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 __RCSID("$FreeBSD$"); 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 #include "blacklist_client.h" 56 57 #ifdef GSSAPI 58 #include "ssh-gss.h" 59 #endif 60 #include "monitor_wrap.h" 61 62 /* import */ 63 extern ServerOptions options; 64 extern u_char *session_id2; 65 extern u_int session_id2_len; 66 extern Buffer loginmsg; 67 68 /* methods */ 69 70 extern Authmethod method_none; 71 extern Authmethod method_pubkey; 72 extern Authmethod method_passwd; 73 extern Authmethod method_kbdint; 74 extern Authmethod method_hostbased; 75 #ifdef GSSAPI 76 extern Authmethod method_gssapi; 77 #endif 78 79 Authmethod *authmethods[] = { 80 &method_none, 81 &method_pubkey, 82 #ifdef GSSAPI 83 &method_gssapi, 84 #endif 85 &method_passwd, 86 &method_kbdint, 87 &method_hostbased, 88 NULL 89 }; 90 91 /* protocol */ 92 93 static int input_service_request(int, u_int32_t, void *); 94 static int input_userauth_request(int, u_int32_t, void *); 95 96 /* helper */ 97 static Authmethod *authmethod_lookup(Authctxt *, const char *); 98 static char *authmethods_get(Authctxt *authctxt); 99 100 #define MATCH_NONE 0 /* method or submethod mismatch */ 101 #define MATCH_METHOD 1 /* method matches (no submethod specified) */ 102 #define MATCH_BOTH 2 /* method and submethod match */ 103 #define MATCH_PARTIAL 3 /* method matches, submethod can't be checked */ 104 static int list_starts_with(const char *, const char *, const char *); 105 106 char * 107 auth2_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 free(banner); 132 return (NULL); 133 } 134 banner[n] = '\0'; 135 136 return (banner); 137 } 138 139 void 140 userauth_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 } 151 152 static void 153 userauth_banner(void) 154 { 155 char *banner = NULL; 156 157 if (options.banner == NULL || (datafellows & SSH_BUG_BANNER) != 0) 158 return; 159 160 if ((banner = PRIVSEP(auth2_read_banner())) == NULL) 161 goto done; 162 userauth_send_banner(banner); 163 164 done: 165 free(banner); 166 } 167 168 /* 169 * loop until authctxt->success == TRUE 170 */ 171 void 172 do_authentication2(Authctxt *authctxt) 173 { 174 dispatch_init(&dispatch_protocol_error); 175 dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request); 176 dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt); 177 } 178 179 /*ARGSUSED*/ 180 static int 181 input_service_request(int type, u_int32_t seq, void *ctxt) 182 { 183 Authctxt *authctxt = ctxt; 184 u_int len; 185 int acceptit = 0; 186 char *service = packet_get_cstring(&len); 187 packet_check_eom(); 188 189 if (authctxt == NULL) 190 fatal("input_service_request: no authctxt"); 191 192 if (strcmp(service, "ssh-userauth") == 0) { 193 if (!authctxt->success) { 194 acceptit = 1; 195 /* now we can handle user-auth requests */ 196 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request); 197 } 198 } 199 /* XXX all other service requests are denied */ 200 201 if (acceptit) { 202 packet_start(SSH2_MSG_SERVICE_ACCEPT); 203 packet_put_cstring(service); 204 packet_send(); 205 packet_write_wait(); 206 } else { 207 debug("bad service request %s", service); 208 packet_disconnect("bad service request %s", service); 209 } 210 free(service); 211 return 0; 212 } 213 214 /*ARGSUSED*/ 215 static int 216 input_userauth_request(int type, u_int32_t seq, void *ctxt) 217 { 218 Authctxt *authctxt = ctxt; 219 Authmethod *m = NULL; 220 char *user, *service, *method, *style = NULL; 221 int authenticated = 0; 222 #ifdef HAVE_LOGIN_CAP 223 login_cap_t *lc; 224 const char *from_host, *from_ip; 225 226 from_host = get_canonical_hostname(options.use_dns); 227 from_ip = get_remote_ipaddr(); 228 #endif 229 230 if (authctxt == NULL) 231 fatal("input_userauth_request: no authctxt"); 232 233 user = packet_get_cstring(NULL); 234 service = packet_get_cstring(NULL); 235 method = packet_get_cstring(NULL); 236 debug("userauth-request for user %s service %s method %s", user, service, method); 