auth2.c revision 323120 
1/* $OpenBSD: auth2.c,v 1.136 2016/05/02 08:49:03 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 323120 2017-09-01 21:24:32Z 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 "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
56#ifdef GSSAPI
57#include "ssh-gss.h"
58#endif
59#include "monitor_wrap.h"
60
61/* import */
62extern ServerOptions options;
63extern u_char *session_id2;
64extern u_int session_id2_len;
65extern Buffer loginmsg;
66
67/* methods */
68
69extern Authmethod method_none;
70extern Authmethod method_pubkey;
71extern Authmethod method_passwd;
72extern Authmethod method_kbdint;
73extern Authmethod method_hostbased;
74#ifdef GSSAPI
75extern Authmethod method_gssapi;
76#endif
77
78Authmethod *authmethods[] = {
79	&method_none,
80	&method_pubkey,
81#ifdef GSSAPI
82	&method_gssapi,
83#endif
84	&method_passwd,
85	&method_kbdint,
86	&method_hostbased,
87	NULL
88};
89
90/* protocol */
91
92static int input_service_request(int, u_int32_t, void *);
93static int input_userauth_request(int, u_int32_t, void *);
94
95/* helper */
96static Authmethod *authmethod_lookup(Authctxt *, const char *);
97static char *authmethods_get(Authctxt *authctxt);
98
99#define MATCH_NONE	0	/* method or submethod mismatch */
100#define MATCH_METHOD	1	/* method matches (no submethod specified) */
101#define MATCH_BOTH	2	/* method and submethod match */
102#define MATCH_PARTIAL	3	/* method matches, submethod can't be checked */
103static int list_starts_with(const char *, const char *, const char *);
104
105char *
106auth2_read_banner(void)
107{
108	struct stat st;
109	char *banner = NULL;
110	size_t len, n;
111	int fd;
112
113	if ((fd = open(options.banner, O_RDONLY)) == -1)
114		return (NULL);
115	if (fstat(fd, &st) == -1) {
116		close(fd);
117		return (NULL);
118	}
119	if (st.st_size <= 0 || st.st_size > 1*1024*1024) {
120		close(fd);
121		return (NULL);
122	}
123
124	len = (size_t)st.st_size;		/* truncate */
125	banner = xmalloc(len + 1);
126	n = atomicio(read, fd, banner, len);
127	close(fd);
128
129	if (n != len) {
130		free(banner);
131		return (NULL);
132	}
133	banner[n] = '\0';
134
135	return (banner);
136}
137
138void
139userauth_send_banner(const char *msg)
140{
141	if (datafellows & SSH_BUG_BANNER)
142		return;
143
144	packet_start(SSH2_MSG_USERAUTH_BANNER);
145	packet_put_cstring(msg);
146	packet_put_cstring("");		/* language, unused */
147	packet_send();
148	debug("%s: sent", __func__);
149}
150
151static void
152userauth_banner(void)
153{
154	char *banner = NULL;
155
156	if (options.banner == NULL || (datafellows & SSH_BUG_BANNER) != 0)
157		return;
158
159	if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
160		goto done;
161	userauth_send_banner(banner);
162
163done:
164	free(banner);
165}
166
167/*
168 * loop until authctxt->success == TRUE
169 */
170void
171do_authentication2(Authctxt *authctxt)
172{
173	dispatch_init(&dispatch_protocol_error);
174	dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
175	dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
176}
177
178/*ARGSUSED*/
179static int
180input_service_request(int type, u_int32_t seq, void *ctxt)
181{
182	Authctxt *authctxt = ctxt;
183	u_int len;
184	int acceptit = 0;
185	char *service = packet_get_cstring(&len);
186	packet_check_eom();
187
188	if (authctxt == NULL)
189		fatal("input_service_request: no authctxt");
190
191	if (strcmp(service, "ssh-userauth") == 0) {
192		if (!authctxt->success) {
193			acceptit = 1;
194			/* now we can handle user-auth requests */
195			dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
196		}
197	}
198	/* XXX all other service requests are denied */
199
200	if (acceptit) {
201		packet_start(SSH2_MSG_SERVICE_ACCEPT);
202		packet_put_cstring(service);
203		packet_send();
204		packet_write_wait();
205	} else {
206		debug("bad service request %s", service);
207		packet_disconnect("bad service request %s", service);
208	}
209	free(service);
210	return 0;
211}
212
213/*ARGSUSED*/
214static int
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	struct ssh *ssh = active_state; /* XXX */
