xref: /openssh-portable/auth2-pubkey.c (revision be02d7cb)
1 /* $OpenBSD: auth2-pubkey.c,v 1.94 2019/09/06 04:53:27 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 
31 #include <stdlib.h>
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 "sshbuf.h"
51 #include "log.h"
52 #include "misc.h"
53 #include "servconf.h"
54 #include "compat.h"
55 #include "sshkey.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 */
73 extern ServerOptions options;
74 extern u_char *session_id2;
75 extern u_int session_id2_len;
76 
77 static char *
format_key(const struct sshkey * key)78 format_key(const struct sshkey *key)
79 {
80 	char *ret, *fp = sshkey_fingerprint(key,
81 	    options.fingerprint_hash, SSH_FP_DEFAULT);
82 
83 	xasprintf(&ret, "%s %s", sshkey_type(key), fp);
84 	free(fp);
85 	return ret;
86 }
87 
88 static int
userauth_pubkey(struct ssh * ssh)89 userauth_pubkey(struct ssh *ssh)
90 {
91 	Authctxt *authctxt = ssh->authctxt;
92 	struct passwd *pw = authctxt->pw;
93 	struct sshbuf *b = NULL;
94 	struct sshkey *key = NULL;
95 	char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL;
96 	u_char *pkblob = NULL, *sig = NULL, have_sig;
97 	size_t blen, slen;
98 	int r, pktype;
99 	int authenticated = 0;
100 	struct sshauthopt *authopts = NULL;
101 
102 	if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 ||
103 	    (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 ||
104 	    (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0)
105 		fatal("%s: parse request failed: %s", __func__, ssh_err(r));
106 
107 	if (log_level_get() >= SYSLOG_LEVEL_DEBUG2) {
108 		char *keystring;
109 		struct sshbuf *pkbuf;
110 
111 		if ((pkbuf = sshbuf_from(pkblob, blen)) == NULL)
112 			fatal("%s: sshbuf_from failed", __func__);
113 		if ((keystring = sshbuf_dtob64_string(pkbuf, 0)) == NULL)
114 			fatal("%s: sshbuf_dtob64 failed", __func__);
115 		debug2("%s: %s user %s %s public key %s %s", __func__,
116 		    authctxt->valid ? "valid" : "invalid", authctxt->user,
117 		    have_sig ? "attempting" : "querying", pkalg, keystring);
118 		sshbuf_free(pkbuf);
119 		free(keystring);
120 	}
121 
122 	pktype = sshkey_type_from_name(pkalg);
123 	if (pktype == KEY_UNSPEC) {
124 		/* this is perfectly legal */
125 		verbose("%s: unsupported public key algorithm: %s",
126 		    __func__, pkalg);
127 		goto done;
128 	}
129 	if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
130 		error("%s: could not parse key: %s", __func__, ssh_err(r));
131 		goto done;
132 	}
133 	if (key == NULL) {
134 		error("%s: cannot decode key: %s", __func__, pkalg);
135 		goto done;
136 	}
137 	if (key->type != pktype) {
138 		error("%s: type mismatch for decoded key "
139 		    "(received %d, expected %d)", __func__, key->type, pktype);
140 		goto done;
141 	}
142 	if (sshkey_type_plain(key->type) == KEY_RSA &&
143 	    (ssh->compat & SSH_BUG_RSASIGMD5) != 0) {
144 		logit("Refusing RSA key because client uses unsafe "
145 		    "signature scheme");
146 		goto done;
147 	}
148 	if (auth2_key_already_used(authctxt, key)) {
149 		logit("refusing previously-used %s key", sshkey_type(key));
150 		goto done;
151 	}
152 	if (match_pattern_list(pkalg, options.pubkey_key_types, 0) != 1) {
153 		logit("%s: key type %s not in PubkeyAcceptedKeyTypes",
154 		    __func__, sshkey_ssh_name(key));
155 		goto done;
156 	}
157 	if ((r = sshkey_check_cert_sigtype(key,
158 	    options.ca_sign_algorithms)) != 0) {
159 		logit("%s: certificate signature algorithm %s: %s", __func__,
160 		    (key->cert == NULL || key->cert->signature_type == NULL) ?
