xref: /openssh-portable/auth.c (revision b4c7cd11)
1 /* $OpenBSD: auth.c,v 1.150 2020/12/20 23:36:51 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 
28 #include <sys/types.h>
29 #include <sys/stat.h>
30 #include <sys/socket.h>
31 #include <sys/wait.h>
32 
33 #include <netinet/in.h>
34 
35 #include <stdlib.h>
36 #include <errno.h>
37 #include <fcntl.h>
38 #ifdef HAVE_PATHS_H
39 # include <paths.h>
40 #endif
41 #include <pwd.h>
42 #ifdef HAVE_LOGIN_H
43 #include <login.h>
44 #endif
45 #ifdef USE_SHADOW
46 #include <shadow.h>
47 #endif
48 #include <stdarg.h>
49 #include <stdio.h>
50 #include <string.h>
51 #include <unistd.h>
52 #include <limits.h>
53 #include <netdb.h>
54 #include <time.h>
55 
56 #include "xmalloc.h"
57 #include "match.h"
58 #include "groupaccess.h"
59 #include "log.h"
60 #include "sshbuf.h"
61 #include "misc.h"
62 #include "servconf.h"
63 #include "sshkey.h"
64 #include "hostfile.h"
65 #include "auth.h"
66 #include "auth-options.h"
67 #include "canohost.h"
68 #include "uidswap.h"
69 #include "packet.h"
70 #include "loginrec.h"
71 #ifdef GSSAPI
72 #include "ssh-gss.h"
73 #endif
74 #include "authfile.h"
75 #include "monitor_wrap.h"
76 #include "ssherr.h"
77 #include "compat.h"
78 #include "channels.h"
79 
80 /* import */
81 extern ServerOptions options;
82 extern struct include_list includes;
83 extern int use_privsep;
84 extern struct sshbuf *loginmsg;
85 extern struct passwd *privsep_pw;
86 extern struct sshauthopt *auth_opts;
87 
88 /* Debugging messages */
89 static struct sshbuf *auth_debug;
90 
91 /*
92  * Check if the user is allowed to log in via ssh. If user is listed
93  * in DenyUsers or one of user's groups is listed in DenyGroups, false
94  * will be returned. If AllowUsers isn't empty and user isn't listed
95  * there, or if AllowGroups isn't empty and one of user's groups isn't
96  * listed there, false will be returned.
97  * If the user's shell is not executable, false will be returned.
98  * Otherwise true is returned.
99  */
100 int
101 allowed_user(struct ssh *ssh, struct passwd * pw)
102 {
103 	struct stat st;
104 	const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL;
105 	u_int i;
106 	int r;
107 #ifdef USE_SHADOW
108 	struct spwd *spw = NULL;
109 #endif
110 
111 	/* Shouldn't be called if pw is NULL, but better safe than sorry... */
112 	if (!pw || !pw->pw_name)
113 		return 0;
114 
115 #ifdef USE_SHADOW
116 	if (!options.use_pam)
117 		spw = getspnam(pw->pw_name);
118 #ifdef HAS_SHADOW_EXPIRE
119 	if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw))
120 		return 0;
121 #endif /* HAS_SHADOW_EXPIRE */
122 #endif /* USE_SHADOW */
123 
124 	/* grab passwd field for locked account check */
125 	passwd = pw->pw_passwd;
126 #ifdef USE_SHADOW
127 	if (spw != NULL)
128 #ifdef USE_LIBIAF
129 		passwd = get_iaf_password(pw);
130 #else
131 		passwd = spw->sp_pwdp;
132 #endif /* USE_LIBIAF */
133 #endif
134 
135 	/* check for locked account */
136 	if (!options.use_pam && passwd && *passwd) {
137 		int locked = 0;
138 
139 #ifdef LOCKED_PASSWD_STRING
140 		if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0)
141 			 locked = 1;
142 #endif
143 #ifdef LOCKED_PASSWD_PREFIX
144 		if (strncmp(passwd, LOCKED_PASSWD_PREFIX,
145 		    strlen(LOCKED_PASSWD_PREFIX)) == 0)
146 			 locked = 1;
147 #endif
148 #ifdef LOCKED_PASSWD_SUBSTR
149 		if (strstr(passwd, LOCKED_PASSWD_SUBSTR))
150 			locked = 1;
151 #endif
152 #ifdef USE_LIBIAF
153 		free((void *) passwd);
154 #endif /* USE_LIBIAF */
155 		if (locked) {
156 			logit("User %.100s not allowed because account is locked",
157 			    pw->pw_name);
158 			return 0;
159 		}
160 	}
161 
162 	/*
163 	 * Deny if shell does not exist or is not executable unless we
164 	 * are chrooting.
165 	 */
166 	if (options.chroot_directory == NULL ||
167 	    strcasecmp(options.chroot_directory, "none") == 0) {
168 		char *shell = xstrdup((pw->pw_shell[0] == '\0') ?
