1 /* $OpenBSD: auth2.c,v 1.136 2016/05/02 08:49:03 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 #include "canohost.h" 54 55 #ifdef GSSAPI 56 #include "ssh-gss.h" 57 #endif 58 #include "monitor_wrap.h" 59 60 /* import */ 61 extern ServerOptions options; 62 extern u_char *session_id2; 63 extern u_int session_id2_len; 64 extern Buffer loginmsg; 65 66 /* methods */ 67 68 extern Authmethod method_none; 69 extern Authmethod method_pubkey; 70 extern Authmethod method_passwd; 71 extern Authmethod method_kbdint; 72 extern Authmethod method_hostbased; 73 #ifdef GSSAPI 74 extern Authmethod method_gssapi; 75 #endif 76 77 Authmethod *authmethods[] = { 78 &method_none, 79 &method_pubkey, 80 #ifdef GSSAPI 81 &method_gssapi, 82 #endif 83 &method_passwd, 84 &method_kbdint, 85 &method_hostbased, 86 NULL 87 }; 88 89 /* protocol */ 90 91 static int input_service_request(int, u_int32_t, void *); 92 static int input_userauth_request(int, u_int32_t, void *); 93 94 /* helper */ 95 static Authmethod *authmethod_lookup(Authctxt *, const char *); 96 static char *authmethods_get(Authctxt *authctxt); 97 98 #define MATCH_NONE 0 /* method or submethod mismatch */ 99 #define MATCH_METHOD 1 /* method matches (no submethod specified) */ 100 #define MATCH_BOTH 2 /* method and submethod match */ 101 #define MATCH_PARTIAL 3 /* method matches, submethod can't be checked */ 102 static int list_starts_with(const char *, const char *, const char *); 103 104 char * 105 auth2_read_banner(void) 106 { 107 struct stat st; 108 char *banner = NULL; 109 size_t len, n; 110 int fd; 111 112 if ((fd = open(options.banner, O_RDONLY)) == -1) 113 return (NULL); 114 if (fstat(fd, &st) == -1) { 115 close(fd); 116 return (NULL); 117 } 118 if (st.st_size <= 0 || st.st_size > 1*1024*1024) { 119 close(fd); 120 return (NULL); 121 } 122 123 len = (size_t)st.st_size; /* truncate */ 124 banner = xmalloc(len + 1); 125 n = atomicio(read, fd, banner, len); 126 close(fd); 127 128 if (n != len) { 129 free(banner); 130 return (NULL); 131 } 132 banner[n] = '\0'; 133 134 return (banner); 135 } 136 137 void 138 userauth_send_banner(const char *msg) 139 { 140 if (datafellows & SSH_BUG_BANNER) 141 return; 142 143 packet_start(SSH2_MSG_USERAUTH_BANNER); 144 packet_put_cstring(msg); 145 packet_put_cstring(""); /* language, unused */ 146 packet_send(); 147 debug("%s: sent", __func__); 148 } 149 150 static void 151 userauth_banner(void) 152 { 153 char *banner = NULL; 154 155 if (options.banner == NULL || (datafellows & SSH_BUG_BANNER) != 0) 156 return; 157 158 if ((banner = PRIVSEP(auth2_read_banner())) == NULL) 159 goto done; 160 userauth_send_banner(banner); 161 162 done: 163 free(banner); 164 } 165 166 /* 167 * loop until authctxt->success == TRUE 168 */ 169 void 170 do_authentication2(Authctxt *authctxt) 171 { 172 dispatch_init(&dispatch_protocol_error); 173 dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request); 174 dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt); 175 } 176 177 /*ARGSUSED*/ 178 static int 179 input_service_request(int type, u_int32_t seq, void *ctxt) 180 { 181 Authctxt *authctxt = ctxt; 182 u_int len; 183 int acceptit = 0; 184 char *service = packet_get_cstring(&len); 185 packet_check_eom(); 186 187 if (authctxt == NULL) 188 fatal("input_service_request: no authctxt"); 189 190 if (strcmp(service, "ssh-userauth") == 0) { 191 if (!authctxt->success) { 192 acceptit = 1; 193 /* now we can handle user-auth requests */ 194 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request); 195 } 196 } 197 /* XXX all other service requests are denied */ 198 199 if (acceptit) { 200 packet_start(SSH2_MSG_SERVICE_ACCEPT); 201 packet_put_cstring(service); 202 packet_send(); 203 packet_write_wait(); 204 } else { 205 debug("bad service request %s", service); 206 packet_disconnect("bad