auth.c revision 100838 
1/*
2 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 *    notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 *    notice, this list of conditions and the following disclaimer in the
11 *    documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
14 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
15 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
16 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
17 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
18 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
22 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
23 */
24
25#include "includes.h"
26RCSID("$OpenBSD: auth.c,v 1.43 2002/05/17 14:27:55 millert Exp $");
27RCSID("$FreeBSD: head/crypto/openssh/auth.c 100838 2002-07-29 00:36:24Z fanf $");
28
29#ifdef HAVE_LOGIN_H
30#include <login.h>
31#endif
32#if defined(HAVE_SHADOW_H) && !defined(DISABLE_SHADOW)
33#include <shadow.h>
34#endif /* defined(HAVE_SHADOW_H) && !defined(DISABLE_SHADOW) */
35
36#ifdef HAVE_LIBGEN_H
37#include <libgen.h>
38#endif
39
40#include "xmalloc.h"
41#include "match.h"
42#include "groupaccess.h"
43#include "log.h"
44#include "servconf.h"
45#include "auth.h"
46#include "auth-options.h"
47#include "canohost.h"
48#include "buffer.h"
49#include "bufaux.h"
50#include "uidswap.h"
51#include "tildexpand.h"
52#include "misc.h"
53#include "bufaux.h"
54#include "packet.h"
55
56/* import */
57extern ServerOptions options;
58
59/* Debugging messages */
60Buffer auth_debug;
61int auth_debug_init;
62
63/*
64 * Check if the user is allowed to log in via ssh. If user is listed
65 * in DenyUsers or one of user's groups is listed in DenyGroups, false
66 * will be returned. If AllowUsers isn't empty and user isn't listed
67 * there, or if AllowGroups isn't empty and one of user's groups isn't
68 * listed there, false will be returned.
69 * If the user's shell is not executable, false will be returned.
70 * Otherwise true is returned.
71 */
72int
73allowed_user(struct passwd * pw)
74{
75	struct stat st;
76	const char *hostname = NULL, *ipaddr = NULL;
77	char *shell;
78	int i;
79#ifdef WITH_AIXAUTHENTICATE
80	char *loginmsg;
81#endif /* WITH_AIXAUTHENTICATE */
82#if !defined(USE_PAM) && defined(HAVE_SHADOW_H) && \
83	!defined(DISABLE_SHADOW) && defined(HAS_SHADOW_EXPIRE)
84	struct spwd *spw;
85
86	/* Shouldn't be called if pw is NULL, but better safe than sorry... */
87	if (!pw || !pw->pw_name)
88		return 0;
89
90#define	DAY		(24L * 60 * 60) /* 1 day in seconds */
91	spw = getspnam(pw->pw_name);
92	if (spw != NULL) {
93		time_t today = time(NULL) / DAY;
94		debug3("allowed_user: today %d sp_expire %d sp_lstchg %d"
95		    " sp_max %d", (int)today, (int)spw->sp_expire,
96		    (int)spw->sp_lstchg, (int)spw->sp_max);
97
98		/*
99		 * We assume account and password expiration occurs the
100		 * day after the day specified.
101		 */
102		if (spw->sp_expire != -1 && today > spw->sp_expire) {
103			log("Account %.100s has expired", pw->pw_name);
104			return 0;
105		}
106
107		if (spw->sp_lstchg == 0) {
108			log("User %.100s password has expired (root forced)",
109			    pw->pw_name);
110			return 0;
111		}
112
113		if (spw->sp_max != -1 &&
114		    today > spw->sp_lstchg + spw->sp_max) {
115			log("User %.100s password has expired (password aged)",
116			    pw->pw_name);
117			return 0;
118		}
119	}
120#else
121	/* Shouldn't be called if pw is NULL, but better safe than sorry... */
122	if (!pw || !pw->pw_name)
123		return 0;
124#endif
125
126	/*
127	 * Get the shell from the password data.  An empty shell field is
128	 * legal, and means /bin/sh.