169 		    _PATH_BSHELL : pw->pw_shell); /* empty = /bin/sh */
170 
171 		if (stat(shell, &st) == -1) {
172 			logit("User %.100s not allowed because shell %.100s "
173 			    "does not exist", pw->pw_name, shell);
174 			free(shell);
175 			return 0;
176 		}
177 		if (S_ISREG(st.st_mode) == 0 ||
178 		    (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
179 			logit("User %.100s not allowed because shell %.100s "
180 			    "is not executable", pw->pw_name, shell);
181 			free(shell);
182 			return 0;
183 		}
184 		free(shell);
185 	}
186 
187 	if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
188 	    options.num_deny_groups > 0 || options.num_allow_groups > 0) {
189 		hostname = auth_get_canonical_hostname(ssh, options.use_dns);
190 		ipaddr = ssh_remote_ipaddr(ssh);
191 	}
192 
193 	/* Return false if user is listed in DenyUsers */
194 	if (options.num_deny_users > 0) {
195 		for (i = 0; i < options.num_deny_users; i++) {
196 			r = match_user(pw->pw_name, hostname, ipaddr,
197 			    options.deny_users[i]);
198 			if (r < 0) {
199 				fatal("Invalid DenyUsers pattern \"%.100s\"",
200 				    options.deny_users[i]);
201 			} else if (r != 0) {
202 				logit("User %.100s from %.100s not allowed "
203 				    "because listed in DenyUsers",
204 				    pw->pw_name, hostname);
205 				return 0;
206 			}
207 		}
208 	}
209 	/* Return false if AllowUsers isn't empty and user isn't listed there */
210 	if (options.num_allow_users > 0) {
211 		for (i = 0; i < options.num_allow_users; i++) {
212 			r = match_user(pw->pw_name, hostname, ipaddr,
213 			    options.allow_users[i]);
214 			if (r < 0) {
215 				fatal("Invalid AllowUsers pattern \"%.100s\"",
216 				    options.allow_users[i]);
217 			} else if (r == 1)
218 				break;
219 		}
220 		/* i < options.num_allow_users iff we break for loop */
221 		if (i >= options.num_allow_users) {
222 			logit("User %.100s from %.100s not allowed because "
223 			    "not listed in AllowUsers", pw->pw_name, hostname);
224 			return 0;
225 		}
226 	}
227 	if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
228 		/* Get the user's group access list (primary and supplementary) */
229 		if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
230 			logit("User %.100s from %.100s not allowed because "
231 			    "not in any group", pw->pw_name, hostname);
232 			return 0;
233 		}
234 
235 		/* Return false if one of user's groups is listed in DenyGroups */
236 		if (options.num_deny_groups > 0)
237 			if (ga_match(options.deny_groups,
238 			    options.num_deny_groups)) {
239 				ga_free();
240 				logit("User %.100s from %.100s not allowed "
241 				    "because a group is listed in DenyGroups",
242 				    pw->pw_name, hostname);
243 				return 0;
244 			}
245 		/*
246 		 * Return false if AllowGroups isn't empty and one of user's groups
247 		 * isn't listed there
248 		 */
249 		if (options.num_allow_groups > 0)
250 			if (!ga_match(options.allow_groups,
251 			    options.num_allow_groups)) {
252 				ga_free();
253 				logit("User %.100s from %.100s not allowed "
254 				    "because none of user's groups are listed "
255 				    "in AllowGroups", pw->pw_name, hostname);
256 				return 0;
257 			}
258 		ga_free();
259 	}
260 
261 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
262 	if (!sys_auth_allowed_user(pw, loginmsg))
263 		return 0;
264 #endif
265 
266 	/* We found no reason not to let this user try to log on... */
267 	return 1;
268 }
269 
270 /*
271  * Formats any key left in authctxt->auth_method_key for inclusion in
272  * auth_log()'s message. Also includes authxtct->auth_method_info if present.
273  */
274 static char *
275 format_method_key(Authctxt *authctxt)
276 {
277 	const struct sshkey *key = authctxt->auth_method_key;
278 	const char *methinfo = authctxt->auth_method_info;
279 	char *fp, *cafp, *ret = NULL;
280 
281 	if (key == NULL)
282 		return NULL;
283 
284 	if (sshkey_is_cert(key)) {
285 		fp = sshkey_fingerprint(key,
286 		    options.fingerprint_hash, SSH_FP_DEFAULT);
287 		cafp = sshkey_fingerprint(key->cert->signature_key,
288 		    options.fingerprint_hash, SSH_FP_DEFAULT);
289 		xasprintf(&ret, "%s %s ID %s (serial %llu) CA %s %s%s%s",
290 		    sshkey_type(key), fp == NULL ? "(null)" : fp,
291 		    key->cert->key_id,
292 		    (unsigned long long)key->cert->serial,
293 		    sshkey_type(key->cert->signature_key),
294 		    cafp == NULL ? "(null)" : cafp,
295 		    methinfo == NULL ? "" : ", ",
296 		    methinfo == NULL ? "" : methinfo);
297 		free(fp);
298 		free(cafp);
299 	} else {
300 		fp = sshkey_fingerprint(key, options.fingerprint_hash,
301 		    SSH_FP_DEFAULT);
302 		xasprintf(&ret, "%s %s%s%s", sshkey_type(key),
303 		    fp == NULL ? "(null)" : fp,
304 		    methinfo == NULL ? "" : ", ",
305 		    methinfo == NULL ? "" : methinfo);
306 		free(fp);
307 	}
308 	return ret;
309 }
310 
311 void
312 auth_log(struct ssh *ssh, int authenticated, int partial,
313     const char *method, const char *submethod)
314 {
315 	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
316 	int level = SYSLOG_LEVEL_VERBOSE;
