auth2.c revision 323129 
1/* $OpenBSD: auth2.c,v 1.136 2016/05/02 08:49:03 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 323129 2017-09-02 14:25:20Z des $");
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	Authctxt *authctxt = ctxt;
218	Authmethod *m = NULL;
219	char *user, *service, *method, *style = NULL;
220	int authenticated = 0;
221#ifdef HAVE_LOGIN_CAP
222	struct ssh *ssh = active_state; /* XXX */
223	login_cap_t *lc;
224	const char *from_host, *from_ip;
225#endif
226	if (authctxt == NULL)
227		fatal("input_userauth_request: no authctxt");
228
229	user = packet_get_cstring(NULL);
230	service = packet_get_cstring(NULL);
231	method = packet_get_cstring(NULL);
232	debug("userauth-request for user %s service %s method %s", user, service, method);
233	debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
234
235	if ((style = strchr(user, ':')) != NULL)
236		*style++ = 0;
237
238	if (authctxt->attempt++ == 0) {
239		/* setup auth context */
240		authctxt->pw = PRIVSEP(getpwnamallow(user));
241		authctxt->user = xstrdup(user);
242		if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
243			authctxt->valid = 1;
244			debug2("input_userauth_request: setting up authctxt for %s", user);
245		} else {
246			logit("input_userauth_request: invalid user %s", user);
247			authctxt->pw = fakepw();
248#ifdef SSH_AUDIT_EVENTS
249			PRIVSEP(audit_event(SSH_INVALID_USER));
250#endif
251		}
252#ifdef USE_PAM
253		if (options.use_pam)
254			PRIVSEP(start_pam(authctxt));
255#endif
256		setproctitle("%s%s", authctxt->valid ? user : "unknown",
257		    use_privsep ? " [net]" : "");
258		authctxt->service = xstrdup(service);
259		authctxt->style = style ? xstrdup(style) : NULL;
260		if (use_privsep)
261			mm_inform_authserv(service, style);
262		userauth_banner();
263		if (auth2_setup_methods_lists(authctxt) != 0)
264			packet_disconnect("no authentication methods enabled");
265	} else if (strcmp(user, authctxt->user) != 0 ||
266	    strcmp(service, authctxt->service) != 0) {
267		packet_disconnect("Change of username or service not allowed: "
268		    "(%s,%s) -> (%s,%s)",
269		    authctxt->user, authctxt->service, user, service);
270	}
271
272#ifdef HAVE_LOGIN_CAP
273	if (authctxt->pw != NULL &&
274	    (lc = login_getpwclass(authctxt->pw)) != NULL) {
275		logit("user %s login class %s", authctxt->pw->pw_name,
276		    authctxt->pw->pw_class);
277		from_host = auth_get_canonical_hostname(ssh, options.use_dns);
278		from_ip = ssh_remote_ipaddr(ssh);
279		if (!auth_hostok(lc, from_host, from_ip)) {
280			logit("Denied connection for %.200s from %.200s [%.200s].",
281			    authctxt->pw->pw_name, from_host, from_ip);
282			packet_disconnect("Sorry, you are not allowed to connect.");
283		}
284		if (!auth_timeok(lc, time(NULL))) {
285			logit("LOGIN %.200s REFUSED (TIME) FROM %.200s",
286			    authctxt->pw->pw_name, from_host);
287			packet_disconnect("Logins not available right now.");
288		}
289		login_close(lc);
290	}
291#endif  /* HAVE_LOGIN_CAP */
292
293	/* reset state */
294	auth2_challenge_stop(authctxt);
295
296#ifdef GSSAPI
297	/* XXX move to auth2_gssapi_stop() */
298	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
299	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
300#endif
301
302	authctxt->postponed = 0;
303	authctxt->server_caused_failure = 0;
304
305	/* try to authenticate user */
306	m = authmethod_lookup(authctxt, method);
307	if (m != NULL && authctxt->failures < options.max_authtries) {
308		debug2("input_userauth_request: try method %s", method);
309		authenticated =	m->userauth(authctxt);
310	}
311	userauth_finish(authctxt, authenticated, method, NULL);
312
313	free(service);
314	free(user);
315	free(method);
316	return 0;
317}
318
319void
320userauth_finish(Authctxt *authctxt, int authenticated, const char *method,
321    const char *submethod)
322{
323	char *methods;
324	int partial = 0;
325
326	if (!authctxt->valid && authenticated)
327		fatal("INTERNAL ERROR: authenticated invalid user %s",
328		    authctxt->user);
329	if (authenticated && authctxt->postponed)
330		fatal("INTERNAL ERROR: authenticated and postponed");
331
332	/* Special handling for root */
333	if (authenticated && authctxt->pw->pw_uid == 0 &&
334	    !auth_root_allowed(method)) {
335		authenticated = 0;
336#ifdef SSH_AUDIT_EVENTS