161 		    "(null)" : key->cert->signature_type, ssh_err(r));
162 		goto done;
163 	}
164 	key_s = format_key(key);
165 	if (sshkey_is_cert(key))
166 		ca_s = format_key(key->cert->signature_key);
167 
168 	if (have_sig) {
169 		debug3("%s: have %s signature for %s%s%s",
170 		    __func__, pkalg, key_s,
171 		    ca_s == NULL ? "" : " CA ",
172 		    ca_s == NULL ? "" : ca_s);
173 		if ((r = sshpkt_get_string(ssh, &sig, &slen)) != 0 ||
174 		    (r = sshpkt_get_end(ssh)) != 0)
175 			fatal("%s: %s", __func__, ssh_err(r));
176 		if ((b = sshbuf_new()) == NULL)
177 			fatal("%s: sshbuf_new failed", __func__);
178 		if (ssh->compat & SSH_OLD_SESSIONID) {
179 			if ((r = sshbuf_put(b, session_id2,
180 			    session_id2_len)) != 0)
181 				fatal("%s: sshbuf_put session id: %s",
182 				    __func__, ssh_err(r));
183 		} else {
184 			if ((r = sshbuf_put_string(b, session_id2,
185 			    session_id2_len)) != 0)
186 				fatal("%s: sshbuf_put_string session id: %s",
187 				    __func__, ssh_err(r));
188 		}
189 		if (!authctxt->valid || authctxt->user == NULL) {
190 			debug2("%s: disabled because of invalid user",
191 			    __func__);
192 			goto done;
193 		}
194 		/* reconstruct packet */
195 		xasprintf(&userstyle, "%s%s%s", authctxt->user,
196 		    authctxt->style ? ":" : "",
197 		    authctxt->style ? authctxt->style : "");
198 		if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
199 		    (r = sshbuf_put_cstring(b, userstyle)) != 0 ||
200 		    (r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
201 		    (r = sshbuf_put_cstring(b, "publickey")) != 0 ||
202 		    (r = sshbuf_put_u8(b, have_sig)) != 0 ||
203 		    (r = sshbuf_put_cstring(b, pkalg)) != 0 ||
204 		    (r = sshbuf_put_string(b, pkblob, blen)) != 0)
205 			fatal("%s: build packet failed: %s",
206 			    __func__, ssh_err(r));
207 #ifdef DEBUG_PK
208 		sshbuf_dump(b, stderr);
209 #endif
210 		/* test for correct signature */
211 		authenticated = 0;
212 		if (PRIVSEP(user_key_allowed(ssh, pw, key, 1, &authopts)) &&
213 		    PRIVSEP(sshkey_verify(key, sig, slen,
214 		    sshbuf_ptr(b), sshbuf_len(b),
215 		    (ssh->compat & SSH_BUG_SIGTYPE) == 0 ? pkalg : NULL,
216 		    ssh->compat)) == 0) {
217 			authenticated = 1;
218 		}
219 		auth2_record_key(authctxt, authenticated, key);
220 	} else {
221 		debug("%s: test pkalg %s pkblob %s%s%s",
222 		    __func__, pkalg, key_s,
223 		    ca_s == NULL ? "" : " CA ",
224 		    ca_s == NULL ? "" : ca_s);
225 
226 		if ((r = sshpkt_get_end(ssh)) != 0)
227 			fatal("%s: %s", __func__, ssh_err(r));
228 
229 		if (!authctxt->valid || authctxt->user == NULL) {
230 			debug2("%s: disabled because of invalid user",
231 			    __func__);
232 			goto done;
233 		}
234 		/* XXX fake reply and always send PK_OK ? */
235 		/*
236 		 * XXX this allows testing whether a user is allowed
237 		 * to login: if you happen to have a valid pubkey this
238 		 * message is sent. the message is NEVER sent at all
239 		 * if a user is not allowed to login. is this an
240 		 * issue? -markus
241 		 */
242 		if (PRIVSEP(user_key_allowed(ssh, pw, key, 0, NULL))) {
243 			if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK))
244 			    != 0 ||
245 			    (r = sshpkt_put_cstring(ssh, pkalg)) != 0 ||
246 			    (r = sshpkt_put_string(ssh, pkblob, blen)) != 0 ||
247 			    (r = sshpkt_send(ssh)) != 0 ||
248 			    (r = ssh_packet_write_wait(ssh)) != 0)
249 				fatal("%s: %s", __func__, ssh_err(r));
250 			authctxt->postponed = 1;
251 		}
252 	}
253 done:
254 	if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) {
255 		debug("%s: key options inconsistent with existing", __func__);
256 		authenticated = 0;
257 	}
258 	debug2("%s: authenticated %d pkalg %s", __func__, authenticated, pkalg);
259 
260 	sshbuf_free(b);
261 	sshauthopt_free(authopts);
262 	sshkey_free(key);
263 	free(userstyle);
264 	free(pkalg);
265 	free(pkblob);
266 	free(key_s);
267 	free(ca_s);
268 	free(sig);
269 	return authenticated;
270 }
271 
272 static int
match_principals_option(const char * principal_list,struct sshkey_cert * cert)273 match_principals_option(const char *principal_list, struct sshkey_cert *cert)
274 {
275 	char *result;
276 	u_int i;
277 
278 	/* XXX percent_expand() sequences for authorized_principals? */
279 
280 	for (i = 0; i < cert->nprincipals; i++) {
281 		if ((result = match_list(cert->principals[i],
282 		    principal_list, NULL)) != NULL) {
283 			debug3("matched principal from key options \"%.100s\"",
284 			    result);
285 			free(result);
286 			return 1;
287 		}
288 	}
289 	return 0;
290 }
291 
292 /*
293  * Process a single authorized_principals format line. Returns 0 and sets
294  * authoptsp is principal is authorised, -1 otherwise. "loc" is used as a
295  * log preamble for file/line information.
