auth.c revision 240075 
1/* $OpenBSD: auth.c,v 1.96 2012/05/13 01:42:32 dtucker 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: head/crypto/openssh/auth.c 240075 2012-09-03 16:51:41Z des $");
28
29#include <sys/types.h>
30#include <sys/stat.h>
31#include <sys/param.h>
32
33#include <netinet/in.h>
34
35#include <errno.h>
36#include <fcntl.h>
37#ifdef HAVE_PATHS_H
38# include <paths.h>
39#endif
40#include <pwd.h>
41#ifdef HAVE_LOGIN_H
42#include <login.h>
43#endif
44#ifdef USE_SHADOW
45#include <shadow.h>
46#endif
47#ifdef HAVE_LIBGEN_H
48#include <libgen.h>
49#endif
50#include <stdarg.h>
51#include <stdio.h>
52#include <string.h>
53#include <unistd.h>
54
55#include "xmalloc.h"
56#include "match.h"
57#include "groupaccess.h"
58#include "log.h"
59#include "buffer.h"
60#include "servconf.h"
61#include "key.h"
62#include "hostfile.h"
63#include "auth.h"
64#include "auth-options.h"
65#include "canohost.h"
66#include "uidswap.h"
67#include "misc.h"
68#include "packet.h"
69#include "loginrec.h"
70#ifdef GSSAPI
71#include "ssh-gss.h"
72#endif
73#include "authfile.h"
74#include "monitor_wrap.h"
75
76/* import */
77extern ServerOptions options;
78extern int use_privsep;
79extern Buffer loginmsg;
80extern struct passwd *privsep_pw;
81
82/* Debugging messages */
83Buffer auth_debug;
84int auth_debug_init;
85
86/*
87 * Check if the user is allowed to log in via ssh. If user is listed
88 * in DenyUsers or one of user's groups is listed in DenyGroups, false
89 * will be returned. If AllowUsers isn't empty and user isn't listed
90 * there, or if AllowGroups isn't empty and one of user's groups isn't
91 * listed there, false will be returned.
92 * If the user's shell is not executable, false will be returned.
93 * Otherwise true is returned.
94 */
95int
96allowed_user(struct passwd * pw)
97{
98	struct stat st;
99	const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL;
100	u_int i;
101#ifdef USE_SHADOW
102	struct spwd *spw = NULL;
103#endif
104
105	/* Shouldn't be called if pw is NULL, but better safe than sorry... */
106	if (!pw || !pw->pw_name)
107		return 0;
108
109#ifdef USE_SHADOW
110	if (!options.use_pam)
111		spw = getspnam(pw->pw_name);
112#ifdef HAS_SHADOW_EXPIRE
113	if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw))
114		return 0;
115#endif /* HAS_SHADOW_EXPIRE */
116#endif /* USE_SHADOW */
117
118	/* grab passwd field for locked account check */
119	passwd = pw->pw_passwd;
120#ifdef USE_SHADOW
121	if (spw != NULL)
122#ifdef USE_LIBIAF
123		passwd = get_iaf_password(pw);
124#else
125		passwd = spw->sp_pwdp;
126#endif /* USE_LIBIAF */
127#endif
128
129	/* check for locked account */
130	if (!options.use_pam && passwd && *passwd) {
131		int locked = 0;
132
133#ifdef LOCKED_PASSWD_STRING
134		if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0)
135			 locked = 1;
136#endif
137#ifdef LOCKED_PASSWD_PREFIX
138		if (strncmp(passwd, LOCKED_PASSWD_PREFIX,
139		    strlen(LOCKED_PASSWD_PREFIX)) == 0)
140			 locked = 1;
141#endif
142#ifdef LOCKED_PASSWD_SUBSTR
143		if (strstr(passwd, LOCKED_PASSWD_SUBSTR))
144			locked = 1;
145#endif
146#ifdef USE_LIBIAF
147		free((void *) passwd);
148#endif /* USE_LIBIAF */
149		if (locked) {
150			logit("User %.100s not allowed because account is locked",
151			    pw->pw_name);
152			return 0;
153		}
154	}
155
156	/*
157	 * Deny if shell does not exist or is not executable unless we
158	 * are chrooting.
