auth2.c revision 362908 
1/* $OpenBSD: auth2.c,v 1.137 2017/02/03 23:05:57 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__RCSID("$FreeBSD: stable/11/crypto/openssh/auth2.c 362908 2020-07-03 07:25:26Z delphij $");
28
29#include <sys/types.h>
30#include <sys/stat.h>
31#include <sys/uio.h>
32
33#include <fcntl.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#include "blacklist_client.h"
55
56#ifdef GSSAPI
57#include "ssh-gss.h"
58#endif
59#include "monitor_wrap.h"
60
61/* import */
62extern ServerOptions options;
63extern u_char *session_id2;
64extern u_int session_id2_len;
65extern Buffer loginmsg;
66
67/* methods */
68
69extern Authmethod method_none;
70extern Authmethod method_pubkey;
71extern Authmethod method_passwd;
72extern Authmethod method_kbdint;
73extern Authmethod method_hostbased;
74#ifdef GSSAPI
75extern Authmethod method_gssapi;
76#endif
77
78Authmethod *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
92static int input_service_request(int, u_int32_t, void *);
93static int input_userauth_request(int, u_int32_t, void *);
94
95/* helper */
96static Authmethod *authmethod_lookup(Authctxt *, const char *);
97static 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 */
103static int list_starts_with(const char *, const char *, const char *);
104
105char *
106auth2_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
138void
139userauth_send_banner(const char *msg)
140{
141	if (datafellows & SSH_BUG_BANNER)
142		return;
143
144	packet_start(SSH2_MSG_USERAUTH_BANNER);
145	packet_put_cstring(msg);
146	packet_put_cstring("");		/* language, unused */
147	packet_send();
148	debug("%s: sent", __func__);
149}
150
151static void
152userauth_banner(void)
153{
154	char *banner = NULL;
155
156	if (options.banner == NULL || (datafellows & SSH_BUG_BANNER) != 0)
157		return;
158
159	if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
160		goto done;
161	userauth_send_banner(banner);
162
163done:
164	free(banner);
165}
166
167/*
168 * loop until authctxt->success == TRUE
169 */
170void
171do_authentication2(Authctxt *authctxt)
172{
173	dispatch_init(&dispatch_protocol_error);
174	dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
175	dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
176}
177
178/*ARGSUSED*/
179static int
180input_service_request(int type, u_int32_t seq, void *ctxt)
181{
182	Authctxt *authctxt = ctxt;
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			dispatch_set(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*/
214static int
215input_userauth_request(int type, u_int32_t seq, void *ctxt)
216{
217	struct ssh *ssh = active_state;	/* XXX */
218	Authctxt *authctxt = ctxt;
219	Authmethod *m = NULL;
220	char *user, *service, *method, *style = NULL;
221	int authenticated = 0;
222#ifdef HAVE_LOGIN_CAP
223	login_cap_t *lc;
224	const char *from_host, *from_ip;
225#endif
226
227	if (authctxt == NULL)
228		fatal("input_userauth_request: no authctxt");
229
230	user = packet_get_cstring(NULL);
231	service = packet_get_cstring(NULL);
232	method = packet_get_cstring(NULL);
233	debug("userauth-request for user %s service %s method %s", user, service, method);
234	debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
235
236	if ((style = strchr(user, ':')) != NULL)
237		*style++ = 0;
238
239	if (authctxt->attempt++ == 0) {
240		/* setup auth context */
241		authctxt->pw = PRIVSEP(getpwnamallow(user));
242		authctxt->user = xstrdup(user);
243		if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
244			authctxt->valid = 1;
245			debug2("%s: setting up authctxt for %s",
246			    __func__, user);
247		} else {
248			/* Invalid user, fake password information */
249			authctxt->pw = fakepw();
250#ifdef SSH_AUDIT_EVENTS
251			PRIVSEP(audit_event(SSH_INVALID_USER));
252#endif
253		}
254#ifdef USE_PAM
255		if (options.use_pam)
256			PRIVSEP(start_pam(authctxt));
257#endif
258		ssh_packet_set_log_preamble(ssh, "%suser %s",
259		    authctxt->valid ? "authenticating " : "invalid ", user);
260		setproctitle("%s%s", authctxt->valid ? user : "unknown",
261		    use_privsep ? " [net]" : "");
262		authctxt->service = xstrdup(service);
263		authctxt->style = style ? xstrdup(style) : NULL;
264		if (use_privsep)
265			mm_inform_authserv(service, style);
266		userauth_banner();
267		if (auth2_setup_methods_lists(authctxt) != 0)
268			packet_disconnect("no authentication methods enabled");
269	} else if (strcmp(user, authctxt->user) != 0 ||
270	    strcmp(service, authctxt->service) != 0) {
271		packet_disconnect("Change of username or service not allowed: "
