auth2-pubkey.c revision 296781 
1/* $OpenBSD: auth2-pubkey.c,v 1.55 2016/01/27 00:53:12 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/wait.h>
31
32#include <errno.h>
33#include <fcntl.h>
34#ifdef HAVE_PATHS_H
35# include <paths.h>
36#endif
37#include <pwd.h>
38#include <signal.h>
39#include <stdio.h>
40#include <stdarg.h>
41#include <string.h>
42#include <time.h>
43#include <unistd.h>
44#include <limits.h>
45
46#include "xmalloc.h"
47#include "ssh.h"
48#include "ssh2.h"
49#include "packet.h"
50#include "buffer.h"
51#include "log.h"
52#include "misc.h"
53#include "servconf.h"
54#include "compat.h"
55#include "key.h"
56#include "hostfile.h"
57#include "auth.h"
58#include "pathnames.h"
59#include "uidswap.h"
60#include "auth-options.h"
61#include "canohost.h"
62#ifdef GSSAPI
63#include "ssh-gss.h"
64#endif
65#include "monitor_wrap.h"
66#include "authfile.h"
67#include "match.h"
68#include "ssherr.h"
69#include "channels.h" /* XXX for session.h */
70#include "session.h" /* XXX for child_set_env(); refactor? */
71
72/* import */
73extern ServerOptions options;
74extern u_char *session_id2;
75extern u_int session_id2_len;
76
77static int
78userauth_pubkey(Authctxt *authctxt)
79{
80	Buffer b;
81	Key *key = NULL;
82	char *pkalg, *userstyle, *fp = NULL;
83	u_char *pkblob, *sig;
84	u_int alen, blen, slen;
85	int have_sig, pktype;
86	int authenticated = 0;
87
88	if (!authctxt->valid) {
89		debug2("%s: disabled because of invalid user", __func__);
90		return 0;
91	}
92	have_sig = packet_get_char();
93	if (datafellows & SSH_BUG_PKAUTH) {
94		debug2("%s: SSH_BUG_PKAUTH", __func__);
95		/* no explicit pkalg given */
96		pkblob = packet_get_string(&blen);
97		buffer_init(&b);
98		buffer_append(&b, pkblob, blen);
99		/* so we have to extract the pkalg from the pkblob */
100		pkalg = buffer_get_string(&b, &alen);
101		buffer_free(&b);
102	} else {
103		pkalg = packet_get_string(&alen);
104		pkblob = packet_get_string(&blen);
105	}
106	pktype = key_type_from_name(pkalg);
107	if (pktype == KEY_UNSPEC) {
108		/* this is perfectly legal */
109		logit("%s: unsupported public key algorithm: %s",
110		    __func__, pkalg);
111		goto done;
112	}
113	key = key_from_blob(pkblob, blen);
114	if (key == NULL) {
115		error("%s: cannot decode key: %s", __func__, pkalg);
116		goto done;
117	}
118	if (key->type != pktype) {
119		error("%s: type mismatch for decoded key "
120		    "(received %d, expected %d)", __func__, key->type, pktype);
121		goto done;
122	}
123	if (key_type_plain(key->type) == KEY_RSA &&
124	    (datafellows & SSH_BUG_RSASIGMD5) != 0) {
125		logit("Refusing RSA key because client uses unsafe "
126		    "signature scheme");
127		goto done;
128	}
129	fp = sshkey_fingerprint(key, options.fingerprint_hash, SSH_FP_DEFAULT);
130	if (auth2_userkey_already_used(authctxt, key)) {
131		logit("refusing previously-used %s key", key_type(key));
132		goto done;
133	}
134	if (match_pattern_list(sshkey_ssh_name(key),
135	    options.pubkey_key_types, 0) != 1) {
136		logit("%s: key type %s not in PubkeyAcceptedKeyTypes",
137		    __func__, sshkey_ssh_name(key));
138		goto done;
139	}
140
141	if (have_sig) {
142		debug3("%s: have signature for %s %s",
143		    __func__, sshkey_type(key), fp);
144		sig = packet_get_string(&slen);
145		packet_check_eom();
146		buffer_init(&b);
147		if (datafellows & SSH_OLD_SESSIONID) {
148			buffer_append(&b, session_id2, session_id2_len);
149		} else {
150			buffer_put_string(&b, session_id2, session_id2_len);
151		}
152		/* reconstruct packet */
153		buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
154		xasprintf(&userstyle, "%s%s%s", authctxt->user,
155		    authctxt->style ? ":" : "",
156		    authctxt->style ? authctxt->style : "");
157		buffer_put_cstring(&b, userstyle);
158		free(userstyle);
159		buffer_put_cstring(&b,
160		    datafellows & SSH_BUG_PKSERVICE ?