317 	const char *authmsg;
318 	char *extra = NULL;
319 
320 	if (use_privsep && !mm_is_monitor() && !authctxt->postponed)
321 		return;
322 
323 	/* Raise logging level */
324 	if (authenticated == 1 ||
325 	    !authctxt->valid ||
326 	    authctxt->failures >= options.max_authtries / 2 ||
327 	    strcmp(method, "password") == 0)
328 		level = SYSLOG_LEVEL_INFO;
329 
330 	if (authctxt->postponed)
331 		authmsg = "Postponed";
332 	else if (partial)
333 		authmsg = "Partial";
334 	else
335 		authmsg = authenticated ? "Accepted" : "Failed";
336 
337 	if ((extra = format_method_key(authctxt)) == NULL) {
338 		if (authctxt->auth_method_info != NULL)
339 			extra = xstrdup(authctxt->auth_method_info);
340 	}
341 
342 	do_log2(level, "%s %s%s%s for %s%.100s from %.200s port %d ssh2%s%s",
343 	    authmsg,
344 	    method,
345 	    submethod != NULL ? "/" : "", submethod == NULL ? "" : submethod,
346 	    authctxt->valid ? "" : "invalid user ",
347 	    authctxt->user,
348 	    ssh_remote_ipaddr(ssh),
349 	    ssh_remote_port(ssh),
350 	    extra != NULL ? ": " : "",
351 	    extra != NULL ? extra : "");
352 
353 	free(extra);
354 
355 #ifdef CUSTOM_FAILED_LOGIN
356 	if (authenticated == 0 && !authctxt->postponed &&
357 	    (strcmp(method, "password") == 0 ||
358 	    strncmp(method, "keyboard-interactive", 20) == 0 ||
359 	    strcmp(method, "challenge-response") == 0))
360 		record_failed_login(ssh, authctxt->user,
361 		    auth_get_canonical_hostname(ssh, options.use_dns), "ssh");
362 # ifdef WITH_AIXAUTHENTICATE
363 	if (authenticated)
364 		sys_auth_record_login(authctxt->user,
365 		    auth_get_canonical_hostname(ssh, options.use_dns), "ssh",
366 		    loginmsg);
367 # endif
368 #endif
369 #ifdef SSH_AUDIT_EVENTS
370 	if (authenticated == 0 && !authctxt->postponed)
371 		audit_event(ssh, audit_classify_auth(method));
372 #endif
373 }
374 
375 
376 void
377 auth_maxtries_exceeded(struct ssh *ssh)
378 {
379 	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
380 
381 	error("maximum authentication attempts exceeded for "
382 	    "%s%.100s from %.200s port %d ssh2",
383 	    authctxt->valid ? "" : "invalid user ",
384 	    authctxt->user,
385 	    ssh_remote_ipaddr(ssh),
386 	    ssh_remote_port(ssh));
387 	ssh_packet_disconnect(ssh, "Too many authentication failures");
388 	/* NOTREACHED */
389 }
390 
391 /*
392  * Check whether root logins are disallowed.
393  */
394 int
395 auth_root_allowed(struct ssh *ssh, const char *method)
396 {
397 	switch (options.permit_root_login) {
398 	case PERMIT_YES:
399 		return 1;
400 	case PERMIT_NO_PASSWD:
401 		if (strcmp(method, "publickey") == 0 ||
402 		    strcmp(method, "hostbased") == 0 ||
403 		    strcmp(method, "gssapi-with-mic") == 0)
404 			return 1;
405 		break;
406 	case PERMIT_FORCED_ONLY:
407 		if (auth_opts->force_command != NULL) {
408 			logit("Root login accepted for forced command.");
409 			return 1;
410 		}
411 		break;
412 	}
413 	logit("ROOT LOGIN REFUSED FROM %.200s port %d",
414 	    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
415 	return 0;
416 }
417 
418 
419 /*
420  * Given a template and a passwd structure, build a filename
421  * by substituting % tokenised options. Currently, %% becomes '%',
422  * %h becomes the home directory and %u the username.
423  *
424  * This returns a buffer allocated by xmalloc.
425  */
426 char *
427 expand_authorized_keys(const char *filename, struct passwd *pw)
428 {
429 	char *file, uidstr[32], ret[PATH_MAX];
430 	int i;
431 
432 	snprintf(uidstr, sizeof(uidstr), "%llu",
433 	    (unsigned long long)pw->pw_uid);
434 	file = percent_expand(filename, "h", pw->pw_dir,
435 	    "u", pw->pw_name, "U", uidstr, (char *)NULL);
436 
437 	/*
438 	 * Ensure that filename starts anchored. If not, be backward
439 	 * compatible and prepend the '%h/'
440 	 */
441 	if (path_absolute(file))
442 		return (file);
443 
444 	i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file);
445 	if (i < 0 || (size_t)i >= sizeof(ret))
446 		fatal("expand_authorized_keys: path too long");
447 	free(file);
448 	return (xstrdup(ret));
449 }
450 
451 char *
452 authorized_principals_file(struct passwd *pw)
453 {
454 	if (options.authorized_principals_file == NULL)
455 		return NULL;
456 	return expand_authorized_keys(options.authorized_principals_file, pw);
457 }
458 
459 /* return ok if key exists in sysfile or userfile */
460 HostStatus
461 check_key_in_hostfiles(struct passwd *pw, struct sshkey *key, const char *host,
462     const char *sysfile, const char *userfile)
463 {
464 	char *user_hostfile;
465 	struct stat st;
466 	HostStatus host_status;
467 	struct hostkeys *hostkeys;
468 	const struct hostkey_entry *found;
469 
470 	hostkeys = init_hostkeys();
471 	load_hostkeys(hostkeys, host, sysfile, 0);
472 	if (userfile != NULL) {
473 		user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
474 		if (options.strict_modes &&
475 		    (stat(user_hostfile, &st) == 0) &&
476 		    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
477 		    (st.st_mode & 022) != 0)) {
478 			logit("Authentication refused for %.100s: "