129	 */
130	shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;
131
132	/* deny if shell does not exists or is not executable */
133	if (stat(shell, &st) != 0) {
134		log("User %.100s not allowed because shell %.100s does not exist",
135		    pw->pw_name, shell);
136		return 0;
137	}
138	if (S_ISREG(st.st_mode) == 0 ||
139	    (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
140		log("User %.100s not allowed because shell %.100s is not executable",
141		    pw->pw_name, shell);
142		return 0;
143	}
144
145	if (options.num_deny_users > 0 || options.num_allow_users > 0) {
146		hostname = get_canonical_hostname(options.verify_reverse_mapping);
147		ipaddr = get_remote_ipaddr();
148	}
149
150	/* Return false if user is listed in DenyUsers */
151	if (options.num_deny_users > 0) {
152		for (i = 0; i < options.num_deny_users; i++)
153			if (match_user(pw->pw_name, hostname, ipaddr,
154			    options.deny_users[i])) {
155				log("User %.100s not allowed because listed in DenyUsers",
156				    pw->pw_name);
157				return 0;
158			}
159	}
160	/* Return false if AllowUsers isn't empty and user isn't listed there */
161	if (options.num_allow_users > 0) {
162		for (i = 0; i < options.num_allow_users; i++)
163			if (match_user(pw->pw_name, hostname, ipaddr,
164			    options.allow_users[i]))
165				break;
166		/* i < options.num_allow_users iff we break for loop */
167		if (i >= options.num_allow_users) {
168			log("User %.100s not allowed because not listed in AllowUsers",
169			    pw->pw_name);
170			return 0;
171		}
172	}
173	if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
174		/* Get the user's group access list (primary and supplementary) */
175		if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
176			log("User %.100s not allowed because not in any group",
177			    pw->pw_name);
178			return 0;
179		}
180
181		/* Return false if one of user's groups is listed in DenyGroups */
182		if (options.num_deny_groups > 0)
183			if (ga_match(options.deny_groups,
184			    options.num_deny_groups)) {
185				ga_free();
186				log("User %.100s not allowed because a group is listed in DenyGroups",
187				    pw->pw_name);
188				return 0;
189			}
190		/*
191		 * Return false if AllowGroups isn't empty and one of user's groups
192		 * isn't listed there
193		 */
194		if (options.num_allow_groups > 0)
195			if (!ga_match(options.allow_groups,
196			    options.num_allow_groups)) {
197				ga_free();
198				log("User %.100s not allowed because none of user's groups are listed in AllowGroups",
199				    pw->pw_name);
200				return 0;
201			}
202		ga_free();
203	}
204
205#ifdef WITH_AIXAUTHENTICATE
206	if (loginrestrictions(pw->pw_name, S_RLOGIN, NULL, &loginmsg) != 0) {
207		if (loginmsg && *loginmsg) {
208			/* Remove embedded newlines (if any) */
209			char *p;
210			for (p = loginmsg; *p; p++) {
211				if (*p == '\n')
212					*p = ' ';
213			}
214			/* Remove trailing newline */
215			*--p = '\0';
216			log("Login restricted for %s: %.100s", pw->pw_name, loginmsg);
217		}
218		return 0;
219	}
220#endif /* WITH_AIXAUTHENTICATE */
221
222	/* We found no reason not to let this user try to log on... */
223	return 1;
224}
225
226Authctxt *
227authctxt_new(void)
228{
229	Authctxt *authctxt = xmalloc(sizeof(*authctxt));
230	memset(authctxt, 0, sizeof(*authctxt));
231	return authctxt;
232}
233
234void
235auth_log(Authctxt *authctxt, int authenticated, char *method, char *info)
236{
237	void (*authlog) (const char *fmt,...) = verbose;
238	char *authmsg;
239
240	/* Raise logging level */
241	if (authenticated == 1 ||
242	    !authctxt->valid ||
243	    authctxt->failures >= AUTH_FAIL_LOG ||
244	    strcmp(method, "password") == 0)
245		authlog = log;
246
247	if (authctxt->postponed)
248		authmsg = "Postponed";
249	else
250		authmsg = authenticated ? "Accepted" : "Failed";
251
252	authlog("%s %s for %s%.100s from %.200s port %d%s",
253	    authmsg,
254	    method,
255	    authctxt->valid ? "" : "illegal user ",
256	    authctxt->user,
257	    get_remote_ipaddr(),
258	    get_remote_port(),
259	    info);
260}
261
262/*
263 * Check whether root logins are disallowed.
