xref: /openssh-portable/auth2.c (revision 552ea155)
1 /* $OpenBSD: auth2.c,v 1.144 2018/01/23 05:27:21 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/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 
39 #include "atomicio.h"
40 #include "xmalloc.h"
41 #include "ssh2.h"
42 #include "packet.h"
43 #include "log.h"
44 #include "buffer.h"
45 #include "misc.h"
46 #include "servconf.h"
47 #include "compat.h"
48 #include "key.h"
49 #include "hostfile.h"
50 #include "auth.h"
51 #include "dispatch.h"
52 #include "pathnames.h"
53 #include "buffer.h"
54 
55 #ifdef GSSAPI
56 #include "ssh-gss.h"
57 #endif
58 #include "monitor_wrap.h"
59 #include "ssherr.h"
60 
61 /* import */
62 extern ServerOptions options;
63 extern u_char *session_id2;
64 extern u_int session_id2_len;
65 extern Buffer loginmsg;
66 
67 /* methods */
68 
69 extern Authmethod method_none;
70 extern Authmethod method_pubkey;
71 extern Authmethod method_passwd;
72 extern Authmethod method_kbdint;
73 extern Authmethod method_hostbased;
74 #ifdef GSSAPI
75 extern Authmethod method_gssapi;
76 #endif
77 
78 Authmethod *authmethods[] = {
79 	&method_none,
80 	&method_pubkey,
81 #ifdef GSSAPI
82 	&method_gssapi,
83 #endif
84 	&method_passwd,
85 	&method_kbdint,
86 	&method_hostbased,
87 	NULL
88 };
89 
90 /* protocol */
91 
92 static int input_service_request(int, u_int32_t, struct ssh *);
93 static int input_userauth_request(int, u_int32_t, struct ssh *);
94 
95 /* helper */
96 static Authmethod *authmethod_lookup(Authctxt *, const char *);
97 static char *authmethods_get(Authctxt *authctxt);
98 
99 #define MATCH_NONE	0	/* method or submethod mismatch */
100 #define MATCH_METHOD	1	/* method matches (no submethod specified) */
101 #define MATCH_BOTH	2	/* method and submethod match */
102 #define MATCH_PARTIAL	3	/* method matches, submethod can't be checked */
103 static int list_starts_with(const char *, const char *, const char *);
104 
105 char *
106 auth2_read_banner(void)
107 {
108 	struct stat st;
109 	char *banner = NULL;
110 	size_t len, n;
111 	int fd;
112 
113 	if ((fd = open(options.banner, O_RDONLY)) == -1)
114 		return (NULL);
115 	if (fstat(fd, &st) == -1) {
116 		close(fd);
117 		return (NULL);
118 	}
119 	if (st.st_size <= 0 || st.st_size > 1*1024*1024) {
120 		close(fd);
121 		return (NULL);
122 	}
123 
124 	len = (size_t)st.st_size;		/* truncate */
125 	banner = xmalloc(len + 1);
126 	n = atomicio(read, fd, banner, len);
127 	close(fd);
128 
129 	if (n != len) {
130 		free(banner);
131 		return (NULL);
132 	}
133 	banner[n] = '\0';
134 
135 	return (banner);
136 }
137 
138 void
139 userauth_send_banner(const char *msg)
140 {
141 	packet_start(SSH2_MSG_USERAUTH_BANNER);
142 	packet_put_cstring(msg);
143 	packet_put_cstring("");		/* language, unused */
144 	packet_send();
145 	debug("%s: sent", __func__);
146 }
147 
148 static void
149 userauth_banner(void)
150 {
151 	char *banner = NULL;
152 
153 	if (options.banner == NULL)
154 		return;
155 
156 	if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
157 		goto done;
158 	userauth_send_banner(banner);
159 
160 done:
161 	free(banner);
162 }
163 
164 /*
165  * loop until authctxt->success == TRUE
166  */
167 void
168 do_authentication2(Authctxt *authctxt)
169 {
170 	struct ssh *ssh = active_state;		/* XXX */
171 	ssh->authctxt = authctxt;		/* XXX move to caller */
172 	ssh_dispatch_init(ssh, &dispatch_protocol_error);
173 	ssh_dispatch_set(ssh, SSH2_MSG_SERVICE_REQUEST, &input_service_request);
174 	ssh_dispatch_run_fatal(ssh, DISPATCH_BLOCK, &authctxt->success);
175 	ssh->authctxt = NULL;
176 }
177 
178 /*ARGSUSED*/
179 static int