479 			    "bad owner or modes for %.200s",
480 			    pw->pw_name, user_hostfile);
481 			auth_debug_add("Ignored %.200s: bad ownership or modes",
482 			    user_hostfile);
483 		} else {
484 			temporarily_use_uid(pw);
485 			load_hostkeys(hostkeys, host, user_hostfile, 0);
486 			restore_uid();
487 		}
488 		free(user_hostfile);
489 	}
490 	host_status = check_key_in_hostkeys(hostkeys, key, &found);
491 	if (host_status == HOST_REVOKED)
492 		error("WARNING: revoked key for %s attempted authentication",
493 		    host);
494 	else if (host_status == HOST_OK)
495 		debug_f("key for %s found at %s:%ld",
496 		    found->host, found->file, found->line);
497 	else
498 		debug_f("key for host %s not found", host);
499 
500 	free_hostkeys(hostkeys);
501 
502 	return host_status;
503 }
504 
505 static FILE *
506 auth_openfile(const char *file, struct passwd *pw, int strict_modes,
507     int log_missing, char *file_type)
508 {
509 	char line[1024];
510 	struct stat st;
511 	int fd;
512 	FILE *f;
513 
514 	if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) {
515 		if (log_missing || errno != ENOENT)
516 			debug("Could not open %s '%s': %s", file_type, file,
517 			   strerror(errno));
518 		return NULL;
519 	}
520 
521 	if (fstat(fd, &st) == -1) {
522 		close(fd);
523 		return NULL;
524 	}
525 	if (!S_ISREG(st.st_mode)) {
526 		logit("User %s %s %s is not a regular file",
527 		    pw->pw_name, file_type, file);
528 		close(fd);
529 		return NULL;
530 	}
531 	unset_nonblock(fd);
532 	if ((f = fdopen(fd, "r")) == NULL) {
533 		close(fd);
534 		return NULL;
535 	}
536 	if (strict_modes &&
537 	    safe_path_fd(fileno(f), file, pw, line, sizeof(line)) != 0) {
538 		fclose(f);
539 		logit("Authentication refused: %s", line);
540 		auth_debug_add("Ignored %s: %s", file_type, line);
541 		return NULL;
542 	}
543 
544 	return f;
545 }
546 
547 
548 FILE *
549 auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes)
550 {
551 	return auth_openfile(file, pw, strict_modes, 1, "authorized keys");
552 }
553 
554 FILE *
555 auth_openprincipals(const char *file, struct passwd *pw, int strict_modes)
556 {
557 	return auth_openfile(file, pw, strict_modes, 0,
558 	    "authorized principals");
559 }
560 
561 struct passwd *
562 getpwnamallow(struct ssh *ssh, const char *user)
563 {
564 #ifdef HAVE_LOGIN_CAP
565 	extern login_cap_t *lc;
566 #ifdef BSD_AUTH
567 	auth_session_t *as;
568 #endif
569 #endif
570 	struct passwd *pw;
571 	struct connection_info *ci;
572 	u_int i;
573 
574 	ci = get_connection_info(ssh, 1, options.use_dns);
575 	ci->user = user;
576 	parse_server_match_config(&options, &includes, ci);
577 	log_change_level(options.log_level);
578 	log_verbose_reset();
579 	for (i = 0; i < options.num_log_verbose; i++)
580 		log_verbose_add(options.log_verbose[i]);
581 	process_permitopen(ssh, &options);
582 
583 #if defined(_AIX) && defined(HAVE_SETAUTHDB)
584 	aix_setauthdb(user);
585 #endif
586 
587 	pw = getpwnam(user);
588 
589 #if defined(_AIX) && defined(HAVE_SETAUTHDB)
590 	aix_restoreauthdb();
591 #endif
592 	if (pw == NULL) {
593 		logit("Invalid user %.100s from %.100s port %d",
594 		    user, ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
595 #ifdef CUSTOM_FAILED_LOGIN
596 		record_failed_login(ssh, user,
597 		    auth_get_canonical_hostname(ssh, options.use_dns), "ssh");
598 #endif
599 #ifdef SSH_AUDIT_EVENTS
600 		audit_event(ssh, SSH_INVALID_USER);
601 #endif /* SSH_AUDIT_EVENTS */
602 		return (NULL);
603 	}
604 	if (!allowed_user(ssh, pw))
605 		return (NULL);
606 #ifdef HAVE_LOGIN_CAP
607 	if ((lc = login_getclass(pw->pw_class)) == NULL) {
608 		debug("unable to get login class: %s", user);
609 		return (NULL);
610 	}
611 #ifdef BSD_AUTH
612 	if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
613 	    auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
614 		debug("Approval failure for %s", user);
615 		pw = NULL;
616 	}
617 	if (as != NULL)
618 		auth_close(as);
619 #endif
620 #endif
621 	if (pw != NULL)
622 		return (pwcopy(pw));
623 	return (NULL);
624 }
625 
626 /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */
627 int
628 auth_key_is_revoked(struct sshkey *key)
629 {
630 	char *fp = NULL;
631 	int r;
632 
633 	if (options.revoked_keys_file == NULL)
634 		return 0;
635 	if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
636 	    SSH_FP_DEFAULT)) == NULL) {
637 		r = SSH_ERR_ALLOC_FAIL;
638 		error_fr(r, "fingerprint key");
639 		goto out;
640 	}
641 
642 	r = sshkey_check_revoked(key, options.revoked_keys_file);
643 	switch (r) {
644 	case 0:
645 		break; /* not revoked */
646 	case SSH_ERR_KEY_REVOKED:
647 		error("Authentication key %s %s revoked by file %s",
648 		    sshkey_type(key), fp, options.revoked_keys_file);
649 		goto out;
650 	default:
651 		error_r(r, "Error checking authentication key %s %s in "
652 		    "revoked keys file %s", sshkey_type(key), fp,
653 		    options.revoked_keys_file);
654 		goto out;
655 	}
656 
657 	/* Success */
658 	r = 0;
659 
660  out:
661 	free(fp);
662 	return r == 0 ? 0 : 1;
663 }
664 
665 void
666 auth_debug_add(const char *fmt,...)
