	free(service);
318	free(user);
319	free(method);
320	return 0;
321}
322
323void
324userauth_finish(Authctxt *authctxt, int authenticated, const char *method,
325    const char *submethod)
326{
327	char *methods;
328	int partial = 0;
329
330	if (!authctxt->valid && authenticated)
331		fatal("INTERNAL ERROR: authenticated invalid user %s",
332		    authctxt->user);
333	if (authenticated && authctxt->postponed)
334		fatal("INTERNAL ERROR: authenticated and postponed");
335
336	/* Special handling for root */
337	if (authenticated && authctxt->pw->pw_uid == 0 &&
338	    !auth_root_allowed(method)) {
339		authenticated = 0;
340#ifdef SSH_AUDIT_EVENTS
341		PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
342#endif
343	}
344
345	if (authenticated && options.num_auth_methods != 0) {
346		if (!auth2_update_methods_lists(authctxt, method, submethod)) {
347			authenticated = 0;
348			partial = 1;
349		}
350	}
351
352	/* Log before sending the reply */
353	auth_log(authctxt, authenticated, partial, method, submethod);
354
355	if (authctxt->postponed)
356		return;
357
358#ifdef USE_PAM
359	if (options.use_pam && authenticated) {
360		if (!PRIVSEP(do_pam_account())) {
361			/* if PAM returned a message, send it to the user */
362			if (buffer_len(&loginmsg) > 0) {
363				buffer_append(&loginmsg, "\0", 1);
364				userauth_send_banner(buffer_ptr(&loginmsg));
365				packet_write_wait();
366			}
367			fatal("Access denied for user %s by PAM account "
368			    "configuration", authctxt->user);
369		}
370	}
371#endif
372
373#ifdef _UNICOS
374	if (authenticated && cray_access_denied(authctxt->user)) {
375		authenticated = 0;
376		fatal("Access denied for user %s.", authctxt->user);
377	}
378#endif /* _UNICOS */
379
380	if (authenticated == 1) {
381		/* turn off userauth */
382		dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
383		packet_start(SSH2_MSG_USERAUTH_SUCCESS);
384		packet_send();
385		packet_write_wait();
386		/* now we can break out */
387		authctxt->success = 1;
388	} else {
389
390		/* Allow initial try of "none" auth without failure penalty */
391		if (!partial && !authctxt->server_caused_failure &&
392		    (authctxt->attempt > 1 || strcmp(method, "none") != 0))
393			authctxt->failures++;
394		if (authctxt->failures >= options.max_authtries) {
395#ifdef SSH_AUDIT_EVENTS
396			PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
397#endif
398			auth_maxtries_exceeded(authctxt);
399		}
400		methods = authmethods_get(authctxt);
401		debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
402		    partial, methods);
403		packet_start(SSH2_MSG_USERAUTH_FAILURE);
404		packet_put_cstring(methods);
405		packet_put_char(partial);
406		packet_send();
407		packet_write_wait();
408		free(methods);
409	}
410}
411
412/*
413 * Checks whether method is allowed by at least one AuthenticationMethods
414 * methods list. Returns 1 if allowed, or no methods lists configured.
415 * 0 otherwise.
416 */
417int
418auth2_method_allowed(Authctxt *authctxt, const char *method,
419    const char *submethod)
420{
421	u_int i;
422
423	/*
424	 * NB. authctxt->num_auth_methods might be zero as a result of
425	 * auth2_setup_methods_lists(), so check the configuration.
426	 */
427	if (options.num_auth_methods == 0)
428		return 1;
429	for (i = 0; i < authctxt->num_auth_methods; i++) {
430		if (list_starts_with(authctxt->auth_methods[i], method,
431		    submethod) != MATCH_NONE)
432			return 1;
433	}
434	return 0;
435}
436
437static char *
438authmethods_get(Authctxt *authctxt)
439{
440	Buffer b;
441	char *list;
442	u_int i;
443
444	buffer_init(&b);
445	for (i = 0; authmethods[i] != NULL; i++) {
446		if (strcmp(authmethods[i]->name, "none") == 0)
447			continue;
448		if (authmethods[i]->enabled == NULL ||
449		    *(authmethods[i]->enabled) == 0)
450			continue;
451		if (!auth2_method_allowed(authctxt, authmethods[i]->name,
452		    NULL))
453			continue;
454		if (buffer_len(&b) > 0)
455			buffer_append(&b, ",", 1);
456		buffer_append(&b, authmethods[i]->name,
457		    strlen(authmethods[i]->name));
458	}
459	buffer_append(&b, "\0", 1);
460	list = xstrdup(buffer_ptr(&b));
461	buffer_free(&b);
462	return list;
463}
464
465static Authmethod *
466authmethod_lookup(Authctxt *authctxt, const char *name)
467{
468	int i;
469
470	if (name != NULL)
471		for (i = 0; authmethods[i] != NULL; i++)
472			if (authmethods[i]->enabled != NULL &&
473			    *(authmethods[i]->enabled) != 0 &&
474			    strcmp(name, authmethods[i]->name) == 0 &&
475			    auth2_method_allowed(authctxt,
476			    authmethods[i]->name, NULL))
477				return authmethods[i];
478	debug2("Unrecognized authentication method name: %s",
479	    name ? name : "NULL");
480	return NULL;
481}
482
483/*
484 * Check a comma-separated list of methods for validity. Is need_enable is
485 * non-zero, then also require that the methods are enabled.
