auth2.c revision 264377 
1/* $OpenBSD: auth2.c,v 1.130 2014/01/29 06:18:35 djm 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/10/crypto/openssh/auth2.c 264377 2014-04-12 20:22:59Z des $");
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 "servconf.h"
46#include "compat.h"
47#include "key.h"
48#include "hostfile.h"
49#include "auth.h"
50#include "dispatch.h"
51#include "pathnames.h"
52#include "buffer.h"
53#include "canohost.h"
54
55#ifdef GSSAPI
56#include "ssh-gss.h"
57#endif
58#include "monitor_wrap.h"
59
60/* import */
61extern ServerOptions options;
62extern u_char *session_id2;
63extern u_int session_id2_len;
64extern Buffer loginmsg;
65
66/* methods */
67
68extern Authmethod method_none;
69extern Authmethod method_pubkey;
70extern Authmethod method_passwd;
71extern Authmethod method_kbdint;
72extern Authmethod method_hostbased;
73#ifdef GSSAPI
74extern Authmethod method_gssapi;
75#endif
76
77Authmethod *authmethods[] = {
78	&method_none,
79	&method_pubkey,
80#ifdef GSSAPI
81	&method_gssapi,
82#endif
83	&method_passwd,
84	&method_kbdint,
85	&method_hostbased,
86	NULL
87};
88
89/* protocol */
90
91static void input_service_request(int, u_int32_t, void *);
92static void input_userauth_request(int, u_int32_t, void *);
93
94/* helper */
95static Authmethod *authmethod_lookup(Authctxt *, const char *);
96static char *authmethods_get(Authctxt *authctxt);
97
98#define MATCH_NONE	0	/* method or submethod mismatch */
99#define MATCH_METHOD	1	/* method matches (no submethod specified) */
100#define MATCH_BOTH	2	/* method and submethod match */
101#define MATCH_PARTIAL	3	/* method matches, submethod can't be checked */
102static int list_starts_with(const char *, const char *, const char *);
103
104char *
105auth2_read_banner(void)
106{
107	struct stat st;
108	char *banner = NULL;
109	size_t len, n;
110	int fd;
111
112	if ((fd = open(options.banner, O_RDONLY)) == -1)
113		return (NULL);
114	if (fstat(fd, &st) == -1) {
115		close(fd);
116		return (NULL);
117	}
118	if (st.st_size <= 0 || st.st_size > 1*1024*1024) {
119		close(fd);
120		return (NULL);
121	}
122
123	len = (size_t)st.st_size;		/* truncate */
124	banner = xmalloc(len + 1);
125	n = atomicio(read, fd, banner, len);
126	close(fd);
127
128	if (n != len) {
129		free(banner);
130		return (NULL);
131	}
132	banner[n] = '\0';
133
134	return (banner);
135}
136
137void
138userauth_send_banner(const char *msg)
139{
140	if (datafellows & SSH_BUG_BANNER)
141		return;
142
143	packet_start(SSH2_MSG_USERAUTH_BANNER);
144	packet_put_cstring(msg);
145	packet_put_cstring("");		/* language, unused */
146	packet_send();
147	debug("%s: sent", __func__);
148}
149
150static void
151userauth_banner(void)
152{
153	char *banner = NULL;
154
155	if (options.banner == NULL ||
156	    strcasecmp(options.banner, "none") == 0 ||
157	    (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 void
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}
212
213/*ARGSUSED*/
214static void
215input_userauth_request(int type, u_int32_t seq, void *ctxt)
216{
217	Authctxt *authctxt = ctxt;
218	Authmethod *m = NULL;
219	char *user, *service, *method, *style = NULL;
220	int authenticated = 0;
221#ifdef HAVE_LOGIN_CAP
222	login_cap_t *lc;
223	const char *from_host, *from_ip;
224
225	from_host = get_canonical_hostname(options.use_dns);
226	from_ip = get_remote_ipaddr();
227#endif
228
229	if (authctxt == NULL)
230		fatal("input_userauth_request: no authctxt");
231
232	user = packet_get_cstring(NULL);
233	service = packet_get_cstring(NULL);
234	method = packet_get_cstring(NULL);
235	debug("userauth-request for user %s service %s method %s", user, service, method);
236	debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
237
238	if ((style = strchr(user, ':')) != NULL)
239		*style++ = 0;
