xref: /openssh-portable/auth2.c (revision e8c97404)
1 /* $OpenBSD: auth2.c,v 1.156 2019/06/28 05:44:09 deraadt 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/uio.h>
31 
32 #include <fcntl.h>
33 #include <limits.h>
34 #include <pwd.h>
35 #include <stdarg.h>
36 #include <string.h>
37 #include <unistd.h>
38 #include <time.h>
39 
40 #include "atomicio.h"
41 #include "xmalloc.h"
42 #include "ssh2.h"
43 #include "packet.h"
44 #include "log.h"
45 #include "sshbuf.h"
46 #include "misc.h"
47 #include "servconf.h"
48 #include "compat.h"
49 #include "sshkey.h"
50 #include "hostfile.h"
51 #include "auth.h"
52 #include "dispatch.h"
53 #include "pathnames.h"
54 #include "sshbuf.h"
55 #include "ssherr.h"
56 
57 #ifdef GSSAPI
58 #include "ssh-gss.h"
59 #endif
60 #include "monitor_wrap.h"
61 #include "ssherr.h"
62 #include "digest.h"
63 
64 /* import */
65 extern ServerOptions options;
66 extern u_char *session_id2;
67 extern u_int session_id2_len;
68 extern struct sshbuf *loginmsg;
69 
70 /* methods */
71 
72 extern Authmethod method_none;
73 extern Authmethod method_pubkey;
74 extern Authmethod method_passwd;
75 extern Authmethod method_kbdint;
76 extern Authmethod method_hostbased;
77 #ifdef GSSAPI
78 extern Authmethod method_gssapi;
79 #endif
80 
81 Authmethod *authmethods[] = {
82 	&method_none,
83 	&method_pubkey,
84 #ifdef GSSAPI
85 	&method_gssapi,
86 #endif
87 	&method_passwd,
88 	&method_kbdint,
89 	&method_hostbased,
90 	NULL
91 };
92 
93 /* protocol */
94 
95 static int input_service_request(int, u_int32_t, struct ssh *);
96 static int input_userauth_request(int, u_int32_t, struct ssh *);
97 
98 /* helper */
99 static Authmethod *authmethod_lookup(Authctxt *, const char *);
100 static char *authmethods_get(Authctxt *authctxt);
101 
102 #define MATCH_NONE	0	/* method or submethod mismatch */
103 #define MATCH_METHOD	1	/* method matches (no submethod specified) */
104 #define MATCH_BOTH	2	/* method and submethod match */
105 #define MATCH_PARTIAL	3	/* method matches, submethod can't be checked */
106 static int list_starts_with(const char *, const char *, const char *);
107 
108 char *
auth2_read_banner(void)109 auth2_read_banner(void)
110 {
111 	struct stat st;
112 	char *banner = NULL;
113 	size_t len, n;
114 	int fd;
115 
116 	if ((fd = open(options.banner, O_RDONLY)) == -1)
117 		return (NULL);
118 	if (fstat(fd, &st) == -1) {
119 		close(fd);
120 		return (NULL);
121 	}
122 	if (st.st_size <= 0 || st.st_size > 1*1024*1024) {
123 		close(fd);
124 		return (NULL);
125 	}
126 
127 	len = (size_t)st.st_size;		/* truncate */
128 	banner = xmalloc(len + 1);
129 	n = atomicio(read, fd, banner, len);
130 	close(fd);
131 
132 	if (n != len) {
133 		free(banner);
134 		return (NULL);
135 	}
136 	banner[n] = '\0';
137 
138 	return (banner);
139 }
140 
141 static void
userauth_send_banner(struct ssh * ssh,const char * msg)142 userauth_send_banner(struct ssh *ssh, const char *msg)
143 {
144 	int r;
145 
146 	if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_BANNER)) != 0 ||
147 	    (r = sshpkt_put_cstring(ssh, msg)) != 0 ||
148 	    (r = sshpkt_put_cstring(ssh, "")) != 0 ||	/* language, unused */
149 	    (r = sshpkt_send(ssh)) != 0)
150 		fatal("%s: %s", __func__, ssh_err(r));
151 	debug("%s: sent", __func__);
152 }
153 
154 static void
userauth_banner(struct ssh * ssh)155 userauth_banner(struct ssh *ssh)
156 {
157 	char *banner = NULL;
