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/10/crypto/openssh/auth2.c 323124 2017-09-01 22:52:18Z 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 "canohost.h"
55
56 #ifdef GSSAPI
57 #include "ssh-gss.h"
58 #endif
59 #include "monitor_wrap.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, void *);
93 static int input_userauth_request(int, u_int32_t, void *);
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 *
auth2_read_banner(void)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
userauth_send_banner(const char * msg)139 userauth_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
151 static void
userauth_banner(void)152 userauth_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
163 done:
164 free(banner);
165 }
166
167 /*
168 * loop until authctxt->success == TRUE
169 */
170 void
do_authentication2(Authctxt * authctxt)171 do_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*/
179 static int
input_service_request(int type,u_int32_t seq,void * ctxt)180 input_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*/
214 static int
input_userauth_request(int type,u_int32_t seq,void * ctxt)215 input_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
319 void
userauth_finish(Authctxt * authctxt,int authenticated,const char * method,const char * submethod)320 userauth_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 if (authctxt->failures >= options.max_authtries) {
391 #ifdef SSH_AUDIT_EVENTS
392 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
393 #endif
394 auth_maxtries_exceeded(authctxt);
395 }
396 methods = authmethods_get(authctxt);
397 debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
398 partial, methods);
399 packet_start(SSH2_MSG_USERAUTH_FAILURE);
400 packet_put_cstring(methods);
401 packet_put_char(partial);
402 packet_send();
403 packet_write_wait();
404 free(methods);
405 }
406 }
407
408 /*
409 * Checks whether method is allowed by at least one AuthenticationMethods
410 * methods list. Returns 1 if allowed, or no methods lists configured.
411 * 0 otherwise.
412 */
413 int
auth2_method_allowed(Authctxt * authctxt,const char * method,const char * submethod)414 auth2_method_allowed(Authctxt *authctxt, const char *method,
415 const char *submethod)
416 {
417 u_int i;
418
419 /*
420 * NB. authctxt->num_auth_methods might be zero as a result of
421 * auth2_setup_methods_lists(), so check the configuration.
422 */
423 if (options.num_auth_methods == 0)
424 return 1;
425 for (i = 0; i < authctxt->num_auth_methods; i++) {
426 if (list_starts_with(authctxt->auth_methods[i], method,
427 submethod) != MATCH_NONE)
428 return 1;
429 }
430 return 0;
431 }
432
433 static char *
authmethods_get(Authctxt * authctxt)434 authmethods_get(Authctxt *authctxt)
435 {
436 Buffer b;
437 char *list;
438 u_int i;
439
440 buffer_init(&b);
441 for (i = 0; authmethods[i] != NULL; i++) {
442 if (strcmp(authmethods[i]->name, "none") == 0)
443 continue;
444 if (authmethods[i]->enabled == NULL ||
445 *(authmethods[i]->enabled) == 0)
446 continue;
447 if (!auth2_method_allowed(authctxt, authmethods[i]->name,
448 NULL))
449 continue;
450 if (buffer_len(&b) > 0)
451 buffer_append(&b, ",", 1);
452 buffer_append(&b, authmethods[i]->name,
453 strlen(authmethods[i]->name));
454 }
455 if ((list = sshbuf_dup_string(&b)) == NULL)
456 fatal("%s: sshbuf_dup_string failed", __func__);
457 buffer_free(&b);
458 return list;
459 }
460
461 static Authmethod *
authmethod_lookup(Authctxt * authctxt,const char * name)462 authmethod_lookup(Authctxt *authctxt, const char *name)
463 {
464 int i;
465
466 if (name != NULL)
467 for (i = 0; authmethods[i] != NULL; i++)
468 if (authmethods[i]->enabled != NULL &&
469 *(authmethods[i]->enabled) != 0 &&
470 strcmp(name, authmethods[i]->name) == 0 &&
471 auth2_method_allowed(authctxt,
472 authmethods[i]->name, NULL))
473 return authmethods[i];
474 debug2("Unrecognized authentication method name: %s",
475 name ? name : "NULL");
476 return NULL;
477 }
478
479 /*
480 * Check a comma-separated list of methods for validity. Is need_enable is
481 * non-zero, then also require that the methods are enabled.
482 * Returns 0 on success or -1 if the methods list is invalid.
