auth2.c revision 248619 
1/* $OpenBSD: auth2.c,v 1.126 2012/12/02 20:34:09 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: head/crypto/openssh/auth2.c 248619 2013-03-22 17:55:38Z 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 "servconf.h"
46#include "compat.h"
47#include "key.h"
48#include "hostfile.h"
49#include "auth.h"
50#include "dispatch.h"
51#include "pathnames.h"
52#include "buffer.h"
53#include "canohost.h"
54
55#ifdef GSSAPI
56#include "ssh-gss.h"
57#endif
58#include "monitor_wrap.h"
59
60/* import */
61extern ServerOptions options;
62extern u_char *session_id2;
63extern u_int session_id2_len;
64extern Buffer loginmsg;
65
66/* methods */
67
68extern Authmethod method_none;
69extern Authmethod method_pubkey;
70extern Authmethod method_passwd;
71extern Authmethod method_kbdint;
72extern Authmethod method_hostbased;
73#ifdef GSSAPI
74extern Authmethod method_gssapi;
75#endif
76#ifdef JPAKE
77extern Authmethod method_jpake;
78#endif
79
80Authmethod *authmethods[] = {
81	&method_none,
82	&method_pubkey,
83#ifdef GSSAPI
84	&method_gssapi,
85#endif
86#ifdef JPAKE
87	&method_jpake,
88#endif
89	&method_passwd,
90	&method_kbdint,
91	&method_hostbased,
92	NULL
93};
94
95/* protocol */
96
97static void input_service_request(int, u_int32_t, void *);
98static void input_userauth_request(int, u_int32_t, void *);
99
100/* helper */
101static Authmethod *authmethod_lookup(Authctxt *, const char *);
102static char *authmethods_get(Authctxt *authctxt);
103static int method_allowed(Authctxt *, const char *);
104static int list_starts_with(const char *, const char *);
105
106char *
107auth2_read_banner(void)
108{
109	struct stat st;
110	char *banner = NULL;
111	size_t len, n;
112	int fd;
113
114	if ((fd = open(options.banner, O_RDONLY)) == -1)
115		return (NULL);
116	if (fstat(fd, &st) == -1) {
117		close(fd);
118		return (NULL);
119	}
120	if (st.st_size <= 0 || st.st_size > 1*1024*1024) {
121		close(fd);
122		return (NULL);
123	}
124
125	len = (size_t)st.st_size;		/* truncate */
126	banner = xmalloc(len + 1);
127	n = atomicio(read, fd, banner, len);
128	close(fd);
129
130	if (n != len) {
131		xfree(banner);
132		return (NULL);
133	}
134	banner[n] = '\0';
135
136	return (banner);
137}
138
139void
140userauth_send_banner(const char *msg)
141{
142	if (datafellows & SSH_BUG_BANNER)
143		return;
144
145	packet_start(SSH2_MSG_USERAUTH_BANNER);
146	packet_put_cstring(msg);
147	packet_put_cstring("");		/* language, unused */
148	packet_send();
149	debug("%s: sent", __func__);
150}
151
152static void
153userauth_banner(void)
154{
155	char *banner = NULL;
156
157	if (options.banner == NULL ||
158	    strcasecmp(options.banner, "none") == 0 ||
159	    (datafellows & SSH_BUG_BANNER) != 0)
160		return;
161
162	if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
163		goto done;
164	userauth_send_banner(banner);
165
166done:
167	if (banner)
168		xfree(banner);
169}
170
171/*
172 * loop until authctxt->success == TRUE
173 */
174void
175do_authentication2(Authctxt *authctxt)
176{
177	dispatch_init(&dispatch_protocol_error);
178	dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
179	dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
180}
181
182/*ARGSUSED*/
183static void
184input_service_request(int type, u_int32_t seq, void *ctxt)
185{
186	Authctxt *authctxt = ctxt;
187	u_int len;
188	int acceptit = 0;
189	char *service = packet_get_cstring(&len);
190	packet_check_eom();
191
192	if (authctxt == NULL)
193		fatal("input_service_request: no authctxt");
194
195	if (strcmp(service, "ssh-userauth") == 0) {
196		if (!authctxt->success) {
197			acceptit = 1;
198			/* now we can handle user-auth requests */
199			dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
200		}
201	}
202	/* XXX all other service requests are denied */
203
204	if (acceptit) {
205		packet_start(SSH2_MSG_SERVICE_ACCEPT);
206		packet_put_cstring(service);
207		packet_send();
208		packet_write_wait();
209	} else {
210		debug("bad service request %s", service);
211		packet_disconnect("bad service request %s", service);