service request %s", service); 207 } 208 free(service); 209 return 0; 210 } 211 212 /*ARGSUSED*/ 213 static int 214 input_userauth_request(int type, u_int32_t seq, void *ctxt) 215 { 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("input_userauth_request: setting up authctxt for %s", user); 240 } else { 241 logit("input_userauth_request: invalid user %s", user); 242 authctxt->pw = fakepw(); 243 #ifdef SSH_AUDIT_EVENTS 244 PRIVSEP(audit_event(SSH_INVALID_USER)); 245 #endif 246 } 247 #ifdef USE_PAM 248 if (options.use_pam) 249 PRIVSEP(start_pam(authctxt)); 250 #endif 251 setproctitle("%s%s", authctxt->valid ? user : "unknown", 252 use_privsep ? " [net]" : ""); 253 authctxt->service = xstrdup(service); 254 authctxt->style = style ? xstrdup(style) : NULL; 255 if (use_privsep) 256 mm_inform_authserv(service, style); 257 userauth_banner(); 258 if (auth2_setup_methods_lists(authctxt) != 0) 259 packet_disconnect("no authentication methods enabled"); 260 } else if (strcmp(user, authctxt->user) != 0 || 261 strcmp(service, authctxt->service) != 0) { 262 packet_disconnect("Change of username or service not allowed: " 263 "(%s,%s) -> (%s,%s)", 264 authctxt->user, authctxt->service, user, service); 265 } 266 /* reset state */ 267 auth2_challenge_stop(authctxt); 268 269 #ifdef GSSAPI 270 /* XXX move to auth2_gssapi_stop() */ 271 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); 272 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL); 273 #endif 274 275 authctxt->postponed = 0; 276 authctxt->server_caused_failure = 0; 277 278 /* try to authenticate user */ 279 m = authmethod_lookup(authctxt, method); 280 if (m != NULL && authctxt->failures < options.max_authtries) { 281 debug2("input_userauth_request: try method %s", method); 282 authenticated = m->userauth(authctxt); 283 } 284 userauth_finish(authctxt, authenticated, method, NULL); 285 286 free(service); 287 free(user); 288 free(method); 289 return 0; 290 } 291 292 void 293 userauth_finish(Authctxt *authctxt, int authenticated, const char *method, 294 const char *submethod) 295 { 296 char *methods; 297 int partial = 0; 298 299 if (!authctxt->valid && authenticated) 300 fatal("INTERNAL ERROR: authenticated invalid user %s", 301 authctxt->user); 302 if (authenticated && authctxt->postponed) 303 fatal("INTERNAL ERROR: authenticated and postponed"); 304 305 /* Special handling for root */ 306 if (authenticated && authctxt->pw->pw_uid == 0 && 307 !auth_root_allowed(method)) { 308 authenticated = 0; 309 #ifdef SSH_AUDIT_EVENTS 310 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED)); 311 #endif 312 } 313 314 if (authenticated && options.num_auth_methods != 0) { 315 if (!auth2_update_methods_lists(authctxt, method, submethod)) { 316 authenticated = 0; 317 partial = 1; 318 } 319 } 320 321 /* Log before sending the reply */ 322 auth_log(authctxt, authenticated, partial, method, submethod); 323 324 if (authctxt->postponed) 325 return; 326 327 #ifdef USE_PAM 328 if (options.use_pam && authenticated) { 329 if (!PRIVSEP(do_pam_account())) { 330 /* if PAM returned a message, send it to the user */ 331 if (buffer_len(&loginmsg) > 0) { 332 buffer_append(&loginmsg, "\0", 1); 333 userauth_send_banner(buffer_ptr(&loginmsg)); 334 packet_write_wait(); 335 } 336 fatal("Access denied for user %s by PAM account " 337 "configuration", authctxt->user); 338 } 339 } 340 #endif 341 342 #ifdef _UNICOS 343 if (authenticated && cray_access_denied(authctxt->user)) { 344 authenticated = 0; 345 fatal("Access denied for user %s.", authctxt->user); 346 } 347 #endif /* _UNICOS */ 348 349 if (authenticated == 1) { 350 /* turn off userauth */ 351 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore); 352 packet_start(SSH2_MSG_USERAUTH_SUCCESS); 353 packet_send(); 354 packet_write_wait(); 355 /* now we can break out */ 356 