296  */
297 static int
check_principals_line(struct ssh * ssh,char * cp,const struct sshkey_cert * cert,const char * loc,struct sshauthopt ** authoptsp)298 check_principals_line(struct ssh *ssh, char *cp, const struct sshkey_cert *cert,
299     const char *loc, struct sshauthopt **authoptsp)
300 {
301 	u_int i, found = 0;
302 	char *ep, *line_opts;
303 	const char *reason = NULL;
304 	struct sshauthopt *opts = NULL;
305 
306 	if (authoptsp != NULL)
307 		*authoptsp = NULL;
308 
309 	/* Trim trailing whitespace. */
310 	ep = cp + strlen(cp) - 1;
311 	while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t'))
312 		*ep-- = '\0';
313 
314 	/*
315 	 * If the line has internal whitespace then assume it has
316 	 * key options.
317 	 */
318 	line_opts = NULL;
319 	if ((ep = strrchr(cp, ' ')) != NULL ||
320 	    (ep = strrchr(cp, '\t')) != NULL) {
321 		for (; *ep == ' ' || *ep == '\t'; ep++)
322 			;
323 		line_opts = cp;
324 		cp = ep;
325 	}
326 	if ((opts = sshauthopt_parse(line_opts, &reason)) == NULL) {
327 		debug("%s: bad principals options: %s", loc, reason);
328 		auth_debug_add("%s: bad principals options: %s", loc, reason);
329 		return -1;
330 	}
331 	/* Check principals in cert against those on line */
332 	for (i = 0; i < cert->nprincipals; i++) {
333 		if (strcmp(cp, cert->principals[i]) != 0)
334 			continue;
335 		debug3("%s: matched principal \"%.100s\"",
336 		    loc, cert->principals[i]);
337 		found = 1;
338 	}
339 	if (found && authoptsp != NULL) {
340 		*authoptsp = opts;
341 		opts = NULL;
342 	}
343 	sshauthopt_free(opts);
344 	return found ? 0 : -1;
345 }
346 
347 static int
process_principals(struct ssh * ssh,FILE * f,const char * file,const struct sshkey_cert * cert,struct sshauthopt ** authoptsp)348 process_principals(struct ssh *ssh, FILE *f, const char *file,
349     const struct sshkey_cert *cert, struct sshauthopt **authoptsp)
350 {
351 	char loc[256], *line = NULL, *cp, *ep;
352 	size_t linesize = 0;
353 	u_long linenum = 0;
354 	u_int found_principal = 0;
355 
356 	if (authoptsp != NULL)
357 		*authoptsp = NULL;
358 
359 	while (getline(&line, &linesize, f) != -1) {
360 		linenum++;
361 		/* Always consume entire input */
362 		if (found_principal)
363 			continue;
364 
365 		/* Skip leading whitespace. */
366 		for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
367 			;
368 		/* Skip blank and comment lines. */
369 		if ((ep = strchr(cp, '#')) != NULL)
370 			*ep = '\0';
371 		if (!*cp || *cp == '\n')
372 			continue;
373 
374 		snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum);
375 		if (check_principals_line(ssh, cp, cert, loc, authoptsp) == 0)
376 			found_principal = 1;
377 	}
378 	free(line);
379 	return found_principal;
380 }
381 
382 /* XXX remove pw args here and elsewhere once ssh->authctxt is guaranteed */
383 
384 static int
match_principals_file(struct ssh * ssh,struct passwd * pw,char * file,struct sshkey_cert * cert,struct sshauthopt ** authoptsp)385 match_principals_file(struct ssh *ssh, struct passwd *pw, char *file,
386     struct sshkey_cert *cert, struct sshauthopt **authoptsp)
387 {
388 	FILE *f;
389 	int success;
390 
391 	if (authoptsp != NULL)
392 		*authoptsp = NULL;
393 
394 	temporarily_use_uid(pw);
395 	debug("trying authorized principals file %s", file);
396 	if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
397 		restore_uid();
398 		return 0;
399 	}
400 	success = process_principals(ssh, f, file, cert, authoptsp);
401 	fclose(f);
402 	restore_uid();
403 	return success;
404 }
405 
406 /*
407  * Checks whether principal is allowed in output of command.
408  * returns 1 if the principal is allowed or 0 otherwise.