161		    "ssh-userauth" :
162		    authctxt->service);
163		if (datafellows & SSH_BUG_PKAUTH) {
164			buffer_put_char(&b, have_sig);
165		} else {
166			buffer_put_cstring(&b, "publickey");
167			buffer_put_char(&b, have_sig);
168			buffer_put_cstring(&b, pkalg);
169		}
170		buffer_put_string(&b, pkblob, blen);
171#ifdef DEBUG_PK
172		buffer_dump(&b);
173#endif
174		pubkey_auth_info(authctxt, key, NULL);
175
176		/* test for correct signature */
177		authenticated = 0;
178		if (PRIVSEP(user_key_allowed(authctxt->pw, key, 1)) &&
179		    PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
180		    buffer_len(&b))) == 1) {
181			authenticated = 1;
182			/* Record the successful key to prevent reuse */
183			auth2_record_userkey(authctxt, key);
184			key = NULL; /* Don't free below */
185		}
186		buffer_free(&b);
187		free(sig);
188	} else {
189		debug("%s: test whether pkalg/pkblob are acceptable for %s %s",
190		    __func__, sshkey_type(key), fp);
191		packet_check_eom();
192
193		/* XXX fake reply and always send PK_OK ? */
194		/*
195		 * XXX this allows testing whether a user is allowed
196		 * to login: if you happen to have a valid pubkey this
197		 * message is sent. the message is NEVER sent at all
198		 * if a user is not allowed to login. is this an
199		 * issue? -markus
200		 */
201		if (PRIVSEP(user_key_allowed(authctxt->pw, key, 0))) {
202			packet_start(SSH2_MSG_USERAUTH_PK_OK);
203			packet_put_string(pkalg, alen);
204			packet_put_string(pkblob, blen);
205			packet_send();
206			packet_write_wait();
207			authctxt->postponed = 1;
208		}
209	}
210	if (authenticated != 1)
211		auth_clear_options();
212done:
213	debug2("%s: authenticated %d pkalg %s", __func__, authenticated, pkalg);
214	if (key != NULL)
215		key_free(key);
216	free(pkalg);
217	free(pkblob);
218	free(fp);
219	return authenticated;
220}
221
222void
223pubkey_auth_info(Authctxt *authctxt, const Key *key, const char *fmt, ...)
224{
225	char *fp, *extra;
226	va_list ap;
227	int i;
228
229	extra = NULL;
230	if (fmt != NULL) {
231		va_start(ap, fmt);
232		i = vasprintf(&extra, fmt, ap);
233		va_end(ap);
234		if (i < 0 || extra == NULL)
235			fatal("%s: vasprintf failed", __func__);
236	}
237
238	if (key_is_cert(key)) {
239		fp = sshkey_fingerprint(key->cert->signature_key,
240		    options.fingerprint_hash, SSH_FP_DEFAULT);
241		auth_info(authctxt, "%s ID %s (serial %llu) CA %s %s%s%s",
242		    key_type(key), key->cert->key_id,
243		    (unsigned long long)key->cert->serial,
244		    key_type(key->cert->signature_key),
245		    fp == NULL ? "(null)" : fp,
246		    extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
247		free(fp);
248	} else {
249		fp = sshkey_fingerprint(key, options.fingerprint_hash,
250		    SSH_FP_DEFAULT);
251		auth_info(authctxt, "%s %s%s%s", key_type(key),
252		    fp == NULL ? "(null)" : fp,
253		    extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
254		free(fp);
255	}
256	free(extra);
257}
258
259/*
260 * Splits 's' into an argument vector. Handles quoted string and basic
261 * escape characters (\\, \", \'). Caller must free the argument vector
262 * and its members.