159	 */
160	if (options.chroot_directory == NULL ||
161	    strcasecmp(options.chroot_directory, "none") == 0) {
162		char *shell = xstrdup((pw->pw_shell[0] == '\0') ?
163		    _PATH_BSHELL : pw->pw_shell); /* empty = /bin/sh */
164
165		if (stat(shell, &st) != 0) {
166			logit("User %.100s not allowed because shell %.100s "
167			    "does not exist", pw->pw_name, shell);
168			xfree(shell);
169			return 0;
170		}
171		if (S_ISREG(st.st_mode) == 0 ||
172		    (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
173			logit("User %.100s not allowed because shell %.100s "
174			    "is not executable", pw->pw_name, shell);
175			xfree(shell);
176			return 0;
177		}
178		xfree(shell);
179	}
180
181	if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
182	    options.num_deny_groups > 0 || options.num_allow_groups > 0) {
183		hostname = get_canonical_hostname(options.use_dns);
184		ipaddr = get_remote_ipaddr();
185	}
186
187	/* Return false if user is listed in DenyUsers */
188	if (options.num_deny_users > 0) {
189		for (i = 0; i < options.num_deny_users; i++)
190			if (match_user(pw->pw_name, hostname, ipaddr,
191			    options.deny_users[i])) {
192				logit("User %.100s from %.100s not allowed "
193				    "because listed in DenyUsers",
194				    pw->pw_name, hostname);
195				return 0;
196			}
197	}
198	/* Return false if AllowUsers isn't empty and user isn't listed there */
199	if (options.num_allow_users > 0) {
200		for (i = 0; i < options.num_allow_users; i++)
201			if (match_user(pw->pw_name, hostname, ipaddr,
202			    options.allow_users[i]))
203				break;
204		/* i < options.num_allow_users iff we break for loop */
205		if (i >= options.num_allow_users) {
206			logit("User %.100s from %.100s not allowed because "
207			    "not listed in AllowUsers", pw->pw_name, hostname);
208			return 0;
209		}
210	}
211	if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
212		/* Get the user's group access list (primary and supplementary) */
213		if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
214			logit("User %.100s from %.100s not allowed because "
215			    "not in any group", pw->pw_name, hostname);
216			return 0;
217		}
218
219		/* Return false if one of user's groups is listed in DenyGroups */
220		if (options.num_deny_groups > 0)
221			if (ga_match(options.deny_groups,
222			    options.num_deny_groups)) {
223				ga_free();
224				logit("User %.100s from %.100s not allowed "
225				    "because a group is listed in DenyGroups",
226				    pw->pw_name, hostname);
227				return 0;
228			}
229		/*
230		 * Return false if AllowGroups isn't empty and one of user's groups
231		 * isn't listed there
232		 */
233		if (options.num_allow_groups > 0)
234			if (!ga_match(options.allow_groups,
235			    options.num_allow_groups)) {
236				ga_free();
237				logit("User %.100s from %.100s not allowed "
238				    "because none of user's groups are listed "
239				    "in AllowGroups", pw->pw_name, hostname);
240				return 0;
241			}
242		ga_free();
243	}
244
245#ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
246	if (!sys_auth_allowed_user(pw, &loginmsg))
247		return 0;
248#endif
249
250	/* We found no reason not to let this user try to log on... */
251	return 1;
252}
253
254void
255auth_log(Authctxt *authctxt, int authenticated, char *method, char *info)
256{
257	void (*authlog) (const char *fmt,...) = verbose;
258	char *authmsg;
259
260	if (use_privsep && !mm_is_monitor() && !authctxt->postponed)
261		return;
262
263	/* Raise logging level */
264	if (authenticated == 1 ||
265	    !authctxt->valid ||
266	    authctxt->failures >= options.max_authtries / 2 ||
267	    strcmp(method, "password") == 0)
268		authlog = logit;
269
270	if (authctxt->postponed)
271		authmsg = "Postponed";
272	else
273		authmsg = authenticated ? "Accepted" : "Failed";
274
275	authlog("%s %s for %s%.100s from %.200s port %d%s",
276	    authmsg,
277	    method,
278	    authctxt->valid ? "" : "invalid user ",
279	    authctxt->user,
280	    get_remote_ipaddr(),
281	    get_remote_port(),
282	    info);
283
284#ifdef CUSTOM_FAILED_LOGIN
285	if (authenticated == 0 && !authctxt->postponed &&
286	    (strcmp(method, "password") == 0 ||
287	    strncmp(method, "keyboard-interactive", 20) == 0 ||
288	    strcmp(method, "challenge-response") == 0))
289		record_failed_login(authctxt->user,
290		    get_canonical_hostname(options.use_dns), "ssh");
291# ifdef WITH_AIXAUTHENTICATE
292	if (authenticated)
293		sys_auth_record_login(authctxt->user,
294		    get_canonical_hostname(options.use_dns), "ssh", &loginmsg);
295# endif
296#endif
297#ifdef SSH_AUDIT_EVENTS
298	if (authenticated == 0 && !authctxt->postponed)
299		audit_event(audit_classify_auth(method));
300#endif
301}
302
303/*
304 * Check whether root logins are disallowed.