237 debug("attempt %d failures %d", authctxt->attempt, authctxt->failures); 238 239 if ((style = strchr(user, ':')) != NULL) 240 *style++ = 0; 241 242 if (authctxt->attempt++ == 0) { 243 /* setup auth context */ 244 authctxt->pw = PRIVSEP(getpwnamallow(user)); 245 authctxt->user = xstrdup(user); 246 if (authctxt->pw && strcmp(service, "ssh-connection")==0) { 247 authctxt->valid = 1; 248 debug2("input_userauth_request: setting up authctxt for %s", user); 249 } else { 250 logit("input_userauth_request: invalid user %s", user); 251 authctxt->pw = fakepw(); 252 BLACKLIST_NOTIFY(BLACKLIST_AUTH_FAIL); 253 #ifdef SSH_AUDIT_EVENTS 254 PRIVSEP(audit_event(SSH_INVALID_USER)); 255 #endif 256 } 257 #ifdef USE_PAM 258 if (options.use_pam) 259 PRIVSEP(start_pam(authctxt)); 260 #endif 261 setproctitle("%s%s", authctxt->valid ? user : "unknown", 262 use_privsep ? " [net]" : ""); 263 authctxt->service = xstrdup(service); 264 authctxt->style = style ? xstrdup(style) : NULL; 265 if (use_privsep) 266 mm_inform_authserv(service, style); 267 userauth_banner(); 268 if (auth2_setup_methods_lists(authctxt) != 0) 269 packet_disconnect("no authentication methods enabled"); 270 } else if (strcmp(user, authctxt->user) != 0 || 271 strcmp(service, authctxt->service) != 0) { 272 packet_disconnect("Change of username or service not allowed: " 273 "(%s,%s) -> (%s,%s)", 274 authctxt->user, authctxt->service, user, service); 275 } 276 277 #ifdef HAVE_LOGIN_CAP 278 if (authctxt->pw != NULL) { 279 lc = login_getpwclass(authctxt->pw); 280 if (lc == NULL) 281 lc = login_getclassbyname(NULL, authctxt->pw); 282 if (!auth_hostok(lc, from_host, from_ip)) { 283 logit("Denied connection for %.200s from %.200s [%.200s].", 284 authctxt->pw->pw_name, from_host, from_ip); 285 packet_disconnect("Sorry, you are not allowed to connect."); 286 } 287 if (!auth_timeok(lc, time(NULL))) { 288 logit("LOGIN %.200s REFUSED (TIME) FROM %.200s", 289 authctxt->pw->pw_name, from_host); 290 packet_disconnect("Logins not available right now."); 291 } 292 login_close(lc); 293 lc = NULL; 294 } 295 #endif /* HAVE_LOGIN_CAP */ 296 297 /* reset state */ 298 auth2_challenge_stop(authctxt); 299 300 #ifdef GSSAPI 301 /* XXX move to auth2_gssapi_stop() */ 302 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); 303 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL); 304 #endif 305 306 authctxt->postponed = 0; 307 authctxt->server_caused_failure = 0; 308 309 /* try to authenticate user */ 310 m = authmethod_lookup(authctxt, method); 311 if (m != NULL && authctxt->failures < options.max_authtries) { 312 debug2("input_userauth_request: try method %s", method); 313 authenticated = m->userauth(authctxt); 314 } 315 userauth_finish(authctxt, authenticated, method, NULL); 316 317 free(service); 318 free(user); 319 free(method); 320 return 0; 321 } 322 323 void 324 userauth_finish(Authctxt *authctxt, int authenticated, const char *method, 325 const char *submethod) 326 { 327 char *methods; 328 int partial = 0; 329 330 if (!authctxt->valid && authenticated) 331 fatal("INTERNAL ERROR: authenticated invalid user %s", 332 authctxt->user); 333 if (authenticated && authctxt->postponed) 334 fatal("INTERNAL ERROR: authenticated and postponed"); 335 336 /* Special handling for root */ 337 if (authenticated && authctxt->pw->pw_uid == 0 && 338 !auth_root_allowed(method)) { 339 authenticated = 0; 340 #ifdef SSH_AUDIT_EVENTS 341 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED)); 342 #endif 343 } 344 345 if (authenticated && options.num_auth_methods != 0) { 346 if (!auth2_update_methods_lists(authctxt, method, submethod)) { 347 authenticated = 0; 348 partial = 1; 349 } 350 } 351 352 /* Log before sending the reply */ 353 auth_log(authctxt, authenticated, partial, method, submethod); 354 355 if (authctxt->postponed) 356 return; 357 358 #ifdef USE_PAM 359 if (options.use_pam && authenticated) { 360 if (!PRIVSEP(do_pam_account())) { 361 /* if PAM returned