263 */
264static int
265split_argv(const char *s, int *argcp, char ***argvp)
266{
267	int r = SSH_ERR_INTERNAL_ERROR;
268	int argc = 0, quote, i, j;
269	char *arg, **argv = xcalloc(1, sizeof(*argv));
270
271	*argvp = NULL;
272	*argcp = 0;
273
274	for (i = 0; s[i] != '\0'; i++) {
275		/* Skip leading whitespace */
276		if (s[i] == ' ' || s[i] == '\t')
277			continue;
278
279		/* Start of a token */
280		quote = 0;
281		if (s[i] == '\\' &&
282		    (s[i + 1] == '\'' || s[i + 1] == '\"' || s[i + 1] == '\\'))
283			i++;
284		else if (s[i] == '\'' || s[i] == '"')
285			quote = s[i++];
286
287		argv = xreallocarray(argv, (argc + 2), sizeof(*argv));
288		arg = argv[argc++] = xcalloc(1, strlen(s + i) + 1);
289		argv[argc] = NULL;
290
291		/* Copy the token in, removing escapes */
292		for (j = 0; s[i] != '\0'; i++) {
293			if (s[i] == '\\') {
294				if (s[i + 1] == '\'' ||
295				    s[i + 1] == '\"' ||
296				    s[i + 1] == '\\') {
297					i++; /* Skip '\' */
298					arg[j++] = s[i];
299				} else {
300					/* Unrecognised escape */
301					arg[j++] = s[i];
302				}
303			} else if (quote == 0 && (s[i] == ' ' || s[i] == '\t'))
304				break; /* done */
305			else if (quote != 0 && s[i] == quote)
306				break; /* done */
307			else
308				arg[j++] = s[i];
309		}
310		if (s[i] == '\0') {
311			if (quote != 0) {
312				/* Ran out of string looking for close quote */
313				r = SSH_ERR_INVALID_FORMAT;
314				goto out;
315			}
316			break;
317		}
318	}
319	/* Success */
320	*argcp = argc;
321	*argvp = argv;
322	argc = 0;
323	argv = NULL;
324	r = 0;
325 out:
326	if (argc != 0 && argv != NULL) {
327		for (i = 0; i < argc; i++)
328			free(argv[i]);
329		free(argv);
330	}
331	return r;
332}
333
334/*
335 * Reassemble an argument vector into a string, quoting and escaping as
336 * necessary. Caller must free returned string.
337 */
338static char *
339assemble_argv(int argc, char **argv)
340{
341	int i, j, ws, r;
342	char c, *ret;
343	struct sshbuf *buf, *arg;
344
345	if ((buf = sshbuf_new()) == NULL || (arg = sshbuf_new()) == NULL)
346		fatal("%s: sshbuf_new failed", __func__);
347
348	for (i = 0; i < argc; i++) {
349		ws = 0;
350		sshbuf_reset(arg);
351		for (j = 0; argv[i][j] != '\0'; j++) {
352			r = 0;
353			c = argv[i][j];
354			switch (c) {
355			case ' ':
356			case '\t':
357				ws = 1;
358				r = sshbuf_put_u8(arg, c);
359				break;
360			case '\\':
361			case '\'':
362			case '"':
363				if ((r = sshbuf_put_u8(arg, '\\')) != 0)
364					break;
365				/* FALLTHROUGH */
366			default:
367				r = sshbuf_put_u8(arg, c);
368				break;
369			}
370			if (r != 0)
371				fatal("%s: sshbuf_put_u8: %s",
372				    __func__, ssh_err(r));
373		}
374		if ((i != 0 && (r = sshbuf_put_u8(buf, ' ')) != 0) ||
375		    (ws != 0 && (r = sshbuf_put_u8(buf, '"')) != 0) ||
376		    (r = sshbuf_putb(buf, arg)) != 0 ||
377		    (ws != 0 && (r = sshbuf_put_u8(buf, '"')) != 0))
378			fatal("%s: buffer error: %s", __func__, ssh_err(r));
379	}
380	if ((ret = malloc(sshbuf_len(buf) + 1)) == NULL)
381		fatal("%s: malloc failed", __func__);
382	memcpy(ret, sshbuf_ptr(buf), sshbuf_len(buf));
383	ret[sshbuf_len(buf)] = '\0';
384	sshbuf_free(buf);
385	sshbuf_free(arg);
386	return ret;
387}
388
389/*
390 * Runs command in a subprocess. Returns pid on success and a FILE* to the
391 * subprocess' stdout or 0 on failure.
392 * NB. "command" is only used for logging.