180 input_service_request(int type, u_int32_t seq, struct ssh *ssh)
181 {
182 	Authctxt *authctxt = ssh->authctxt;
183 	u_int len;
184 	int acceptit = 0;
185 	char *service = packet_get_cstring(&len);
186 	packet_check_eom();
187 
188 	if (authctxt == NULL)
189 		fatal("input_service_request: no authctxt");
190 
191 	if (strcmp(service, "ssh-userauth") == 0) {
192 		if (!authctxt->success) {
193 			acceptit = 1;
194 			/* now we can handle user-auth requests */
195 			ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
196 		}
197 	}
198 	/* XXX all other service requests are denied */
199 
200 	if (acceptit) {
201 		packet_start(SSH2_MSG_SERVICE_ACCEPT);
202 		packet_put_cstring(service);
203 		packet_send();
204 		packet_write_wait();
205 	} else {
206 		debug("bad service request %s", service);
207 		packet_disconnect("bad service request %s", service);
208 	}
209 	free(service);
210 	return 0;
211 }
212 
213 /*ARGSUSED*/
214 static int
215 input_userauth_request(int type, u_int32_t seq, struct ssh *ssh)
216 {
217 	Authctxt *authctxt = ssh->authctxt;
218 	Authmethod *m = NULL;
219 	char *user, *service, *method, *style = NULL;
220 	int authenticated = 0;
221 
222 	if (authctxt == NULL)
223 		fatal("input_userauth_request: no authctxt");
224 
225 	user = packet_get_cstring(NULL);
226 	service = packet_get_cstring(NULL);
227 	method = packet_get_cstring(NULL);
228 	debug("userauth-request for user %s service %s method %s", user, service, method);
229 	debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
230 
231 	if ((style = strchr(user, ':')) != NULL)
232 		*style++ = 0;
233 
234 	if (authctxt->attempt++ == 0) {
235 		/* setup auth context */
236 		authctxt->pw = PRIVSEP(getpwnamallow(user));
237 		authctxt->user = xstrdup(user);
238 		if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
239 			authctxt->valid = 1;
240 			debug2("%s: setting up authctxt for %s",
241 			    __func__, user);
242 		} else {
243 			/* Invalid user, fake password information */
244 			authctxt->pw = fakepw();
245 #ifdef SSH_AUDIT_EVENTS
246 			PRIVSEP(audit_event(SSH_INVALID_USER));
247 #endif
248 		}
249 #ifdef USE_PAM
250 		if (options.use_pam)
251 			PRIVSEP(start_pam(authctxt));
252 #endif
253 		ssh_packet_set_log_preamble(ssh, "%suser %s",
254 		    authctxt->valid ? "authenticating " : "invalid ", user);
255 		setproctitle("%s%s", authctxt->valid ? user : "unknown",
256 		    use_privsep ? " [net]" : "");
257 		authctxt->service = xstrdup(service);
258 		authctxt->style = style ? xstrdup(style) : NULL;
259 		if (use_privsep)
260 			mm_inform_authserv(service, style);
261 		userauth_banner();
262 		if (auth2_setup_methods_lists(authctxt) != 0)
263 			packet_disconnect("no authentication methods enabled");
264 	} else if (strcmp(user, authctxt->user) != 0 ||
265 	    strcmp(service, authctxt->service) != 0) {
266 		packet_disconnect("Change of username or service not allowed: "
267 		    "(%s,%s) -> (%s,%s)",
268 		    authctxt->user, authctxt->service, user, service);
269 	}
270 	/* reset state */
271 	auth2_challenge_stop(ssh);
272 
273 #ifdef GSSAPI
274 	/* XXX move to auth2_gssapi_stop() */
275 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
276 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
277 #endif
278 
279 	auth2_authctxt_reset_info(authctxt);
280 	authctxt->postponed = 0;
281 	authctxt->server_caused_failure = 0;
282 
283 	/* try to authenticate user */
284 	m = authmethod_lookup(authctxt, method);
285 	if (m != NULL && authctxt->failures < options.max_authtries) {
286 		debug2("input_userauth_request: try method %s", method);
287 		authenticated =	m->userauth(ssh);
