xref: /openbsd-src/usr.bin/ssh/auth.c (revision a28daedfc357b214be5c701aa8ba8adb29a7f1c2)
1 /* $OpenBSD: auth.c,v 1.80 2008/11/04 07:58:09 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 <sys/types.h>
27 #include <sys/stat.h>
28 #include <sys/param.h>
29 
30 #include <errno.h>
31 #include <fcntl.h>
32 #include <libgen.h>
33 #include <login_cap.h>
34 #include <paths.h>
35 #include <pwd.h>
36 #include <stdarg.h>
37 #include <stdio.h>
38 #include <string.h>
39 #include <unistd.h>
40 
41 #include "xmalloc.h"
42 #include "match.h"
43 #include "groupaccess.h"
44 #include "log.h"
45 #include "buffer.h"
46 #include "servconf.h"
47 #include "key.h"
48 #include "hostfile.h"
49 #include "auth.h"
50 #include "auth-options.h"
51 #include "canohost.h"
52 #include "uidswap.h"
53 #include "misc.h"
54 #include "packet.h"
55 #ifdef GSSAPI
56 #include "ssh-gss.h"
57 #endif
58 #include "monitor_wrap.h"
59 
60 /* import */
61 extern ServerOptions options;
62 extern int use_privsep;
63 
64 /* Debugging messages */
65 Buffer auth_debug;
66 int auth_debug_init;
67 
68 /*
69  * Check if the user is allowed to log in via ssh. If user is listed
70  * in DenyUsers or one of user's groups is listed in DenyGroups, false
71  * will be returned. If AllowUsers isn't empty and user isn't listed
72  * there, or if AllowGroups isn't empty and one of user's groups isn't
73  * listed there, false will be returned.
74  * If the user's shell is not executable, false will be returned.
75  * Otherwise true is returned.
76  */
77 int
78 allowed_user(struct passwd * pw)
79 {
80 	struct stat st;
81 	const char *hostname = NULL, *ipaddr = NULL;
82 	char *shell;
83 	u_int i;
84 
85 	/* Shouldn't be called if pw is NULL, but better safe than sorry... */
86 	if (!pw || !pw->pw_name)
87 		return 0;
88 
89 	/*
90 	 * Get the shell from the password data.  An empty shell field is
91 	 * legal, and means /bin/sh.
92 	 */
93 	shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;
94 
95 	/* deny if shell does not exists or is not executable */
96 	if (stat(shell, &st) != 0) {
97 		logit("User %.100s not allowed because shell %.100s does not exist",
98 		    pw->pw_name, shell);
99 		return 0;
100 	}
101 	if (S_ISREG(st.st_mode) == 0 ||
102 	    (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
103 		logit("User %.100s not allowed because shell %.100s is not executable",
104 		    pw->pw_name, shell);
105 		return 0;
106 	}
107 
108 	if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
109 	    options.num_deny_groups > 0 || options.num_allow_groups > 0) {
110 		hostname = get_canonical_hostname(options.use_dns);
111 		ipaddr = get_remote_ipaddr();
112 	}
113 
114 	/* Return false if user is listed in DenyUsers */
115 	if (options.num_deny_users > 0) {
116 		for (i = 0; i < options.num_deny_users; i++)
117 			if (match_user(pw->pw_name, hostname, ipaddr,
118 			    options.deny_users[i])) {
119 				logit("User %.100s from %.100s not allowed "
120 				    "because listed in DenyUsers",
121 				    pw->pw_name, hostname);
122 				return 0;
123 			}
124 	}
125 	/* Return false if AllowUsers isn't empty and user isn't listed there */
126 	if (options.num_allow_users > 0) {
127 		for (i = 0; i < options.num_allow_users; i++)
128 			if (match_user(pw->pw_name, hostname, ipaddr,
