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 * 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 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 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 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 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 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 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 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 * 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 * 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 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 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 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 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 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
