auth.c revision 164149 
1/* $OpenBSD: auth.c,v 1.75 2006/08/03 03:34:41 deraadt 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 164149 2006-11-10 16:52:41Z 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#ifdef HAVE_PATHS_H
37# include <paths.h>
38#endif
39#include <pwd.h>
40#ifdef HAVE_LOGIN_H
41#include <login.h>
42#endif
43#ifdef USE_SHADOW
44#include <shadow.h>
45#endif
46#ifdef HAVE_LIBGEN_H
47#include <libgen.h>
48#endif
49#include <stdarg.h>
50#include <stdio.h>
51#include <string.h>
52
53#include "xmalloc.h"
54#include "match.h"
55#include "groupaccess.h"
56#include "log.h"
57#include "buffer.h"
58#include "servconf.h"
59#include "key.h"
60#include "hostfile.h"
61#include "auth.h"
62#include "auth-options.h"
63#include "canohost.h"
64#include "uidswap.h"
65#include "misc.h"
66#include "packet.h"
67#include "loginrec.h"
68#ifdef GSSAPI
69#include "ssh-gss.h"
70#endif
71#include "monitor_wrap.h"
72
73/* import */
74extern ServerOptions options;
75extern int use_privsep;
76extern Buffer loginmsg;
77extern struct passwd *privsep_pw;
78
79/* Debugging messages */
80Buffer auth_debug;
81int auth_debug_init;
82
83/*
84 * Check if the user is allowed to log in via ssh. If user is listed
85 * in DenyUsers or one of user's groups is listed in DenyGroups, false
86 * will be returned. If AllowUsers isn't empty and user isn't listed
87 * there, or if AllowGroups isn't empty and one of user's groups isn't
88 * listed there, false will be returned.
89 * If the user's shell is not executable, false will be returned.
90 * Otherwise true is returned.
91 */
92int
93allowed_user(struct passwd * pw)
94{
95	struct stat st;
96	const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL;
97	char *shell;
98	u_int i;
99#ifdef USE_SHADOW
100	struct spwd *spw = NULL;
101#endif
102
103	/* Shouldn't be called if pw is NULL, but better safe than sorry... */
104	if (!pw || !pw->pw_name)
105		return 0;
106
107#ifdef USE_SHADOW
108	if (!options.use_pam)
109		spw = getspnam(pw->pw_name);
110#ifdef HAS_SHADOW_EXPIRE
111	if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw))
112		return 0;
113#endif /* HAS_SHADOW_EXPIRE */
114#endif /* USE_SHADOW */
115
116	/* grab passwd field for locked account check */
117#ifdef USE_SHADOW
118	if (spw != NULL)
119#if defined(HAVE_LIBIAF)  &&  !defined(BROKEN_LIBIAF)
120		passwd = get_iaf_password(pw);
121#else
122		passwd = spw->sp_pwdp;
123#endif /* HAVE_LIBIAF  && !BROKEN_LIBIAF */
124#else
125	passwd = pw->pw_passwd;
126#endif
127
128	/* check for locked account */
129	if (!options.use_pam && passwd && *passwd) {
130		int locked = 0;
131
132#ifdef LOCKED_PASSWD_STRING
133		if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0)
134			 locked = 1;
135#endif
136#ifdef LOCKED_PASSWD_PREFIX
137		if (strncmp(passwd, LOCKED_PASSWD_PREFIX,
138		    strlen(LOCKED_PASSWD_PREFIX)) == 0)
139			 locked = 1;
140#endif
141#ifdef LOCKED_PASSWD_SUBSTR
142		if (strstr(passwd, LOCKED_PASSWD_SUBSTR))
143			locked = 1;
144#endif
145#if defined(HAVE_LIBIAF)  &&  !defined(BROKEN_LIBIAF)
146		free(passwd);
147#endif /* HAVE_LIBIAF  && !BROKEN_LIBIAF */
148		if (locked) {
149			logit("User %.100s not allowed because account is locked",
150			    pw->pw_name);
151			return 0;
152		}
153	}
154
155	/*
156	 * Get the shell from the password data.  An empty shell field is
157	 * legal, and means /bin/sh.