158 
159 	if (options.banner == NULL)
160 		return;
161 
162 	if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
163 		goto done;
164 	userauth_send_banner(ssh, banner);
165 
166 done:
167 	free(banner);
168 }
169 
170 /*
171  * loop until authctxt->success == TRUE
172  */
173 void
do_authentication2(struct ssh * ssh)174 do_authentication2(struct ssh *ssh)
175 {
176 	Authctxt *authctxt = ssh->authctxt;
177 
178 	ssh_dispatch_init(ssh, &dispatch_protocol_error);
179 	ssh_dispatch_set(ssh, SSH2_MSG_SERVICE_REQUEST, &input_service_request);
180 	ssh_dispatch_run_fatal(ssh, DISPATCH_BLOCK, &authctxt->success);
181 	ssh->authctxt = NULL;
182 }
183 
184 /*ARGSUSED*/
185 static int
input_service_request(int type,u_int32_t seq,struct ssh * ssh)186 input_service_request(int type, u_int32_t seq, struct ssh *ssh)
187 {
188 	Authctxt *authctxt = ssh->authctxt;
189 	char *service = NULL;
190 	int r, acceptit = 0;
191 
192 	if ((r = sshpkt_get_cstring(ssh, &service, NULL)) != 0 ||
193 	    (r = sshpkt_get_end(ssh)) != 0)
194 		goto out;
195 
196 	if (authctxt == NULL)
197 		fatal("input_service_request: no authctxt");
198 
199 	if (strcmp(service, "ssh-userauth") == 0) {
200 		if (!authctxt->success) {
201 			acceptit = 1;
202 			/* now we can handle user-auth requests */
203 			ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_REQUEST,
204 			    &input_userauth_request);
205 		}
206 	}
207 	/* XXX all other service requests are denied */
208 
209 	if (acceptit) {
210 		if ((r = sshpkt_start(ssh, SSH2_MSG_SERVICE_ACCEPT)) != 0 ||
211 		    (r = sshpkt_put_cstring(ssh, service)) != 0 ||
212 		    (r = sshpkt_send(ssh)) != 0 ||
213 		    (r = ssh_packet_write_wait(ssh)) != 0)
214 			goto out;
215 	} else {
216 		debug("bad service request %s", service);
217 		ssh_packet_disconnect(ssh, "bad service request %s", service);
218 	}
219 	r = 0;
220  out:
221 	free(service);
222 	return 0;
223 }
224 
225 #define MIN_FAIL_DELAY_SECONDS 0.005
226 static double
user_specific_delay(const char * user)227 user_specific_delay(const char *user)
228 {
229 	char b[512];
230 	size_t len = ssh_digest_bytes(SSH_DIGEST_SHA512);
231 	u_char *hash = xmalloc(len);
232 	double delay;
233 
234 	(void)snprintf(b, sizeof b, "%llu%s",
235 	     (unsigned long long)options.timing_secret, user);
236 	if (ssh_digest_memory(SSH_DIGEST_SHA512, b, strlen(b), hash, len) != 0)
237 		fatal("%s: ssh_digest_memory", __func__);
238 	/* 0-4.2 ms of delay */
239 	delay = (double)PEEK_U32(hash) / 1000 / 1000 / 1000 / 1000;
240 	freezero(hash, len);
241 	debug3("%s: user specific delay %0.3lfms", __func__, delay/1000);
242 	return MIN_FAIL_DELAY_SECONDS + delay;
243 }
244 
245 static void
ensure_minimum_time_since(double start,double seconds)246 ensure_minimum_time_since(double start, double seconds)
247 {
248 	struct timespec ts;
249 	double elapsed = monotime_double() - start, req = seconds, remain;
250 
251 	/* if we've already passed the requested time, scale up */
252 	while ((remain = seconds - elapsed) < 0.0)
253 		seconds *= 2;
254 
255 	ts.tv_sec = remain;
256 	ts.tv_nsec = (remain - ts.tv_sec) * 1000000000;
257 	debug3("%s: elapsed %0.3lfms, delaying %0.3lfms (requested %0.3lfms)",
258 	    __func__, elapsed*1000, remain*1000, req*1000);
259 	nanosleep(&ts, NULL);
260 }
261 
262 /*ARGSUSED*/
263 static int
