1 /* $OpenBSD: auth2.c,v 1.135 2015/01/19 20:07:45 markus 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 <pwd.h>
34 #include <stdarg.h>
35 #include <string.h>
36 #include <unistd.h>
37
38 #include "atomicio.h"
39 #include "xmalloc.h"
40 #include "ssh2.h"
41 #include "packet.h"
42 #include "log.h"
43 #include "buffer.h"
44 #include "misc.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
54 #ifdef GSSAPI
55 #include "ssh-gss.h"
56 #endif
57 #include "monitor_wrap.h"
58
59 /* import */
60 extern ServerOptions options;
61 extern u_char *session_id2;
62 extern u_int session_id2_len;
63 extern Buffer loginmsg;
64
65 /* methods */
66
67 extern Authmethod method_none;
68 extern Authmethod method_pubkey;
69 extern Authmethod method_passwd;
70 extern Authmethod method_kbdint;
71 extern Authmethod method_hostbased;
72 #ifdef GSSAPI
73 extern Authmethod method_gssapi;
74 #endif
75
76 Authmethod *authmethods[] = {
77 &method_none,
78 &method_pubkey,
79 #ifdef GSSAPI
80 &method_gssapi,
81 #endif
82 &method_passwd,
83 &method_kbdint,
84 &method_hostbased,
85 NULL
86 };
87
88 /* protocol */
89
90 static int input_service_request(int, u_int32_t, void *);
91 static int input_userauth_request(int, u_int32_t, void *);
92
93 /* helper */
94 static Authmethod *authmethod_lookup(Authctxt *, const char *);
95 static char *authmethods_get(Authctxt *authctxt);
96
97 #define MATCH_NONE 0 /* method or submethod mismatch */
98 #define MATCH_METHOD 1 /* method matches (no submethod specified) */
99 #define MATCH_BOTH 2 /* method and submethod match */
100 #define MATCH_PARTIAL 3 /* method matches, submethod can't be checked */
101 static int list_starts_with(const char *, const char *, const char *);
102
103 char *
auth2_read_banner(void)104 auth2_read_banner(void)
105 {
106 struct stat st;
107 char *banner = NULL;
108 size_t len, n;
109 int fd;
110
111 if ((fd = open(options.banner, O_RDONLY)) == -1)
112 return (NULL);
113 if (fstat(fd, &st) == -1) {
114 close(fd);
115 return (NULL);
116 }
117 if (st.st_size <= 0 || st.st_size > 1*1024*1024) {
118 close(fd);
119 return (NULL);
120 }
121
122 len = (size_t)st.st_size; /* truncate */
123 banner = xmalloc(len + 1);
124 n = atomicio(read, fd, banner, len);
125 close(fd);
126
127 if (n != len) {
128 free(banner);
129 return (NULL);
130 }
131 banner[n] = '\0';
132
133 return (banner);
134 }
135
136 void
userauth_send_banner(const char * msg)137 userauth_send_banner(const char *msg)
138 {
139 if (datafellows & SSH_BUG_BANNER)
140 return;
141
142 packet_start(SSH2_MSG_USERAUTH_BANNER);
143 packet_put_cstring(msg);
144 packet_put_cstring(""); /* language, unused */
145 packet_send();
146 debug("%s: sent", __func__);
147 }
148
149 static void
userauth_banner(void)150 userauth_banner(void)
151 {
152 char *banner = NULL;
153
154 if (options.banner == NULL || (datafellows & SSH_BUG_BANNER) != 0)
155 return;
156
157 if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
158 goto done;
159 userauth_send_banner(banner);
160
161 done:
162 free(banner);
163 }
164
165 /*
166 * loop until authctxt->success == TRUE
167 */
168 void
do_authentication2(Authctxt * authctxt)169 do_authentication2(Authctxt *authctxt)
170 {
171 dispatch_init(&dispatch_protocol_error);
172 dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
173 dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
174 }
175
176 /*ARGSUSED*/
177 static int
input_service_request(int type,u_int32_t seq,void * ctxt)178 input_service_request(int type, u_int32_t seq, void *ctxt)
179 {
180 Authctxt *authctxt = ctxt;
181 u_int len;
182 int acceptit = 0;
183 char *service = packet_get_cstring(&len);
184 packet_check_eom();
185
186 if (authctxt == NULL)
187 fatal("input_service_request: no authctxt");
188
189 if (strcmp(service, "ssh-userauth") == 0) {
190 if (!authctxt->success) {
191 acceptit = 1;
192 /* now we can handle user-auth requests */
193 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
194 }
195 }
196 /* XXX all other service requests are denied */