264 */
265int
266auth_root_allowed(char *method)
267{
268	switch (options.permit_root_login) {
269	case PERMIT_YES:
270		return 1;
271		break;
272	case PERMIT_NO_PASSWD:
273		if (strcmp(method, "password") != 0)
274			return 1;
275		break;
276	case PERMIT_FORCED_ONLY:
277		if (forced_command) {
278			log("Root login accepted for forced command.");
279			return 1;
280		}
281		break;
282	}
283	log("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr());
284	return 0;
285}
286
287
288/*
289 * Given a template and a passwd structure, build a filename
290 * by substituting % tokenised options. Currently, %% becomes '%',
291 * %h becomes the home directory and %u the username.
292 *
293 * This returns a buffer allocated by xmalloc.
294 */
295char *
296expand_filename(const char *filename, struct passwd *pw)
297{
298	Buffer buffer;
299	char *file;
300	const char *cp;
301
302	/*
303	 * Build the filename string in the buffer by making the appropriate
304	 * substitutions to the given file name.
305	 */
306	buffer_init(&buffer);
307	for (cp = filename; *cp; cp++) {
308		if (cp[0] == '%' && cp[1] == '%') {
309			buffer_append(&buffer, "%", 1);
310			cp++;
311			continue;
312		}
313		if (cp[0] == '%' && cp[1] == 'h') {
314			buffer_append(&buffer, pw->pw_dir, strlen(pw->pw_dir));
315			cp++;
316			continue;
317		}
318		if (cp[0] == '%' && cp[1] == 'u') {
319			buffer_append(&buffer, pw->pw_name,
320			    strlen(pw->pw_name));
321			cp++;
322			continue;
323		}
324		buffer_append(&buffer, cp, 1);
325	}
326	buffer_append(&buffer, "\0", 1);
327
328	/*
329	 * Ensure that filename starts anchored. If not, be backward
330	 * compatible and prepend the '%h/'
331	 */
332	file = xmalloc(MAXPATHLEN);
333	cp = buffer_ptr(&buffer);
334	if (*cp != '/')
335		snprintf(file, MAXPATHLEN, "%s/%s", pw->pw_dir, cp);
336	else
337		strlcpy(file, cp, MAXPATHLEN);
338
339	buffer_free(&buffer);
340	return file;
341}
342
343char *
344authorized_keys_file(struct passwd *pw)
345{
346	return expand_filename(options.authorized_keys_file, pw);
347}
348
349char *
350authorized_keys_file2(struct passwd *pw)
351{
352	return expand_filename(options.authorized_keys_file2, pw);
353}
354
355/* return ok if key exists in sysfile or userfile */
356HostStatus
357check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host,
358    const char *sysfile, const char *userfile)
359{
360	Key *found;
361	char *user_hostfile;
362	struct stat st;
363	HostStatus host_status;
364
365	/* Check if we know the host and its host key. */
366	found = key_new(key->type);
367	host_status = check_host_in_hostfile(sysfile, host, key, found, NULL);
368
369	if (host_status != HOST_OK && userfile != NULL) {
370		user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
371		if (options.strict_modes &&
372		    (stat(user_hostfile, &st) == 0) &&
373		    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
374		    (st.st_mode & 022) != 0)) {
375			log("Authentication refused for %.100s: "
376			    "bad owner or modes for %.200s",
377			    pw->pw_name, user_hostfile);
378		} else {
379			temporarily_use_uid(pw);
380			host_status = check_host_in_hostfile(user_hostfile,
381			    host, key, found, NULL);
382			restore_uid();
383		}
384		xfree(user_hostfile);
385	}
386	key_free(found);
387
388	debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ?
389	    "ok" : "not found", host);
390	return host_status;
391}
392
393
394/*
395 * Check a given file for security. This is defined as all components
396 * of the path to the file must either be owned by either the owner of
397 * of the file or root and no directories must be group or world writable.