input_userauth_request(int type,u_int32_t seq,struct ssh * ssh)264 input_userauth_request(int type, u_int32_t seq, struct ssh *ssh)
265 {
266 	Authctxt *authctxt = ssh->authctxt;
267 	Authmethod *m = NULL;
268 	char *user = NULL, *service = NULL, *method = NULL, *style = NULL;
269 	int r, authenticated = 0;
270 	double tstart = monotime_double();
271 
272 	if (authctxt == NULL)
273 		fatal("input_userauth_request: no authctxt");
274 
275 	if ((r = sshpkt_get_cstring(ssh, &user, NULL)) != 0 ||
276 	    (r = sshpkt_get_cstring(ssh, &service, NULL)) != 0 ||
277 	    (r = sshpkt_get_cstring(ssh, &method, NULL)) != 0)
278 		goto out;
279 	debug("userauth-request for user %s service %s method %s", user, service, method);
280 	debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
281 
282 	if ((style = strchr(user, ':')) != NULL)
283 		*style++ = 0;
284 
285 	if (authctxt->attempt++ == 0) {
286 		/* setup auth context */
287 		authctxt->pw = PRIVSEP(getpwnamallow(ssh, user));
288 		authctxt->user = xstrdup(user);
289 		if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
290 			authctxt->valid = 1;
291 			debug2("%s: setting up authctxt for %s",
292 			    __func__, user);
293 		} else {
294 			/* Invalid user, fake password information */
295 			authctxt->pw = fakepw();
296 #ifdef SSH_AUDIT_EVENTS
297 			PRIVSEP(audit_event(ssh, SSH_INVALID_USER));
298 #endif
299 		}
300 #ifdef USE_PAM
301 		if (options.use_pam)
302 			PRIVSEP(start_pam(ssh));
303 #endif
304 		ssh_packet_set_log_preamble(ssh, "%suser %s",
305 		    authctxt->valid ? "authenticating " : "invalid ", user);
306 		setproctitle("%s%s", authctxt->valid ? user : "unknown",
307 		    use_privsep ? " [net]" : "");
308 		authctxt->service = xstrdup(service);
309 		authctxt->style = style ? xstrdup(style) : NULL;
310 		if (use_privsep)
311 			mm_inform_authserv(service, style);
312 		userauth_banner(ssh);
313 		if (auth2_setup_methods_lists(authctxt) != 0)
314 			ssh_packet_disconnect(ssh,
315 			    "no authentication methods enabled");
316 	} else if (strcmp(user, authctxt->user) != 0 ||
317 	    strcmp(service, authctxt->service) != 0) {
318 		ssh_packet_disconnect(ssh, "Change of username or service "
319 		    "not allowed: (%s,%s) -> (%s,%s)",
320 		    authctxt->user, authctxt->service, user, service);
321 	}
322 	/* reset state */
323 	auth2_challenge_stop(ssh);
324 
325 #ifdef GSSAPI
326 	/* XXX move to auth2_gssapi_stop() */
327 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
328 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
329 #endif
330 
331 	auth2_authctxt_reset_info(authctxt);
332 	authctxt->postponed = 0;
333 	authctxt->server_caused_failure = 0;
334 
335 	/* try to authenticate user */
336 	m = authmethod_lookup(authctxt, method);
337 	if (m != NULL && authctxt->failures < options.max_authtries) {
338 		debug2("input_userauth_request: try method %s", method);
339 		authenticated =	m->userauth(ssh);
340 	}
341 	if (!authctxt->authenticated)
342 		ensure_minimum_time_since(tstart,
343 		    user_specific_delay(authctxt->user));
344 	userauth_finish(ssh, authenticated, method, NULL);
345 	r = 0;
346  out:
347 	free(service);
348 	free(user);
349 	free(method);
350 	return r;
351 }
352 
353 void
userauth_finish(struct ssh * ssh,int authenticated,const char * method,const char * submethod)354 userauth_finish(struct ssh *ssh, int authenticated, const char *method,
355     const char *submethod)
356 {