393 */
394static pid_t
395subprocess(const char *tag, struct passwd *pw, const char *command,
396    int ac, char **av, FILE **child)
397{
398	FILE *f;
399	struct stat st;
400	int devnull, p[2], i;
401	pid_t pid;
402	char *cp, errmsg[512];
403	u_int envsize;
404	char **child_env;
405
406	*child = NULL;
407
408	debug3("%s: %s command \"%s\" running as %s", __func__,
409	    tag, command, pw->pw_name);
410
411	/* Verify the path exists and is safe-ish to execute */
412	if (*av[0] != '/') {
413		error("%s path is not absolute", tag);
414		return 0;
415	}
416	temporarily_use_uid(pw);
417	if (stat(av[0], &st) < 0) {
418		error("Could not stat %s \"%s\": %s", tag,
419		    av[0], strerror(errno));
420		restore_uid();
421		return 0;
422	}
423	if (auth_secure_path(av[0], &st, NULL, 0,
424	    errmsg, sizeof(errmsg)) != 0) {
425		error("Unsafe %s \"%s\": %s", tag, av[0], errmsg);
426		restore_uid();
427		return 0;
428	}
429
430	/*
431	 * Run the command; stderr is left in place, stdout is the
432	 * authorized_keys output.
433	 */
434	if (pipe(p) != 0) {
435		error("%s: pipe: %s", tag, strerror(errno));
436		restore_uid();
437		return 0;
438	}
439
440	/*
441	 * Don't want to call this in the child, where it can fatal() and
442	 * run cleanup_exit() code.
443	 */
444	restore_uid();
445
446	switch ((pid = fork())) {
447	case -1: /* error */
448		error("%s: fork: %s", tag, strerror(errno));
449		close(p[0]);
450		close(p[1]);
451		return 0;
452	case 0: /* child */
453		/* Prepare a minimal environment for the child. */
454		envsize = 5;
455		child_env = xcalloc(sizeof(*child_env), envsize);
456		child_set_env(&child_env, &envsize, "PATH", _PATH_STDPATH);
457		child_set_env(&child_env, &envsize, "USER", pw->pw_name);
458		child_set_env(&child_env, &envsize, "LOGNAME", pw->pw_name);
459		child_set_env(&child_env, &envsize, "HOME", pw->pw_dir);
460		if ((cp = getenv("LANG")) != NULL)
461			child_set_env(&child_env, &envsize, "LANG", cp);
462
463		for (i = 0; i < NSIG; i++)
464			signal(i, SIG_DFL);
465
466		if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
467			error("%s: open %s: %s", tag, _PATH_DEVNULL,
468			    strerror(errno));
469			_exit(1);
470		}
471		/* Keep stderr around a while longer to catch errors */
472		if (dup2(devnull, STDIN_FILENO) == -1 ||
473		    dup2(p[1], STDOUT_FILENO) == -1) {
474			error("%s: dup2: %s", tag, strerror(errno));
475			_exit(1);
476		}
477		closefrom(STDERR_FILENO + 1);
478
479		/* Don't use permanently_set_uid() here to avoid fatal() */
480		if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) {
481			error("%s: setresgid %u: %s", tag, (u_int)pw->pw_gid,
482			    strerror(errno));
483			_exit(1);
484		}
485		if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) {
486			error("%s: setresuid %u: %s", tag, (u_int)pw->pw_uid,
487			    strerror(errno));
488			_exit(1);
489		}
490		/* stdin is pointed to /dev/null at this point */
491		if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
492			error("%s: dup2: %s", tag, strerror(errno));
493			_exit(1);
494		}
495
496		execve(av[0], av, child_env);
497		error("%s exec \"%s\": %s", tag, command, strerror(errno));
498		_exit(127);
499	default: /* parent */
500		break;
501	}
502
503	close(p[1]);
504	if ((f = fdopen(p[0], "r")) == NULL) {
505		error("%s: fdopen: %s", tag, strerror(errno));
506		close(p[0]);
507		/* Don't leave zombie child */
508		kill(pid, SIGTERM);
509		while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
510			;
511		return 0;
512	}
513	/* Success */
514	debug3("%s: %s pid %ld", __func__, tag, (long)pid);
515	*child = f;
516	return pid;
517}
518
519/* Returns 0 if pid exited cleanly, non-zero otherwise */
520static int
521exited_cleanly(pid_t pid, const char *tag, const char *cmd)
522{
523	int status;
524
525	while (waitpid(pid, &status, 0) == -1) {
526		if (errno != EINTR) {
527			error("%s: waitpid: %s", tag, strerror(errno));
528			return -1;
529		}
530	}
531	if (WIFSIGNALED(status)) {
532		error("%s %s exited on signal %d", tag, cmd, WTERMSIG(status));
533		return -1;
534	} else if (WEXITSTATUS(status) != 0) {
535		error("%s %s failed, status %d", tag, cmd, WEXITSTATUS(status));
536		return -1;
537	}
538	return 0;
539}
540
541static int
542match_principals_option(const char *principal_list, struct sshkey_cert *cert)
543{
544	char *result;
545	u_int i;
546
547	/* XXX percent_expand() sequences for authorized_principals? */
548
549	for (i = 0; i < cert->nprincipals; i++) {
550		if ((result = match_list(cert->principals[i],
551		    principal_list, NULL)) != NULL) {
552			debug3("matched principal from key options \"%.100s\"",
553			    result);
554			free(result);
555			return 1;
556		}
557	}
558	return 0;
559}
560
561static int
562process_principals(FILE *f, char *file, struct passwd *pw,
563    struct sshkey_cert *cert)
564{
565	char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts;
566	u_long linenum = 0;
567	u_int i;
568
569	while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
570		/* Skip leading whitespace. */
571		for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
572			;
573		/* Skip blank and comment lines. */
574		if ((ep = strchr(cp, '#')) != NULL)
575			*ep = '\0';
576		if (!*cp || *cp == '\n')
577			continue;
578		/* Trim trailing whitespace. */
579		ep = cp + strlen(cp) - 1;
580		while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t'))
581			*ep-- = '\0';
582		/*
583		 * If the line has internal whitespace then assume it has
584		 * key options.