223	login_cap_t *lc;
224	const char *from_host, *from_ip;
225#endif
226	if (authctxt == NULL)
227		fatal("input_userauth_request: no authctxt");
228
229	user = packet_get_cstring(NULL);
230	service = packet_get_cstring(NULL);
231	method = packet_get_cstring(NULL);
232	debug("userauth-request for user %s service %s method %s", user, service, method);
233	debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
234
235	if ((style = strchr(user, ':')) != NULL)
236		*style++ = 0;
237
238	if (authctxt->attempt++ == 0) {
239		/* setup auth context */
240		authctxt->pw = PRIVSEP(getpwnamallow(user));
241		authctxt->user = xstrdup(user);
242		if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
243			authctxt->valid = 1;
244			debug2("input_userauth_request: setting up authctxt for %s", user);
245		} else {
246			logit("input_userauth_request: invalid user %s", user);
247			authctxt->pw = fakepw();
248#ifdef SSH_AUDIT_EVENTS
249			PRIVSEP(audit_event(SSH_INVALID_USER));
250#endif
251		}
252#ifdef USE_PAM
253		if (options.use_pam)
254			PRIVSEP(start_pam(authctxt));
255#endif
256		setproctitle("%s%s", authctxt->valid ? user : "unknown",
257		    use_privsep ? " [net]" : "");
258		authctxt->service = xstrdup(service);
259		authctxt->style = style ? xstrdup(style) : NULL;
260		if (use_privsep)
261			mm_inform_authserv(service, style);
262		userauth_banner();
263		if (auth2_setup_methods_lists(authctxt) != 0)
264			packet_disconnect("no authentication methods enabled");
265	} else if (strcmp(user, authctxt->user) != 0 ||
266	    strcmp(service, authctxt->service) != 0) {
267		packet_disconnect("Change of username or service not allowed: "
268		    "(%s,%s) -> (%s,%s)",
269		    authctxt->user, authctxt->service, user, service);
270	}
271
272#ifdef HAVE_LOGIN_CAP
273	if (authctxt->pw != NULL &&
274	    (lc = login_getpwclass(authctxt->pw)) != NULL) {
275		logit("user %s login class %s", authctxt->pw->pw_name,
276		    authctxt->pw->pw_class);
277		from_host = auth_get_canonical_hostname(ssh, options.use_dns);
278		from_ip = ssh_remote_ipaddr(ssh);
279		if (!auth_hostok(lc, from_host, from_ip)) {
280			logit("Denied connection for %.200s from %.200s [%.200s].",
281			    authctxt->pw->pw_name, from_host, from_ip);
282			packet_disconnect("Sorry, you are not allowed to connect.");
283		}
284		if (!auth_timeok(lc, time(NULL))) {
285			logit("LOGIN %.200s REFUSED (TIME) FROM %.200s",
286			    authctxt->pw->pw_name, from_host);
287			packet_disconnect("Logins not available right now.");
288		}
289		login_close(lc);
290	}
291#endif  /* HAVE_LOGIN_CAP */
292
293	/* reset state */
294	auth2_challenge_stop(authctxt);
295
296#ifdef GSSAPI
297	/* XXX move to auth2_gssapi_stop() */
298	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
299	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
300#endif
301
302	authctxt->postponed = 0;
303	authctxt->server_caused_failure = 0;
304
305	/* try to authenticate user */
306	m = authmethod_lookup(authctxt, method);
307	if (m != NULL && authctxt->failures < options.max_authtries) {
308		debug2("input_userauth_request: try method %s", method);
309		authenticated =	m->userauth(authctxt);
310	}
311	userauth_finish(authctxt, authenticated, method, NULL);
312
313	free(service);
314	free(user);
315	free(method);
316	return 0;
317}
318
319void
320userauth_finish(Authctxt *authctxt, int authenticated, const char *method,
321    const char *submethod)
322{
323	char *methods;
324	int partial = 0;
325
326	if (!authctxt->valid && authenticated)
327		fatal("INTERNAL ERROR: authenticated invalid user %s",
328		    authctxt->user);
329	if (authenticated && authctxt->postponed)
330		fatal("INTERNAL ERROR: authenticated and postponed");
331
332	/* Special handling for root */
333	if (authenticated && authctxt->pw->pw_uid == 0 &&
334	    !auth_root_allowed(method)) {
335		authenticated = 0;
336#ifdef SSH_AUDIT_EVENTS
337		PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
338#endif
339	}
340
341	if (authenticated && options.num_auth_methods != 0) {
342		if (!auth2_update_methods_lists(authctxt, method, submethod)) {