197
198 if (acceptit) {
199 packet_start(SSH2_MSG_SERVICE_ACCEPT);
200 packet_put_cstring(service);
201 packet_send();
202 packet_write_wait();
203 } else {
204 debug("bad service request %s", service);
205 packet_disconnect("bad service request %s", service);
206 }
207 free(service);
208 return 0;
209 }
210
211 /*ARGSUSED*/
212 static int
input_userauth_request(int type,u_int32_t seq,void * ctxt)213 input_userauth_request(int type, u_int32_t seq, void *ctxt)
214 {
215 Authctxt *authctxt = ctxt;
216 Authmethod *m = NULL;
217 char *user, *service, *method, *style = NULL;
218 int authenticated = 0;
219
220 if (authctxt == NULL)
221 fatal("input_userauth_request: no authctxt");
222
223 user = packet_get_cstring(NULL);
224 service = packet_get_cstring(NULL);
225 method = packet_get_cstring(NULL);
226 debug("userauth-request for user %s service %s method %s", user, service, method);
227 debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
228
229 if ((style = strchr(user, ':')) != NULL)
230 *style++ = 0;
231
232 if (authctxt->attempt++ == 0) {
233 /* setup auth context */
234 authctxt->pw = PRIVSEP(getpwnamallow(user));
235 authctxt->user = xstrdup(user);
236 if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
237 authctxt->valid = 1;
238 debug2("input_userauth_request: setting up authctxt for %s", user);
239 } else {
240 logit("input_userauth_request: invalid user %s", user);
241 authctxt->pw = fakepw();
242 #ifdef SSH_AUDIT_EVENTS
243 PRIVSEP(audit_event(SSH_INVALID_USER));
244 #endif
245 }
246 #ifdef USE_PAM
247 if (options.use_pam)
248 PRIVSEP(start_pam(authctxt));
249 #endif
250 setproctitle("%s%s", authctxt->valid ? user : "unknown",
251 use_privsep ? " [net]" : "");
252 authctxt->service = xstrdup(service);
253 authctxt->style = style ? xstrdup(style) : NULL;
254 if (use_privsep)
255 mm_inform_authserv(service, style);
256 userauth_banner();
257 if (auth2_setup_methods_lists(authctxt) != 0)
258 packet_disconnect("no authentication methods enabled");
259 } else if (strcmp(user, authctxt->user) != 0 ||
260 strcmp(service, authctxt->service) != 0) {
261 packet_disconnect("Change of username or service not allowed: "
262 "(%s,%s) -> (%s,%s)",
263 authctxt->user, authctxt->service, user, service);
264 }
265 /* reset state */
266 auth2_challenge_stop(authctxt);
267
268 #ifdef GSSAPI
269 /* XXX move to auth2_gssapi_stop() */
270 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
271 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
272 #endif
273
274 authctxt->postponed = 0;
275 authctxt->server_caused_failure = 0;
276
277 /* try to authenticate user */
278 m = authmethod_lookup(authctxt, method);
279 if (m != NULL && authctxt->failures < options.max_authtries) {
280 debug2("input_userauth_request: try method %s", method);
281 authenticated = m->userauth(authctxt);
282 }
283 userauth_finish(authctxt, authenticated, method, NULL);
284
285 free(service);
286 free(user);
287 free(method);
288 return 0;
289 }
290
291 void
userauth_finish(Authctxt * authctxt,int authenticated,const char * method,const char * submethod)292 userauth_finish(Authctxt *authctxt, int authenticated, const char *method,
293 const char *submethod)
294 {
295 char *methods;
296 int partial = 0;
297
298 if (!authctxt->valid && authenticated)
299 fatal("INTERNAL ERROR: authenticated invalid user %s",
300 authctxt->user);
301 if (authenticated && authctxt->postponed)
302 fatal("INTERNAL ERROR: authenticated and postponed");
303
304 /* Special handling for root */
305 if (authenticated && authctxt->pw->pw_uid == 0 &&
306 !auth_root_allowed(method)) {
307 authenticated = 0;
308 #ifdef SSH_AUDIT_EVENTS
309 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
310 #endif
311 }
312
313 if (authenticated && options.num_auth_methods != 0) {
314 if (!auth2_update_methods_lists(authctxt, method, submethod)) {
315 authenticated = 0;
316 partial = 1;
317 }
318 }
319
320 /* Log before sending the reply */