357 	Authctxt *authctxt = ssh->authctxt;
358 	char *methods;
359 	int r, partial = 0;
360 
361 	if (!authctxt->valid && authenticated)
362 		fatal("INTERNAL ERROR: authenticated invalid user %s",
363 		    authctxt->user);
364 	if (authenticated && authctxt->postponed)
365 		fatal("INTERNAL ERROR: authenticated and postponed");
366 
367 	/* Special handling for root */
368 	if (authenticated && authctxt->pw->pw_uid == 0 &&
369 	    !auth_root_allowed(ssh, method)) {
370 		authenticated = 0;
371 #ifdef SSH_AUDIT_EVENTS
372 		PRIVSEP(audit_event(ssh, SSH_LOGIN_ROOT_DENIED));
373 #endif
374 	}
375 
376 	if (authenticated && options.num_auth_methods != 0) {
377 		if (!auth2_update_methods_lists(authctxt, method, submethod)) {
378 			authenticated = 0;
379 			partial = 1;
380 		}
381 	}
382 
383 	/* Log before sending the reply */
384 	auth_log(ssh, authenticated, partial, method, submethod);
385 
386 	/* Update information exposed to session */
387 	if (authenticated || partial)
388 		auth2_update_session_info(authctxt, method, submethod);
389 
390 	if (authctxt->postponed)
391 		return;
392 
393 #ifdef USE_PAM
394 	if (options.use_pam && authenticated) {
395 		int r;
396 
397 		if (!PRIVSEP(do_pam_account())) {
398 			/* if PAM returned a message, send it to the user */
399 			if (sshbuf_len(loginmsg) > 0) {
400 				if ((r = sshbuf_put(loginmsg, "\0", 1)) != 0)
401 					fatal("%s: buffer error: %s",
402 					    __func__, ssh_err(r));
403 				userauth_send_banner(ssh, sshbuf_ptr(loginmsg));
404 				if ((r = ssh_packet_write_wait(ssh)) != 0) {
405 					sshpkt_fatal(ssh, r,
406 					    "%s: send PAM banner", __func__);
407 				}
408 			}
409 			fatal("Access denied for user %s by PAM account "
410 			    "configuration", authctxt->user);
411 		}
412 	}
413 #endif
414 
415 	if (authenticated == 1) {
416 		/* turn off userauth */
417 		ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_REQUEST,
418 		    &dispatch_protocol_ignore);
419 		if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_SUCCESS)) != 0 ||
420 		    (r = sshpkt_send(ssh)) != 0 ||
421 		    (r = ssh_packet_write_wait(ssh)) != 0)
422 			fatal("%s: %s", __func__, ssh_err(r));
423 		/* now we can break out */
424 		authctxt->success = 1;
425 		ssh_packet_set_log_preamble(ssh, "user %s", authctxt->user);
426 	} else {
427 		/* Allow initial try of "none" auth without failure penalty */
428 		if (!partial && !authctxt->server_caused_failure &&
429 		    (authctxt->attempt > 1 || strcmp(method, "none") != 0))
430 			authctxt->failures++;
431 		if (authctxt->failures >= options.max_authtries) {
432 #ifdef SSH_AUDIT_EVENTS
433 			PRIVSEP(audit_event(ssh, SSH_LOGIN_EXCEED_MAXTRIES));
434 #endif
435 			auth_maxtries_exceeded(ssh);
436 		}
437 		methods = authmethods_get(authctxt);
438 		debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
439 		    partial, methods);
440 		if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_FAILURE)) != 0 ||
441 		    (r = sshpkt_put_cstring(ssh, methods)) != 0 ||
442 		    (r = sshpkt_put_u8(ssh, partial)) != 0 ||
443 		    (r = sshpkt_send(ssh)) != 0 ||
444 		    (r = ssh_packet_write_wait(ssh)) != 0)
445 			fatal("%s: %s", __func__, ssh_err(r));
446 		free(methods);
447 	}
448 }
449 
450 /*
451  * Checks whether method is allowed by at least one AuthenticationMethods
452  * methods list. Returns 1 if allowed, or no methods lists configured.