337		PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
338#endif
339	}
340
341	if (authenticated && options.num_auth_methods != 0) {
342		if (!auth2_update_methods_lists(authctxt, method, submethod)) {
343			authenticated = 0;
344			partial = 1;
345		}
346	}
347
348	/* Log before sending the reply */
349	auth_log(authctxt, authenticated, partial, method, submethod);
350
351	if (authctxt->postponed)
352		return;
353
354#ifdef USE_PAM
355	if (options.use_pam && authenticated) {
356		if (!PRIVSEP(do_pam_account())) {
357			/* if PAM returned a message, send it to the user */
358			if (buffer_len(&loginmsg) > 0) {
359				buffer_append(&loginmsg, "\0", 1);
360				userauth_send_banner(buffer_ptr(&loginmsg));
361				packet_write_wait();
362			}
363			fatal("Access denied for user %s by PAM account "
364			    "configuration", authctxt->user);
365		}
366	}
367#endif
368
369#ifdef _UNICOS
370	if (authenticated && cray_access_denied(authctxt->user)) {
371		authenticated = 0;
372		fatal("Access denied for user %s.", authctxt->user);
373	}
374#endif /* _UNICOS */
375
376	if (authenticated == 1) {
377		/* turn off userauth */
378		dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
379		packet_start(SSH2_MSG_USERAUTH_SUCCESS);
380		packet_send();
381		packet_write_wait();
382		/* now we can break out */
383		authctxt->success = 1;
384	} else {
385
386		/* Allow initial try of "none" auth without failure penalty */
387		if (!partial && !authctxt->server_caused_failure &&
388		    (authctxt->attempt > 1 || strcmp(method, "none") != 0)) {
389			authctxt->failures++;
390			BLACKLIST_NOTIFY(BLACKLIST_AUTH_FAIL, "ssh");
391		}
392		if (authctxt->failures >= options.max_authtries) {
393#ifdef SSH_AUDIT_EVENTS
394			PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
395#endif
396			auth_maxtries_exceeded(authctxt);
397		}
398		methods = authmethods_get(authctxt);
399		debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
400		    partial, methods);
401		packet_start(SSH2_MSG_USERAUTH_FAILURE);
402		packet_put_cstring(methods);
403		packet_put_char(partial);
404		packet_send();
405		packet_write_wait();
406		free(methods);
407	}
408}
409
410/*
411 * Checks whether method is allowed by at least one AuthenticationMethods
412 * methods list. Returns 1 if allowed, or no methods lists configured.
413 * 0 otherwise.
414 */
415int
416auth2_method_allowed(Authctxt *authctxt, const char *method,
417    const char *submethod)
418{
419	u_int i;
420
421	/*
422	 * NB. authctxt->num_auth_methods might be zero as a result of
423	 * auth2_setup_methods_lists(), so check the configuration.
424	 */
425	if (options.num_auth_methods == 0)
426		return 1;
427	for (i = 0; i < authctxt->num_auth_methods; i++) {
428		if (list_starts_with(authctxt->auth_methods[i], method,
429		    submethod) != MATCH_NONE)
430			return 1;
431	}
432	return 0;
433}
434
435static char *
436authmethods_get(Authctxt *authctxt)
437{
438	Buffer b;
439	char *list;
440	u_int i;
441
442	buffer_init(&b);
443	for (i = 0; authmethods[i] != NULL; i++) {
444		if (strcmp(authmethods[i]->name, "none") == 0)
445			continue;
446		if (authmethods[i]->enabled == NULL ||
447		    *(authmethods[i]->enabled) == 0)
448			continue;
449		if (!auth2_method_allowed(authctxt, authmethods[i]->name,
450		    NULL))
451			continue;
452		if (buffer_len(&b) > 0)
453			buffer_append(&b, ",", 1);
454		buffer_append(&b, authmethods[i]->name,
455		    strlen(authmethods[i]->name));
456	}
457	if ((list = sshbuf_dup_string(&b)) == NULL)
458		fatal("%s: sshbuf_dup_string failed", __func__);
459	buffer_free(&b);
460	return list;
461}
462
463static Authmethod *
464authmethod_lookup(Authctxt *authctxt, const char *name)
465{
466	int i;
467
468	if (name != NULL)
469		for (i = 0; authmethods[i] != NULL; i++)
470			if (authmethods[i]->enabled != NULL &&
471			    *(authmethods[i]->enabled) != 0 &&
472			    strcmp(name, authmethods[i]->name) == 0 &&
473			    auth2_method_allowed(authctxt,
474			    authmethods[i]->name, NULL))
475				return authmethods[i];
476	debug2("Unrecognized authentication method name: %s",
477	    name ? name : "NULL");
478	return NULL;
479}
480
481/*
482 * Check a comma-separated list of methods for validity. Is need_enable is
483 * non-zero, then also require that the methods are enabled.
484 * Returns 0 on success or -1 if the methods list is invalid.