585		 */
586		line_opts = NULL;
587		if ((ep = strrchr(cp, ' ')) != NULL ||
588		    (ep = strrchr(cp, '\t')) != NULL) {
589			for (; *ep == ' ' || *ep == '\t'; ep++)
590				;
591			line_opts = cp;
592			cp = ep;
593		}
594		for (i = 0; i < cert->nprincipals; i++) {
595			if (strcmp(cp, cert->principals[i]) == 0) {
596				debug3("%s:%lu: matched principal \"%.100s\"",
597				    file == NULL ? "(command)" : file,
598				    linenum, cert->principals[i]);
599				if (auth_parse_options(pw, line_opts,
600				    file, linenum) != 1)
601					continue;
602				return 1;
603			}
604		}
605	}
606	return 0;
607}
608
609static int
610match_principals_file(char *file, struct passwd *pw, struct sshkey_cert *cert)
611{
612	FILE *f;
613	int success;
614
615	temporarily_use_uid(pw);
616	debug("trying authorized principals file %s", file);
617	if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
618		restore_uid();
619		return 0;
620	}
621	success = process_principals(f, file, pw, cert);
622	fclose(f);
623	restore_uid();
624	return success;
625}
626
627/*
628 * Checks whether principal is allowed in output of command.
629 * returns 1 if the principal is allowed or 0 otherwise.
630 */
631static int
632match_principals_command(struct passwd *user_pw, struct sshkey_cert *cert)
633{
634	FILE *f = NULL;
635	int ok, found_principal = 0;
636	struct passwd *pw;
637	int i, ac = 0, uid_swapped = 0;
638	pid_t pid;
639	char *tmp, *username = NULL, *command = NULL, **av = NULL;
640	void (*osigchld)(int);
641
642	if (options.authorized_principals_command == NULL)
643		return 0;
644	if (options.authorized_principals_command_user == NULL) {
645		error("No user for AuthorizedPrincipalsCommand specified, "
646		    "skipping");
647		return 0;
648	}
649
650	/*
651	 * NB. all returns later this function should go via "out" to
652	 * ensure the original SIGCHLD handler is restored properly.
653	 */
654	osigchld = signal(SIGCHLD, SIG_DFL);
655
656	/* Prepare and verify the user for the command */
657	username = percent_expand(options.authorized_principals_command_user,
658	    "u", user_pw->pw_name, (char *)NULL);
659	pw = getpwnam(username);
660	if (pw == NULL) {
661		error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s",
662		    username, strerror(errno));
663		goto out;
664	}
665
666	/* Turn the command into an argument vector */
667	if (split_argv(options.authorized_principals_command, &ac, &av) != 0) {
668		error("AuthorizedPrincipalsCommand \"%s\" contains "
669		    "invalid quotes", command);
670		goto out;
671	}
672	if (ac == 0) {
673		error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments",
674		    command);
675		goto out;
676	}
677	for (i = 1; i < ac; i++) {
678		tmp = percent_expand(av[i],
679		    "u", user_pw->pw_name,
680		    "h", user_pw->pw_dir,
681		    (char *)NULL);
682		if (tmp == NULL)
683			fatal("%s: percent_expand failed", __func__);
684		free(av[i]);
685		av[i] = tmp;
686	}
687	/* Prepare a printable command for logs, etc. */
688	command = assemble_argv(ac, av);
689
690	if ((pid = subprocess("AuthorizedPrincipalsCommand", pw, command,
691	    ac, av, &f)) == 0)
692		goto out;
693
694	uid_swapped = 1;
695	temporarily_use_uid(pw);
696
697	ok = process_principals(f, NULL, pw, cert);
698
699	if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command) != 0)
700		goto out;
701
702	/* Read completed successfully */
703	found_principal = ok;
704 out:
705	if (f != NULL)
706		fclose(f);
707	signal(SIGCHLD, osigchld);
708	for (i = 0; i < ac; i++)
709		free(av[i]);
710	free(av);
711	if (uid_swapped)
712		restore_uid();
713	free(command);
714	free(username);
715	return found_principal;
716}
717/*
718 * Checks whether key is allowed in authorized_keys-format file,
719 * returns 1 if the key is allowed or 0 otherwise.