398 *
399 * XXX Should any specific check be done for sym links ?
400 *
401 * Takes an open file descriptor, the file name, a uid and and
402 * error buffer plus max size as arguments.
403 *
404 * Returns 0 on success and -1 on failure
405 */
406int
407secure_filename(FILE *f, const char *file, struct passwd *pw,
408    char *err, size_t errlen)
409{
410	uid_t uid = pw->pw_uid;
411	char buf[MAXPATHLEN], homedir[MAXPATHLEN];
412	char *cp;
413	struct stat st;
414
415	if (realpath(file, buf) == NULL) {
416		snprintf(err, errlen, "realpath %s failed: %s", file,
417		    strerror(errno));
418		return -1;
419	}
420	if (realpath(pw->pw_dir, homedir) == NULL) {
421		snprintf(err, errlen, "realpath %s failed: %s", pw->pw_dir,
422		    strerror(errno));
423		return -1;
424	}
425
426	/* check the open file to avoid races */
427	if (fstat(fileno(f), &st) < 0 ||
428	    (st.st_uid != 0 && st.st_uid != uid) ||
429	    (st.st_mode & 022) != 0) {
430		snprintf(err, errlen, "bad ownership or modes for file %s",
431		    buf);
432		return -1;
433	}
434
435	/* for each component of the canonical path, walking upwards */
436	for (;;) {
437		if ((cp = dirname(buf)) == NULL) {
438			snprintf(err, errlen, "dirname() failed");
439			return -1;
440		}
441		strlcpy(buf, cp, sizeof(buf));
442
443		debug3("secure_filename: checking '%s'", buf);
444		if (stat(buf, &st) < 0 ||
445		    (st.st_uid != 0 && st.st_uid != uid) ||
446		    (st.st_mode & 022) != 0) {
447			snprintf(err, errlen,
448			    "bad ownership or modes for directory %s", buf);
449			return -1;
450		}
451
452		/* If are passed the homedir then we can stop */
453		if (strcmp(homedir, buf) == 0) {
454			debug3("secure_filename: terminating check at '%s'",
455			    buf);
456			break;
457		}
458		/*
459		 * dirname should always complete with a "/" path,
460		 * but we can be paranoid and check for "." too
461		 */
462		if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0))
463			break;
464	}
465	return 0;
466}
467
468struct passwd *
469getpwnamallow(const char *user)
470{
471#ifdef HAVE_LOGIN_CAP
472	extern login_cap_t *lc;
473#ifdef BSD_AUTH
474	auth_session_t *as;
475#endif
476#endif
477	struct passwd *pw;
478
479	pw = getpwnam(user);
480	if (pw == NULL || !allowed_user(pw))
481		return (NULL);
482#ifdef HAVE_LOGIN_CAP
483	if ((lc = login_getpwclass(pw)) == NULL) {
484		debug("unable to get login class: %s", user);
485		return (NULL);
486	}
487#ifdef BSD_AUTH
488	if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
489	    auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
490		debug("Approval failure for %s", user);
491		pw = NULL;
492	}
493	if (as != NULL)
494		auth_close(as);
495#endif
496#endif
497	if (pw != NULL)
498		return (pwcopy(pw));
499	return (NULL);
500}
501
502void
503auth_debug_add(const char *fmt,...)
504{
505	char buf[1024];
506	va_list args;
507
508	if (!auth_debug_init)
509		return;
510
511	va_start(args, fmt);
512	vsnprintf(buf, sizeof(buf), fmt, args);
513	va_end(args);
514	buffer_put_cstring(&auth_debug, buf);
515}
516
517void
518auth_debug_send(void)
519{
520	char *msg;
521
522	if (!auth_debug_init)
523		return;
524	while (buffer_len(&auth_debug)) {
525		msg = buffer_get_string(&auth_debug, NULL);
526		packet_send_debug("%s", msg);
527		xfree(msg);
528	}
529}
530
531void
532auth_debug_reset(void)
533{
534	if (auth_debug_init)
535		buffer_clear(&auth_debug);
536	else {
537		buffer_init(&auth_debug);
538		auth_debug_init = 1;
539	}
540}
541