288 	}
289 	userauth_finish(ssh, authenticated, method, NULL);
290 
291 	free(service);
292 	free(user);
293 	free(method);
294 	return 0;
295 }
296 
297 void
298 userauth_finish(struct ssh *ssh, int authenticated, const char *method,
299     const char *submethod)
300 {
301 	Authctxt *authctxt = ssh->authctxt;
302 	char *methods;
303 	int partial = 0;
304 
305 	if (!authctxt->valid && authenticated)
306 		fatal("INTERNAL ERROR: authenticated invalid user %s",
307 		    authctxt->user);
308 	if (authenticated && authctxt->postponed)
309 		fatal("INTERNAL ERROR: authenticated and postponed");
310 
311 	/* Special handling for root */
312 	if (authenticated && authctxt->pw->pw_uid == 0 &&
313 	    !auth_root_allowed(method)) {
314 		authenticated = 0;
315 #ifdef SSH_AUDIT_EVENTS
316 		PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
317 #endif
318 	}
319 
320 	if (authenticated && options.num_auth_methods != 0) {
321 		if (!auth2_update_methods_lists(authctxt, method, submethod)) {
322 			authenticated = 0;
323 			partial = 1;
324 		}
325 	}
326 
327 	/* Log before sending the reply */
328 	auth_log(authctxt, authenticated, partial, method, submethod);
329 
330 	/* Update information exposed to session */
331 	if (authenticated || partial)
332 		auth2_update_session_info(authctxt, method, submethod);
333 
334 	if (authctxt->postponed)
335 		return;
336 
337 #ifdef USE_PAM
338 	if (options.use_pam && authenticated) {
339 		if (!PRIVSEP(do_pam_account())) {
340 			/* if PAM returned a message, send it to the user */
341 			if (buffer_len(&loginmsg) > 0) {
342 				buffer_append(&loginmsg, "\0", 1);
343 				userauth_send_banner(buffer_ptr(&loginmsg));
344 				packet_write_wait();
345 			}
346 			fatal("Access denied for user %s by PAM account "
347 			    "configuration", authctxt->user);
348 		}
349 	}
350 #endif
351 
352 #ifdef _UNICOS
353 	if (authenticated && cray_access_denied(authctxt->user)) {
354 		authenticated = 0;
355 		fatal("Access denied for user %s.", authctxt->user);
356 	}
357 #endif /* _UNICOS */
358 
359 	if (authenticated == 1) {
360 		/* turn off userauth */
361 		ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
362 		packet_start(SSH2_MSG_USERAUTH_SUCCESS);
363 		packet_send();
364 		packet_write_wait();
365 		/* now we can break out */
366 		authctxt->success = 1;
367 		ssh_packet_set_log_preamble(ssh, "user %s", authctxt->user);
368 	} else {
369 
370 		/* Allow initial try of "none" auth without failure penalty */
371 		if (!partial && !authctxt->server_caused_failure &&
372 		    (authctxt->attempt > 1 || strcmp(method, "none") != 0))
373 			authctxt->failures++;
374 		if (authctxt->failures >= options.max_authtries) {
375 #ifdef SSH_AUDIT_EVENTS
376 			PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
377 #endif
378 			auth_maxtries_exceeded(authctxt);
379 		}
380 		methods = authmethods_get(authctxt);
381 		debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
382 		    partial, methods);
383 		packet_start(SSH2_MSG_USERAUTH_FAILURE);
384 		packet_put_cstring(methods);
385 		packet_put_char(partial);
386 		packet_send();
387 		packet_write_wait();
388 		free(methods);
389 	}
390 }
391 
392 /*
393  * Checks whether method is allowed by at least one AuthenticationMethods
394  * methods list. Returns 1 if allowed, or no methods lists configured.
395  * 0 otherwise.
396  */
397 int
398 auth2_method_allowed(Authctxt *authctxt, const char *method,
399     const char *submethod)
400 {
401 	u_int i;
402 
403 	/*
404 	 * NB. authctxt->num_auth_methods might be zero as a result of
405 	 * auth2_setup_methods_lists(), so check the configuration.
