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