667 {
668 	char buf[1024];
669 	va_list args;
670 	int r;
671 
672 	if (auth_debug == NULL)
673 		return;
674 
675 	va_start(args, fmt);
676 	vsnprintf(buf, sizeof(buf), fmt, args);
677 	va_end(args);
678 	if ((r = sshbuf_put_cstring(auth_debug, buf)) != 0)
679 		fatal_fr(r, "sshbuf_put_cstring");
680 }
681 
682 void
683 auth_debug_send(struct ssh *ssh)
684 {
685 	char *msg;
686 	int r;
687 
688 	if (auth_debug == NULL)
689 		return;
690 	while (sshbuf_len(auth_debug) != 0) {
691 		if ((r = sshbuf_get_cstring(auth_debug, &msg, NULL)) != 0)
692 			fatal_fr(r, "sshbuf_get_cstring");
693 		ssh_packet_send_debug(ssh, "%s", msg);
694 		free(msg);
695 	}
696 }
697 
698 void
699 auth_debug_reset(void)
700 {
701 	if (auth_debug != NULL)
702 		sshbuf_reset(auth_debug);
703 	else if ((auth_debug = sshbuf_new()) == NULL)
704 		fatal_f("sshbuf_new failed");
705 }
706 
707 struct passwd *
708 fakepw(void)
709 {
710 	static struct passwd fake;
711 
712 	memset(&fake, 0, sizeof(fake));
713 	fake.pw_name = "NOUSER";
714 	fake.pw_passwd =
715 	    "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK";
716 #ifdef HAVE_STRUCT_PASSWD_PW_GECOS
717 	fake.pw_gecos = "NOUSER";
718 #endif
719 	fake.pw_uid = privsep_pw == NULL ? (uid_t)-1 : privsep_pw->pw_uid;
720 	fake.pw_gid = privsep_pw == NULL ? (gid_t)-1 : privsep_pw->pw_gid;
721 #ifdef HAVE_STRUCT_PASSWD_PW_CLASS
722 	fake.pw_class = "";
723 #endif
724 	fake.pw_dir = "/nonexist";
725 	fake.pw_shell = "/nonexist";
726 
727 	return (&fake);
728 }
729 
730 /*
731  * Returns the remote DNS hostname as a string. The returned string must not
732  * be freed. NB. this will usually trigger a DNS query the first time it is
733  * called.
734  * This function does additional checks on the hostname to mitigate some
735  * attacks on legacy rhosts-style authentication.
736  * XXX is RhostsRSAAuthentication vulnerable to these?
737  * XXX Can we remove these checks? (or if not, remove RhostsRSAAuthentication?)
738  */
739 
740 static char *
741 remote_hostname(struct ssh *ssh)
742 {
743 	struct sockaddr_storage from;
744 	socklen_t fromlen;
745 	struct addrinfo hints, *ai, *aitop;
746 	char name[NI_MAXHOST], ntop2[NI_MAXHOST];
747 	const char *ntop = ssh_remote_ipaddr(ssh);
748 
749 	/* Get IP address of client. */
750 	fromlen = sizeof(from);
751 	memset(&from, 0, sizeof(from));
752 	if (getpeername(ssh_packet_get_connection_in(ssh),
753 	    (struct sockaddr *)&from, &fromlen) == -1) {
754 		debug("getpeername failed: %.100s", strerror(errno));
755 		return xstrdup(ntop);
756 	}
757 
758 	ipv64_normalise_mapped(&from, &fromlen);
759 	if (from.ss_family == AF_INET6)
760 		fromlen = sizeof(struct sockaddr_in6);
761 
762 	debug3("Trying to reverse map address %.100s.", ntop);
763 	/* Map the IP address to a host name. */
764 	if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name),
765 	    NULL, 0, NI_NAMEREQD) != 0) {
766 		/* Host name not found.  Use ip address. */
767 		return xstrdup(ntop);
768 	}
769 
770 	/*
771 	 * if reverse lookup result looks like a numeric hostname,
772 	 * someone is trying to trick us by PTR record like following:
773 	 *	1.1.1.10.in-addr.arpa.	IN PTR	2.3.4.5
774 	 */
775 	memset(&hints, 0, sizeof(hints));
776 	hints.ai_socktype = SOCK_DGRAM;	/*dummy*/
777 	hints.ai_flags = AI_NUMERICHOST;
778 	if (getaddrinfo(name, NULL, &hints, &ai) == 0) {
779 		logit("Nasty PTR record \"%s\" is set up for %s, ignoring",
780 		    name, ntop);
781 		freeaddrinfo(ai);
782 		return xstrdup(ntop);
783 	}
784 
785 	/* Names are stored in lowercase. */
786 	lowercase(name);
787 
788 	/*
789 	 * Map it back to an IP address and check that the given
790 	 * address actually is an address of this host.  This is
791 	 * necessary because anyone with access to a name server can
792 	 * define arbitrary names for an IP address. Mapping from
793 	 * name to IP address can be trusted better (but can still be
794 	 * fooled if the intruder has access to the name server of
795 	 * the domain).