a message, send it to the user */ 362 if (buffer_len(&loginmsg) > 0) { 363 buffer_append(&loginmsg, "\0", 1); 364 userauth_send_banner(buffer_ptr(&loginmsg)); 365 packet_write_wait(); 366 } 367 fatal("Access denied for user %s by PAM account " 368 "configuration", authctxt->user); 369 } 370 } 371 #endif 372 373 #ifdef _UNICOS 374 if (authenticated && cray_access_denied(authctxt->user)) { 375 authenticated = 0; 376 fatal("Access denied for user %s.", authctxt->user); 377 } 378 #endif /* _UNICOS */ 379 380 if (authenticated == 1) { 381 /* turn off userauth */ 382 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore); 383 packet_start(SSH2_MSG_USERAUTH_SUCCESS); 384 packet_send(); 385 packet_write_wait(); 386 /* now we can break out */ 387 authctxt->success = 1; 388 } else { 389 390 /* Allow initial try of "none" auth without failure penalty */ 391 if (!partial && !authctxt->server_caused_failure && 392 (authctxt->attempt > 1 || strcmp(method, "none") != 0)) 393 authctxt->failures++; 394 if (authctxt->failures >= options.max_authtries) { 395 #ifdef SSH_AUDIT_EVENTS 396 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES)); 397 #endif 398 auth_maxtries_exceeded(authctxt); 399 } 400 methods = authmethods_get(authctxt); 401 debug3("%s: failure partial=%d next methods=\"%s\"", __func__, 402 partial, methods); 403 packet_start(SSH2_MSG_USERAUTH_FAILURE); 404 packet_put_cstring(methods); 405 packet_put_char(partial); 406 packet_send(); 407 packet_write_wait(); 408 free(methods); 409 } 410 } 411 412 /* 413 * Checks whether method is allowed by at least one AuthenticationMethods 414 * methods list. Returns 1 if allowed, or no methods lists configured. 415 * 0 otherwise. 416 */ 417 int 418 auth2_method_allowed(Authctxt *authctxt, const char *method, 419 const char *submethod) 420 { 421 u_int i; 422 423 /* 424 * NB. authctxt->num_auth_methods might be zero as a result of 425 * auth2_setup_methods_lists(), so check the configuration. 426 */ 427 if (options.num_auth_methods == 0) 428 return 1; 429 for (i = 0; i < authctxt->num_auth_methods; i++) { 430 if (list_starts_with(authctxt->auth_methods[i], method, 431 submethod) != MATCH_NONE) 432 return 1; 433 } 434 return 0; 435 } 436 437 static char * 438 authmethods_get(Authctxt *authctxt) 439 { 440 Buffer b; 441 char *list; 442 u_int i; 443 444 buffer_init(&b); 445 for (i = 0; authmethods[i] != NULL; i++) { 446 if (strcmp(authmethods[i]->name, "none") == 0) 447 continue; 448 if (authmethods[i]->enabled == NULL || 449 *(authmethods[i]->enabled) == 0) 450 continue; 451 if (!auth2_method_allowed(authctxt, authmethods[i]->name, 452 NULL)) 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 } 464 465 static Authmethod * 466 authmethod_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 auth2_method_allowed(authctxt, 476 authmethods[i]->name, NULL)) 477 return authmethods[i]; 478 debug2("Unrecognized authentication method name: %s", 479 name ? name : "NULL"); 480 return NULL; 481 } 482 483 /* 484 * Check a comma-separated list of methods for validity. Is need_enable is 485 * non-zero, then also require that the methods are enabled. 486 * Returns 0 on success or -1 if the methods list is invalid. 487 */ 488 int 489 auth2_methods_valid(const char *_methods, int need_enable) 490 { 491 char *methods, *omethods, *method, *p; 492 u_int i, found; 493 int ret = -1; 494 495 if (*_methods == '\0') { 496 error("empty authentication method list"); 497 return -1; 498 } 499 omethods = methods = xstrdup(_methods); 500 while ((method = strsep(&methods, ",")) != NULL) { 501 for (found = i = 0; !found && authmethods[i] != NULL; i++) { 502 if ((p = strchr(method, ':')) != NULL) 503 *p = '\0'; 504 if (strcmp(method, authmethods[i]->name) != 0) 505 continue; 506 if (need_enable) { 507 if (authmethods[i]->enabled == NULL || 508 *(authmethods[i]->enabled) == 0) { 509 error("Disabled method \"%s\" in " 510 "AuthenticationMethods list \"%s\"", 511 method, _methods); 