240
241	if (authctxt->attempt++ == 0) {
242		/* setup auth context */
243		authctxt->pw = PRIVSEP(getpwnamallow(user));
244		authctxt->user = xstrdup(user);
245		if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
246			authctxt->valid = 1;
247			debug2("input_userauth_request: setting up authctxt for %s", user);
248		} else {
249			logit("input_userauth_request: invalid user %s", user);
250			authctxt->pw = fakepw();
251#ifdef SSH_AUDIT_EVENTS
252			PRIVSEP(audit_event(SSH_INVALID_USER));
253#endif
254		}
255#ifdef USE_PAM
256		if (options.use_pam)
257			PRIVSEP(start_pam(authctxt));
258#endif
259		setproctitle("%s%s", authctxt->valid ? user : "unknown",
260		    use_privsep ? " [net]" : "");
261		authctxt->service = xstrdup(service);
262		authctxt->style = style ? xstrdup(style) : NULL;
263		if (use_privsep)
264			mm_inform_authserv(service, style);
265		userauth_banner();
266		if (auth2_setup_methods_lists(authctxt) != 0)
267			packet_disconnect("no authentication methods enabled");
268	} else if (strcmp(user, authctxt->user) != 0 ||
269	    strcmp(service, authctxt->service) != 0) {
270		packet_disconnect("Change of username or service not allowed: "
271		    "(%s,%s) -> (%s,%s)",
272		    authctxt->user, authctxt->service, user, service);
273	}
274
275#ifdef HAVE_LOGIN_CAP
276	if (authctxt->pw != NULL) {
277		lc = login_getpwclass(authctxt->pw);
278		if (lc == NULL)
279			lc = login_getclassbyname(NULL, authctxt->pw);
280		if (!auth_hostok(lc, from_host, from_ip)) {
281			logit("Denied connection for %.200s from %.200s [%.200s].",
282			    authctxt->pw->pw_name, from_host, from_ip);
283			packet_disconnect("Sorry, you are not allowed to connect.");
284		}
285		if (!auth_timeok(lc, time(NULL))) {
286			logit("LOGIN %.200s REFUSED (TIME) FROM %.200s",
287			    authctxt->pw->pw_name, from_host);
288			packet_disconnect("Logins not available right now.");
289		}
290		login_close(lc);
291		lc = NULL;
292	}
293#endif  /* HAVE_LOGIN_CAP */
294
295	/* reset state */
296	auth2_challenge_stop(authctxt);
297
298#ifdef GSSAPI
299	/* XXX move to auth2_gssapi_stop() */
300	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
301	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
302#endif
303
304	authctxt->postponed = 0;
305	authctxt->server_caused_failure = 0;
306
307	/* try to authenticate user */
308	m = authmethod_lookup(authctxt, method);
309	if (m != NULL && authctxt->failures < options.max_authtries) {
310		debug2("input_userauth_request: try method %s", method);
311		authenticated =	m->userauth(authctxt);
312	}
313	userauth_finish(authctxt, authenticated, method, NULL);
314
315	free(service);
316	free(user);
317	free(method);
318}
319
320void
321userauth_finish(Authctxt *authctxt, int authenticated, const char *method,
322    const char *submethod)
323{
324	char *methods;
325	int partial = 0;
326
327	if (!authctxt->valid && authenticated)
328		fatal("INTERNAL ERROR: authenticated invalid user %s",
329		    authctxt->user);
330	if (authenticated && authctxt->postponed)
331		fatal("INTERNAL ERROR: authenticated and postponed");
332
333	/* Special handling for root */
334	if (authenticated && authctxt->pw->pw_uid == 0 &&
335	    !auth_root_allowed(method)) {
336		authenticated = 0;
337#ifdef SSH_AUDIT_EVENTS
338		PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
339#endif
340	}
341
342	if (authenticated && options.num_auth_methods != 0) {
343		if (!auth2_update_methods_lists(authctxt, method, submethod)) {
344			authenticated = 0;
345			partial = 1;
346		}
347	}
348
349	/* Log before sending the reply */
350	auth_log(authctxt, authenticated, partial, method, submethod);
351
352	if (authctxt->postponed)
353		return;
354
355#ifdef USE_PAM
356	if (options.use_pam && authenticated) {