272		    "(%s,%s) -> (%s,%s)",
273		    authctxt->user, authctxt->service, user, service);
274	}
275
276#ifdef HAVE_LOGIN_CAP
277	if (authctxt->pw != NULL &&
278	    (lc = login_getpwclass(authctxt->pw)) != NULL) {
279		from_host = auth_get_canonical_hostname(ssh, options.use_dns);
280		from_ip = ssh_remote_ipaddr(ssh);
281		if (!auth_hostok(lc, from_host, from_ip)) {
282			logit("Denied connection for %.200s from %.200s [%.200s].",
283			    authctxt->pw->pw_name, from_host, from_ip);
284			packet_disconnect("Sorry, you are not allowed to connect.");
285		}
286		if (!auth_timeok(lc, time(NULL))) {
287			logit("LOGIN %.200s REFUSED (TIME) FROM %.200s",
288			    authctxt->pw->pw_name, from_host);
289			packet_disconnect("Logins not available right now.");
290		}
291		login_close(lc);
292	}
293#endif  /* HAVE_LOGIN_CAP */
294
295	/* reset state */
296	auth2_challenge_stop(authctxt);
297
298#ifdef GSSAPI
299	/* XXX move to auth2_gssapi_stop() */
300	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
301	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
302#endif
303
304	authctxt->postponed = 0;
305	authctxt->server_caused_failure = 0;
306
307	/* try to authenticate user */
308	m = authmethod_lookup(authctxt, method);
309	if (m != NULL && authctxt->failures < options.max_authtries) {
310		debug2("input_userauth_request: try method %s", method);
311		authenticated =	m->userauth(authctxt);
312	}
313	userauth_finish(authctxt, authenticated, method, NULL);
314
315	free(service);
316	free(user);
317	free(method);
318	return 0;
319}
320
321void
322userauth_finish(Authctxt *authctxt, int authenticated, const char *method,
323    const char *submethod)
324{
325	struct ssh *ssh = active_state;	/* XXX */
326	char *methods;
327	int partial = 0;
328
329	if (!authctxt->valid && authenticated)
330		fatal("INTERNAL ERROR: authenticated invalid user %s",
331		    authctxt->user);
332	if (authenticated && authctxt->postponed)
333		fatal("INTERNAL ERROR: authenticated and postponed");
334
335	/* Special handling for root */
336	if (authenticated && authctxt->pw->pw_uid == 0 &&
337	    !auth_root_allowed(method)) {
338		authenticated = 0;
339#ifdef SSH_AUDIT_EVENTS
340		PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
341#endif
342	}
343
344	if (authenticated && options.num_auth_methods != 0) {
345		if (!auth2_update_methods_lists(authctxt, method, submethod)) {
346			authenticated = 0;
347			partial = 1;
348		}
349	}
350
351	/* Log before sending the reply */
352	auth_log(authctxt, authenticated, partial, method, submethod);
353
354	if (authctxt->postponed)
355		return;
356
357#ifdef USE_PAM
358	if (options.use_pam && authenticated) {
359		if (!PRIVSEP(do_pam_account())) {
360			/* if PAM returned a message, send it to the user */
361			if (buffer_len(&loginmsg) > 0) {
362				buffer_append(&loginmsg, "\0", 1);
363				userauth_send_banner(buffer_ptr(&loginmsg));
364				packet_write_wait();
365			}
366			fatal("Access denied for user %s by PAM account "
367			    "configuration", authctxt->user);
368		}
369	}
370#endif
371
372#ifdef _UNICOS
373	if (authenticated && cray_access_denied(authctxt->user)) {
374		authenticated = 0;
375		fatal("Access denied for user %s.", authctxt->user);
376	}
377#endif /* _UNICOS */
378
379	if (authenticated == 1) {
380		/* turn off userauth */
381		dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
382		packet_start(SSH2_MSG_USERAUTH_SUCCESS);
383		packet_send();
384		packet_write_wait();
385		/* now we can break out */
386		authctxt->success = 1;
387		ssh_packet_set_log_preamble(ssh, "user %s", authctxt->user);
388	} else {
389
390		/* Allow initial try of "none" auth without failure penalty */
391		if (!partial && !authctxt->server_caused_failure &&
392		    (authctxt->attempt > 1 || strcmp(method, "none") != 0)) {
393			authctxt->failures++;
394			BLACKLIST_NOTIFY(BLACKLIST_AUTH_FAIL, "ssh");
395		}
396		if (authctxt->failures >= options.max_authtries) {
397#ifdef SSH_AUDIT_EVENTS
398			PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
399#endif
400			auth_maxtries_exceeded(authctxt);
401		}
402		methods = authmethods_get(authctxt);
403		debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
404		    partial, methods);
405		packet_start(SSH2_MSG_USERAUTH_FAILURE);
406		packet_put_cstring(methods);
407		packet_put_char(partial);
408		packet_send();
409		packet_write_wait();
410		free(methods);
411	}
412}
413
414/*
415 * Checks whether method is allowed by at least one AuthenticationMethods
416 * methods list. Returns 1 if allowed, or no methods lists configured.