512 goto out; 513 } 514 } 515 found = 1; 516 break; 517 } 518 if (!found) { 519 error("Unknown authentication method \"%s\" in list", 520 method); 521 goto out; 522 } 523 } 524 ret = 0; 525 out: 526 free(omethods); 527 return ret; 528 } 529 530 /* 531 * Prune the AuthenticationMethods supplied in the configuration, removing 532 * any methods lists that include disabled methods. Note that this might 533 * leave authctxt->num_auth_methods == 0, even when multiple required auth 534 * has been requested. For this reason, all tests for whether multiple is 535 * enabled should consult options.num_auth_methods directly. 536 */ 537 int 538 auth2_setup_methods_lists(Authctxt *authctxt) 539 { 540 u_int i; 541 542 if (options.num_auth_methods == 0) 543 return 0; 544 debug3("%s: checking methods", __func__); 545 authctxt->auth_methods = xcalloc(options.num_auth_methods, 546 sizeof(*authctxt->auth_methods)); 547 authctxt->num_auth_methods = 0; 548 for (i = 0; i < options.num_auth_methods; i++) { 549 if (auth2_methods_valid(options.auth_methods[i], 1) != 0) { 550 logit("Authentication methods list \"%s\" contains " 551 "disabled method, skipping", 552 options.auth_methods[i]); 553 continue; 554 } 555 debug("authentication methods list %d: %s", 556 authctxt->num_auth_methods, options.auth_methods[i]); 557 authctxt->auth_methods[authctxt->num_auth_methods++] = 558 xstrdup(options.auth_methods[i]); 559 } 560 if (authctxt->num_auth_methods == 0) { 561 error("No AuthenticationMethods left after eliminating " 562 "disabled methods"); 563 return -1; 564 } 565 return 0; 566 } 567 568 static int 569 list_starts_with(const char *methods, const char *method, 570 const char *submethod) 571 { 572 size_t l = strlen(method); 573 int match; 574 const char *p; 575 576 if (strncmp(methods, method, l) != 0) 577 return MATCH_NONE; 578 p = methods + l; 579 match = MATCH_METHOD; 580 if (*p == ':') { 581 if (!submethod) 582 return MATCH_PARTIAL; 583 l = strlen(submethod); 584 p += 1; 585 if (strncmp(submethod, p, l)) 586 return MATCH_NONE; 587 p += l; 588 match = MATCH_BOTH; 589 } 590 if (*p != ',' && *p != '\0') 591 return MATCH_NONE; 592 return match; 593 } 594 595 /* 596 * Remove method from the start of a comma-separated list of methods. 597 * Returns 0 if the list of methods did not start with that method or 1 598 * if it did. 599 */ 600 static int 601 remove_method(char **methods, const char *method, const char *submethod) 602 { 603 char *omethods = *methods, *p; 604 size_t l = strlen(method); 605 int match; 606 607 match = list_starts_with(omethods, method, submethod); 608 if (match != MATCH_METHOD && match != MATCH_BOTH) 609 return 0; 610 p = omethods + l; 611 if (submethod && match == MATCH_BOTH) 612 p += 1 + strlen(submethod); /* include colon */ 613 if (*p == ',') 614 p++; 615 *methods = xstrdup(p); 616 free(omethods); 617 return 1; 618 } 619 620 /* 621 * Called after successful authentication. Will remove the successful method 622 * from the start of each list in which it occurs. If it was the last method 623 * in any list, then authentication is deemed successful. 624 * Returns 1 if the method completed any authentication list or 0 otherwise. 625 */ 626 int 627 auth2_update_methods_lists(Authctxt *authctxt, const char *method, 628 const char *submethod) 629 { 630 u_int i, found = 0; 631 632 debug3("%s: updating methods list after \"%s\"", __func__, method); 633 for (i = 0; i < authctxt->num_auth_methods; i++) { 634 if (!remove_method(&(authctxt->auth_methods[i]), method, 635 submethod)) 636 continue; 637 found = 1; 638 if (*authctxt->auth_methods[i] == '\0') { 639 debug2("authentication methods list %d complete", i); 640 return 1; 641 } 642 debug3("authentication methods list %d remaining: \"%s\"", 643 i, authctxt->auth_methods[i]); 644 } 645 /* This should not happen, but would be bad if it did */ 646 if (!found) 647 fatal("%s: method not in AuthenticationMethods", __func__); 648 return 0; 649 } 650 651 652