409  */
410 static int
match_principals_command(struct ssh * ssh,struct passwd * user_pw,const struct sshkey * key,struct sshauthopt ** authoptsp)411 match_principals_command(struct ssh *ssh, struct passwd *user_pw,
412     const struct sshkey *key, struct sshauthopt **authoptsp)
413 {
414 	struct passwd *runas_pw = NULL;
415 	const struct sshkey_cert *cert = key->cert;
416 	FILE *f = NULL;
417 	int r, ok, found_principal = 0;
418 	int i, ac = 0, uid_swapped = 0;
419 	pid_t pid;
420 	char *tmp, *username = NULL, *command = NULL, **av = NULL;
421 	char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL;
422 	char serial_s[32], uidstr[32];
423 	void (*osigchld)(int);
424 
425 	if (authoptsp != NULL)
426 		*authoptsp = NULL;
427 	if (options.authorized_principals_command == NULL)
428 		return 0;
429 	if (options.authorized_principals_command_user == NULL) {
430 		error("No user for AuthorizedPrincipalsCommand specified, "
431 		    "skipping");
432 		return 0;
433 	}
434 
435 	/*
436 	 * NB. all returns later this function should go via "out" to
437 	 * ensure the original SIGCHLD handler is restored properly.
438 	 */
439 	osigchld = signal(SIGCHLD, SIG_DFL);
440 
441 	/* Prepare and verify the user for the command */
442 	username = percent_expand(options.authorized_principals_command_user,
443 	    "u", user_pw->pw_name, (char *)NULL);
444 	runas_pw = getpwnam(username);
445 	if (runas_pw == NULL) {
446 		error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s",
447 		    username, strerror(errno));
448 		goto out;
449 	}
450 
451 	/* Turn the command into an argument vector */
452 	if (argv_split(options.authorized_principals_command, &ac, &av) != 0) {
453 		error("AuthorizedPrincipalsCommand \"%s\" contains "
454 		    "invalid quotes", options.authorized_principals_command);
455 		goto out;
456 	}
457 	if (ac == 0) {
458 		error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments",
459 		    options.authorized_principals_command);
460 		goto out;
461 	}
462 	if ((ca_fp = sshkey_fingerprint(cert->signature_key,
463 	    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
464 		error("%s: sshkey_fingerprint failed", __func__);
465 		goto out;
466 	}
467 	if ((key_fp = sshkey_fingerprint(key,
468 	    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
469 		error("%s: sshkey_fingerprint failed", __func__);
470 		goto out;
471 	}
472 	if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) {
473 		error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r));
474 		goto out;
475 	}
476 	if ((r = sshkey_to_base64(key, &keytext)) != 0) {
477 		error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r));
478 		goto out;
479 	}
480 	snprintf(serial_s, sizeof(serial_s), "%llu",
481 	    (unsigned long long)cert->serial);
482 	snprintf(uidstr, sizeof(uidstr), "%llu",
483 	    (unsigned long long)user_pw->pw_uid);
484 	for (i = 1; i < ac; i++) {
485 		tmp = percent_expand(av[i],
486 		    "U", uidstr,
487 		    "u", user_pw->pw_name,
488 		    "h", user_pw->pw_dir,
489 		    "t", sshkey_ssh_name(key),
490 		    "T", sshkey_ssh_name(cert->signature_key),
491 		    "f", key_fp,
492 		    "F", ca_fp,
493 		    "k", keytext,
494 		    "K", catext,
495 		    "i", cert->key_id,
496 		    "s", serial_s,
497 		    (char *)NULL);
498 		if (tmp == NULL)
499 			fatal("%s: percent_expand failed", __func__);
500 		free(av[i]);
501 		av[i] = tmp;
502 	}
503 	/* Prepare a printable command for logs, etc. */
504 	command = argv_assemble(ac, av);
505 
506 	if ((pid = subprocess("AuthorizedPrincipalsCommand", runas_pw, command,
507 	    ac, av, &f,
508 	    SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD)) == 0)
509 		goto out;
510 
511 	uid_swapped = 1;
512 	temporarily_use_uid(runas_pw);
513 
514 	ok = process_principals(ssh, f, "(command)", cert, authoptsp);
515 
516 	fclose(f);
517 	f = NULL;
518 
519 	if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0)
520 		goto out;
521 
522 	/* Read completed successfully */
523 	found_principal = ok;
524  out:
525 	if (f != NULL)
526 		fclose(f);
527 	signal(SIGCHLD, osigchld);
528 	for (i = 0; i < ac; i++)
529 		free(av[i]);
530 	free(av);
531 	if (uid_swapped)
532 		restore_uid();
533 	free(command);
534 	free(username);
535 	free(ca_fp);
536 	free(key_fp);
537 	free(catext);
538 	free(keytext);
539 	return found_principal;
540 }
541 
542 /*
543  * Check a single line of an authorized_keys-format file. Returns 0 if key
544  * matches, -1 otherwise. Will return key/cert options via *authoptsp
545  * on success. "loc" is used as file/line location in log messages.