357		if (!PRIVSEP(do_pam_account())) {
358			/* if PAM returned a message, send it to the user */
359			if (buffer_len(&loginmsg) > 0) {
360				buffer_append(&loginmsg, "\0", 1);
361				userauth_send_banner(buffer_ptr(&loginmsg));
362				packet_write_wait();
363			}
364			fatal("Access denied for user %s by PAM account "
365			    "configuration", authctxt->user);
366		}
367	}
368#endif
369
370#ifdef _UNICOS
371	if (authenticated && cray_access_denied(authctxt->user)) {
372		authenticated = 0;
373		fatal("Access denied for user %s.", authctxt->user);
374	}
375#endif /* _UNICOS */
376
377	if (authenticated == 1) {
378		/* turn off userauth */
379		dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
380		packet_start(SSH2_MSG_USERAUTH_SUCCESS);
381		packet_send();
382		packet_write_wait();
383		/* now we can break out */
384		authctxt->success = 1;
385	} else {
386
387		/* Allow initial try of "none" auth without failure penalty */
388		if (!authctxt->server_caused_failure &&
389		    (authctxt->attempt > 1 || strcmp(method, "none") != 0))
390			authctxt->failures++;
391		if (authctxt->failures >= options.max_authtries) {
392#ifdef SSH_AUDIT_EVENTS
393			PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
394#endif
395			packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
396		}
397		methods = authmethods_get(authctxt);
398		debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
399		    partial, methods);
400		packet_start(SSH2_MSG_USERAUTH_FAILURE);
401		packet_put_cstring(methods);
402		packet_put_char(partial);
403		packet_send();
404		packet_write_wait();
405		free(methods);
406	}
407}
408
409/*
410 * Checks whether method is allowed by at least one AuthenticationMethods
411 * methods list. Returns 1 if allowed, or no methods lists configured.
412 * 0 otherwise.
413 */
414int
415auth2_method_allowed(Authctxt *authctxt, const char *method,
416    const char *submethod)
417{
418	u_int i;
419
420	/*
421	 * NB. authctxt->num_auth_methods might be zero as a result of
422	 * auth2_setup_methods_lists(), so check the configuration.
423	 */
424	if (options.num_auth_methods == 0)
425		return 1;
426	for (i = 0; i < authctxt->num_auth_methods; i++) {
427		if (list_starts_with(authctxt->auth_methods[i], method,
428		    submethod) != MATCH_NONE)
429			return 1;
430	}
431	return 0;
432}
433
434static char *
435authmethods_get(Authctxt *authctxt)
436{
437	Buffer b;
438	char *list;
439	u_int i;
440
441	buffer_init(&b);
442	for (i = 0; authmethods[i] != NULL; i++) {
443		if (strcmp(authmethods[i]->name, "none") == 0)
444			continue;
445		if (authmethods[i]->enabled == NULL ||
446		    *(authmethods[i]->enabled) == 0)
447			continue;
448		if (!auth2_method_allowed(authctxt, authmethods[i]->name,
449		    NULL))
450			continue;
451		if (buffer_len(&b) > 0)
452			buffer_append(&b, ",", 1);
453		buffer_append(&b, authmethods[i]->name,
454		    strlen(authmethods[i]->name));
455	}
456	buffer_append(&b, "\0", 1);
457	list = xstrdup(buffer_ptr(&b));
458	buffer_free(&b);
459	return list;
460}
461
462static Authmethod *
463authmethod_lookup(Authctxt *authctxt, const char *name)
464{
465	int i;
466
467	if (name != NULL)
468		for (i = 0; authmethods[i] != NULL; i++)
469			if (authmethods[i]->enabled != NULL &&
470			    *(authmethods[i]->enabled) != 0 &&
471			    strcmp(name, authmethods[i]->name) == 0 &&
472			    auth2_method_allowed(authctxt,
473			    authmethods[i]->name, NULL))
474				return authmethods[i];
475	debug2("Unrecognized authentication method name: %s",
476	    name ? name : "NULL");
477	return NULL;
478}
479
480/*
481 * Check a comma-separated list of methods for validity. Is need_enable is
482 * non-zero, then also require that the methods are enabled.
483 * Returns 0 on success or -1 if the methods list is invalid.