129 			    options.allow_users[i]))
130 				break;
131 		/* i < options.num_allow_users iff we break for loop */
132 		if (i >= options.num_allow_users) {
133 			logit("User %.100s from %.100s not allowed because "
134 			    "not listed in AllowUsers", pw->pw_name, hostname);
135 			return 0;
136 		}
137 	}
138 	if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
139 		/* Get the user's group access list (primary and supplementary) */
140 		if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
141 			logit("User %.100s from %.100s not allowed because "
142 			    "not in any group", pw->pw_name, hostname);
143 			return 0;
144 		}
145 
146 		/* Return false if one of user's groups is listed in DenyGroups */
147 		if (options.num_deny_groups > 0)
148 			if (ga_match(options.deny_groups,
149 			    options.num_deny_groups)) {
150 				ga_free();
151 				logit("User %.100s from %.100s not allowed "
152 				    "because a group is listed in DenyGroups",
153 				    pw->pw_name, hostname);
154 				return 0;
155 			}
156 		/*
157 		 * Return false if AllowGroups isn't empty and one of user's groups
158 		 * isn't listed there
159 		 */
160 		if (options.num_allow_groups > 0)
161 			if (!ga_match(options.allow_groups,
162 			    options.num_allow_groups)) {
163 				ga_free();
164 				logit("User %.100s from %.100s not allowed "
165 				    "because none of user's groups are listed "
166 				    "in AllowGroups", pw->pw_name, hostname);
167 				return 0;
168 			}
169 		ga_free();
170 	}
171 	/* We found no reason not to let this user try to log on... */
172 	return 1;
173 }
174 
175 void
176 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info)
177 {
178 	void (*authlog) (const char *fmt,...) = verbose;
179 	char *authmsg;
180 
181 	if (use_privsep && !mm_is_monitor() && !authctxt->postponed)
182 		return;
183 
184 	/* Raise logging level */
185 	if (authenticated == 1 ||
186 	    !authctxt->valid ||
187 	    authctxt->failures >= options.max_authtries / 2 ||
188 	    strcmp(method, "password") == 0)
189 		authlog = logit;
190 
191 	if (authctxt->postponed)
192 		authmsg = "Postponed";
193 	else
194 		authmsg = authenticated ? "Accepted" : "Failed";
195 
196 	authlog("%s %s for %s%.100s from %.200s port %d%s",
197 	    authmsg,
198 	    method,
199 	    authctxt->valid ? "" : "invalid user ",
200 	    authctxt->user,
201 	    get_remote_ipaddr(),
202 	    get_remote_port(),
203 	    info);
204 }
205 
206 /*
207  * Check whether root logins are disallowed.
208  */
209 int
210 auth_root_allowed(char *method)
211 {
212 	switch (options.permit_root_login) {
213 	case PERMIT_YES:
214 		return 1;
215 	case PERMIT_NO_PASSWD:
216 		if (strcmp(method, "password") != 0)
217 			return 1;
218 		break;
219 	case PERMIT_FORCED_ONLY:
220 		if (forced_command) {
221 			logit("Root login accepted for forced command.");
222 			return 1;
223 		}
224 		break;
225 	}
226 	logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr());
227 	return 0;
228 }
229 
230 
231 /*
232  * Given a template and a passwd structure, build a filename
233  * by substituting % tokenised options. Currently, %% becomes '%',
234  * %h becomes the home directory and %u the username.
235  *
236  * This returns a buffer allocated by xmalloc.