720 */
721static int
722check_authkeys_file(FILE *f, char *file, Key* key, struct passwd *pw)
723{
724	char line[SSH_MAX_PUBKEY_BYTES];
725	const char *reason;
726	int found_key = 0;
727	u_long linenum = 0;
728	Key *found;
729	char *fp;
730
731	found_key = 0;
732
733	found = NULL;
734	while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
735		char *cp, *key_options = NULL;
736		if (found != NULL)
737			key_free(found);
738		found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
739		auth_clear_options();
740
741		/* Skip leading whitespace, empty and comment lines. */
742		for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
743			;
744		if (!*cp || *cp == '\n' || *cp == '#')
745			continue;
746
747		if (key_read(found, &cp) != 1) {
748			/* no key?  check if there are options for this key */
749			int quoted = 0;
750			debug2("user_key_allowed: check options: '%s'", cp);
751			key_options = cp;
752			for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
753				if (*cp == '\\' && cp[1] == '"')
754					cp++;	/* Skip both */
755				else if (*cp == '"')
756					quoted = !quoted;
757			}
758			/* Skip remaining whitespace. */
759			for (; *cp == ' ' || *cp == '\t'; cp++)
760				;
761			if (key_read(found, &cp) != 1) {
762				debug2("user_key_allowed: advance: '%s'", cp);
763				/* still no key?  advance to next line*/
764				continue;
765			}
766		}
767		if (key_is_cert(key)) {
768			if (!key_equal(found, key->cert->signature_key))
769				continue;
770			if (auth_parse_options(pw, key_options, file,
771			    linenum) != 1)
772				continue;
773			if (!key_is_cert_authority)
774				continue;
775			if ((fp = sshkey_fingerprint(found,
776			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
777				continue;
778			debug("matching CA found: file %s, line %lu, %s %s",
779			    file, linenum, key_type(found), fp);
780			/*
781			 * If the user has specified a list of principals as
782			 * a key option, then prefer that list to matching
783			 * their username in the certificate principals list.
784			 */
785			if (authorized_principals != NULL &&
786			    !match_principals_option(authorized_principals,
787			    key->cert)) {
788				reason = "Certificate does not contain an "
789				    "authorized principal";
790 fail_reason:
791				free(fp);
792				error("%s", reason);
793				auth_debug_add("%s", reason);
794				continue;
795			}
796			if (key_cert_check_authority(key, 0, 0,
797			    authorized_principals == NULL ? pw->pw_name : NULL,
798			    &reason) != 0)
799				goto fail_reason;
800			if (auth_cert_options(key, pw) != 0) {
801				free(fp);
802				continue;
803			}
804			verbose("Accepted certificate ID \"%s\" (serial %llu) "
805			    "signed by %s CA %s via %s", key->cert->key_id,
806			    (unsigned long long)key->cert->serial,
807			    key_type(found), fp, file);
808			free(fp);
809			found_key = 1;
810			break;
811		} else if (key_equal(found, key)) {
812			if (auth_parse_options(pw, key_options, file,
813			    linenum) != 1)
814				continue;
815			if (key_is_cert_authority)
816				continue;
817			if ((fp = sshkey_fingerprint(found,
818			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
819				continue;
820			debug("matching key found: file %s, line %lu %s %s",
821			    file, linenum, key_type(found), fp);
822			free(fp);
823			found_key = 1;
824			break;
825		}
826	}
827	if (found != NULL)
828		key_free(found);
829	if (!found_key)
830		debug2("key not found");
831	return found_key;
832}
833
834/* Authenticate a certificate key against TrustedUserCAKeys */
835static int
836user_cert_trusted_ca(struct passwd *pw, Key *key)
837{
838	char *ca_fp, *principals_file = NULL;
839	const char *reason;
840	int ret = 0, found_principal = 0, use_authorized_principals;
841
842	if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL)
843		return 0;
844
845	if ((ca_fp = sshkey_fingerprint(key->cert->signature_key,
846	    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
847		return 0;
848
849	if (sshkey_in_file(key->cert->signature_key,
850	    options.trusted_user_ca_keys, 1, 0) != 0) {
851		debug2("%s: CA %s %s is not listed in %s", __func__,
852		    key_type(key->cert->signature_key), ca_fp,
853		    options.trusted_user_ca_keys);
854		goto out;
855	}
856	/*
857	 * If AuthorizedPrincipals is in use, then compare the certificate
858	 * principals against the names in that file rather than matching
859	 * against the username.