321 auth_log(authctxt, authenticated, partial, method, submethod);
322
323 if (authctxt->postponed)
324 return;
325
326 #ifdef USE_PAM
327 if (options.use_pam && authenticated) {
328 if (!PRIVSEP(do_pam_account())) {
329 /* if PAM returned a message, send it to the user */
330 if (buffer_len(&loginmsg) > 0) {
331 buffer_append(&loginmsg, "\0", 1);
332 userauth_send_banner(buffer_ptr(&loginmsg));
333 packet_write_wait();
334 }
335 fatal("Access denied for user %s by PAM account "
336 "configuration", authctxt->user);
337 }
338 }
339 #endif
340
341 #ifdef _UNICOS
342 if (authenticated && cray_access_denied(authctxt->user)) {
343 authenticated = 0;
344 fatal("Access denied for user %s.", authctxt->user);
345 }
346 #endif /* _UNICOS */
347
348 if (authenticated == 1) {
349 /* turn off userauth */
350 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
351 packet_start(SSH2_MSG_USERAUTH_SUCCESS);
352 packet_send();
353 packet_write_wait();
354 /* now we can break out */
355 authctxt->success = 1;
356 } else {
357
358 /* Allow initial try of "none" auth without failure penalty */
359 if (!partial && !authctxt->server_caused_failure &&
360 (authctxt->attempt > 1 || strcmp(method, "none") != 0))
361 authctxt->failures++;
362 if (authctxt->failures >= options.max_authtries) {
363 #ifdef SSH_AUDIT_EVENTS
364 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
365 #endif
366 auth_maxtries_exceeded(authctxt);
367 }
368 methods = authmethods_get(authctxt);
369 debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
370 partial, methods);
371 packet_start(SSH2_MSG_USERAUTH_FAILURE);
372 packet_put_cstring(methods);
373 packet_put_char(partial);
374 packet_send();
375 packet_write_wait();
376 free(methods);
377 }
378 }
379
380 /*
381 * Checks whether method is allowed by at least one AuthenticationMethods
382 * methods list. Returns 1 if allowed, or no methods lists configured.
383 * 0 otherwise.
384 */
385 int
auth2_method_allowed(Authctxt * authctxt,const char * method,const char * submethod)386 auth2_method_allowed(Authctxt *authctxt, const char *method,
387 const char *submethod)
388 {
389 u_int i;
390
391 /*
392 * NB. authctxt->num_auth_methods might be zero as a result of
393 * auth2_setup_methods_lists(), so check the configuration.
394 */
395 if (options.num_auth_methods == 0)
396 return 1;
397 for (i = 0; i < authctxt->num_auth_methods; i++) {
398 if (list_starts_with(authctxt->auth_methods[i], method,
399 submethod) != MATCH_NONE)
400 return 1;
401 }
402 return 0;
403 }
404
405 static char *
authmethods_get(Authctxt * authctxt)406 authmethods_get(Authctxt *authctxt)
407 {
408 Buffer b;
409 char *list;
410 u_int i;
411
412 buffer_init(&b);
413 for (i = 0; authmethods[i] != NULL; i++) {
414 if (strcmp(authmethods[i]->name, "none") == 0)
415 continue;
416 if (authmethods[i]->enabled == NULL ||
417 *(authmethods[i]->enabled) == 0)
418 continue;
419 if (!auth2_method_allowed(authctxt, authmethods[i]->name,
420 NULL))
421 continue;
422 if (buffer_len(&b) > 0)
423 buffer_append(&b, ",", 1);
424 buffer_append(&b, authmethods[i]->name,
425 strlen(authmethods[i]->name));
426 }
427 buffer_append(&b, "\0", 1);
428 list = xstrdup(buffer_ptr(&b));
429 buffer_free(&b);
430 return list;
431 }
432
433 static Authmethod *
authmethod_lookup(Authctxt * authctxt,const char * name)434 authmethod_lookup(Authctxt *authctxt, const char *name)
435 {
436 int i;
437
438 if (name != NULL)
439 for (i = 0; authmethods[i] != NULL; i++)
440 if (authmethods[i]->enabled != NULL &&
441 *(authmethods[i]->enabled) != 0 &&
442 strcmp(name, authmethods[i]->name) == 0 &&
443 auth2_method_allowed(authctxt,
444 authmethods[i]->name, NULL))
445 return authmethods[i];
446 debug2("Unrecognized authentication method name: %s",
447 name ? name : "NULL");
448 return NULL;
449 }
450
451 /*
452 * Check a comma-separated list of methods for validity. Is need_enable is
453 * non-zero, then also require that the methods are enabled.
454 * Returns 0 on success or -1 if the methods list is invalid.
