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 * 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 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 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 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 * 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 * 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 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 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 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 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 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