796 	 */
797 	memset(&hints, 0, sizeof(hints));
798 	hints.ai_family = from.ss_family;
799 	hints.ai_socktype = SOCK_STREAM;
800 	if (getaddrinfo(name, NULL, &hints, &aitop) != 0) {
801 		logit("reverse mapping checking getaddrinfo for %.700s "
802 		    "[%s] failed.", name, ntop);
803 		return xstrdup(ntop);
804 	}
805 	/* Look for the address from the list of addresses. */
806 	for (ai = aitop; ai; ai = ai->ai_next) {
807 		if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop2,
808 		    sizeof(ntop2), NULL, 0, NI_NUMERICHOST) == 0 &&
809 		    (strcmp(ntop, ntop2) == 0))
810 				break;
811 	}
812 	freeaddrinfo(aitop);
813 	/* If we reached the end of the list, the address was not there. */
814 	if (ai == NULL) {
815 		/* Address not found for the host name. */
816 		logit("Address %.100s maps to %.600s, but this does not "
817 		    "map back to the address.", ntop, name);
818 		return xstrdup(ntop);
819 	}
820 	return xstrdup(name);
821 }
822 
823 /*
824  * Return the canonical name of the host in the other side of the current
825  * connection.  The host name is cached, so it is efficient to call this
826  * several times.
827  */
828 
829 const char *
830 auth_get_canonical_hostname(struct ssh *ssh, int use_dns)
831 {
832 	static char *dnsname;
833 
834 	if (!use_dns)
835 		return ssh_remote_ipaddr(ssh);
836 	else if (dnsname != NULL)
837 		return dnsname;
838 	else {
839 		dnsname = remote_hostname(ssh);
840 		return dnsname;
841 	}
842 }
843 
844 /*
845  * Runs command in a subprocess with a minimal environment.
846  * Returns pid on success, 0 on failure.
847  * The child stdout and stderr maybe captured, left attached or sent to
848  * /dev/null depending on the contents of flags.
849  * "tag" is prepended to log messages.
850  * NB. "command" is only used for logging; the actual command executed is
851  * av[0].
852  */
853 pid_t
854 subprocess(const char *tag, struct passwd *pw, const char *command,
855     int ac, char **av, FILE **child, u_int flags)
856 {
857 	FILE *f = NULL;
858 	struct stat st;
859 	int fd, devnull, p[2], i;
860 	pid_t pid;
861 	char *cp, errmsg[512];
862 	u_int envsize;
863 	char **child_env;
864 
865 	if (child != NULL)
866 		*child = NULL;
867 
868 	debug3_f("%s command \"%s\" running as %s (flags 0x%x)",
869 	    tag, command, pw->pw_name, flags);
870 
871 	/* Check consistency */
872 	if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
873 	    (flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0) {
874 		error_f("inconsistent flags");
875 		return 0;
876 	}
877 	if (((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0) != (child == NULL)) {
878 		error_f("inconsistent flags/output");
879 		return 0;
880 	}
881 
882 	/*
883 	 * If executing an explicit binary, then verify the it exists
884 	 * and appears safe-ish to execute
885 	 */
886 	if (!path_absolute(av[0])) {
887 		error("%s path is not absolute", tag);
888 		return 0;
889 	}
890 	temporarily_use_uid(pw);
891 	if (stat(av[0], &st) == -1) {
892 		error("Could not stat %s \"%s\": %s", tag,
893 		    av[0], strerror(errno));
894 		restore_uid();
895 		return 0;
896 	}
897 	if (safe_path(av[0], &st, NULL, 0, errmsg, sizeof(errmsg)) != 0) {
898 		error("Unsafe %s \"%s\": %s", tag, av[0], errmsg);
899 		restore_uid();
900 		return 0;
901 	}
902 	/* Prepare to keep the child's stdout if requested */
903 	if (pipe(p) == -1) {
904 		error("%s: pipe: %s", tag, strerror(errno));
905 		restore_uid();
906 		return 0;
907 	}
908 	restore_uid();
909 
910 	switch ((pid = fork())) {
911 	case -1: /* error */
912 		error("%s: fork: %s", tag, strerror(errno));
913 		close(p[0]);
914 		close(p[1]);
915 		return 0;
916 	case 0: /* child */
917 		/* Prepare a minimal environment for the child. */
918 		envsize = 5;
919 		child_env = xcalloc(sizeof(*child_env), envsize);
920 		child_set_env(&child_env, &envsize, "PATH", _PATH_STDPATH);
921 		child_set_env(&child_env, &envsize, "USER", pw->pw_name);
922 		child_set_env(&child_env, &envsize, "LOGNAME", pw->pw_name);
923 		child_set_env(&child_env, &envsize, "HOME", pw->pw_dir);
924 		if ((cp = getenv("LANG")) != NULL)
925 			child_set_env(&child_env, &envsize, "LANG", cp);
926 
927 		for (i = 0; i < NSIG; i++)
928 			ssh_signal(i, SIG_DFL);
929 
930 		if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
931 			error("%s: open %s: %s", tag, _PATH_DEVNULL,
932 			    strerror(errno));
933 			_exit(1);
934 		}
935 		if (dup2(devnull, STDIN_FILENO) == -1) {
936 			error("%s: dup2: %s", tag, strerror(errno));