860	 */
861	if ((principals_file = authorized_principals_file(pw)) != NULL) {
862		if (match_principals_file(principals_file, pw, key->cert))
863			found_principal = 1;
864	}
865	/* Try querying command if specified */
866	if (!found_principal && match_principals_command(pw, key->cert))
867		found_principal = 1;
868	/* If principals file or command is specified, then require a match */
869	use_authorized_principals = principals_file != NULL ||
870            options.authorized_principals_command != NULL;
871	if (!found_principal && use_authorized_principals) {
872		reason = "Certificate does not contain an authorized principal";
873 fail_reason:
874		error("%s", reason);
875		auth_debug_add("%s", reason);
876		goto out;
877	}
878	if (key_cert_check_authority(key, 0, 1,
879	    use_authorized_principals ? NULL : pw->pw_name, &reason) != 0)
880		goto fail_reason;
881	if (auth_cert_options(key, pw) != 0)
882		goto out;
883
884	verbose("Accepted certificate ID \"%s\" (serial %llu) signed by "
885	    "%s CA %s via %s", key->cert->key_id,
886	    (unsigned long long)key->cert->serial,
887	    key_type(key->cert->signature_key), ca_fp,
888	    options.trusted_user_ca_keys);
889	ret = 1;
890
891 out:
892	free(principals_file);
893	free(ca_fp);
894	return ret;
895}
896
897/*
898 * Checks whether key is allowed in file.
899 * returns 1 if the key is allowed or 0 otherwise.
900 */
901static int
902user_key_allowed2(struct passwd *pw, Key *key, char *file)
903{
904	FILE *f;
905	int found_key = 0;
906
907	/* Temporarily use the user's uid. */
908	temporarily_use_uid(pw);
909
910	debug("trying public key file %s", file);
911	if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) {
912		found_key = check_authkeys_file(f, file, key, pw);
913		fclose(f);
914	}
915
916	restore_uid();
917	return found_key;
918}
919
920/*
921 * Checks whether key is allowed in output of command.
922 * returns 1 if the key is allowed or 0 otherwise.
923 */
924static int
925user_key_command_allowed2(struct passwd *user_pw, Key *key)
926{
927	FILE *f = NULL;
928	int r, ok, found_key = 0;
929	struct passwd *pw;
930	int i, uid_swapped = 0, ac = 0;
931	pid_t pid;
932	char *username = NULL, *key_fp = NULL, *keytext = NULL;
933	char *tmp, *command = NULL, **av = NULL;
934	void (*osigchld)(int);
935
936	if (options.authorized_keys_command == NULL)
937		return 0;
938	if (options.authorized_keys_command_user == NULL) {
939		error("No user for AuthorizedKeysCommand specified, skipping");
940		return 0;
941	}
942
943	/*
944	 * NB. all returns later this function should go via "out" to
945	 * ensure the original SIGCHLD handler is restored properly.