406 	 */
407 	if (options.num_auth_methods == 0)
408 		return 1;
409 	for (i = 0; i < authctxt->num_auth_methods; i++) {
410 		if (list_starts_with(authctxt->auth_methods[i], method,
411 		    submethod) != MATCH_NONE)
412 			return 1;
413 	}
414 	return 0;
415 }
416 
417 static char *
418 authmethods_get(Authctxt *authctxt)
419 {
420 	Buffer b;
421 	char *list;
422 	u_int i;
423 
424 	buffer_init(&b);
425 	for (i = 0; authmethods[i] != NULL; i++) {
426 		if (strcmp(authmethods[i]->name, "none") == 0)
427 			continue;
428 		if (authmethods[i]->enabled == NULL ||
429 		    *(authmethods[i]->enabled) == 0)
430 			continue;
431 		if (!auth2_method_allowed(authctxt, authmethods[i]->name,
432 		    NULL))
433 			continue;
434 		if (buffer_len(&b) > 0)
435 			buffer_append(&b, ",", 1);
436 		buffer_append(&b, authmethods[i]->name,
437 		    strlen(authmethods[i]->name));
438 	}
439 	if ((list = sshbuf_dup_string(&b)) == NULL)
440 		fatal("%s: sshbuf_dup_string failed", __func__);
441 	buffer_free(&b);
442 	return list;
443 }
444 
445 static Authmethod *
446 authmethod_lookup(Authctxt *authctxt, const char *name)
447 {
448 	int i;
449 
450 	if (name != NULL)
451 		for (i = 0; authmethods[i] != NULL; i++)
452 			if (authmethods[i]->enabled != NULL &&
453 			    *(authmethods[i]->enabled) != 0 &&
454 			    strcmp(name, authmethods[i]->name) == 0 &&
455 			    auth2_method_allowed(authctxt,
456 			    authmethods[i]->name, NULL))
457 				return authmethods[i];
458 	debug2("Unrecognized authentication method name: %s",
459 	    name ? name : "NULL");
460 	return NULL;
461 }
462 
463 /*
464  * Check a comma-separated list of methods for validity. Is need_enable is
465  * non-zero, then also require that the methods are enabled.
466  * Returns 0 on success or -1 if the methods list is invalid.
467  */
468 int
469 auth2_methods_valid(const char *_methods, int need_enable)
470 {
471 	char *methods, *omethods, *method, *p;
472 	u_int i, found;
473 	int ret = -1;
474 
475 	if (*_methods == '\0') {
476 		error("empty authentication method list");
477 		return -1;
478 	}
479 	omethods = methods = xstrdup(_methods);
480 	while ((method = strsep(&methods, ",")) != NULL) {
481 		for (found = i = 0; !found && authmethods[i] != NULL; i++) {
482 			if ((p = strchr(method, ':')) != NULL)
483 				*p = '\0';
484 			if (strcmp(method, authmethods[i]->name) != 0)
485 				continue;
486 			if (need_enable) {
487 				if (authmethods[i]->enabled == NULL ||
488 				    *(authmethods[i]->enabled) == 0) {
489 					error("Disabled method \"%s\" in "
490 					    "AuthenticationMethods list \"%s\"",
491 					    method, _methods);
492 					goto out;
493 				}
494 			}
495 			found = 1;
496 			break;
497 		}
498 		if (!found) {
499 			error("Unknown authentication method \"%s\" in list",
500 			    method);
501 			goto out;
502 		}
503 	}
504 	ret = 0;
505  out:
506 	free(omethods);
507 	return ret;
508 }
509 
510 /*
511  * Prune the AuthenticationMethods supplied in the configuration, removing
512  * any methods lists that include disabled methods. Note that this might
513  * leave authctxt->num_auth_methods == 0, even when multiple required auth
514  * has been requested. For this reason, all tests for whether multiple is
515  * enabled should consult options.num_auth_methods directly.