453  * 0 otherwise.
454  */
455 int
auth2_method_allowed(Authctxt * authctxt,const char * method,const char * submethod)456 auth2_method_allowed(Authctxt *authctxt, const char *method,
457     const char *submethod)
458 {
459 	u_int i;
460 
461 	/*
462 	 * NB. authctxt->num_auth_methods might be zero as a result of
463 	 * auth2_setup_methods_lists(), so check the configuration.
464 	 */
465 	if (options.num_auth_methods == 0)
466 		return 1;
467 	for (i = 0; i < authctxt->num_auth_methods; i++) {
468 		if (list_starts_with(authctxt->auth_methods[i], method,
469 		    submethod) != MATCH_NONE)
470 			return 1;
471 	}
472 	return 0;
473 }
474 
475 static char *
authmethods_get(Authctxt * authctxt)476 authmethods_get(Authctxt *authctxt)
477 {
478 	struct sshbuf *b;
479 	char *list;
480 	int i, r;
481 
482 	if ((b = sshbuf_new()) == NULL)
483 		fatal("%s: sshbuf_new failed", __func__);
484 	for (i = 0; authmethods[i] != NULL; i++) {
485 		if (strcmp(authmethods[i]->name, "none") == 0)
486 			continue;
487 		if (authmethods[i]->enabled == NULL ||
488 		    *(authmethods[i]->enabled) == 0)
489 			continue;
490 		if (!auth2_method_allowed(authctxt, authmethods[i]->name,
491 		    NULL))
492 			continue;
493 		if ((r = sshbuf_putf(b, "%s%s", sshbuf_len(b) ? "," : "",
494 		    authmethods[i]->name)) != 0)
495 			fatal("%s: buffer error: %s", __func__, ssh_err(r));
496 	}
497 	if ((list = sshbuf_dup_string(b)) == NULL)
498 		fatal("%s: sshbuf_dup_string failed", __func__);
499 	sshbuf_free(b);
500 	return list;
501 }
502 
503 static Authmethod *
authmethod_lookup(Authctxt * authctxt,const char * name)504 authmethod_lookup(Authctxt *authctxt, const char *name)
505 {
506 	int i;
507 
508 	if (name != NULL)
509 		for (i = 0; authmethods[i] != NULL; i++)
510 			if (authmethods[i]->enabled != NULL &&
511 			    *(authmethods[i]->enabled) != 0 &&
512 			    strcmp(name, authmethods[i]->name) == 0 &&
513 			    auth2_method_allowed(authctxt,
514 			    authmethods[i]->name, NULL))
515 				return authmethods[i];
516 	debug2("Unrecognized authentication method name: %s",
517 	    name ? name : "NULL");
518 	return NULL;
519 }
520 
521 /*
522  * Check a comma-separated list of methods for validity. Is need_enable is
523  * non-zero, then also require that the methods are enabled.
524  * Returns 0 on success or -1 if the methods list is invalid.