343			authenticated = 0;
344			partial = 1;
345		}
346	}
347
348	/* Log before sending the reply */
349	auth_log(authctxt, authenticated, partial, method, submethod);
350
351	if (authctxt->postponed)
352		return;
353
354#ifdef USE_PAM
355	if (options.use_pam && authenticated) {
356		if (!PRIVSEP(do_pam_account())) {
357			/* if PAM returned a message, send it to the user */
358			if (buffer_len(&loginmsg) > 0) {
359				buffer_append(&loginmsg, "\0", 1);
360				userauth_send_banner(buffer_ptr(&loginmsg));
361				packet_write_wait();
362			}
363			fatal("Access denied for user %s by PAM account "
364			    "configuration", authctxt->user);
365		}
366	}
367#endif
368
369#ifdef _UNICOS
370	if (authenticated && cray_access_denied(authctxt->user)) {
371		authenticated = 0;
372		fatal("Access denied for user %s.", authctxt->user);
373	}
374#endif /* _UNICOS */
375
376	if (authenticated == 1) {
377		/* turn off userauth */
378		dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
379		packet_start(SSH2_MSG_USERAUTH_SUCCESS);
380		packet_send();
381		packet_write_wait();
382		/* now we can break out */
383		authctxt->success = 1;
384	} else {
385
386		/* Allow initial try of "none" auth without failure penalty */
387		if (!partial && !authctxt->server_caused_failure &&
388		    (authctxt->attempt > 1 || strcmp(method, "none") != 0))
389			authctxt->failures++;
390		if (authctxt->failures >= options.max_authtries) {
391#ifdef SSH_AUDIT_EVENTS
392			PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
393#endif
394			auth_maxtries_exceeded(authctxt);
395		}
396		methods = authmethods_get(authctxt);
397		debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
398		    partial, methods);
399		packet_start(SSH2_MSG_USERAUTH_FAILURE);
400		packet_put_cstring(methods);
401		packet_put_char(partial);
402		packet_send();
403		packet_write_wait();
404		free(methods);
405	}
406}
407
408/*
409 * Checks whether method is allowed by at least one AuthenticationMethods
410 * methods list. Returns 1 if allowed, or no methods lists configured.
411 * 0 otherwise.
412 */
413int
414auth2_method_allowed(Authctxt *authctxt, const char *method,
415    const char *submethod)
416{
417	u_int i;
418
419	/*
420	 * NB. authctxt->num_auth_methods might be zero as a result of
421	 * auth2_setup_methods_lists(), so check the configuration.
422	 */
423	if (options.num_auth_methods == 0)
424		return 1;
425	for (i = 0; i < authctxt->num_auth_methods; i++) {
426		if (list_starts_with(authctxt->auth_methods[i], method,
427		    submethod) != MATCH_NONE)
428			return 1;
429	}
430	return 0;
431}
432
433static char *
434authmethods_get(Authctxt *authctxt)
435{
436	Buffer b;
437	char *list;
438	u_int i;
439
440	buffer_init(&b);
441	for (i = 0; authmethods[i] != NULL; i++) {
442		if (strcmp(authmethods[i]->name, "none") == 0)
443			continue;
444		if (authmethods[i]->enabled == NULL ||
445		    *(authmethods[i]->enabled) == 0)
446			continue;
447		if (!auth2_method_allowed(authctxt, authmethods[i]->name,
448		    NULL))
449			continue;
450		if (buffer_len(&b) > 0)
451			buffer_append(&b, ",", 1);
452		buffer_append(&b, authmethods[i]->name,
453		    strlen(authmethods[i]->name));
454	}
455	if ((list = sshbuf_dup_string(&b)) == NULL)
456		fatal("%s: sshbuf_dup_string failed", __func__);
457	buffer_free(&b);
458	return list;
459}
460
461static Authmethod *
462authmethod_lookup(Authctxt *authctxt, const char *name)
463{
464	int i;
465
466	if (name != NULL)
467		for (i = 0; authmethods[i] != NULL; i++)
468			if (authmethods[i]->enabled != NULL &&
469			    *(authmethods[i]->enabled) != 0 &&
470			    strcmp(name, authmethods[i]->name) == 0 &&
471			    auth2_method_allowed(authctxt,
472			    authmethods[i]->name, NULL))
473				return authmethods[i];
474	debug2("Unrecognized authentication method name: %s",
475	    name ? name : "NULL");
476	return NULL;
477}
478
479/*
480 * Check a comma-separated list of methods for validity. Is need_enable is
481 * non-zero, then also require that the methods are enabled.
482 * Returns 0 on success or -1 if the methods list is invalid.