937 			_exit(1);
938 		}
939 
940 		/* Set up stdout as requested; leave stderr in place for now. */
941 		fd = -1;
942 		if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0)
943 			fd = p[1];
944 		else if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0)
945 			fd = devnull;
946 		if (fd != -1 && dup2(fd, STDOUT_FILENO) == -1) {
947 			error("%s: dup2: %s", tag, strerror(errno));
948 			_exit(1);
949 		}
950 		closefrom(STDERR_FILENO + 1);
951 
952 		/* Don't use permanently_set_uid() here to avoid fatal() */
953 		if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) == -1) {
954 			error("%s: setresgid %u: %s", tag, (u_int)pw->pw_gid,
955 			    strerror(errno));
956 			_exit(1);
957 		}
958 		if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) == -1) {
959 			error("%s: setresuid %u: %s", tag, (u_int)pw->pw_uid,
960 			    strerror(errno));
961 			_exit(1);
962 		}
963 		/* stdin is pointed to /dev/null at this point */
964 		if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
965 		    dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
966 			error("%s: dup2: %s", tag, strerror(errno));
967 			_exit(1);
968 		}
969 
970 		execve(av[0], av, child_env);
971 		error("%s exec \"%s\": %s", tag, command, strerror(errno));
972 		_exit(127);
973 	default: /* parent */
974 		break;
975 	}
976 
977 	close(p[1]);
978 	if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0)
979 		close(p[0]);
980 	else if ((f = fdopen(p[0], "r")) == NULL) {
981 		error("%s: fdopen: %s", tag, strerror(errno));
982 		close(p[0]);
983 		/* Don't leave zombie child */
984 		kill(pid, SIGTERM);
985 		while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
986 			;
987 		return 0;
988 	}
989 	/* Success */
990 	debug3_f("%s pid %ld", tag, (long)pid);
991 	if (child != NULL)
992 		*child = f;
993 	return pid;
994 }
995 
996 /* These functions link key/cert options to the auth framework */
997 
998 /* Log sshauthopt options locally and (optionally) for remote transmission */
999 void
1000 auth_log_authopts(const char *loc, const struct sshauthopt *opts, int do_remote)
1001 {
1002 	int do_env = options.permit_user_env && opts->nenv > 0;
1003 	int do_permitopen = opts->npermitopen > 0 &&
1004 	    (options.allow_tcp_forwarding & FORWARD_LOCAL) != 0;
1005 	int do_permitlisten = opts->npermitlisten > 0 &&
1006 	    (options.allow_tcp_forwarding & FORWARD_REMOTE) != 0;
1007 	size_t i;
1008 	char msg[1024], buf[64];
1009 
1010 	snprintf(buf, sizeof(buf), "%d", opts->force_tun_device);
1011 	/* Try to keep this alphabetically sorted */
1012 	snprintf(msg, sizeof(msg), "key options:%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s",
1013 	    opts->permit_agent_forwarding_flag ? " agent-forwarding" : "",
1014 	    opts->force_command == NULL ? "" : " command",
1015 	    do_env ?  " environment" : "",
1016 	    opts->valid_before == 0 ? "" : "expires",
1017 	    opts->no_require_user_presence ? " no-touch-required" : "",
1018 	    do_permitopen ?  " permitopen" : "",
1019 	    do_permitlisten ?  " permitlisten" : "",
1020 	    opts->permit_port_forwarding_flag ? " port-forwarding" : "",
1021 	    opts->cert_principals == NULL ? "" : " principals",
1022 	    opts->permit_pty_flag ? " pty" : "",
1023 	    opts->require_verify ? " uv" : "",
1024 	    opts->force_tun_device == -1 ? "" : " tun=",
1025 	    opts->force_tun_device == -1 ? "" : buf,
1026 	    opts->permit_user_rc ? " user-rc" : "",
1027 	    opts->permit_x11_forwarding_flag ? " x11-forwarding" : "");
1028 
1029 	debug("%s: %s", loc, msg);
1030 	if (do_remote)
1031 		auth_debug_add("%s: %s", loc, msg);
1032 
1033 	if (options.permit_user_env) {
1034 		for (i = 0; i < opts->nenv; i++) {
1035 			debug("%s: environment: %s", loc, opts->env[i]);
1036 			if (do_remote) {
1037 				auth_debug_add("%s: environment: %s",
1038 				    loc, opts->env[i]);
1039 			}
1040 		}
1041 	}
1042 
1043 	/* Go into a little more details for the local logs. */
1044 	if (opts->valid_before != 0) {
1045 		format_absolute_time(opts->valid_before, buf, sizeof(buf));
1046 		debug("%s: expires at %s", loc, buf);
1047 	}
1048 	if (opts->cert_principals != NULL) {
1049 		debug("%s: authorized principals: \"%s\"",
1050 		    loc, opts->cert_principals);
1051 	}
1052 	if (opts->force_command != NULL)
1053 		debug("%s: forced command: \"%s\"", loc, opts->force_command);
1054 	if (do_permitopen) {
1055 		for (i = 0; i < opts->npermitopen; i++) {
1056 			debug("%s: permitted open: %s",
1057 			    loc, opts->permitopen[i]);
1058 		}