483 */
484 int
auth2_methods_valid(const char * _methods,int need_enable)485 auth2_methods_valid(const char *_methods, int need_enable)
486 {
487 char *methods, *omethods, *method, *p;
488 u_int i, found;
489 int ret = -1;
490
491 if (*_methods == '\0') {
492 error("empty authentication method list");
493 return -1;
494 }
495 omethods = methods = xstrdup(_methods);
496 while ((method = strsep(&methods, ",")) != NULL) {
497 for (found = i = 0; !found && authmethods[i] != NULL; i++) {
498 if ((p = strchr(method, ':')) != NULL)
499 *p = '\0';
500 if (strcmp(method, authmethods[i]->name) != 0)
501 continue;
502 if (need_enable) {
503 if (authmethods[i]->enabled == NULL ||
504 *(authmethods[i]->enabled) == 0) {
505 error("Disabled method \"%s\" in "
506 "AuthenticationMethods list \"%s\"",
507 method, _methods);
508 goto out;
509 }
510 }
511 found = 1;
512 break;
513 }
514 if (!found) {
515 error("Unknown authentication method \"%s\" in list",
516 method);
517 goto out;
518 }
519 }
520 ret = 0;
521 out:
522 free(omethods);
523 return ret;
524 }
525
526 /*
527 * Prune the AuthenticationMethods supplied in the configuration, removing
528 * any methods lists that include disabled methods. Note that this might
529 * leave authctxt->num_auth_methods == 0, even when multiple required auth
530 * has been requested. For this reason, all tests for whether multiple is
531 * enabled should consult options.num_auth_methods directly.
532 */
533 int
auth2_setup_methods_lists(Authctxt * authctxt)534 auth2_setup_methods_lists(Authctxt *authctxt)
535 {
536 u_int i;
537
538 if (options.num_auth_methods == 0)
539 return 0;
540 debug3("%s: checking methods", __func__);
541 authctxt->auth_methods = xcalloc(options.num_auth_methods,
542 sizeof(*authctxt->auth_methods));
543 authctxt->num_auth_methods = 0;
544 for (i = 0; i < options.num_auth_methods; i++) {
545 if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
546 logit("Authentication methods list \"%s\" contains "
547 "disabled method, skipping",
548 options.auth_methods[i]);
549 continue;
550 }
551 debug("authentication methods list %d: %s",
552 authctxt->num_auth_methods, options.auth_methods[i]);
553 authctxt->auth_methods[authctxt->num_auth_methods++] =
554 xstrdup(options.auth_methods[i]);
555 }
556 if (authctxt->num_auth_methods == 0) {
557 error("No AuthenticationMethods left after eliminating "
558 "disabled methods");
559 return -1;
560 }
561 return 0;
562 }
563
564 static int
list_starts_with(const char * methods,const char * method,const char * submethod)565 list_starts_with(const char *methods, const char *method,
566 const char *submethod)
567 {
568 size_t l = strlen(method);
569 int match;
570 const char *p;
571
572 if (strncmp(methods, method, l) != 0)
573 return MATCH_NONE;
574 p = methods + l;
575 match = MATCH_METHOD;
576 if (*p == ':') {
577 if (!submethod)
578 return MATCH_PARTIAL;
579 l = strlen(submethod);
580 p += 1;
581 if (strncmp(submethod, p, l))
582 return MATCH_NONE;
583 p += l;
584 match = MATCH_BOTH;
585 }
586 if (*p != ',' && *p != '\0')
587 return MATCH_NONE;
588 return match;
589 }
590
591 /*
592 * Remove method from the start of a comma-separated list of methods.
593 * Returns 0 if the list of methods did not start with that method or 1
594 * if it did.
595 */
596 static int
remove_method(char ** methods,const char * method,const char * submethod)597 remove_method(char **methods, const char *method, const char *submethod)
598 {
599 char *omethods = *methods, *p;
600 size_t l = strlen(method);
601 int match;
602
603 match = list_starts_with(omethods, method, submethod);
604 if (match != MATCH_METHOD && match != MATCH_BOTH)
605 return 0;
606 p = omethods + l;
607 if (submethod && match == MATCH_BOTH)
608 p += 1 + strlen(submethod); /* include colon */
609 if (*p == ',')
610 p++;
611 *methods = xstrdup(p);
612 free(omethods);
613 return 1;
614 }
615
616 /*
617 * Called after successful authentication. Will remove the successful method
618 * from the start of each list in which it occurs. If it was the last method
619 * in any list, then authentication is deemed successful.
620 * Returns 1 if the method completed any authentication list or 0 otherwise.
621 */
622 int
auth2_update_methods_lists(Authctxt * authctxt,const char * method,const char * submethod)623 auth2_update_methods_lists(Authctxt *authctxt, const char *method,
624 const char *submethod)
625 {
626 u_int i, found = 0;
627
628 debug3("%s: updating methods list after \"%s\"", __func__, method);
629 for (i = 0; i < authctxt->num_auth_methods; i++) {
630 if (!remove_method(&(authctxt->auth_methods[i]), method,
631 submethod))
632 continue;
633 found = 1;
634 if (*authctxt->auth_methods[i] == '\0') {
635 debug2("authentication methods list %d complete", i);
636 return 1;
637 }
638 debug3("authentication methods list %d remaining: \"%s\"",
639 i, authctxt->auth_methods[i]);
640 }
641 /* This should not happen, but would be bad if it did */
642 if (!found)
643 fatal("%s: method not in AuthenticationMethods", __func__);
644 return 0;
645 }
646
647
648