237  */
238 static char *
239 expand_authorized_keys(const char *filename, struct passwd *pw)
240 {
241 	char *file, ret[MAXPATHLEN];
242 	int i;
243 
244 	file = percent_expand(filename, "h", pw->pw_dir,
245 	    "u", pw->pw_name, (char *)NULL);
246 
247 	/*
248 	 * Ensure that filename starts anchored. If not, be backward
249 	 * compatible and prepend the '%h/'
250 	 */
251 	if (*file == '/')
252 		return (file);
253 
254 	i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file);
255 	if (i < 0 || (size_t)i >= sizeof(ret))
256 		fatal("expand_authorized_keys: path too long");
257 	xfree(file);
258 	return (xstrdup(ret));
259 }
260 
261 char *
262 authorized_keys_file(struct passwd *pw)
263 {
264 	return expand_authorized_keys(options.authorized_keys_file, pw);
265 }
266 
267 char *
268 authorized_keys_file2(struct passwd *pw)
269 {
270 	return expand_authorized_keys(options.authorized_keys_file2, pw);
271 }
272 
273 /* return ok if key exists in sysfile or userfile */
274 HostStatus
275 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host,
276     const char *sysfile, const char *userfile)
277 {
278 	Key *found;
279 	char *user_hostfile;
280 	struct stat st;
281 	HostStatus host_status;
282 
283 	/* Check if we know the host and its host key. */
284 	found = key_new(key->type);
285 	host_status = check_host_in_hostfile(sysfile, host, key, found, NULL);
286 
287 	if (host_status != HOST_OK && userfile != NULL) {
288 		user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
289 		if (options.strict_modes &&
290 		    (stat(user_hostfile, &st) == 0) &&
291 		    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
292 		    (st.st_mode & 022) != 0)) {
293 			logit("Authentication refused for %.100s: "
294 			    "bad owner or modes for %.200s",
295 			    pw->pw_name, user_hostfile);
296 		} else {
297 			temporarily_use_uid(pw);
298 			host_status = check_host_in_hostfile(user_hostfile,
299 			    host, key, found, NULL);
300 			restore_uid();
301 		}
302 		xfree(user_hostfile);
303 	}
304 	key_free(found);
305 
306 	debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ?
307 	    "ok" : "not found", host);
308 	return host_status;
309 }
310 
311 
312 /*
313  * Check a given file for security. This is defined as all components
314  * of the path to the file must be owned by either the owner of
315  * of the file or root and no directories must be group or world writable.
316  *
317  * XXX Should any specific check be done for sym links ?
318  *
319  * Takes an open file descriptor, the file name, a uid and and
320  * error buffer plus max size as arguments.
321  *
322  * Returns 0 on success and -1 on failure
323  */
324 static int
325 secure_filename(FILE *f, const char *file, struct passwd *pw,
326     char *err, size_t errlen)
327 {
328 	uid_t uid = pw->pw_uid;
329 	char buf[MAXPATHLEN], homedir[MAXPATHLEN];
330 	char *cp;
331 	int comparehome = 0;
332 	struct stat st;
333 
334 	if (realpath(file, buf) == NULL) {
335 		snprintf(err, errlen, "realpath %s failed: %s", file,
336 		    strerror(errno));
337 		return -1;
338 	}
339 	if (realpath(pw->pw_dir, homedir) != NULL)
340 		comparehome = 1;
341 
342 	/* check the open file to avoid races */
343 	if (fstat(fileno(f), &st) < 0 ||
344 	    (st.st_uid != 0 && st.st_uid != uid) ||
345 	    (st.st_mode & 022) != 0) {
346 		snprintf(err, errlen, "bad ownership or modes for file %s",
347 		    buf);
348 		return -1;
349 	}
350 
351 	/* for each component of the canonical path, walking upwards */
352 	for (;;) {
353 		if ((cp = dirname(buf)) == NULL) {
354 			snprintf(err, errlen, "dirname() failed");
355 			return -1;
356 		}
357 		strlcpy(buf, cp, sizeof(buf));
358 
359 		debug3("secure_filename: checking '%s'", buf);