1059 	}
1060 	if (do_permitlisten) {
1061 		for (i = 0; i < opts->npermitlisten; i++) {
1062 			debug("%s: permitted listen: %s",
1063 			    loc, opts->permitlisten[i]);
1064 		}
1065 	}
1066 }
1067 
1068 /* Activate a new set of key/cert options; merging with what is there. */
1069 int
1070 auth_activate_options(struct ssh *ssh, struct sshauthopt *opts)
1071 {
1072 	struct sshauthopt *old = auth_opts;
1073 	const char *emsg = NULL;
1074 
1075 	debug_f("setting new authentication options");
1076 	if ((auth_opts = sshauthopt_merge(old, opts, &emsg)) == NULL) {
1077 		error("Inconsistent authentication options: %s", emsg);
1078 		return -1;
1079 	}
1080 	return 0;
1081 }
1082 
1083 /* Disable forwarding, etc for the session */
1084 void
1085 auth_restrict_session(struct ssh *ssh)
1086 {
1087 	struct sshauthopt *restricted;
1088 
1089 	debug_f("restricting session");
1090 
1091 	/* A blank sshauthopt defaults to permitting nothing */
1092 	restricted = sshauthopt_new();
1093 	restricted->permit_pty_flag = 1;
1094 	restricted->restricted = 1;
1095 
1096 	if (auth_activate_options(ssh, restricted) != 0)
1097 		fatal_f("failed to restrict session");
1098 	sshauthopt_free(restricted);
1099 }
1100 
1101 int
1102 auth_authorise_keyopts(struct ssh *ssh, struct passwd *pw,
1103     struct sshauthopt *opts, int allow_cert_authority, const char *loc)
1104 {
1105 	const char *remote_ip = ssh_remote_ipaddr(ssh);
1106 	const char *remote_host = auth_get_canonical_hostname(ssh,
1107 	    options.use_dns);
1108 	time_t now = time(NULL);
1109 	char buf[64];
1110 
1111 	/*
1112 	 * Check keys/principals file expiry time.
1113 	 * NB. validity interval in certificate is handled elsewhere.
1114 	 */
1115 	if (opts->valid_before && now > 0 &&
1116 	    opts->valid_before < (uint64_t)now) {
1117 		format_absolute_time(opts->valid_before, buf, sizeof(buf));
1118 		debug("%s: entry expired at %s", loc, buf);
1119 		auth_debug_add("%s: entry expired at %s", loc, buf);
1120 		return -1;
1121 	}
1122 	/* Consistency checks */
1123 	if (opts->cert_principals != NULL && !opts->cert_authority) {
1124 		debug("%s: principals on non-CA key", loc);
1125 		auth_debug_add("%s: principals on non-CA key", loc);
1126 		/* deny access */
1127 		return -1;
1128 	}
1129 	/* cert-authority flag isn't valid in authorized_principals files */
1130 	if (!allow_cert_authority && opts->cert_authority) {
1131 		debug("%s: cert-authority flag invalid here", loc);
1132 		auth_debug_add("%s: cert-authority flag invalid here", loc);
1133 		/* deny access */
1134 		return -1;
1135 	}
1136 
1137 	/* Perform from= checks */
1138 	if (opts->required_from_host_keys != NULL) {
1139 		switch (match_host_and_ip(remote_host, remote_ip,
1140 		    opts->required_from_host_keys )) {
1141 		case 1:
1142 			/* Host name matches. */
1143 			break;
1144 		case -1:
1145 		default:
1146 			debug("%s: invalid from criteria", loc);
1147 			auth_debug_add("%s: invalid from criteria", loc);
1148 			/* FALLTHROUGH */
1149 		case 0:
1150 			logit("%s: Authentication tried for %.100s with "
1151 			    "correct key but not from a permitted "
1152 			    "host (host=%.200s, ip=%.200s, required=%.200s).",
1153 			    loc, pw->pw_name, remote_host, remote_ip,
1154 			    opts->required_from_host_keys);
1155 			auth_debug_add("%s: Your host '%.200s' is not "
1156 			    "permitted to use this key for login.",
1157 			    loc, remote_host);
1158 			/* deny access */
1159 			return -1;
1160 		}
1161 	}
1162 	/* Check source-address restriction from certificate */
1163 	if (opts->required_from_host_cert != NULL) {
1164 		switch (addr_match_cidr_list(remote_ip,
1165 		    opts->required_from_host_cert)) {
1166 		case 1:
1167 			/* accepted */
1168 			break;
1169 		case -1:
1170 		default:
1171 			/* invalid */
1172 			error("%s: Certificate source-address invalid", loc);
1173 			/* FALLTHROUGH */
1174 		case 0:
1175 			logit("%s: Authentication tried for %.100s with valid "
1176 			    "certificate but not from a permitted source "
1177 			    "address (%.200s).", loc, pw->pw_name, remote_ip);
1178 			auth_debug_add("%s: Your address '%.200s' is not "
1179 			    "permitted to use this certificate for login.",
1180 			    loc, remote_ip);
1181 			return -1;
1182 		}
1183 	}
1184 	/*
1185 	 *
1186 	 * XXX this is spammy. We should report remotely only for keys
1187 	 *     that are successful in actual auth attempts, and not PK_OK
1188 	 *     tests.
1189 	 */
1190 	auth_log_authopts(loc, opts, 1);
1191 
1192 	return 0;
1193 }
1194