158	 */
159	shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;
160
161	/* deny if shell does not exists or is not executable */
162	if (stat(shell, &st) != 0) {
163		logit("User %.100s not allowed because shell %.100s does not exist",
164		    pw->pw_name, shell);
165		return 0;
166	}
167	if (S_ISREG(st.st_mode) == 0 ||
168	    (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
169		logit("User %.100s not allowed because shell %.100s is not executable",
170		    pw->pw_name, shell);
171		return 0;
172	}
173
174	if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
175	    options.num_deny_groups > 0 || options.num_allow_groups > 0) {
176		hostname = get_canonical_hostname(options.use_dns);
177		ipaddr = get_remote_ipaddr();
178	}
179
180	/* Return false if user is listed in DenyUsers */
181	if (options.num_deny_users > 0) {
182		for (i = 0; i < options.num_deny_users; i++)
183			if (match_user(pw->pw_name, hostname, ipaddr,
184			    options.deny_users[i])) {
185				logit("User %.100s from %.100s not allowed "
186				    "because listed in DenyUsers",
187				    pw->pw_name, hostname);
188				return 0;
189			}
190	}
191	/* Return false if AllowUsers isn't empty and user isn't listed there */
192	if (options.num_allow_users > 0) {
193		for (i = 0; i < options.num_allow_users; i++)
194			if (match_user(pw->pw_name, hostname, ipaddr,
195			    options.allow_users[i]))
196				break;
197		/* i < options.num_allow_users iff we break for loop */
198		if (i >= options.num_allow_users) {
199			logit("User %.100s from %.100s not allowed because "
200			    "not listed in AllowUsers", pw->pw_name, hostname);
201			return 0;
202		}
203	}
204	if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
205		/* Get the user's group access list (primary and supplementary) */
206		if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
207			logit("User %.100s from %.100s not allowed because "
208			    "not in any group", pw->pw_name, hostname);
209			return 0;
210		}
211
212		/* Return false if one of user's groups is listed in DenyGroups */
213		if (options.num_deny_groups > 0)
214			if (ga_match(options.deny_groups,
215			    options.num_deny_groups)) {
216				ga_free();
217				logit("User %.100s from %.100s not allowed "
218				    "because a group is listed in DenyGroups",
219				    pw->pw_name, hostname);
220				return 0;
221			}
222		/*
223		 * Return false if AllowGroups isn't empty and one of user's groups
224		 * isn't listed there
225		 */
226		if (options.num_allow_groups > 0)
227			if (!ga_match(options.allow_groups,
228			    options.num_allow_groups)) {
229				ga_free();
230				logit("User %.100s from %.100s not allowed "
231				    "because none of user's groups are listed "
232				    "in AllowGroups", pw->pw_name, hostname);
233				return 0;
234			}
235		ga_free();
236	}
237
238#ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
239	if (!sys_auth_allowed_user(pw, &loginmsg))
240		return 0;
241#endif
242
243	/* We found no reason not to let this user try to log on... */
244	return 1;
245}
246
247void
248auth_log(Authctxt *authctxt, int authenticated, char *method, char *info)
249{
250	void (*authlog) (const char *fmt,...) = verbose;
251	char *authmsg;
252
253	if (use_privsep && !mm_is_monitor() && !authctxt->postponed)
254		return;
255
256	/* Raise logging level */
257	if (authenticated == 1 ||
258	    !authctxt->valid ||
259	    authctxt->failures >= options.max_authtries / 2 ||
260	    strcmp(method, "password") == 0)
261		authlog = logit;
262
263	if (authctxt->postponed)
264		authmsg = "Postponed";
265	else
266		authmsg = authenticated ? "Accepted" : "Failed";
267
268	authlog("%s %s for %s%.100s from %.200s port %d%s",
269	    authmsg,
270	    method,
271	    authctxt->valid ? "" : "invalid user ",
272	    authctxt->user,
273	    get_remote_ipaddr(),
274	    get_remote_port(),
275	    info);
276
277#ifdef CUSTOM_FAILED_LOGIN
278	if (authenticated == 0 && !authctxt->postponed &&
279	    (strcmp(method, "password") == 0 ||
280	    strncmp(method, "keyboard-interactive", 20) == 0 ||
281	    strcmp(method, "challenge-response") == 0))
282		record_failed_login(authctxt->user,
283		    get_canonical_hostname(options.use_dns), "ssh");
284# ifdef WITH_AIXAUTHENTICATE
285	if (authenticated)
286		sys_auth_record_login(authctxt->user,
287		    get_canonical_hostname(options.use_dns), "ssh", &loginmsg);
288# endif
289#endif
290#ifdef SSH_AUDIT_EVENTS
291	if (authenticated == 0 && !authctxt->postponed)
292		audit_event(audit_classify_auth(method));
293#endif
294}
295
296/*
297 * Check whether root logins are disallowed.