212	}
213	xfree(service);
214}
215
216/*ARGSUSED*/
217static void
218input_userauth_request(int type, u_int32_t seq, void *ctxt)
219{
220	Authctxt *authctxt = ctxt;
221	Authmethod *m = NULL;
222	char *user, *service, *method, *style = NULL;
223	int authenticated = 0;
224#ifdef HAVE_LOGIN_CAP
225	login_cap_t *lc;
226	const char *from_host, *from_ip;
227
228	from_host = get_canonical_hostname(options.use_dns);
229	from_ip = get_remote_ipaddr();
230#endif
231
232	if (authctxt == NULL)
233		fatal("input_userauth_request: no authctxt");
234
235	user = packet_get_cstring(NULL);
236	service = packet_get_cstring(NULL);
237	method = packet_get_cstring(NULL);
238	debug("userauth-request for user %s service %s method %s", user, service, method);
239	debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
240
241	if ((style = strchr(user, ':')) != NULL)
242		*style++ = 0;
243
244	if (authctxt->attempt++ == 0) {
245		/* setup auth context */
246		authctxt->pw = PRIVSEP(getpwnamallow(user));
247		authctxt->user = xstrdup(user);
248		if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
249			authctxt->valid = 1;
250			debug2("input_userauth_request: setting up authctxt for %s", user);
251		} else {
252			logit("input_userauth_request: invalid user %s", user);
253			authctxt->pw = fakepw();
254#ifdef SSH_AUDIT_EVENTS
255			PRIVSEP(audit_event(SSH_INVALID_USER));
256#endif
257		}
258#ifdef USE_PAM
259		if (options.use_pam)
260			PRIVSEP(start_pam(authctxt));
261#endif
262		setproctitle("%s%s", authctxt->valid ? user : "unknown",
263		    use_privsep ? " [net]" : "");
264		authctxt->service = xstrdup(service);
265		authctxt->style = style ? xstrdup(style) : NULL;
266		if (use_privsep)
267			mm_inform_authserv(service, style);
268		userauth_banner();
269		if (auth2_setup_methods_lists(authctxt) != 0)
270			packet_disconnect("no authentication methods enabled");
271	} else if (strcmp(user, authctxt->user) != 0 ||
272	    strcmp(service, authctxt->service) != 0) {
273		packet_disconnect("Change of username or service not allowed: "
274		    "(%s,%s) -> (%s,%s)",
275		    authctxt->user, authctxt->service, user, service);
276	}
277
278#ifdef HAVE_LOGIN_CAP
279	if (authctxt->pw != NULL) {
280		lc = login_getpwclass(authctxt->pw);
281		if (lc == NULL)
282			lc = login_getclassbyname(NULL, authctxt->pw);
283		if (!auth_hostok(lc, from_host, from_ip)) {
284			logit("Denied connection for %.200s from %.200s [%.200s].",
285			    authctxt->pw->pw_name, from_host, from_ip);
286			packet_disconnect("Sorry, you are not allowed to connect.");
287		}
288		if (!auth_timeok(lc, time(NULL))) {
289			logit("LOGIN %.200s REFUSED (TIME) FROM %.200s",
290			    authctxt->pw->pw_name, from_host);
291			packet_disconnect("Logins not available right now.");
292		}
293		login_close(lc);
294		lc = NULL;
295	}
296#endif  /* HAVE_LOGIN_CAP */
297
298	/* reset state */
299	auth2_challenge_stop(authctxt);
300#ifdef JPAKE
301	auth2_jpake_stop(authctxt);
302#endif
303
304#ifdef GSSAPI
305	/* XXX move to auth2_gssapi_stop() */
306	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
307	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
308#endif
309
310	authctxt->postponed = 0;
311	authctxt->server_caused_failure = 0;
312
313	/* try to authenticate user */
314	m = authmethod_lookup(authctxt, method);
315	if (m != NULL && authctxt->failures < options.max_authtries) {
316		debug2("input_userauth_request: try method %s", method);
317		authenticated =	m->userauth(authctxt);
318	}
319	userauth_finish(authctxt, authenticated, method, NULL);
320
321	xfree(service);
322	xfree(user);
323	xfree(method);
324}
325
326void
327userauth_finish(Authctxt *authctxt, int authenticated, const char *method,
328    const char *submethod)
329{
330	char *methods;
331	int partial = 0;
332
333	if (!authctxt->valid && authenticated)
334		fatal("INTERNAL ERROR: authenticated invalid user %s",
335		    authctxt->user);
336	if (authenticated && authctxt->postponed)
337		fatal("INTERNAL ERROR: authenticated and postponed");