946	 */
947	osigchld = signal(SIGCHLD, SIG_DFL);
948
949	/* Prepare and verify the user for the command */
950	username = percent_expand(options.authorized_keys_command_user,
951	    "u", user_pw->pw_name, (char *)NULL);
952	pw = getpwnam(username);
953	if (pw == NULL) {
954		error("AuthorizedKeysCommandUser \"%s\" not found: %s",
955		    username, strerror(errno));
956		goto out;
957	}
958
959	/* Prepare AuthorizedKeysCommand */
960	if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash,
961	    SSH_FP_DEFAULT)) == NULL) {
962		error("%s: sshkey_fingerprint failed", __func__);
963		goto out;
964	}
965	if ((r = sshkey_to_base64(key, &keytext)) != 0) {
966		error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r));
967		goto out;
968	}
969
970	/* Turn the command into an argument vector */
971	if (split_argv(options.authorized_keys_command, &ac, &av) != 0) {
972		error("AuthorizedKeysCommand \"%s\" contains invalid quotes",
973		    command);
974		goto out;
975	}
976	if (ac == 0) {
977		error("AuthorizedKeysCommand \"%s\" yielded no arguments",
978		    command);
979		goto out;
980	}
981	for (i = 1; i < ac; i++) {
982		tmp = percent_expand(av[i],
983		    "u", user_pw->pw_name,
984		    "h", user_pw->pw_dir,
985		    "t", sshkey_ssh_name(key),
986		    "f", key_fp,
987		    "k", keytext,
988		    (char *)NULL);
989		if (tmp == NULL)
990			fatal("%s: percent_expand failed", __func__);
991		free(av[i]);
992		av[i] = tmp;
993	}
994	/* Prepare a printable command for logs, etc. */
995	command = assemble_argv(ac, av);
996
997	/*
998	 * If AuthorizedKeysCommand was run without arguments
999	 * then fall back to the old behaviour of passing the
1000	 * target username as a single argument.
1001	 */
1002	if (ac == 1) {
1003		av = xreallocarray(av, ac + 2, sizeof(*av));
1004		av[1] = xstrdup(user_pw->pw_name);
1005		av[2] = NULL;
1006		/* Fix up command too, since it is used in log messages */
1007		free(command);
1008		xasprintf(&command, "%s %s", av[0], av[1]);
1009	}
1010
1011	if ((pid = subprocess("AuthorizedKeysCommand", pw, command,
1012	    ac, av, &f)) == 0)
1013		goto out;
1014
1015	uid_swapped = 1;
1016	temporarily_use_uid(pw);
1017
1018	ok = check_authkeys_file(f, options.authorized_keys_command, key, pw);
1019
1020	if (exited_cleanly(pid, "AuthorizedKeysCommand", command) != 0)
1021		goto out;
1022
1023	/* Read completed successfully */
1024	found_key = ok;
1025 out:
1026	if (f != NULL)
1027		fclose(f);
1028	signal(SIGCHLD, osigchld);
1029	for (i = 0; i < ac; i++)
1030		free(av[i]);
1031	free(av);
1032	if (uid_swapped)
1033		restore_uid();
1034	free(command);
1035	free(username);
1036	free(key_fp);
1037	free(keytext);
1038	return found_key;
1039}
1040
1041/*
1042 * Check whether key authenticates and authorises the user.
1043 */
1044int
1045user_key_allowed(struct passwd *pw, Key *key, int auth_attempt)
1046{
1047	u_int success, i;
1048	char *file;
1049
1050	if (auth_key_is_revoked(key))
1051		return 0;
1052	if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))
1053		return 0;
1054
1055	success = user_cert_trusted_ca(pw, key);
1056	if (success)
1057		return success;
1058
1059	success = user_key_command_allowed2(pw, key);
1060	if (success > 0)
1061		return success;
1062
1063	for (i = 0; !success && i < options.num_authkeys_files; i++) {
1064
1065		if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
1066			continue;
1067		file = expand_authorized_keys(
1068		    options.authorized_keys_files[i], pw);
1069
1070		success = user_key_allowed2(pw, key, file);
1071		free(file);
1072	}
1073
1074	return success;
1075}
1076
1077/* Records a public key in the list of previously-successful keys */
1078void
1079auth2_record_userkey(Authctxt *authctxt, struct sshkey *key)
1080{
1081	struct sshkey **tmp;
1082
1083	if (authctxt->nprev_userkeys >= INT_MAX ||
1084	    (tmp = reallocarray(authctxt->prev_userkeys,
1085	    authctxt->nprev_userkeys + 1, sizeof(*tmp))) == NULL)
1086		fatal("%s: reallocarray failed", __func__);
1087	authctxt->prev_userkeys = tmp;
1088	authctxt->prev_userkeys[authctxt->nprev_userkeys] = key;
1089	authctxt->nprev_userkeys++;
1090}
1091
1092/* Checks whether a key has already been used successfully for authentication */
1093int
1094auth2_userkey_already_used(Authctxt *authctxt, struct sshkey *key)
1095{
1096	u_int i;
1097
1098	for (i = 0; i < authctxt->nprev_userkeys; i++) {
1099		if (sshkey_equal_public(key, authctxt->prev_userkeys[i])) {
1100			return 1;
1101		}
1102	}
1103	return 0;
1104}
1105
1106Authmethod method_pubkey = {
1107	"publickey",
1108	userauth_pubkey,
1109	&options.pubkey_authentication
1110};
1111