305 */
306int
307auth_root_allowed(char *method)
308{
309	switch (options.permit_root_login) {
310	case PERMIT_YES:
311		return 1;
312	case PERMIT_NO_PASSWD:
313		if (strcmp(method, "password") != 0)
314			return 1;
315		break;
316	case PERMIT_FORCED_ONLY:
317		if (forced_command) {
318			logit("Root login accepted for forced command.");
319			return 1;
320		}
321		break;
322	}
323	logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr());
324	return 0;
325}
326
327
328/*
329 * Given a template and a passwd structure, build a filename
330 * by substituting % tokenised options. Currently, %% becomes '%',
331 * %h becomes the home directory and %u the username.
332 *
333 * This returns a buffer allocated by xmalloc.
334 */
335char *
336expand_authorized_keys(const char *filename, struct passwd *pw)
337{
338	char *file, ret[MAXPATHLEN];
339	int i;
340
341	file = percent_expand(filename, "h", pw->pw_dir,
342	    "u", pw->pw_name, (char *)NULL);
343
344	/*
345	 * Ensure that filename starts anchored. If not, be backward
346	 * compatible and prepend the '%h/'
347	 */
348	if (*file == '/')
349		return (file);
350
351	i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file);
352	if (i < 0 || (size_t)i >= sizeof(ret))
353		fatal("expand_authorized_keys: path too long");
354	xfree(file);
355	return (xstrdup(ret));
356}
357
358char *
359authorized_principals_file(struct passwd *pw)
360{
361	if (options.authorized_principals_file == NULL ||
362	    strcasecmp(options.authorized_principals_file, "none") == 0)
363		return NULL;
364	return expand_authorized_keys(options.authorized_principals_file, pw);
365}
366
367/* return ok if key exists in sysfile or userfile */
368HostStatus
369check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host,
370    const char *sysfile, const char *userfile)
371{
372	char *user_hostfile;
373	struct stat st;
374	HostStatus host_status;
375	struct hostkeys *hostkeys;
376	const struct hostkey_entry *found;
377
378	hostkeys = init_hostkeys();
379	load_hostkeys(hostkeys, host, sysfile);
380	if (userfile != NULL) {
381		user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
382		if (options.strict_modes &&
383		    (stat(user_hostfile, &st) == 0) &&
384		    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
385		    (st.st_mode & 022) != 0)) {
386			logit("Authentication refused for %.100s: "
387			    "bad owner or modes for %.200s",
388			    pw->pw_name, user_hostfile);
389			auth_debug_add("Ignored %.200s: bad ownership or modes",
390			    user_hostfile);
391		} else {
392			temporarily_use_uid(pw);
393			load_hostkeys(hostkeys, host, user_hostfile);
394			restore_uid();
395		}
396		xfree(user_hostfile);
397	}
398	host_status = check_key_in_hostkeys(hostkeys, key, &found);
399	if (host_status == HOST_REVOKED)
400		error("WARNING: revoked key for %s attempted authentication",
401		    found->host);
402	else if (host_status == HOST_OK)
403		debug("%s: key for %s found at %s:%ld", __func__,
404		    found->host, found->file, found->line);
405	else
406		debug("%s: key for host %s not found", __func__, host);
407
408	free_hostkeys(hostkeys);
409
410	return host_status;
411}
412
413
414/*
415 * Check a given file for security. This is defined as all components
416 * of the path to the file must be owned by either the owner of
417 * of the file or root and no directories must be group or world writable.