338
339	/* Special handling for root */
340	if (authenticated && authctxt->pw->pw_uid == 0 &&
341	    !auth_root_allowed(method)) {
342		authenticated = 0;
343#ifdef SSH_AUDIT_EVENTS
344		PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
345#endif
346	}
347
348	if (authenticated && options.num_auth_methods != 0) {
349		if (!auth2_update_methods_lists(authctxt, method)) {
350			authenticated = 0;
351			partial = 1;
352		}
353	}
354
355	/* Log before sending the reply */
356	auth_log(authctxt, authenticated, partial, method, submethod, " ssh2");
357
358	if (authctxt->postponed)
359		return;
360
361#ifdef USE_PAM
362	if (options.use_pam && authenticated) {
363		if (!PRIVSEP(do_pam_account())) {
364			/* if PAM returned a message, send it to the user */
365			if (buffer_len(&loginmsg) > 0) {
366				buffer_append(&loginmsg, "\0", 1);
367				userauth_send_banner(buffer_ptr(&loginmsg));
368				packet_write_wait();
369			}
370			fatal("Access denied for user %s by PAM account "
371			    "configuration", authctxt->user);
372		}
373	}
374#endif
375
376#ifdef _UNICOS
377	if (authenticated && cray_access_denied(authctxt->user)) {
378		authenticated = 0;
379		fatal("Access denied for user %s.", authctxt->user);
380	}
381#endif /* _UNICOS */
382
383	if (authenticated == 1) {
384		/* turn off userauth */
385		dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
386		packet_start(SSH2_MSG_USERAUTH_SUCCESS);
387		packet_send();
388		packet_write_wait();
389		/* now we can break out */
390		authctxt->success = 1;
391	} else {
392
393		/* Allow initial try of "none" auth without failure penalty */
394		if (!authctxt->server_caused_failure &&
395		    (authctxt->attempt > 1 || strcmp(method, "none") != 0))
396			authctxt->failures++;
397		if (authctxt->failures >= options.max_authtries) {
398#ifdef SSH_AUDIT_EVENTS
399			PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
400#endif
401			packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
402		}
403		methods = authmethods_get(authctxt);
404		debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
405		    partial, methods);
406		packet_start(SSH2_MSG_USERAUTH_FAILURE);
407		packet_put_cstring(methods);
408		packet_put_char(partial);
409		packet_send();
410		packet_write_wait();
411		xfree(methods);
412	}
413}
414
415/*
416 * Checks whether method is allowed by at least one AuthenticationMethods
417 * methods list. Returns 1 if allowed, or no methods lists configured.
418 * 0 otherwise.
419 */
420static int
421method_allowed(Authctxt *authctxt, const char *method)
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			return 1;
434	}
435	return 0;
436}
437
438static char *
439authmethods_get(Authctxt *authctxt)
440{
441	Buffer b;
442	char *list;
443	u_int i;
444
445	buffer_init(&b);
446	for (i = 0; authmethods[i] != NULL; i++) {
447		if (strcmp(authmethods[i]->name, "none") == 0)
448			continue;
449		if (authmethods[i]->enabled == NULL ||
450		    *(authmethods[i]->enabled) == 0)
451			continue;
452		if (!method_allowed(authctxt, authmethods[i]->name))
453			continue;
454		if (buffer_len(&b) > 0)
455			buffer_append(&b, ",", 1);
456		buffer_append(&b, authmethods[i]->name,
457		    strlen(authmethods[i]->name));
458	}
459	buffer_append(&b, "\0", 1);
460	list = xstrdup(buffer_ptr(&b));
461	buffer_free(&b);
462	return list;
463}
464
465static Authmethod *
466authmethod_lookup(Authctxt *authctxt, const char *name)
467{
468	int i;
469
470	if (name != NULL)
471		for (i = 0; authmethods[i] != NULL; i++)
472			if (authmethods[i]->enabled != NULL &&
473			    *(authmethods[i]->enabled) != 0 &&
474			    strcmp(name, authmethods[i]->name) == 0 &&
475			    method_allowed(authctxt, authmethods[i]->name))
476				return authmethods[i];
477	debug2("Unrecognized authentication method name: %s",
478	    name ? name : "NULL");
479	return NULL;
480}
481
482/*
483 * Check a comma-separated list of methods for validity. Is need_enable is
484 * non-zero, then also require that the methods are enabled.