360 		if (stat(buf, &st) < 0 ||
361 		    (st.st_uid != 0 && st.st_uid != uid) ||
362 		    (st.st_mode & 022) != 0) {
363 			snprintf(err, errlen,
364 			    "bad ownership or modes for directory %s", buf);
365 			return -1;
366 		}
367 
368 		/* If are passed the homedir then we can stop */
369 		if (comparehome && strcmp(homedir, buf) == 0) {
370 			debug3("secure_filename: terminating check at '%s'",
371 			    buf);
372 			break;
373 		}
374 		/*
375 		 * dirname should always complete with a "/" path,
376 		 * but we can be paranoid and check for "." too
377 		 */
378 		if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0))
379 			break;
380 	}
381 	return 0;
382 }
383 
384 FILE *
385 auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes)
386 {
387 	char line[1024];
388 	struct stat st;
389 	int fd;
390 	FILE *f;
391 
392 	/*
393 	 * Open the file containing the authorized keys
394 	 * Fail quietly if file does not exist
395 	 */
396 	if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1)
397 		return NULL;
398 
399 	if (fstat(fd, &st) < 0) {
400 		close(fd);
401 		return NULL;
402 	}
403 	if (!S_ISREG(st.st_mode)) {
404 		logit("User %s authorized keys %s is not a regular file",
405 		    pw->pw_name, file);
406 		close(fd);
407 		return NULL;
408 	}
409 	unset_nonblock(fd);
410 	if ((f = fdopen(fd, "r")) == NULL) {
411 		close(fd);
412 		return NULL;
413 	}
414 	if (options.strict_modes &&
415 	    secure_filename(f, file, pw, line, sizeof(line)) != 0) {
416 		fclose(f);
417 		logit("Authentication refused: %s", line);
418 		return NULL;
419 	}
420 
421 	return f;
422 }
423 
424 struct passwd *
425 getpwnamallow(const char *user)
426 {
427 	extern login_cap_t *lc;
428 	auth_session_t *as;
429 	struct passwd *pw;
430 
431 	parse_server_match_config(&options, user,
432 	    get_canonical_hostname(options.use_dns), get_remote_ipaddr());
433 
434 	pw = getpwnam(user);
435 	if (pw == NULL) {
436 		logit("Invalid user %.100s from %.100s",
437 		    user, get_remote_ipaddr());
438 		return (NULL);
439 	}
440 	if (!allowed_user(pw))
441 		return (NULL);
442 	if ((lc = login_getclass(pw->pw_class)) == NULL) {
443 		debug("unable to get login class: %s", user);
444 		return (NULL);
445 	}
446 	if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
447 	    auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
448 		debug("Approval failure for %s", user);
449 		pw = NULL;
450 	}
451 	if (as != NULL)
452 		auth_close(as);
453 	if (pw != NULL)
454 		return (pwcopy(pw));
455 	return (NULL);
456 }
457 
458 void
459 auth_debug_add(const char *fmt,...)
460 {
461 	char buf[1024];
462 	va_list args;
463 
464 	if (!auth_debug_init)
465 		return;
466 
467 	va_start(args, fmt);
468 	vsnprintf(buf, sizeof(buf), fmt, args);
469 	va_end(args);
470 	buffer_put_cstring(&auth_debug, buf);
471 }
472 
473 void
474 auth_debug_send(void)
475 {
476 	char *msg;
477 
478 	if (!auth_debug_init)
479 		return;
480 	while (buffer_len(&auth_debug)) {
481 		msg = buffer_get_string(&auth_debug, NULL);
482 		packet_send_debug("%s", msg);
483 		xfree(msg);
484 	}
485 }
486 
487 void
488 auth_debug_reset(void)
489 {
490 	if (auth_debug_init)
491 		buffer_clear(&auth_debug);
492 	else {
493 		buffer_init(&auth_debug);
494 		auth_debug_init = 1;
495 	}
496 }
497 
498 struct passwd *
499 fakepw(void)
500 {
501 	static struct passwd fake;
502 
503 	memset(&fake, 0, sizeof(fake));
504 	fake.pw_name = "NOUSER";
505 	fake.pw_passwd =
506 	    "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK";
507 	fake.pw_gecos = "NOUSER";
508 	fake.pw_uid = (uid_t)-1;
509 	fake.pw_gid = (gid_t)-1;
510 	fake.pw_class = "";
511 	fake.pw_dir = "/nonexist";
512 	fake.pw_shell = "/nonexist";
513 
514 	return (&fake);
515 }
516