418 *
419 * XXX Should any specific check be done for sym links ?
420 *
421 * Takes an open file descriptor, the file name, a uid and and
422 * error buffer plus max size as arguments.
423 *
424 * Returns 0 on success and -1 on failure
425 */
426static int
427secure_filename(FILE *f, const char *file, struct passwd *pw,
428    char *err, size_t errlen)
429{
430	uid_t uid = pw->pw_uid;
431	char buf[MAXPATHLEN], homedir[MAXPATHLEN];
432	char *cp;
433	int comparehome = 0;
434	struct stat st;
435
436	if (realpath(file, buf) == NULL) {
437		snprintf(err, errlen, "realpath %s failed: %s", file,
438		    strerror(errno));
439		return -1;
440	}
441	if (realpath(pw->pw_dir, homedir) != NULL)
442		comparehome = 1;
443
444	/* check the open file to avoid races */
445	if (fstat(fileno(f), &st) < 0 ||
446	    (st.st_uid != 0 && st.st_uid != uid) ||
447	    (st.st_mode & 022) != 0) {
448		snprintf(err, errlen, "bad ownership or modes for file %s",
449		    buf);
450		return -1;
451	}
452
453	/* for each component of the canonical path, walking upwards */
454	for (;;) {
455		if ((cp = dirname(buf)) == NULL) {
456			snprintf(err, errlen, "dirname() failed");
457			return -1;
458		}
459		strlcpy(buf, cp, sizeof(buf));
460
461		if (stat(buf, &st) < 0 ||
462		    (st.st_uid != 0 && st.st_uid != uid) ||
463		    (st.st_mode & 022) != 0) {
464			snprintf(err, errlen,
465			    "bad ownership or modes for directory %s", buf);
466			return -1;
467		}
468
469		/* If are past the homedir then we can stop */
470		if (comparehome && strcmp(homedir, buf) == 0)
471			break;
472
473		/*
474		 * dirname should always complete with a "/" path,
475		 * but we can be paranoid and check for "." too
476		 */
477		if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0))
478			break;
479	}
480	return 0;
481}
482
483static FILE *
484auth_openfile(const char *file, struct passwd *pw, int strict_modes,
485    int log_missing, char *file_type)
486{
487	char line[1024];
488	struct stat st;
489	int fd;
490	FILE *f;
491
492	if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) {
493		if (log_missing || errno != ENOENT)
494			debug("Could not open %s '%s': %s", file_type, file,
495			   strerror(errno));
496		return NULL;
497	}
498
499	if (fstat(fd, &st) < 0) {
500		close(fd);
501		return NULL;
502	}
503	if (!S_ISREG(st.st_mode)) {
504		logit("User %s %s %s is not a regular file",
505		    pw->pw_name, file_type, file);
506		close(fd);
507		return NULL;
508	}
509	unset_nonblock(fd);
510	if ((f = fdopen(fd, "r")) == NULL) {
511		close(fd);
512		return NULL;
513	}
514	if (strict_modes &&
515	    secure_filename(f, file, pw, line, sizeof(line)) != 0) {
516		fclose(f);
517		logit("Authentication refused: %s", line);
518		auth_debug_add("Ignored %s: %s", file_type, line);
519		return NULL;
520	}
521
522	return f;
523}
524
525
526FILE *
527auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes)
528{
529	return auth_openfile(file, pw, strict_modes, 1, "authorized keys");
530}
531
532FILE *
533auth_openprincipals(const char *file, struct passwd *pw, int strict_modes)
534{
535	return auth_openfile(file, pw, strict_modes, 0,
536	    "authorized principals");
537}
538
539struct passwd *
540getpwnamallow(const char *user)
541{
542#ifdef HAVE_LOGIN_CAP
543	extern login_cap_t *lc;
544#ifdef BSD_AUTH
545	auth_session_t *as;
546#endif
547#endif
548	struct passwd *pw;
549	struct connection_info *ci = get_connection_info(1, options.use_dns);
550
551	ci->user = user;
552	parse_server_match_config(&options, ci);
553
554#if defined(_AIX) && defined(HAVE_SETAUTHDB)
555	aix_setauthdb(user);
556#endif
557
558	pw = getpwnam(user);
559
560#if defined(_AIX) && defined(HAVE_SETAUTHDB)
561	aix_restoreauthdb();
562#endif
563#ifdef HAVE_CYGWIN
564	/*
565	 * Windows usernames are case-insensitive.  To avoid later problems
566	 * when trying to match the username, the user is only allowed to
567	 * login if the username is given in the same case as stored in the
568	 * user database.