546  */
547 static int
check_authkey_line(struct ssh * ssh,struct passwd * pw,struct sshkey * key,char * cp,const char * loc,struct sshauthopt ** authoptsp)548 check_authkey_line(struct ssh *ssh, struct passwd *pw, struct sshkey *key,
549     char *cp, const char *loc, struct sshauthopt **authoptsp)
550 {
551 	int want_keytype = sshkey_is_cert(key) ? KEY_UNSPEC : key->type;
552 	struct sshkey *found = NULL;
553 	struct sshauthopt *keyopts = NULL, *certopts = NULL, *finalopts = NULL;
554 	char *key_options = NULL, *fp = NULL;
555 	const char *reason = NULL;
556 	int ret = -1;
557 
558 	if (authoptsp != NULL)
559 		*authoptsp = NULL;
560 
561 	if ((found = sshkey_new(want_keytype)) == NULL) {
562 		debug3("%s: keytype %d failed", __func__, want_keytype);
563 		goto out;
564 	}
565 
566 	/* XXX djm: peek at key type in line and skip if unwanted */
567 
568 	if (sshkey_read(found, &cp) != 0) {
569 		/* no key?  check for options */
570 		debug2("%s: check options: '%s'", loc, cp);
571 		key_options = cp;
572 		if (sshkey_advance_past_options(&cp) != 0) {
573 			reason = "invalid key option string";
574 			goto fail_reason;
575 		}
576 		skip_space(&cp);
577 		if (sshkey_read(found, &cp) != 0) {
578 			/* still no key?  advance to next line*/
579 			debug2("%s: advance: '%s'", loc, cp);
580 			goto out;
581 		}
582 	}
583 	/* Parse key options now; we need to know if this is a CA key */
584 	if ((keyopts = sshauthopt_parse(key_options, &reason)) == NULL) {
585 		debug("%s: bad key options: %s", loc, reason);
586 		auth_debug_add("%s: bad key options: %s", loc, reason);
587 		goto out;
588 	}
589 	/* Ignore keys that don't match or incorrectly marked as CAs */
590 	if (sshkey_is_cert(key)) {
591 		/* Certificate; check signature key against CA */
592 		if (!sshkey_equal(found, key->cert->signature_key) ||
593 		    !keyopts->cert_authority)
594 			goto out;
595 	} else {
596 		/* Plain key: check it against key found in file */
597 		if (!sshkey_equal(found, key) || keyopts->cert_authority)
598 			goto out;
599 	}
600 
601 	/* We have a candidate key, perform authorisation checks */
602 	if ((fp = sshkey_fingerprint(found,
603 	    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
604 		fatal("%s: fingerprint failed", __func__);
605 
606 	debug("%s: matching %s found: %s %s", loc,
607 	    sshkey_is_cert(key) ? "CA" : "key", sshkey_type(found), fp);
608 
609 	if (auth_authorise_keyopts(ssh, pw, keyopts,
610 	    sshkey_is_cert(key), loc) != 0) {
611 		reason = "Refused by key options";
612 		goto fail_reason;
613 	}
614 	/* That's all we need for plain keys. */
615 	if (!sshkey_is_cert(key)) {
616 		verbose("Accepted key %s %s found at %s",
617 		    sshkey_type(found), fp, loc);
618 		finalopts = keyopts;
619 		keyopts = NULL;
620 		goto success;
621 	}
622 
623 	/*
624 	 * Additional authorisation for certificates.
625 	 */
626 
627 	/* Parse and check options present in certificate */
628 	if ((certopts = sshauthopt_from_cert(key)) == NULL) {
629 		reason = "Invalid certificate options";
630 		goto fail_reason;
631 	}
632 	if (auth_authorise_keyopts(ssh, pw, certopts, 0, loc) != 0) {
633 		reason = "Refused by certificate options";
634 		goto fail_reason;
635 	}
636 	if ((finalopts = sshauthopt_merge(keyopts, certopts, &reason)) == NULL)
637 		goto fail_reason;
638 
639 	/*
640 	 * If the user has specified a list of principals as
641 	 * a key option, then prefer that list to matching
642 	 * their username in the certificate principals list.