516  */
517 int
518 auth2_setup_methods_lists(Authctxt *authctxt)
519 {
520 	u_int i;
521 
522 	if (options.num_auth_methods == 0)
523 		return 0;
524 	debug3("%s: checking methods", __func__);
525 	authctxt->auth_methods = xcalloc(options.num_auth_methods,
526 	    sizeof(*authctxt->auth_methods));
527 	authctxt->num_auth_methods = 0;
528 	for (i = 0; i < options.num_auth_methods; i++) {
529 		if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
530 			logit("Authentication methods list \"%s\" contains "
531 			    "disabled method, skipping",
532 			    options.auth_methods[i]);
533 			continue;
534 		}
535 		debug("authentication methods list %d: %s",
536 		    authctxt->num_auth_methods, options.auth_methods[i]);
537 		authctxt->auth_methods[authctxt->num_auth_methods++] =
538 		    xstrdup(options.auth_methods[i]);
539 	}
540 	if (authctxt->num_auth_methods == 0) {
541 		error("No AuthenticationMethods left after eliminating "
542 		    "disabled methods");
543 		return -1;
544 	}
545 	return 0;
546 }
547 
548 static int
549 list_starts_with(const char *methods, const char *method,
550     const char *submethod)
551 {
552 	size_t l = strlen(method);
553 	int match;
554 	const char *p;
555 
556 	if (strncmp(methods, method, l) != 0)
557 		return MATCH_NONE;
558 	p = methods + l;
559 	match = MATCH_METHOD;
560 	if (*p == ':') {
561 		if (!submethod)
562 			return MATCH_PARTIAL;
563 		l = strlen(submethod);
564 		p += 1;
565 		if (strncmp(submethod, p, l))
566 			return MATCH_NONE;
567 		p += l;
568 		match = MATCH_BOTH;
569 	}
570 	if (*p != ',' && *p != '\0')
571 		return MATCH_NONE;
572 	return match;
573 }
574 
575 /*
576  * Remove method from the start of a comma-separated list of methods.
577  * Returns 0 if the list of methods did not start with that method or 1
578  * if it did.
579  */
580 static int
581 remove_method(char **methods, const char *method, const char *submethod)
582 {
583 	char *omethods = *methods, *p;
584 	size_t l = strlen(method);
585 	int match;
586 
587 	match = list_starts_with(omethods, method, submethod);
588 	if (match != MATCH_METHOD && match != MATCH_BOTH)
589 		return 0;
590 	p = omethods + l;
591 	if (submethod && match == MATCH_BOTH)
592 		p += 1 + strlen(submethod); /* include colon */
593 	if (*p == ',')
594 		p++;
595 	*methods = xstrdup(p);
596 	free(omethods);
597 	return 1;
598 }
599 
600 /*
601  * Called after successful authentication. Will remove the successful method
602  * from the start of each list in which it occurs. If it was the last method
603  * in any list, then authentication is deemed successful.
604  * Returns 1 if the method completed any authentication list or 0 otherwise.
605  */
606 int
607 auth2_update_methods_lists(Authctxt *authctxt, const char *method,
608     const char *submethod)
609 {
610 	u_int i, found = 0;
611 
612 	debug3("%s: updating methods list after \"%s\"", __func__, method);
613 	for (i = 0; i < authctxt->num_auth_methods; i++) {
614 		if (!remove_method(&(authctxt->auth_methods[i]), method,
615 		    submethod))
616 			continue;
617 		found = 1;
618 		if (*authctxt->auth_methods[i] == '\0') {
619 			debug2("authentication methods list %d complete", i);
620 			return 1;
621 		}
622 		debug3("authentication methods list %d remaining: \"%s\"",
623 		    i, authctxt->auth_methods[i]);
624 	}
625 	/* This should not happen, but would be bad if it did */
626 	if (!found)
627 		fatal("%s: method not in AuthenticationMethods", __func__);
628 	return 0;
629 }
630 
631 /* Reset method-specific information */
632 void auth2_authctxt_reset_info(Authctxt *authctxt)
633 {
634 	sshkey_free(authctxt->auth_method_key);
635 	free(authctxt->auth_method_info);
636 	authctxt->auth_method_key = NULL;
637 	authctxt->auth_method_info = NULL;
638 }
639 
640 /* Record auth method-specific information for logs */
641 void
642 auth2_record_info(Authctxt *authctxt, const char *fmt, ...)
643 {
644 	va_list ap;
645         int i;
646 
647 	free(authctxt->auth_method_info);
648 	authctxt->auth_method_info = NULL;
649 
650 	va_start(ap, fmt);
651 	i = vasprintf(&authctxt->auth_method_info, fmt, ap);
652 	va_end(ap);
653 
654 	if (i < 0 || authctxt->auth_method_info == NULL)
655 		fatal("%s: vasprintf failed", __func__);
656 }
657 
658 /*
659  * Records a public key used in authentication. This is used for logging
660  * and to ensure that the same key is not subsequently accepted again for
661  * multiple authentication.