525  */
526 int
auth2_methods_valid(const char * _methods,int need_enable)527 auth2_methods_valid(const char *_methods, int need_enable)
528 {
529 	char *methods, *omethods, *method, *p;
530 	u_int i, found;
531 	int ret = -1;
532 
533 	if (*_methods == '\0') {
534 		error("empty authentication method list");
535 		return -1;
536 	}
537 	omethods = methods = xstrdup(_methods);
538 	while ((method = strsep(&methods, ",")) != NULL) {
539 		for (found = i = 0; !found && authmethods[i] != NULL; i++) {
540 			if ((p = strchr(method, ':')) != NULL)
541 				*p = '\0';
542 			if (strcmp(method, authmethods[i]->name) != 0)
543 				continue;
544 			if (need_enable) {
545 				if (authmethods[i]->enabled == NULL ||
546 				    *(authmethods[i]->enabled) == 0) {
547 					error("Disabled method \"%s\" in "
548 					    "AuthenticationMethods list \"%s\"",
549 					    method, _methods);
550 					goto out;
551 				}
552 			}
553 			found = 1;
554 			break;
555 		}
556 		if (!found) {
557 			error("Unknown authentication method \"%s\" in list",
558 			    method);
559 			goto out;
560 		}
561 	}
562 	ret = 0;
563  out:
564 	free(omethods);
565 	return ret;
566 }
567 
568 /*
569  * Prune the AuthenticationMethods supplied in the configuration, removing
570  * any methods lists that include disabled methods. Note that this might
571  * leave authctxt->num_auth_methods == 0, even when multiple required auth
572  * has been requested. For this reason, all tests for whether multiple is
573  * enabled should consult options.num_auth_methods directly.
574  */
575 int
auth2_setup_methods_lists(Authctxt * authctxt)576 auth2_setup_methods_lists(Authctxt *authctxt)
577 {
578 	u_int i;
579 
580 	/* First, normalise away the "any" pseudo-method */
581 	if (options.num_auth_methods == 1 &&
582 	    strcmp(options.auth_methods[0], "any") == 0) {
583 		free(options.auth_methods[0]);
584 		options.auth_methods[0] = NULL;
585 		options.num_auth_methods = 0;
586 	}
587 
588 	if (options.num_auth_methods == 0)
589 		return 0;
590 	debug3("%s: checking methods", __func__);
591 	authctxt->auth_methods = xcalloc(options.num_auth_methods,
592 	    sizeof(*authctxt->auth_methods));
593 	authctxt->num_auth_methods = 0;
594 	for (i = 0; i < options.num_auth_methods; i++) {
595 		if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
596 			logit("Authentication methods list \"%s\" contains "
597 			    "disabled method, skipping",
598 			    options.auth_methods[i]);
599 			continue;
600 		}
601 		debug("authentication methods list %d: %s",
602 		    authctxt->num_auth_methods, options.auth_methods[i]);
603 		authctxt->auth_methods[authctxt->num_auth_methods++] =
604 		    xstrdup(options.auth_methods[i]);
605 	}
606 	if (authctxt->num_auth_methods == 0) {
607 		error("No AuthenticationMethods left after eliminating "
608 		    "disabled methods");
609 		return -1;
610 	}
611 	return 0;
612 }
613 
614 static int
list_starts_with(const char * methods,const char * method,const char * submethod)615 list_starts_with(const char *methods, const char *method,
616     const char *submethod)
617 {
618 	size_t l = strlen(method);
619 	int match;
620 	const char *p;
621 
622 	if (strncmp(methods, method, l) != 0)
623 		return MATCH_NONE;
624 	p = methods + l;
625 	match = MATCH_METHOD;
626 	if (*p == ':') {
627 		if (!submethod)
628 			return MATCH_PARTIAL;
629 		l = strlen(submethod);
630 		p += 1;
631 		if (strncmp(submethod, p, l))
632 			return MATCH_NONE;
633 		p += l;
634 		match = MATCH_BOTH;
635 	}
636 	if (*p != ',' && *p != '\0')
637 		return MATCH_NONE;
638 	return match;
639 }
640 
641 /*
642  * Remove method from the start of a comma-separated list of methods.