455 */
456 int
auth2_methods_valid(const char * _methods,int need_enable)457 auth2_methods_valid(const char *_methods, int need_enable)
458 {
459 char *methods, *omethods, *method, *p;
460 u_int i, found;
461 int ret = -1;
462
463 if (*_methods == '\0') {
464 error("empty authentication method list");
465 return -1;
466 }
467 omethods = methods = xstrdup(_methods);
468 while ((method = strsep(&methods, ",")) != NULL) {
469 for (found = i = 0; !found && authmethods[i] != NULL; i++) {
470 if ((p = strchr(method, ':')) != NULL)
471 *p = '\0';
472 if (strcmp(method, authmethods[i]->name) != 0)
473 continue;
474 if (need_enable) {
475 if (authmethods[i]->enabled == NULL ||
476 *(authmethods[i]->enabled) == 0) {
477 error("Disabled method \"%s\" in "
478 "AuthenticationMethods list \"%s\"",
479 method, _methods);
480 goto out;
481 }
482 }
483 found = 1;
484 break;
485 }
486 if (!found) {
487 error("Unknown authentication method \"%s\" in list",
488 method);
489 goto out;
490 }
491 }
492 ret = 0;
493 out:
494 free(omethods);
495 return ret;
496 }
497
498 /*
499 * Prune the AuthenticationMethods supplied in the configuration, removing
500 * any methods lists that include disabled methods. Note that this might
501 * leave authctxt->num_auth_methods == 0, even when multiple required auth
502 * has been requested. For this reason, all tests for whether multiple is
503 * enabled should consult options.num_auth_methods directly.
504 */
505 int
auth2_setup_methods_lists(Authctxt * authctxt)506 auth2_setup_methods_lists(Authctxt *authctxt)
507 {
508 u_int i;
509
510 if (options.num_auth_methods == 0)
511 return 0;
512 debug3("%s: checking methods", __func__);
513 authctxt->auth_methods = xcalloc(options.num_auth_methods,
514 sizeof(*authctxt->auth_methods));
515 authctxt->num_auth_methods = 0;
516 for (i = 0; i < options.num_auth_methods; i++) {
517 if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
518 logit("Authentication methods list \"%s\" contains "
519 "disabled method, skipping",
520 options.auth_methods[i]);
521 continue;
522 }
523 debug("authentication methods list %d: %s",
524 authctxt->num_auth_methods, options.auth_methods[i]);
525 authctxt->auth_methods[authctxt->num_auth_methods++] =
526 xstrdup(options.auth_methods[i]);
527 }
528 if (authctxt->num_auth_methods == 0) {
529 error("No AuthenticationMethods left after eliminating "
530 "disabled methods");
531 return -1;
532 }
533 return 0;
534 }
535
536 static int
list_starts_with(const char * methods,const char * method,const char * submethod)537 list_starts_with(const char *methods, const char *method,
538 const char *submethod)
539 {
540 size_t l = strlen(method);
541 int match;
542 const char *p;
543
544 if (strncmp(methods, method, l) != 0)
545 return MATCH_NONE;
546 p = methods + l;
547 match = MATCH_METHOD;
548 if (*p == ':') {
549 if (!submethod)
550 return MATCH_PARTIAL;
551 l = strlen(submethod);
552 p += 1;
553 if (strncmp(submethod, p, l))
554 return MATCH_NONE;
555 p += l;
556 match = MATCH_BOTH;
557 }
558 if (*p != ',' && *p != '\0')
559 return MATCH_NONE;
560 return match;
561 }
562
563 /*
564 * Remove method from the start of a comma-separated list of methods.
565 * Returns 0 if the list of methods did not start with that method or 1
566 * if it did.
567 */
568 static int
remove_method(char ** methods,const char * method,const char * submethod)569 remove_method(char **methods, const char *method, const char *submethod)
570 {
571 char *omethods = *methods, *p;
572 size_t l = strlen(method);
573 int match;
574
575 match = list_starts_with(omethods, method, submethod);
576 if (match != MATCH_METHOD && match != MATCH_BOTH)
577 return 0;
578 p = omethods + l;
579 if (submethod && match == MATCH_BOTH)
580 p += 1 + strlen(submethod); /* include colon */
581 if (*p == ',')
582 p++;
583 *methods = xstrdup(p);
584 free(omethods);
585 return 1;
586 }
587
588 /*
589 * Called after successful authentication. Will remove the successful method
590 * from the start of each list in which it occurs. If it was the last method
591 * in any list, then authentication is deemed successful.
592 * Returns 1 if the method completed any authentication list or 0 otherwise.
593 */
594 int
auth2_update_methods_lists(Authctxt * authctxt,const char * method,const char * submethod)595 auth2_update_methods_lists(Authctxt *authctxt, const char *method,
596 const char *submethod)
597 {
598 u_int i, found = 0;
599
600 debug3("%s: updating methods list after \"%s\"", __func__, method);
601 for (i = 0; i < authctxt->num_auth_methods; i++) {
602 if (!remove_method(&(authctxt->auth_methods[i]), method,
603 submethod))
604 continue;
605 found = 1;
606 if (*authctxt->auth_methods[i] == '\0') {
607 debug2("authentication methods list %d complete", i);
608 return 1;
609 }
610 debug3("authentication methods list %d remaining: \"%s\"",
611 i, authctxt->auth_methods[i]);
612 }
613 /* This should not happen, but would be bad if it did */
614 if (!found)
615 fatal("%s: method not in AuthenticationMethods", __func__);
616 return 0;
617 }
618
619
620