298 */
299int
300auth_root_allowed(char *method)
301{
302	switch (options.permit_root_login) {
303	case PERMIT_YES:
304		return 1;
305	case PERMIT_NO_PASSWD:
306		if (strcmp(method, "password") != 0)
307			return 1;
308		break;
309	case PERMIT_FORCED_ONLY:
310		if (forced_command) {
311			logit("Root login accepted for forced command.");
312			return 1;
313		}
314		break;
315	}
316	logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr());
317	return 0;
318}
319
320
321/*
322 * Given a template and a passwd structure, build a filename
323 * by substituting % tokenised options. Currently, %% becomes '%',
324 * %h becomes the home directory and %u the username.
325 *
326 * This returns a buffer allocated by xmalloc.
327 */
328static char *
329expand_authorized_keys(const char *filename, struct passwd *pw)
330{
331	char *file, ret[MAXPATHLEN];
332	int i;
333
334	file = percent_expand(filename, "h", pw->pw_dir,
335	    "u", pw->pw_name, (char *)NULL);
336
337	/*
338	 * Ensure that filename starts anchored. If not, be backward
339	 * compatible and prepend the '%h/'
340	 */
341	if (*file == '/')
342		return (file);
343
344	i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file);
345	if (i < 0 || (size_t)i >= sizeof(ret))
346		fatal("expand_authorized_keys: path too long");
347	xfree(file);
348	return (xstrdup(ret));
349}
350
351char *
352authorized_keys_file(struct passwd *pw)
353{
354	return expand_authorized_keys(options.authorized_keys_file, pw);
355}
356
357char *
358authorized_keys_file2(struct passwd *pw)
359{
360	return expand_authorized_keys(options.authorized_keys_file2, pw);
361}
362
363/* return ok if key exists in sysfile or userfile */
364HostStatus
365check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host,
366    const char *sysfile, const char *userfile)
367{
368	Key *found;
369	char *user_hostfile;
370	struct stat st;
371	HostStatus host_status;
372
373	/* Check if we know the host and its host key. */
374	found = key_new(key->type);
375	host_status = check_host_in_hostfile(sysfile, host, key, found, NULL);
376
377	if (host_status != HOST_OK && userfile != NULL) {
378		user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
379		if (options.strict_modes &&
380		    (stat(user_hostfile, &st) == 0) &&
381		    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
382		    (st.st_mode & 022) != 0)) {
383			logit("Authentication refused for %.100s: "
384			    "bad owner or modes for %.200s",
385			    pw->pw_name, user_hostfile);
386		} else {
387			temporarily_use_uid(pw);
388			host_status = check_host_in_hostfile(user_hostfile,
389			    host, key, found, NULL);
390			restore_uid();
391		}
392		xfree(user_hostfile);
393	}
394	key_free(found);
395
396	debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ?
397	    "ok" : "not found", host);
398	return host_status;
399}
400
401
402/*
403 * Check a given file for security. This is defined as all components
404 * of the path to the file must be owned by either the owner of
405 * of the file or root and no directories must be group or world writable.
406 *
407 * XXX Should any specific check be done for sym links ?
408 *
409 * Takes an open file descriptor, the file name, a uid and and
410 * error buffer plus max size as arguments.