417 * 0 otherwise.
418 */
419int
420auth2_method_allowed(Authctxt *authctxt, const char *method,
421    const char *submethod)
422{
423	u_int i;
424
425	/*
426	 * NB. authctxt->num_auth_methods might be zero as a result of
427	 * auth2_setup_methods_lists(), so check the configuration.
428	 */
429	if (options.num_auth_methods == 0)
430		return 1;
431	for (i = 0; i < authctxt->num_auth_methods; i++) {
432		if (list_starts_with(authctxt->auth_methods[i], method,
433		    submethod) != MATCH_NONE)
434			return 1;
435	}
436	return 0;
437}
438
439static char *
440authmethods_get(Authctxt *authctxt)
441{
442	Buffer b;
443	char *list;
444	u_int i;
445
446	buffer_init(&b);
447	for (i = 0; authmethods[i] != NULL; i++) {
448		if (strcmp(authmethods[i]->name, "none") == 0)
449			continue;
450		if (authmethods[i]->enabled == NULL ||
451		    *(authmethods[i]->enabled) == 0)
452			continue;
453		if (!auth2_method_allowed(authctxt, authmethods[i]->name,
454		    NULL))
455			continue;
456		if (buffer_len(&b) > 0)
457			buffer_append(&b, ",", 1);
458		buffer_append(&b, authmethods[i]->name,
459		    strlen(authmethods[i]->name));
460	}
461	if ((list = sshbuf_dup_string(&b)) == NULL)
462		fatal("%s: sshbuf_dup_string failed", __func__);
463	buffer_free(&b);
464	return list;
465}
466
467static Authmethod *
468authmethod_lookup(Authctxt *authctxt, const char *name)
469{
470	int i;
471
472	if (name != NULL)
473		for (i = 0; authmethods[i] != NULL; i++)
474			if (authmethods[i]->enabled != NULL &&
475			    *(authmethods[i]->enabled) != 0 &&
476			    strcmp(name, authmethods[i]->name) == 0 &&
477			    auth2_method_allowed(authctxt,
478			    authmethods[i]->name, NULL))
479				return authmethods[i];
480	debug2("Unrecognized authentication method name: %s",
481	    name ? name : "NULL");
482	return NULL;
483}
484
485/*
486 * Check a comma-separated list of methods for validity. Is need_enable is
487 * non-zero, then also require that the methods are enabled.
488 * Returns 0 on success or -1 if the methods list is invalid.
489 */
490int
491auth2_methods_valid(const char *_methods, int need_enable)
492{
493	char *methods, *omethods, *method, *p;
494	u_int i, found;
495	int ret = -1;
496
497	if (*_methods == '\0') {
498		error("empty authentication method list");
499		return -1;
500	}
501	omethods = methods = xstrdup(_methods);
502	while ((method = strsep(&methods, ",")) != NULL) {
503		for (found = i = 0; !found && authmethods[i] != NULL; i++) {
504			if ((p = strchr(method, ':')) != NULL)
505				*p = '\0';
506			if (strcmp(method, authmethods[i]->name) != 0)
507				continue;
508			if (need_enable) {
509				if (authmethods[i]->enabled == NULL ||
510				    *(authmethods[i]->enabled) == 0) {
511					error("Disabled method \"%s\" in "
512					    "AuthenticationMethods list \"%s\"",
513					    method, _methods);
514					goto out;
515				}
516			}
517			found = 1;
518			break;
519		}
520		if (!found) {
521			error("Unknown authentication method \"%s\" in list",
522			    method);
523			goto out;
524		}
525	}
526	ret = 0;
527 out:
528	free(omethods);
529	return ret;
530}
531
532/*
533 * Prune the AuthenticationMethods supplied in the configuration, removing
534 * any methods lists that include disabled methods. Note that this might
535 * leave authctxt->num_auth_methods == 0, even when multiple required auth
536 * has been requested. For this reason, all tests for whether multiple is
537 * enabled should consult options.num_auth_methods directly.