569	 */
570	if (pw != NULL && strcmp(user, pw->pw_name) != 0) {
571		logit("Login name %.100s does not match stored username %.100s",
572		    user, pw->pw_name);
573		pw = NULL;
574	}
575#endif
576	if (pw == NULL) {
577		logit("Invalid user %.100s from %.100s",
578		    user, get_remote_ipaddr());
579#ifdef CUSTOM_FAILED_LOGIN
580		record_failed_login(user,
581		    get_canonical_hostname(options.use_dns), "ssh");
582#endif
583#ifdef SSH_AUDIT_EVENTS
584		audit_event(SSH_INVALID_USER);
585#endif /* SSH_AUDIT_EVENTS */
586		return (NULL);
587	}
588	if (!allowed_user(pw))
589		return (NULL);
590#ifdef HAVE_LOGIN_CAP
591	if ((lc = login_getpwclass(pw)) == NULL) {
592		debug("unable to get login class: %s", user);
593		return (NULL);
594	}
595#ifdef BSD_AUTH
596	if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
597	    auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
598		debug("Approval failure for %s", user);
599		pw = NULL;
600	}
601	if (as != NULL)
602		auth_close(as);
603#endif
604#endif
605	if (pw != NULL)
606		return (pwcopy(pw));
607	return (NULL);
608}
609
610/* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */
611int
612auth_key_is_revoked(Key *key)
613{
614	char *key_fp;
615
616	if (options.revoked_keys_file == NULL)
617		return 0;
618
619	switch (key_in_file(key, options.revoked_keys_file, 0)) {
620	case 0:
621		/* key not revoked */
622		return 0;
623	case -1:
624		/* Error opening revoked_keys_file: refuse all keys */
625		error("Revoked keys file is unreadable: refusing public key "
626		    "authentication");
627		return 1;
628	case 1:
629		/* Key revoked */
630		key_fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
631		error("WARNING: authentication attempt with a revoked "
632		    "%s key %s ", key_type(key), key_fp);
633		xfree(key_fp);
634		return 1;
635	}
636	fatal("key_in_file returned junk");
637}
638
639void
640auth_debug_add(const char *fmt,...)
641{
642	char buf[1024];
643	va_list args;
644
645	if (!auth_debug_init)
646		return;
647
648	va_start(args, fmt);
649	vsnprintf(buf, sizeof(buf), fmt, args);
650	va_end(args);
651	buffer_put_cstring(&auth_debug, buf);
652}
653
654void
655auth_debug_send(void)
656{
657	char *msg;
658
659	if (!auth_debug_init)
660		return;
661	while (buffer_len(&auth_debug)) {
662		msg = buffer_get_string(&auth_debug, NULL);
663		packet_send_debug("%s", msg);
664		xfree(msg);
665	}
666}
667
668void
669auth_debug_reset(void)
670{
671	if (auth_debug_init)
672		buffer_clear(&auth_debug);
673	else {
674		buffer_init(&auth_debug);
675		auth_debug_init = 1;
676	}
677}
678
679struct passwd *
680fakepw(void)
681{
682	static struct passwd fake;
683
684	memset(&fake, 0, sizeof(fake));
685	fake.pw_name = "NOUSER";
686	fake.pw_passwd =
687	    "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK";
688	fake.pw_gecos = "NOUSER";
689	fake.pw_uid = privsep_pw == NULL ? (uid_t)-1 : privsep_pw->pw_uid;
690	fake.pw_gid = privsep_pw == NULL ? (gid_t)-1 : privsep_pw->pw_gid;
691#ifdef HAVE_PW_CLASS_IN_PASSWD
692	fake.pw_class = "";
693#endif
694	fake.pw_dir = "/nonexist";
695	fake.pw_shell = "/nonexist";
696
697	return (&fake);
698}
699