483 */
484int
485auth2_methods_valid(const char *_methods, int need_enable)
486{
487	char *methods, *omethods, *method, *p;
488	u_int i, found;
489	int ret = -1;
490
491	if (*_methods == '\0') {
492		error("empty authentication method list");
493		return -1;
494	}
495	omethods = methods = xstrdup(_methods);
496	while ((method = strsep(&methods, ",")) != NULL) {
497		for (found = i = 0; !found && authmethods[i] != NULL; i++) {
498			if ((p = strchr(method, ':')) != NULL)
499				*p = '\0';
500			if (strcmp(method, authmethods[i]->name) != 0)
501				continue;
502			if (need_enable) {
503				if (authmethods[i]->enabled == NULL ||
504				    *(authmethods[i]->enabled) == 0) {
505					error("Disabled method \"%s\" in "
506					    "AuthenticationMethods list \"%s\"",
507					    method, _methods);
508					goto out;
509				}
510			}
511			found = 1;
512			break;
513		}
514		if (!found) {
515			error("Unknown authentication method \"%s\" in list",
516			    method);
517			goto out;
518		}
519	}
520	ret = 0;
521 out:
522	free(omethods);
523	return ret;
524}
525
526/*
527 * Prune the AuthenticationMethods supplied in the configuration, removing
528 * any methods lists that include disabled methods. Note that this might
529 * leave authctxt->num_auth_methods == 0, even when multiple required auth
530 * has been requested. For this reason, all tests for whether multiple is
531 * enabled should consult options.num_auth_methods directly.
532 */
533int
534auth2_setup_methods_lists(Authctxt *authctxt)
535{
536	u_int i;
537
538	if (options.num_auth_methods == 0)
539		return 0;
540	debug3("%s: checking methods", __func__);
541	authctxt->auth_methods = xcalloc(options.num_auth_methods,
542	    sizeof(*authctxt->auth_methods));
543	authctxt->num_auth_methods = 0;
544	for (i = 0; i < options.num_auth_methods; i++) {
545		if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
546			logit("Authentication methods list \"%s\" contains "
547			    "disabled method, skipping",
548			    options.auth_methods[i]);
549			continue;
550		}
551		debug("authentication methods list %d: %s",
552		    authctxt->num_auth_methods, options.auth_methods[i]);
553		authctxt->auth_methods[authctxt->num_auth_methods++] =
554		    xstrdup(options.auth_methods[i]);
555	}
556	if (authctxt->num_auth_methods == 0) {
557		error("No AuthenticationMethods left after eliminating "
558		    "disabled methods");
559		return -1;
560	}
561	return 0;
562}
563
564static int
565list_starts_with(const char *methods, const char *method,
566    const char *submethod)
567{
568	size_t l = strlen(method);
569	int match;
570	const char *p;
571
572	if (strncmp(methods, method, l) != 0)
573		return MATCH_NONE;
574	p = methods + l;
575	match = MATCH_METHOD;
576	if (*p == ':') {
577		if (!submethod)
578			return MATCH_PARTIAL;
579		l = strlen(submethod);
580		p += 1;
581		if (strncmp(submethod, p, l))
582			return MATCH_NONE;
583		p += l;
584		match = MATCH_BOTH;
585	}
586	if (*p != ',' && *p != '\0')
587		return MATCH_NONE;
588	return match;
589}
590
591/*
592 * Remove method from the start of a comma-separated list of methods.
593 * Returns 0 if the list of methods did not start with that method or 1
594 * if it did.
595 */
596static int
597remove_method(char **methods, const char *method, const char *submethod)
598{
599	char *omethods = *methods, *p;
600	size_t l = strlen(method);
601	int match;
602
603	match = list_starts_with(omethods, method, submethod);
604	if (match != MATCH_METHOD && match != MATCH_BOTH)
605		return 0;
606	p = omethods + l;
607	if (submethod && match == MATCH_BOTH)
608		p += 1 + strlen(submethod); /* include colon */
609	if (*p == ',')
610		p++;
611	*methods = xstrdup(p);
612	free(omethods);
613	return 1;
614}
615
616/*
617 * Called after successful authentication. Will remove the successful method
618 * from the start of each list in which it occurs. If it was the last method
619 * in any list, then authentication is deemed successful.
620 * Returns 1 if the method completed any authentication list or 0 otherwise.
621 */
622int
623auth2_update_methods_lists(Authctxt *authctxt, const char *method,
624    const char *submethod)
625{
626	u_int i, found = 0;
627
628	debug3("%s: updating methods list after \"%s\"", __func__, method);
629	for (i = 0; i < authctxt->num_auth_methods; i++) {
630		if (!remove_method(&(authctxt->auth_methods[i]), method,
631		    submethod))
632			continue;
633		found = 1;
634		if (*authctxt->auth_methods[i] == '\0') {
635			debug2("authentication methods list %d complete", i);
636			return 1;
637		}
638		debug3("authentication methods list %d remaining: \"%s\"",
639		    i, authctxt->auth_methods[i]);
640	}
641	/* This should not happen, but would be bad if it did */
642	if (!found)
643		fatal("%s: method not in AuthenticationMethods", __func__);
644	return 0;
645}
646
647
648