643  * Returns 0 if the list of methods did not start with that method or 1
644  * if it did.
645  */
646 static int
remove_method(char ** methods,const char * method,const char * submethod)647 remove_method(char **methods, const char *method, const char *submethod)
648 {
649 	char *omethods = *methods, *p;
650 	size_t l = strlen(method);
651 	int match;
652 
653 	match = list_starts_with(omethods, method, submethod);
654 	if (match != MATCH_METHOD && match != MATCH_BOTH)
655 		return 0;
656 	p = omethods + l;
657 	if (submethod && match == MATCH_BOTH)
658 		p += 1 + strlen(submethod); /* include colon */
659 	if (*p == ',')
660 		p++;
661 	*methods = xstrdup(p);
662 	free(omethods);
663 	return 1;
664 }
665 
666 /*
667  * Called after successful authentication. Will remove the successful method
668  * from the start of each list in which it occurs. If it was the last method
669  * in any list, then authentication is deemed successful.
670  * Returns 1 if the method completed any authentication list or 0 otherwise.
671  */
672 int
auth2_update_methods_lists(Authctxt * authctxt,const char * method,const char * submethod)673 auth2_update_methods_lists(Authctxt *authctxt, const char *method,
674     const char *submethod)
675 {
676 	u_int i, found = 0;
677 
678 	debug3("%s: updating methods list after \"%s\"", __func__, method);
679 	for (i = 0; i < authctxt->num_auth_methods; i++) {
680 		if (!remove_method(&(authctxt->auth_methods[i]), method,
681 		    submethod))
682 			continue;
683 		found = 1;
684 		if (*authctxt->auth_methods[i] == '\0') {
685 			debug2("authentication methods list %d complete", i);
686 			return 1;
687 		}
688 		debug3("authentication methods list %d remaining: \"%s\"",
689 		    i, authctxt->auth_methods[i]);
690 	}
691 	/* This should not happen, but would be bad if it did */
692 	if (!found)
693 		fatal("%s: method not in AuthenticationMethods", __func__);
694 	return 0;
695 }
696 
697 /* Reset method-specific information */
auth2_authctxt_reset_info(Authctxt * authctxt)698 void auth2_authctxt_reset_info(Authctxt *authctxt)
699 {
700 	sshkey_free(authctxt->auth_method_key);
701 	free(authctxt->auth_method_info);
702 	authctxt->auth_method_key = NULL;
703 	authctxt->auth_method_info = NULL;
704 }
705 
706 /* Record auth method-specific information for logs */
707 void
auth2_record_info(Authctxt * authctxt,const char * fmt,...)708 auth2_record_info(Authctxt *authctxt, const char *fmt, ...)
709 {
710 	va_list ap;
711         int i;
712 
713 	free(authctxt->auth_method_info);
714 	authctxt->auth_method_info = NULL;
715 
716 	va_start(ap, fmt);
717 	i = vasprintf(&authctxt->auth_method_info, fmt, ap);
718 	va_end(ap);
719 
720 	if (i == -1)
721 		fatal("%s: vasprintf failed", __func__);
722 }
723 
724 /*
725  * Records a public key used in authentication. This is used for logging
726  * and to ensure that the same key is not subsequently accepted again for
727  * multiple authentication.