484 */
485int
486auth2_methods_valid(const char *_methods, int need_enable)
487{
488	char *methods, *omethods, *method, *p;
489	u_int i, found;
490	int ret = -1;
491
492	if (*_methods == '\0') {
493		error("empty authentication method list");
494		return -1;
495	}
496	omethods = methods = xstrdup(_methods);
497	while ((method = strsep(&methods, ",")) != NULL) {
498		for (found = i = 0; !found && authmethods[i] != NULL; i++) {
499			if ((p = strchr(method, ':')) != NULL)
500				*p = '\0';
501			if (strcmp(method, authmethods[i]->name) != 0)
502				continue;
503			if (need_enable) {
504				if (authmethods[i]->enabled == NULL ||
505				    *(authmethods[i]->enabled) == 0) {
506					error("Disabled method \"%s\" in "
507					    "AuthenticationMethods list \"%s\"",
508					    method, _methods);
509					goto out;
510				}
511			}
512			found = 1;
513			break;
514		}
515		if (!found) {
516			error("Unknown authentication method \"%s\" in list",
517			    method);
518			goto out;
519		}
520	}
521	ret = 0;
522 out:
523	free(omethods);
524	return ret;
525}
526
527/*
528 * Prune the AuthenticationMethods supplied in the configuration, removing
529 * any methods lists that include disabled methods. Note that this might
530 * leave authctxt->num_auth_methods == 0, even when multiple required auth
531 * has been requested. For this reason, all tests for whether multiple is
532 * enabled should consult options.num_auth_methods directly.
533 */
534int
535auth2_setup_methods_lists(Authctxt *authctxt)
536{
537	u_int i;
538
539	if (options.num_auth_methods == 0)
540		return 0;
541	debug3("%s: checking methods", __func__);
542	authctxt->auth_methods = xcalloc(options.num_auth_methods,
543	    sizeof(*authctxt->auth_methods));
544	authctxt->num_auth_methods = 0;
545	for (i = 0; i < options.num_auth_methods; i++) {
546		if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
547			logit("Authentication methods list \"%s\" contains "
548			    "disabled method, skipping",
549			    options.auth_methods[i]);
550			continue;
551		}
552		debug("authentication methods list %d: %s",
553		    authctxt->num_auth_methods, options.auth_methods[i]);
554		authctxt->auth_methods[authctxt->num_auth_methods++] =
555		    xstrdup(options.auth_methods[i]);
556	}
557	if (authctxt->num_auth_methods == 0) {
558		error("No AuthenticationMethods left after eliminating "
559		    "disabled methods");
560		return -1;
561	}
562	return 0;
563}
564
565static int
566list_starts_with(const char *methods, const char *method,
567    const char *submethod)
568{
569	size_t l = strlen(method);
570	int match;
571	const char *p;
572
573	if (strncmp(methods, method, l) != 0)
574		return MATCH_NONE;
575	p = methods + l;
576	match = MATCH_METHOD;
577	if (*p == ':') {
578		if (!submethod)
579			return MATCH_PARTIAL;
580		l = strlen(submethod);
581		p += 1;
582		if (strncmp(submethod, p, l))
583			return MATCH_NONE;
584		p += l;
585		match = MATCH_BOTH;
586	}
587	if (*p != ',' && *p != '\0')
588		return MATCH_NONE;
589	return match;
590}
591
592/*
593 * Remove method from the start of a comma-separated list of methods.
594 * Returns 0 if the list of methods did not start with that method or 1
595 * if it did.
596 */
597static int
598remove_method(char **methods, const char *method, const char *submethod)
599{
600	char *omethods = *methods, *p;
601	size_t l = strlen(method);
602	int match;
603
604	match = list_starts_with(omethods, method, submethod);
605	if (match != MATCH_METHOD && match != MATCH_BOTH)
606		return 0;
607	p = omethods + l;
608	if (submethod && match == MATCH_BOTH)
609		p += 1 + strlen(submethod); /* include colon */
610	if (*p == ',')
611		p++;
612	*methods = xstrdup(p);
613	free(omethods);
614	return 1;
615}
616
617/*
618 * Called after successful authentication. Will remove the successful method
619 * from the start of each list in which it occurs. If it was the last method
620 * in any list, then authentication is deemed successful.
621 * Returns 1 if the method completed any authentication list or 0 otherwise.
622 */
623int
624auth2_update_methods_lists(Authctxt *authctxt, const char *method,
625    const char *submethod)
626{
627	u_int i, found = 0;
628
629	debug3("%s: updating methods list after \"%s\"", __func__, method);
630	for (i = 0; i < authctxt->num_auth_methods; i++) {
631		if (!remove_method(&(authctxt->auth_methods[i]), method,
632		    submethod))
633			continue;
634		found = 1;
635		if (*authctxt->auth_methods[i] == '\0') {
636			debug2("authentication methods list %d complete", i);
637			return 1;
638		}
639		debug3("authentication methods list %d remaining: \"%s\"",
640		    i, authctxt->auth_methods[i]);
641	}
642	/* This should not happen, but would be bad if it did */
643	if (!found)
644		fatal("%s: method not in AuthenticationMethods", __func__);
645	return 0;
646}
647
648
649