authctxt->success = 1; 357 } else { 358 359 /* Allow initial try of "none" auth without failure penalty */ 360 if (!partial && !authctxt->server_caused_failure && 361 (authctxt->attempt > 1 || strcmp(method, "none") != 0)) 362 authctxt->failures++; 363 if (authctxt->failures >= options.max_authtries) { 364 #ifdef SSH_AUDIT_EVENTS 365 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES)); 366 #endif 367 auth_maxtries_exceeded(authctxt); 368 } 369 methods = authmethods_get(authctxt); 370 debug3("%s: failure partial=%d next methods=\"%s\"", __func__, 371 partial, methods); 372 packet_start(SSH2_MSG_USERAUTH_FAILURE); 373 packet_put_cstring(methods); 374 packet_put_char(partial); 375 packet_send(); 376 packet_write_wait(); 377 free(methods); 378 } 379 } 380 381 /* 382 * Checks whether method is allowed by at least one AuthenticationMethods 383 * methods list. Returns 1 if allowed, or no methods lists configured. 384 * 0 otherwise. 385 */ 386 int 387 auth2_method_allowed(Authctxt *authctxt, const char *method, 388 const char *submethod) 389 { 390 u_int i; 391 392 /* 393 * NB. authctxt->num_auth_methods might be zero as a result of 394 * auth2_setup_methods_lists(), so check the configuration. 395 */ 396 if (options.num_auth_methods == 0) 397 return 1; 398 for (i = 0; i < authctxt->num_auth_methods; i++) { 399 if (list_starts_with(authctxt->auth_methods[i], method, 400 submethod) != MATCH_NONE) 401 return 1; 402 } 403 return 0; 404 } 405 406 static char * 407 authmethods_get(Authctxt *authctxt) 408 { 409 Buffer b; 410 char *list; 411 u_int i; 412 413 buffer_init(&b); 414 for (i = 0; authmethods[i] != NULL; i++) { 415 if (strcmp(authmethods[i]->name, "none") == 0) 416 continue; 417 if (authmethods[i]->enabled == NULL || 418 *(authmethods[i]->enabled) == 0) 419 continue; 420 if (!auth2_method_allowed(authctxt, authmethods[i]->name, 421 NULL)) 422 continue; 423 if (buffer_len(&b) > 0) 424 buffer_append(&b, ",", 1); 425 buffer_append(&b, authmethods[i]->name, 426 strlen(authmethods[i]->name)); 427 } 428 if ((list = sshbuf_dup_string(&b)) == NULL) 429 fatal("%s: sshbuf_dup_string failed", __func__); 430 buffer_free(&b); 431 return list; 432 } 433 434 static Authmethod * 435 authmethod_lookup(Authctxt *authctxt, const char *name) 436 { 437 int i; 438 439 if (name != NULL) 440 for (i = 0; authmethods[i] != NULL; i++) 441 if (authmethods[i]->enabled != NULL && 442 *(authmethods[i]->enabled) != 0 && 443 strcmp(name, authmethods[i]->name) == 0 && 444 auth2_method_allowed(authctxt, 445 authmethods[i]->name, NULL)) 446 return authmethods[i]; 447 debug2("Unrecognized authentication method name: %s", 448 name ? name : "NULL"); 449 return NULL; 450 } 451 452 /* 453 * Check a comma-separated list of methods for validity. Is need_enable is 454 * non-zero, then also require that the methods are enabled. 455 * Returns 0 on success or -1 if the methods list is invalid. 456 */ 457 int 458 auth2_methods_valid(const char *_methods, int need_enable) 459 { 460 char *methods, *omethods, *method, *p; 461 u_int i, found; 462 int ret = -1; 463 464 if (*_methods == '\0') { 465 error("empty authentication method list"); 466 return -1; 467 } 468 omethods = methods = xstrdup(_methods); 469 while ((method = strsep(&methods, ",")) != NULL) { 470 for (found = i = 0; !found && authmethods[i] != NULL; i++) { 471 if ((p = strchr(method, ':')) != NULL) 472 *p = '\0'; 473 if (strcmp(method, authmethods[i]->name) != 0) 474 continue; 475 if (need_enable) { 476 if (authmethods[i]->enabled == NULL || 477 *(authmethods[i]->enabled) == 0) { 478 error("Disabled method \"%s\" in " 479 "AuthenticationMethods list \"%s\"", 480 method, _methods); 481 goto out; 482 } 483 } 484 found = 1; 485 break; 486 } 487 if (!found) { 488 error("Unknown authentication method \"%s\" in list", 489 method); 490 goto out; 491 } 492 } 493 ret = 0; 494 out: 495 free(omethods); 496 return ret; 497 } 498 499 /* 500 * Prune the AuthenticationMethods supplied in the configuration, removing 501 * any methods lists that include disabled methods. Note that this might 502 * leave authctxt->num_auth_methods == 0, even when multiple required auth 503 * has been requested. For this reason, all tests for whether multiple is 504 * enabled should consult options.num_auth_methods directly. 