485 */
486int
487auth2_methods_valid(const char *_methods, int need_enable)
488{
489	char *methods, *omethods, *method, *p;
490	u_int i, found;
491	int ret = -1;
492
493	if (*_methods == '\0') {
494		error("empty authentication method list");
495		return -1;
496	}
497	omethods = methods = xstrdup(_methods);
498	while ((method = strsep(&methods, ",")) != NULL) {
499		for (found = i = 0; !found && authmethods[i] != NULL; i++) {
500			if ((p = strchr(method, ':')) != NULL)
501				*p = '\0';
502			if (strcmp(method, authmethods[i]->name) != 0)
503				continue;
504			if (need_enable) {
505				if (authmethods[i]->enabled == NULL ||
506				    *(authmethods[i]->enabled) == 0) {
507					error("Disabled method \"%s\" in "
508					    "AuthenticationMethods list \"%s\"",
509					    method, _methods);
510					goto out;
511				}
512			}
513			found = 1;
514			break;
515		}
516		if (!found) {
517			error("Unknown authentication method \"%s\" in list",
518			    method);
519			goto out;
520		}
521	}
522	ret = 0;
523 out:
524	free(omethods);
525	return ret;
526}
527
528/*
529 * Prune the AuthenticationMethods supplied in the configuration, removing
530 * any methods lists that include disabled methods. Note that this might
531 * leave authctxt->num_auth_methods == 0, even when multiple required auth
532 * has been requested. For this reason, all tests for whether multiple is
533 * enabled should consult options.num_auth_methods directly.
534 */
535int
536auth2_setup_methods_lists(Authctxt *authctxt)
537{
538	u_int i;
539
540	if (options.num_auth_methods == 0)
541		return 0;
542	debug3("%s: checking methods", __func__);
543	authctxt->auth_methods = xcalloc(options.num_auth_methods,
544	    sizeof(*authctxt->auth_methods));
545	authctxt->num_auth_methods = 0;
546	for (i = 0; i < options.num_auth_methods; i++) {
547		if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
548			logit("Authentication methods list \"%s\" contains "
549			    "disabled method, skipping",
550			    options.auth_methods[i]);
551			continue;
552		}
553		debug("authentication methods list %d: %s",
554		    authctxt->num_auth_methods, options.auth_methods[i]);
555		authctxt->auth_methods[authctxt->num_auth_methods++] =
556		    xstrdup(options.auth_methods[i]);
557	}
558	if (authctxt->num_auth_methods == 0) {
559		error("No AuthenticationMethods left after eliminating "
560		    "disabled methods");
561		return -1;
562	}
563	return 0;
564}
565
566static int
567list_starts_with(const char *methods, const char *method,
568    const char *submethod)
569{
570	size_t l = strlen(method);
571	int match;
572	const char *p;
573
574	if (strncmp(methods, method, l) != 0)
575		return MATCH_NONE;
576	p = methods + l;
577	match = MATCH_METHOD;
578	if (*p == ':') {
579		if (!submethod)
580			return MATCH_PARTIAL;
581		l = strlen(submethod);
582		p += 1;
583		if (strncmp(submethod, p, l))
584			return MATCH_NONE;
585		p += l;
586		match = MATCH_BOTH;
587	}
588	if (*p != ',' && *p != '\0')
589		return MATCH_NONE;
590	return match;
591}
592
593/*
594 * Remove method from the start of a comma-separated list of methods.
595 * Returns 0 if the list of methods did not start with that method or 1
596 * if it did.
597 */
598static int
599remove_method(char **methods, const char *method, const char *submethod)
600{
601	char *omethods = *methods, *p;
602	size_t l = strlen(method);
603	int match;
604
605	match = list_starts_with(omethods, method, submethod);
606	if (match != MATCH_METHOD && match != MATCH_BOTH)
607		return 0;
608	p = omethods + l;
609	if (submethod && match == MATCH_BOTH)
610		p += 1 + strlen(submethod); /* include colon */
611	if (*p == ',')
612		p++;
613	*methods = xstrdup(p);
614	free(omethods);
615	return 1;
616}
617
618/*
619 * Called after successful authentication. Will remove the successful method
620 * from the start of each list in which it occurs. If it was the last method
621 * in any list, then authentication is deemed successful.
622 * Returns 1 if the method completed any authentication list or 0 otherwise.
623 */
624int
625auth2_update_methods_lists(Authctxt *authctxt, const char *method,
626    const char *submethod)
627{
628	u_int i, found = 0;
629
630	debug3("%s: updating methods list after \"%s\"", __func__, method);
631	for (i = 0; i < authctxt->num_auth_methods; i++) {
632		if (!remove_method(&(authctxt->auth_methods[i]), method,
633		    submethod))
634			continue;
635		found = 1;
636		if (*authctxt->auth_methods[i] == '\0') {
637			debug2("authentication methods list %d complete", i);
638			return 1;
639		}
640		debug3("authentication methods list %d remaining: \"%s\"",
641		    i, authctxt->auth_methods[i]);
642	}
643	/* This should not happen, but would be bad if it did */
644	if (!found)
645		fatal("%s: method not in AuthenticationMethods", __func__);
646	return 0;
647}
648
649
650