411 *
412 * Returns 0 on success and -1 on failure
413 */
414int
415secure_filename(FILE *f, const char *file, struct passwd *pw,
416    char *err, size_t errlen)
417{
418	uid_t uid = pw->pw_uid;
419	char buf[MAXPATHLEN], homedir[MAXPATHLEN];
420	char *cp;
421	int comparehome = 0;
422	struct stat st;
423
424	if (realpath(file, buf) == NULL) {
425		snprintf(err, errlen, "realpath %s failed: %s", file,
426		    strerror(errno));
427		return -1;
428	}
429	if (realpath(pw->pw_dir, homedir) != NULL)
430		comparehome = 1;
431
432	/* check the open file to avoid races */
433	if (fstat(fileno(f), &st) < 0 ||
434	    (st.st_uid != 0 && st.st_uid != uid) ||
435	    (st.st_mode & 022) != 0) {
436		snprintf(err, errlen, "bad ownership or modes for file %s",
437		    buf);
438		return -1;
439	}
440
441	/* for each component of the canonical path, walking upwards */
442	for (;;) {
443		if ((cp = dirname(buf)) == NULL) {
444			snprintf(err, errlen, "dirname() failed");
445			return -1;
446		}
447		strlcpy(buf, cp, sizeof(buf));
448
449		debug3("secure_filename: checking '%s'", buf);
450		if (stat(buf, &st) < 0 ||
451		    (st.st_uid != 0 && st.st_uid != uid) ||
452		    (st.st_mode & 022) != 0) {
453			snprintf(err, errlen,
454			    "bad ownership or modes for directory %s", buf);
455			return -1;
456		}
457
458		/* If are passed the homedir then we can stop */
459		if (comparehome && strcmp(homedir, buf) == 0) {
460			debug3("secure_filename: terminating check at '%s'",
461			    buf);
462			break;
463		}
464		/*
465		 * dirname should always complete with a "/" path,
466		 * but we can be paranoid and check for "." too
467		 */
468		if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0))
469			break;
470	}
471	return 0;
472}
473
474struct passwd *
475getpwnamallow(const char *user)
476{
477#ifdef HAVE_LOGIN_CAP
478	extern login_cap_t *lc;
479#ifdef BSD_AUTH
480	auth_session_t *as;
481#endif
482#endif
483	struct passwd *pw;
484
485	parse_server_match_config(&options, user,
486	    get_canonical_hostname(options.use_dns), get_remote_ipaddr());
487
488	pw = getpwnam(user);
489	if (pw == NULL) {
490		logit("Invalid user %.100s from %.100s",
491		    user, get_remote_ipaddr());
492#ifdef CUSTOM_FAILED_LOGIN
493		record_failed_login(user,
494		    get_canonical_hostname(options.use_dns), "ssh");
495#endif
496#ifdef SSH_AUDIT_EVENTS
497		audit_event(SSH_INVALID_USER);
498#endif /* SSH_AUDIT_EVENTS */
499		return (NULL);
500	}
501	if (!allowed_user(pw))
502		return (NULL);
503#ifdef HAVE_LOGIN_CAP
504	if ((lc = login_getpwclass(pw)) == NULL) {
505		debug("unable to get login class: %s", user);
506		return (NULL);
507	}
508#ifdef BSD_AUTH
509	if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
510	    auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
511		debug("Approval failure for %s", user);
512		pw = NULL;
513	}
514	if (as != NULL)
515		auth_close(as);
516#endif
517#endif
518	if (pw != NULL)
519		return (pwcopy(pw));
520	return (NULL);
521}
522
523void
524auth_debug_add(const char *fmt,...)
525{
526	char buf[1024];
527	va_list args;
528
529	if (!auth_debug_init)
530		return;
531
532	va_start(args, fmt);
533	vsnprintf(buf, sizeof(buf), fmt, args);
534	va_end(args);
535	buffer_put_cstring(&auth_debug, buf);
536}
537
538void
539auth_debug_send(void)
540{
541	char *msg;
542
543	if (!auth_debug_init)
544		return;
545	while (buffer_len(&auth_debug)) {
546		msg = buffer_get_string(&auth_debug, NULL);
547		packet_send_debug("%s", msg);
548		xfree(msg);
549	}
550}
551
552void
553auth_debug_reset(void)
554{
555	if (auth_debug_init)
556		buffer_clear(&auth_debug);
557	else {
558		buffer_init(&auth_debug);
559		auth_debug_init = 1;
560	}
561}
562
563struct passwd *
564fakepw(void)
565{
566	static struct passwd fake;
567
568	memset(&fake, 0, sizeof(fake));
569	fake.pw_name = "NOUSER";
570	fake.pw_passwd =
571	    "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK";
572	fake.pw_gecos = "NOUSER";
573	fake.pw_uid = privsep_pw->pw_uid;
574	fake.pw_gid = privsep_pw->pw_gid;
575#ifdef HAVE_PW_CLASS_IN_PASSWD
576	fake.pw_class = "";
577#endif
578	fake.pw_dir = "/nonexist";
579	fake.pw_shell = "/nonexist";
580
581	return (&fake);
582}
583