505 */ 506 int 507 auth2_setup_methods_lists(Authctxt *authctxt) 508 { 509 u_int i; 510 511 if (options.num_auth_methods == 0) 512 return 0; 513 debug3("%s: checking methods", __func__); 514 authctxt->auth_methods = xcalloc(options.num_auth_methods, 515 sizeof(*authctxt->auth_methods)); 516 authctxt->num_auth_methods = 0; 517 for (i = 0; i < options.num_auth_methods; i++) { 518 if (auth2_methods_valid(options.auth_methods[i], 1) != 0) { 519 logit("Authentication methods list \"%s\" contains " 520 "disabled method, skipping", 521 options.auth_methods[i]); 522 continue; 523 } 524 debug("authentication methods list %d: %s", 525 authctxt->num_auth_methods, options.auth_methods[i]); 526 authctxt->auth_methods[authctxt->num_auth_methods++] = 527 xstrdup(options.auth_methods[i]); 528 } 529 if (authctxt->num_auth_methods == 0) { 530 error("No AuthenticationMethods left after eliminating " 531 "disabled methods"); 532 return -1; 533 } 534 return 0; 535 } 536 537 static int 538 list_starts_with(const char *methods, const char *method, 539 const char *submethod) 540 { 541 size_t l = strlen(method); 542 int match; 543 const char *p; 544 545 if (strncmp(methods, method, l) != 0) 546 return MATCH_NONE; 547 p = methods + l; 548 match = MATCH_METHOD; 549 if (*p == ':') { 550 if (!submethod) 551 return MATCH_PARTIAL; 552 l = strlen(submethod); 553 p += 1; 554 if (strncmp(submethod, p, l)) 555 return MATCH_NONE; 556 p += l; 557 match = MATCH_BOTH; 558 } 559 if (*p != ',' && *p != '\0') 560 return MATCH_NONE; 561 return match; 562 } 563 564 /* 565 * Remove method from the start of a comma-separated list of methods. 566 * Returns 0 if the list of methods did not start with that method or 1 567 * if it did. 568 */ 569 static int 570 remove_method(char **methods, const char *method, const char *submethod) 571 { 572 char *omethods = *methods, *p; 573 size_t l = strlen(method); 574 int match; 575 576 match = list_starts_with(omethods, method, submethod); 577 if (match != MATCH_METHOD && match != MATCH_BOTH) 578 return 0; 579 p = omethods + l; 580 if (submethod && match == MATCH_BOTH) 581 p += 1 + strlen(submethod); /* include colon */ 582 if (*p == ',') 583 p++; 584 *methods = xstrdup(p); 585 free(omethods); 586 return 1; 587 } 588 589 /* 590 * Called after successful authentication. Will remove the successful method 591 * from the start of each list in which it occurs. If it was the last method 592 * in any list, then authentication is deemed successful. 593 * Returns 1 if the method completed any authentication list or 0 otherwise. 594 */ 595 int 596 auth2_update_methods_lists(Authctxt *authctxt, const char *method, 597 const char *submethod) 598 { 599 u_int i, found = 0; 600 601 debug3("%s: updating methods list after \"%s\"", __func__, method); 602 for (i = 0; i < authctxt->num_auth_methods; i++) { 603 if (!remove_method(&(authctxt->auth_methods[i]), method, 604 submethod)) 605 continue; 606 found = 1; 607 if (*authctxt->auth_methods[i] == '\0') { 608 debug2("authentication methods list %d complete", i); 609 return 1; 610 } 611 debug3("authentication methods list %d remaining: \"%s\"", 612 i, authctxt->auth_methods[i]); 613 } 614 /* This should not happen, but would be bad if it did */ 615 if (!found) 616 fatal("%s: method not in AuthenticationMethods", __func__); 617 return 0; 618 } 619 620 621