662  */
663 void
664 auth2_record_key(Authctxt *authctxt, int authenticated,
665     const struct sshkey *key)
666 {
667 	struct sshkey **tmp, *dup;
668 	int r;
669 
670 	if ((r = sshkey_demote(key, &dup)) != 0)
671 		fatal("%s: copy key: %s", __func__, ssh_err(r));
672 	sshkey_free(authctxt->auth_method_key);
673 	authctxt->auth_method_key = dup;
674 
675 	if (!authenticated)
676 		return;
677 
678 	/* If authenticated, make sure we don't accept this key again */
679 	if ((r = sshkey_demote(key, &dup)) != 0)
680 		fatal("%s: copy key: %s", __func__, ssh_err(r));
681 	if (authctxt->nprev_keys >= INT_MAX ||
682 	    (tmp = recallocarray(authctxt->prev_keys, authctxt->nprev_keys,
683 	    authctxt->nprev_keys + 1, sizeof(*authctxt->prev_keys))) == NULL)
684 		fatal("%s: reallocarray failed", __func__);
685 	authctxt->prev_keys = tmp;
686 	authctxt->prev_keys[authctxt->nprev_keys] = dup;
687 	authctxt->nprev_keys++;
688 
689 }
690 
691 /* Checks whether a key has already been previously used for authentication */
692 int
693 auth2_key_already_used(Authctxt *authctxt, const struct sshkey *key)
694 {
695 	u_int i;
696 	char *fp;
697 
698 	for (i = 0; i < authctxt->nprev_keys; i++) {
699 		if (sshkey_equal_public(key, authctxt->prev_keys[i])) {
700 			fp = sshkey_fingerprint(authctxt->prev_keys[i],
701 			    options.fingerprint_hash, SSH_FP_DEFAULT);
702 			debug3("%s: key already used: %s %s", __func__,
703 			    sshkey_type(authctxt->prev_keys[i]),
704 			    fp == NULL ? "UNKNOWN" : fp);
705 			free(fp);
706 			return 1;
707 		}
708 	}
709 	return 0;
710 }
711 
712 /*
713  * Updates authctxt->session_info with details of authentication. Should be
714  * whenever an authentication method succeeds.
715  */
716 void
717 auth2_update_session_info(Authctxt *authctxt, const char *method,
718     const char *submethod)
719 {
720 	int r;
721 
722 	if (authctxt->session_info == NULL) {
723 		if ((authctxt->session_info = sshbuf_new()) == NULL)
724 			fatal("%s: sshbuf_new", __func__);
725 	}
726 
727 	/* Append method[/submethod] */
728 	if ((r = sshbuf_putf(authctxt->session_info, "%s%s%s",
729 	    method, submethod == NULL ? "" : "/",
730 	    submethod == NULL ? "" : submethod)) != 0)
731 		fatal("%s: append method: %s", __func__, ssh_err(r));
732 
733 	/* Append key if present */
734 	if (authctxt->auth_method_key != NULL) {
735 		if ((r = sshbuf_put_u8(authctxt->session_info, ' ')) != 0 ||
736 		    (r = sshkey_format_text(authctxt->auth_method_key,
737 		    authctxt->session_info)) != 0)
738 			fatal("%s: append key: %s", __func__, ssh_err(r));
739 	}
740 
741 	if (authctxt->auth_method_info != NULL) {
742 		/* Ensure no ambiguity here */
743 		if (strchr(authctxt->auth_method_info, '\n') != NULL)
744 			fatal("%s: auth_method_info contains \\n", __func__);
745 		if ((r = sshbuf_put_u8(authctxt->session_info, ' ')) != 0 ||
746 		    (r = sshbuf_putf(authctxt->session_info, "%s",
747 		    authctxt->auth_method_info)) != 0) {
748 			fatal("%s: append method info: %s",
749 			    __func__, ssh_err(r));
750 		}
751 	}
752 	if ((r = sshbuf_put_u8(authctxt->session_info, '\n')) != 0)
753 		fatal("%s: append: %s", __func__, ssh_err(r));
754 }
755 
756