643 	 */
644 	if (keyopts->cert_principals != NULL &&
645 	    !match_principals_option(keyopts->cert_principals, key->cert)) {
646 		reason = "Certificate does not contain an authorized principal";
647 		goto fail_reason;
648 	}
649 	if (sshkey_cert_check_authority(key, 0, 0,
650 	   keyopts->cert_principals == NULL ? pw->pw_name : NULL, &reason) != 0)
651 		goto fail_reason;
652 
653 	verbose("Accepted certificate ID \"%s\" (serial %llu) "
654 	    "signed by CA %s %s found at %s",
655 	    key->cert->key_id,
656 	    (unsigned long long)key->cert->serial,
657 	    sshkey_type(found), fp, loc);
658 
659  success:
660 	if (finalopts == NULL)
661 		fatal("%s: internal error: missing options", __func__);
662 	if (authoptsp != NULL) {
663 		*authoptsp = finalopts;
664 		finalopts = NULL;
665 	}
666 	/* success */
667 	ret = 0;
668 	goto out;
669 
670  fail_reason:
671 	error("%s", reason);
672 	auth_debug_add("%s", reason);
673  out:
674 	free(fp);
675 	sshauthopt_free(keyopts);
676 	sshauthopt_free(certopts);
677 	sshauthopt_free(finalopts);
678 	sshkey_free(found);
679 	return ret;
680 }
681 
682 /*
683  * Checks whether key is allowed in authorized_keys-format file,
684  * returns 1 if the key is allowed or 0 otherwise.
685  */
686 static int
check_authkeys_file(struct ssh * ssh,struct passwd * pw,FILE * f,char * file,struct sshkey * key,struct sshauthopt ** authoptsp)687 check_authkeys_file(struct ssh *ssh, struct passwd *pw, FILE *f,
688     char *file, struct sshkey *key, struct sshauthopt **authoptsp)
689 {
690 	char *cp, *line = NULL, loc[256];
691 	size_t linesize = 0;
692 	int found_key = 0;
693 	u_long linenum = 0;
694 
695 	if (authoptsp != NULL)
696 		*authoptsp = NULL;
697 
698 	while (getline(&line, &linesize, f) != -1) {
699 		linenum++;
700 		/* Always consume entire file */
701 		if (found_key)
702 			continue;
703 
704 		/* Skip leading whitespace, empty and comment lines. */
705 		cp = line;
706 		skip_space(&cp);
707 		if (!*cp || *cp == '\n' || *cp == '#')
708 			continue;
709 		snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum);
710 		if (check_authkey_line(ssh, pw, key, cp, loc, authoptsp) == 0)
711 			found_key = 1;
712 	}
713 	free(line);
714 	return found_key;
715 }
716 
717 /* Authenticate a certificate key against TrustedUserCAKeys */
718 static int
user_cert_trusted_ca(struct ssh * ssh,struct passwd * pw,struct sshkey * key,struct sshauthopt ** authoptsp)719 user_cert_trusted_ca(struct ssh *ssh, struct passwd *pw, struct sshkey *key,
720     struct sshauthopt **authoptsp)
721 {
722 	char *ca_fp, *principals_file = NULL;
723 	const char *reason;
724 	struct sshauthopt *principals_opts = NULL, *cert_opts = NULL;
725 	struct sshauthopt *final_opts = NULL;
726 	int r, ret = 0, found_principal = 0, use_authorized_principals;
727 
728 	if (authoptsp != NULL)
729 		*authoptsp = NULL;
730 
731 	if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL)
732 		return 0;
733 
734 	if ((ca_fp = sshkey_fingerprint(key->cert->signature_key,
735 	    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
736 		return 0;
737 
738 	if ((r = sshkey_in_file(key->cert->signature_key,
739 	    options.trusted_user_ca_keys, 1, 0)) != 0) {
740 		debug2("%s: CA %s %s is not listed in %s: %s", __func__,
741 		    sshkey_type(key->cert->signature_key), ca_fp,
742 		    options.trusted_user_ca_keys, ssh_err(r));
743 		goto out;
744 	}
745 	/*
746 	 * If AuthorizedPrincipals is in use, then compare the certificate
747 	 * principals against the names in that file rather than matching
748 	 * against the username.