485 * Returns 0 on success or -1 if the methods list is invalid.
486 */
487int
488auth2_methods_valid(const char *_methods, int need_enable)
489{
490	char *methods, *omethods, *method;
491	u_int i, found;
492	int ret = -1;
493
494	if (*_methods == '\0') {
495		error("empty authentication method list");
496		return -1;
497	}
498	omethods = methods = xstrdup(_methods);
499	while ((method = strsep(&methods, ",")) != NULL) {
500		for (found = i = 0; !found && authmethods[i] != NULL; i++) {
501			if (strcmp(method, authmethods[i]->name) != 0)
502				continue;
503			if (need_enable) {
504				if (authmethods[i]->enabled == NULL ||
505				    *(authmethods[i]->enabled) == 0) {
506					error("Disabled method \"%s\" in "
507					    "AuthenticationMethods list \"%s\"",
508					    method, _methods);
509					goto out;
510				}
511			}
512			found = 1;
513			break;
514		}
515		if (!found) {
516			error("Unknown authentication method \"%s\" in list",
517			    method);
518			goto out;
519		}
520	}
521	ret = 0;
522 out:
523	free(omethods);
524	return ret;
525}
526
527/*
528 * Prune the AuthenticationMethods supplied in the configuration, removing
529 * any methods lists that include disabled methods. Note that this might
530 * leave authctxt->num_auth_methods == 0, even when multiple required auth
531 * has been requested. For this reason, all tests for whether multiple is
532 * enabled should consult options.num_auth_methods directly.
533 */
534int
535auth2_setup_methods_lists(Authctxt *authctxt)
536{
537	u_int i;
538
539	if (options.num_auth_methods == 0)
540		return 0;
541	debug3("%s: checking methods", __func__);
542	authctxt->auth_methods = xcalloc(options.num_auth_methods,
543	    sizeof(*authctxt->auth_methods));
544	authctxt->num_auth_methods = 0;
545	for (i = 0; i < options.num_auth_methods; i++) {
546		if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
547			logit("Authentication methods list \"%s\" contains "
548			    "disabled method, skipping",
549			    options.auth_methods[i]);
550			continue;
551		}
552		debug("authentication methods list %d: %s",
553		    authctxt->num_auth_methods, options.auth_methods[i]);
554		authctxt->auth_methods[authctxt->num_auth_methods++] =
555		    xstrdup(options.auth_methods[i]);
556	}
557	if (authctxt->num_auth_methods == 0) {
558		error("No AuthenticationMethods left after eliminating "
559		    "disabled methods");
560		return -1;
561	}
562	return 0;
563}
564
565static int
566list_starts_with(const char *methods, const char *method)
567{
568	size_t l = strlen(method);
569
570	if (strncmp(methods, method, l) != 0)
571		return 0;
572	if (methods[l] != ',' && methods[l] != '\0')
573		return 0;
574	return 1;
575}
576
577/*
578 * Remove method from the start of a comma-separated list of methods.
579 * Returns 0 if the list of methods did not start with that method or 1
580 * if it did.
581 */
582static int
583remove_method(char **methods, const char *method)
584{
585	char *omethods = *methods;
586	size_t l = strlen(method);
587
588	if (!list_starts_with(omethods, method))
589		return 0;
590	*methods = xstrdup(omethods + l + (omethods[l] == ',' ? 1 : 0));
591	free(omethods);
592	return 1;
593}
594
595/*
596 * Called after successful authentication. Will remove the successful method
597 * from the start of each list in which it occurs. If it was the last method
598 * in any list, then authentication is deemed successful.
599 * Returns 1 if the method completed any authentication list or 0 otherwise.
600 */
601int
602auth2_update_methods_lists(Authctxt *authctxt, const char *method)
603{
604	u_int i, found = 0;
605
606	debug3("%s: updating methods list after \"%s\"", __func__, method);
607	for (i = 0; i < authctxt->num_auth_methods; i++) {
608		if (!remove_method(&(authctxt->auth_methods[i]), method))
609			continue;
610		found = 1;
611		if (*authctxt->auth_methods[i] == '\0') {
612			debug2("authentication methods list %d complete", i);
613			return 1;
614		}
615		debug3("authentication methods list %d remaining: \"%s\"",
616		    i, authctxt->auth_methods[i]);
617	}
618	/* This should not happen, but would be bad if it did */
619	if (!found)
620		fatal("%s: method not in AuthenticationMethods", __func__);
621	return 0;
622}
623
624
625