538 */
539int
540auth2_setup_methods_lists(Authctxt *authctxt)
541{
542	u_int i;
543
544	if (options.num_auth_methods == 0)
545		return 0;
546	debug3("%s: checking methods", __func__);
547	authctxt->auth_methods = xcalloc(options.num_auth_methods,
548	    sizeof(*authctxt->auth_methods));
549	authctxt->num_auth_methods = 0;
550	for (i = 0; i < options.num_auth_methods; i++) {
551		if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
552			logit("Authentication methods list \"%s\" contains "
553			    "disabled method, skipping",
554			    options.auth_methods[i]);
555			continue;
556		}
557		debug("authentication methods list %d: %s",
558		    authctxt->num_auth_methods, options.auth_methods[i]);
559		authctxt->auth_methods[authctxt->num_auth_methods++] =
560		    xstrdup(options.auth_methods[i]);
561	}
562	if (authctxt->num_auth_methods == 0) {
563		error("No AuthenticationMethods left after eliminating "
564		    "disabled methods");
565		return -1;
566	}
567	return 0;
568}
569
570static int
571list_starts_with(const char *methods, const char *method,
572    const char *submethod)
573{
574	size_t l = strlen(method);
575	int match;
576	const char *p;
577
578	if (strncmp(methods, method, l) != 0)
579		return MATCH_NONE;
580	p = methods + l;
581	match = MATCH_METHOD;
582	if (*p == ':') {
583		if (!submethod)
584			return MATCH_PARTIAL;
585		l = strlen(submethod);
586		p += 1;
587		if (strncmp(submethod, p, l))
588			return MATCH_NONE;
589		p += l;
590		match = MATCH_BOTH;
591	}
592	if (*p != ',' && *p != '\0')
593		return MATCH_NONE;
594	return match;
595}
596
597/*
598 * Remove method from the start of a comma-separated list of methods.
599 * Returns 0 if the list of methods did not start with that method or 1
600 * if it did.
601 */
602static int
603remove_method(char **methods, const char *method, const char *submethod)
604{
605	char *omethods = *methods, *p;
606	size_t l = strlen(method);
607	int match;
608
609	match = list_starts_with(omethods, method, submethod);
610	if (match != MATCH_METHOD && match != MATCH_BOTH)
611		return 0;
612	p = omethods + l;
613	if (submethod && match == MATCH_BOTH)
614		p += 1 + strlen(submethod); /* include colon */
615	if (*p == ',')
616		p++;
617	*methods = xstrdup(p);
618	free(omethods);
619	return 1;
620}
621
622/*
623 * Called after successful authentication. Will remove the successful method
624 * from the start of each list in which it occurs. If it was the last method
625 * in any list, then authentication is deemed successful.
626 * Returns 1 if the method completed any authentication list or 0 otherwise.
627 */
628int
629auth2_update_methods_lists(Authctxt *authctxt, const char *method,
630    const char *submethod)
631{
632	u_int i, found = 0;
633
634	debug3("%s: updating methods list after \"%s\"", __func__, method);
635	for (i = 0; i < authctxt->num_auth_methods; i++) {
636		if (!remove_method(&(authctxt->auth_methods[i]), method,
637		    submethod))
638			continue;
639		found = 1;
640		if (*authctxt->auth_methods[i] == '\0') {
641			debug2("authentication methods list %d complete", i);
642			return 1;
643		}
644		debug3("authentication methods list %d remaining: \"%s\"",
645		    i, authctxt->auth_methods[i]);
646	}
647	/* This should not happen, but would be bad if it did */
648	if (!found)
649		fatal("%s: method not in AuthenticationMethods", __func__);
650	return 0;
651}
652
653
654