749 	 */
750 	if ((principals_file = authorized_principals_file(pw)) != NULL) {
751 		if (match_principals_file(ssh, pw, principals_file,
752 		    key->cert, &principals_opts))
753 			found_principal = 1;
754 	}
755 	/* Try querying command if specified */
756 	if (!found_principal && match_principals_command(ssh, pw, key,
757 	    &principals_opts))
758 		found_principal = 1;
759 	/* If principals file or command is specified, then require a match */
760 	use_authorized_principals = principals_file != NULL ||
761             options.authorized_principals_command != NULL;
762 	if (!found_principal && use_authorized_principals) {
763 		reason = "Certificate does not contain an authorized principal";
764 		goto fail_reason;
765 	}
766 	if (use_authorized_principals && principals_opts == NULL)
767 		fatal("%s: internal error: missing principals_opts", __func__);
768 	if (sshkey_cert_check_authority(key, 0, 1,
769 	    use_authorized_principals ? NULL : pw->pw_name, &reason) != 0)
770 		goto fail_reason;
771 
772 	/* Check authority from options in key and from principals file/cmd */
773 	if ((cert_opts = sshauthopt_from_cert(key)) == NULL) {
774 		reason = "Invalid certificate options";
775 		goto fail_reason;
776 	}
777 	if (auth_authorise_keyopts(ssh, pw, cert_opts, 0, "cert") != 0) {
778 		reason = "Refused by certificate options";
779 		goto fail_reason;
780 	}
781 	if (principals_opts == NULL) {
782 		final_opts = cert_opts;
783 		cert_opts = NULL;
784 	} else {
785 		if (auth_authorise_keyopts(ssh, pw, principals_opts, 0,
786 		    "principals") != 0) {
787 			reason = "Refused by certificate principals options";
788 			goto fail_reason;
789 		}
790 		if ((final_opts = sshauthopt_merge(principals_opts,
791 		    cert_opts, &reason)) == NULL) {
792  fail_reason:
793 			error("%s", reason);
794 			auth_debug_add("%s", reason);
795 			goto out;
796 		}
797 	}
798 
799 	/* Success */
800 	verbose("Accepted certificate ID \"%s\" (serial %llu) signed by "
801 	    "%s CA %s via %s", key->cert->key_id,
802 	    (unsigned long long)key->cert->serial,
803 	    sshkey_type(key->cert->signature_key), ca_fp,
804 	    options.trusted_user_ca_keys);
805 	if (authoptsp != NULL) {
806 		*authoptsp = final_opts;
807 		final_opts = NULL;
808 	}
809 	ret = 1;
810  out:
811 	sshauthopt_free(principals_opts);
812 	sshauthopt_free(cert_opts);
813 	sshauthopt_free(final_opts);
814 	free(principals_file);
815 	free(ca_fp);
816 	return ret;
817 }
818 
819 /*
820  * Checks whether key is allowed in file.
821  * returns 1 if the key is allowed or 0 otherwise.
822  */
823 static int
user_key_allowed2(struct ssh * ssh,struct passwd * pw,struct sshkey * key,char * file,struct sshauthopt ** authoptsp)824 user_key_allowed2(struct ssh *ssh, struct passwd *pw, struct sshkey *key,
825     char *file, struct sshauthopt **authoptsp)
826 {
827 	FILE *f;
828 	int found_key = 0;
829 
830 	if (authoptsp != NULL)
831 		*authoptsp = NULL;
832 
833 	/* Temporarily use the user's uid. */
834 	temporarily_use_uid(pw);
835 
836 	debug("trying public key file %s", file);
837 	if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) {
838 		found_key = check_authkeys_file(ssh, pw, f, file,
839 		    key, authoptsp);
840 		fclose(f);
841 	}
842 
843 	restore_uid();
844 	return found_key;
845 }
846 
847 /*
848  * Checks whether key is allowed in output of command.
849  * returns 1 if the key is allowed or 0 otherwise.
850  */
851 static int
user_key_command_allowed2(struct ssh * ssh,struct passwd * user_pw,struct sshkey * key,struct sshauthopt ** authoptsp)852 user_key_command_allowed2(struct ssh *ssh, struct passwd *user_pw,
853     struct sshkey *key, struct sshauthopt **authoptsp)
854 {
855 	struct passwd *runas_pw = NULL;
856 	FILE *f = NULL;
857 	int r, ok, found_key = 0;
858 	int i, uid_swapped = 0, ac = 0;
859 	pid_t pid;
860 	char *username = NULL, *key_fp = NULL, *keytext = NULL;
861 	char uidstr[32], *tmp, *command = NULL, **av = NULL;
862 	void (*osigchld)(int);
863 
864 	if (authoptsp != NULL)
865 		*authoptsp = NULL;
866 	if (options.authorized_keys_command == NULL)
867 		return 0;
868 	if (options.authorized_keys_command_user == NULL) {
869 		error("No user for AuthorizedKeysCommand specified, skipping");
870 		return 0;
871 	}
872 
873 	/*
874 	 * NB. all returns later this function should go via "out" to
875 	 * ensure the original SIGCHLD handler is restored properly.