728  */
729 void
auth2_record_key(Authctxt * authctxt,int authenticated,const struct sshkey * key)730 auth2_record_key(Authctxt *authctxt, int authenticated,
731     const struct sshkey *key)
732 {
733 	struct sshkey **tmp, *dup;
734 	int r;
735 
736 	if ((r = sshkey_from_private(key, &dup)) != 0)
737 		fatal("%s: copy key: %s", __func__, ssh_err(r));
738 	sshkey_free(authctxt->auth_method_key);
739 	authctxt->auth_method_key = dup;
740 
741 	if (!authenticated)
742 		return;
743 
744 	/* If authenticated, make sure we don't accept this key again */
745 	if ((r = sshkey_from_private(key, &dup)) != 0)
746 		fatal("%s: copy key: %s", __func__, ssh_err(r));
747 	if (authctxt->nprev_keys >= INT_MAX ||
748 	    (tmp = recallocarray(authctxt->prev_keys, authctxt->nprev_keys,
749 	    authctxt->nprev_keys + 1, sizeof(*authctxt->prev_keys))) == NULL)
750 		fatal("%s: reallocarray failed", __func__);
751 	authctxt->prev_keys = tmp;
752 	authctxt->prev_keys[authctxt->nprev_keys] = dup;
753 	authctxt->nprev_keys++;
754 
755 }
756 
757 /* Checks whether a key has already been previously used for authentication */
758 int
auth2_key_already_used(Authctxt * authctxt,const struct sshkey * key)759 auth2_key_already_used(Authctxt *authctxt, const struct sshkey *key)
760 {
761 	u_int i;
762 	char *fp;
763 
764 	for (i = 0; i < authctxt->nprev_keys; i++) {
765 		if (sshkey_equal_public(key, authctxt->prev_keys[i])) {
766 			fp = sshkey_fingerprint(authctxt->prev_keys[i],
767 			    options.fingerprint_hash, SSH_FP_DEFAULT);
768 			debug3("%s: key already used: %s %s", __func__,
769 			    sshkey_type(authctxt->prev_keys[i]),
770 			    fp == NULL ? "UNKNOWN" : fp);
771 			free(fp);
772 			return 1;
773 		}
774 	}
775 	return 0;
776 }
777 
778 /*
779  * Updates authctxt->session_info with details of authentication. Should be
780  * whenever an authentication method succeeds.
781  */
782 void
auth2_update_session_info(Authctxt * authctxt,const char * method,const char * submethod)783 auth2_update_session_info(Authctxt *authctxt, const char *method,
784     const char *submethod)
785 {
786 	int r;
787 
788 	if (authctxt->session_info == NULL) {
789 		if ((authctxt->session_info = sshbuf_new()) == NULL)
790 			fatal("%s: sshbuf_new", __func__);
791 	}
792 
793 	/* Append method[/submethod] */
794 	if ((r = sshbuf_putf(authctxt->session_info, "%s%s%s",
795 	    method, submethod == NULL ? "" : "/",
796 	    submethod == NULL ? "" : submethod)) != 0)
797 		fatal("%s: append method: %s", __func__, ssh_err(r));
798 
799 	/* Append key if present */
800 	if (authctxt->auth_method_key != NULL) {
801 		if ((r = sshbuf_put_u8(authctxt->session_info, ' ')) != 0 ||
802 		    (r = sshkey_format_text(authctxt->auth_method_key,
803 		    authctxt->session_info)) != 0)
804 			fatal("%s: append key: %s", __func__, ssh_err(r));
805 	}
806 
807 	if (authctxt->auth_method_info != NULL) {
808 		/* Ensure no ambiguity here */
809 		if (strchr(authctxt->auth_method_info, '\n') != NULL)
810 			fatal("%s: auth_method_info contains \\n", __func__);
811 		if ((r = sshbuf_put_u8(authctxt->session_info, ' ')) != 0 ||
812 		    (r = sshbuf_putf(authctxt->session_info, "%s",
813 		    authctxt->auth_method_info)) != 0) {
814 			fatal("%s: append method info: %s",
815 			    __func__, ssh_err(r));
816 		}
817 	}
818 	if ((r = sshbuf_put_u8(authctxt->session_info, '\n')) != 0)
819 		fatal("%s: append: %s", __func__, ssh_err(r));
820 }
821 
822