486 * Returns 0 on success or -1 if the methods list is invalid.
487 */
488int
489auth2_methods_valid(const char *_methods, int need_enable)
490{
491	char *methods, *omethods, *method, *p;
492	u_int i, found;
493	int ret = -1;
494
495	if (*_methods == '\0') {
496		error("empty authentication method list");
497		return -1;
498	}
499	omethods = methods = xstrdup(_methods);
500	while ((method = strsep(&methods, ",")) != NULL) {
501		for (found = i = 0; !found && authmethods[i] != NULL; i++) {
502			if ((p = strchr(method, ':')) != NULL)
503				*p = '\0';
504			if (strcmp(method, authmethods[i]->name) != 0)
505				continue;
506			if (need_enable) {
507				if (authmethods[i]->enabled == NULL ||
508				    *(authmethods[i]->enabled) == 0) {
509					error("Disabled method \"%s\" in "
510					    "AuthenticationMethods list \"%s\"",
511					    method, _methods);
512					goto out;
513				}
514			}
515			found = 1;
516			break;
517		}
518		if (!found) {
519			error("Unknown authentication method \"%s\" in list",
520			    method);
521			goto out;
522		}
523	}
524	ret = 0;
525 out:
526	free(omethods);
527	return ret;
528}
529
530/*
531 * Prune the AuthenticationMethods supplied in the configuration, removing
532 * any methods lists that include disabled methods. Note that this might
533 * leave authctxt->num_auth_methods == 0, even when multiple required auth
534 * has been requested. For this reason, all tests for whether multiple is
535 * enabled should consult options.num_auth_methods directly.
536 */
537int
538auth2_setup_methods_lists(Authctxt *authctxt)
539{
540	u_int i;
541
542	if (options.num_auth_methods == 0)
543		return 0;
544	debug3("%s: checking methods", __func__);
545	authctxt->auth_methods = xcalloc(options.num_auth_methods,
546	    sizeof(*authctxt->auth_methods));
547	authctxt->num_auth_methods = 0;
548	for (i = 0; i < options.num_auth_methods; i++) {
549		if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
550			logit("Authentication methods list \"%s\" contains "
551			    "disabled method, skipping",
552			    options.auth_methods[i]);
553			continue;
554		}
555		debug("authentication methods list %d: %s",
556		    authctxt->num_auth_methods, options.auth_methods[i]);
557		authctxt->auth_methods[authctxt->num_auth_methods++] =
558		    xstrdup(options.auth_methods[i]);
559	}
560	if (authctxt->num_auth_methods == 0) {
561		error("No AuthenticationMethods left after eliminating "
562		    "disabled methods");
563		return -1;
564	}
565	return 0;
566}
567
568static int
569list_starts_with(const char *methods, const char *method,
570    const char *submethod)
571{
572	size_t l = strlen(method);
573	int match;
574	const char *p;
575
576	if (strncmp(methods, method, l) != 0)
577		return MATCH_NONE;
578	p = methods + l;
579	match = MATCH_METHOD;
580	if (*p == ':') {
581		if (!submethod)
582			return MATCH_PARTIAL;
583		l = strlen(submethod);
584		p += 1;
585		if (strncmp(submethod, p, l))
586			return MATCH_NONE;
587		p += l;
588		match = MATCH_BOTH;
589	}
590	if (*p != ',' && *p != '\0')
591		return MATCH_NONE;
592	return match;
593}
594
595/*
596 * Remove method from the start of a comma-separated list of methods.
597 * Returns 0 if the list of methods did not start with that method or 1
598 * if it did.
599 */
600static int
601remove_method(char **methods, const char *method, const char *submethod)
602{
603	char *omethods = *methods, *p;
604	size_t l = strlen(method);
605	int match;
606
607	match = list_starts_with(omethods, method, submethod);
608	if (match != MATCH_METHOD && match != MATCH_BOTH)
609		return 0;
610	p = omethods + l;
611	if (submethod && match == MATCH_BOTH)
612		p += 1 + strlen(submethod); /* include colon */
613	if (*p == ',')
614		p++;
615	*methods = xstrdup(p);
616	free(omethods);
617	return 1;
618}
619
620/*
621 * Called after successful authentication. Will remove the successful method
622 * from the start of each list in which it occurs. If it was the last method
623 * in any list, then authentication is deemed successful.
624 * Returns 1 if the method completed any authentication list or 0 otherwise.
625 */
626int
627auth2_update_methods_lists(Authctxt *authctxt, const char *method,
628    const char *submethod)
629{
630	u_int i, found = 0;
631
632	debug3("%s: updating methods list after \"%s\"", __func__, method);
633	for (i = 0; i < authctxt->num_auth_methods; i++) {
634		if (!remove_method(&(authctxt->auth_methods[i]), method,
635		    submethod))
636			continue;
637		found = 1;
638		if (*authctxt->auth_methods[i] == '\0') {
639			debug2("authentication methods list %d complete", i);
640			return 1;
641		}
642		debug3("authentication methods list %d remaining: \"%s\"",
643		    i, authctxt->auth_methods[i]);
644	}
645	/* This should not happen, but would be bad if it did */
646	if (!found)
647		fatal("%s: method not in AuthenticationMethods", __func__);
648	return 0;
649}
650
651
652