876 	 */
877 	osigchld = signal(SIGCHLD, SIG_DFL);
878 
879 	/* Prepare and verify the user for the command */
880 	username = percent_expand(options.authorized_keys_command_user,
881 	    "u", user_pw->pw_name, (char *)NULL);
882 	runas_pw = getpwnam(username);
883 	if (runas_pw == NULL) {
884 		error("AuthorizedKeysCommandUser \"%s\" not found: %s",
885 		    username, strerror(errno));
886 		goto out;
887 	}
888 
889 	/* Prepare AuthorizedKeysCommand */
890 	if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash,
891 	    SSH_FP_DEFAULT)) == NULL) {
892 		error("%s: sshkey_fingerprint failed", __func__);
893 		goto out;
894 	}
895 	if ((r = sshkey_to_base64(key, &keytext)) != 0) {
896 		error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r));
897 		goto out;
898 	}
899 
900 	/* Turn the command into an argument vector */
901 	if (argv_split(options.authorized_keys_command, &ac, &av) != 0) {
902 		error("AuthorizedKeysCommand \"%s\" contains invalid quotes",
903 		    command);
904 		goto out;
905 	}
906 	if (ac == 0) {
907 		error("AuthorizedKeysCommand \"%s\" yielded no arguments",
908 		    command);
909 		goto out;
910 	}
911 	snprintf(uidstr, sizeof(uidstr), "%llu",
912 	    (unsigned long long)user_pw->pw_uid);
913 	for (i = 1; i < ac; i++) {
914 		tmp = percent_expand(av[i],
915 		    "U", uidstr,
916 		    "u", user_pw->pw_name,
917 		    "h", user_pw->pw_dir,
918 		    "t", sshkey_ssh_name(key),
919 		    "f", key_fp,
920 		    "k", keytext,
921 		    (char *)NULL);
922 		if (tmp == NULL)
923 			fatal("%s: percent_expand failed", __func__);
924 		free(av[i]);
925 		av[i] = tmp;
926 	}
927 	/* Prepare a printable command for logs, etc. */
928 	command = argv_assemble(ac, av);
929 
930 	/*
931 	 * If AuthorizedKeysCommand was run without arguments
932 	 * then fall back to the old behaviour of passing the
933 	 * target username as a single argument.
934 	 */
935 	if (ac == 1) {
936 		av = xreallocarray(av, ac + 2, sizeof(*av));
937 		av[1] = xstrdup(user_pw->pw_name);
938 		av[2] = NULL;
939 		/* Fix up command too, since it is used in log messages */
940 		free(command);
941 		xasprintf(&command, "%s %s", av[0], av[1]);
942 	}
943 
944 	if ((pid = subprocess("AuthorizedKeysCommand", runas_pw, command,
945 	    ac, av, &f,
946 	    SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD)) == 0)
947 		goto out;
948 
949 	uid_swapped = 1;
950 	temporarily_use_uid(runas_pw);
951 
952 	ok = check_authkeys_file(ssh, user_pw, f,
953 	    options.authorized_keys_command, key, authoptsp);
954 
955 	fclose(f);
956 	f = NULL;
957 
958 	if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0)
959 		goto out;
960 
961 	/* Read completed successfully */
962 	found_key = ok;
963  out:
964 	if (f != NULL)
965 		fclose(f);
966 	signal(SIGCHLD, osigchld);
967 	for (i = 0; i < ac; i++)
968 		free(av[i]);
969 	free(av);
970 	if (uid_swapped)
971 		restore_uid();
972 	free(command);
973 	free(username);
974 	free(key_fp);
975 	free(keytext);
976 	return found_key;
977 }
978 
979 /*
980  * Check whether key authenticates and authorises the user.
981  */
982 int
user_key_allowed(struct ssh * ssh,struct passwd * pw,struct sshkey * key,int auth_attempt,struct sshauthopt ** authoptsp)983 user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key,
984     int auth_attempt, struct sshauthopt **authoptsp)
985 {
986 	u_int success = 0, i;
987 	char *file;
988 	struct sshauthopt *opts = NULL;
989 
990 	if (authoptsp != NULL)
991 		*authoptsp = NULL;
992 
993 	if (auth_key_is_revoked(key))
994 		return 0;
995 	if (sshkey_is_cert(key) &&
996 	    auth_key_is_revoked(key->cert->signature_key))
997 		return 0;
998 
999 	for (i = 0; !success && i < options.num_authkeys_files; i++) {
1000 		if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
1001 			continue;
1002 		file = expand_authorized_keys(
1003 		    options.authorized_keys_files[i], pw);
1004 		success = user_key_allowed2(ssh, pw, key, file, &opts);
1005 		free(file);
1006 		if (!success) {
1007 			sshauthopt_free(opts);
1008 			opts = NULL;
1009 		}
1010 	}
1011 	if (success)
1012 		goto out;
1013 
1014 	if ((success = user_cert_trusted_ca(ssh, pw, key, &opts)) != 0)
1015 		goto out;
1016 	sshauthopt_free(opts);
1017 	opts = NULL;
1018 
1019 	if ((success = user_key_command_allowed2(ssh, pw, key, &opts)) != 0)
1020 		goto out;
1021 	sshauthopt_free(opts);
1022 	opts = NULL;
1023 
1024  out:
1025 	if (success && authoptsp != NULL) {
1026 		*authoptsp = opts;
1027 		opts = NULL;
1028 	}
1029 	sshauthopt_free(opts);
1030 	return success;
1031 }
1032 
1033 Authmethod method_pubkey = {
1034 	"publickey",
1035 	userauth_pubkey,
1036 	&options.pubkey_authentication
1037 };
1038