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 27 #include <sys/types.h> 28 #include <sys/stat.h> 29 #include <sys/uio.h> 30 31 #include <fcntl.h> 32 #include <pwd.h> 33 #include <stdarg.h> 34 #include <string.h> 35 #include <unistd.h> 36 37 #include "atomicio.h" 38 #include "xmalloc.h" 39 #include "ssh2.h" 40 #include "packet.h" 41 #include "log.h" 42 #include "buffer.h" 43 #include "misc.h" 44 #include "servconf.h" 45 #include "compat.h" 46 #include "key.h" 47 #include "hostfile.h" 48 #include "auth.h" 49 #include "dispatch.h" 50 #include "pathnames.h" 51 #ifdef GSSAPI 52 #include "ssh-gss.h" 53 #endif 54 #include "monitor_wrap.h" 55 56 /* import */ 57 extern ServerOptions options; 58 extern u_char *session_id2; 59 extern u_int session_id2_len; 60 61 /* methods */ 62 63 extern Authmethod method_none; 64 extern Authmethod method_pubkey; 65 extern Authmethod method_passwd; 66 extern Authmethod method_kbdint; 67 extern Authmethod method_hostbased; 68 #ifdef GSSAPI 69 extern Authmethod method_gssapi; 70 #endif 71 72 Authmethod *authmethods[] = { 73 &method_none, 74 &method_pubkey, 75 #ifdef GSSAPI 76 &method_gssapi, 77 #endif 78 &method_passwd, 79 &method_kbdint, 80 &method_hostbased, 81 NULL 82 }; 83 84 /* protocol */ 85 86 static int input_service_request(int, u_int32_t, void *); 87 static int input_userauth_request(int, u_int32_t, void *); 88 89 /* helper */ 90 static Authmethod *authmethod_lookup(Authctxt *, const char *); 91 static char *authmethods_get(Authctxt *authctxt); 92 93 #define MATCH_NONE 0 /* method or submethod mismatch */ 94 #define MATCH_METHOD 1 /* method matches (no submethod specified) */ 95 #define MATCH_BOTH 2 /* method and submethod match */ 96 #define MATCH_PARTIAL 3 /* method matches, submethod can't be checked */ 97 static int list_starts_with(const char *, const char *, const char *); 98 99 char * 100 auth2_read_banner(void) 101 { 102 struct stat st; 103 char *banner = NULL; 104 size_t len, n; 105 int fd; 106 107 if ((fd = open(options.banner, O_RDONLY)) == -1) 108 return (NULL); 109 if (fstat(fd, &st) == -1) { 110 close(fd); 111 return (NULL); 112 } 113 if (st.st_size <= 0 || st.st_size > 1*1024*1024) { 114 close(fd); 115 return (NULL); 116 } 117 118 len = (size_t)st.st_size; /* truncate */ 119 banner = xmalloc(len + 1); 120 n = atomicio(read, fd, banner, len); 121 close(fd); 122 123 if (n != len) { 124 free(banner); 125 return (NULL); 126 } 127 banner[n] = '\0'; 128 129 return (banner); 130 } 131 132 static void 133 userauth_banner(void) 134 { 135 char *banner = NULL; 136 137 if (options.banner == NULL || (datafellows & SSH_BUG_BANNER) != 0) 138 return; 139 140 if ((banner = PRIVSEP(auth2_read_banner())) == NULL) 141 goto done; 142 143 packet_start(SSH2_MSG_USERAUTH_BANNER); 144 packet_put_cstring(banner); 145 packet_put_cstring(""); /* language, unused */ 146 packet_send(); 147 debug("userauth_banner: sent"); 148 done: 149 free(banner); 150 } 151 152 /* 153 * loop until authctxt->success == TRUE 154 */ 155 void 156 do_authentication2(Authctxt *authctxt) 157 { 158 dispatch_init(&dispatch_protocol_error); 159 dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request); 160 dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt); 161 } 162 163 /*ARGSUSED*/ 164 static int 165 input_service_request(int type, u_int32_t seq, void *ctxt) 166 { 167 Authctxt *authctxt = ctxt; 168 u_int len; 169 int acceptit = 0; 170 char *service = packet_get_cstring(&len); 171 packet_check_eom(); 172 173 if (authctxt == NULL) 174 fatal("input_service_request: no authctxt"); 175 176 if (strcmp(service, "ssh-userauth") == 0) { 177 if (!authctxt->success) { 178 acceptit = 1; 179 /* now we can handle user-auth requests */ 180 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request); 181 } 182 } 183 /* XXX all other service requests are denied */ 184 185 if (acceptit) { 186 packet_start(SSH2_MSG_SERVICE_ACCEPT); 187 packet_put_cstring(service); 188 packet_send(); 189 packet_write_wait(); 190 } else { 191 debug("bad service request %s", service); 192 packet_disconnect("bad service request %s", service); 193 } 194 free(service); 195 return 0; 196 } 197 198 /*ARGSUSED*/ 199 static int 200 input_userauth_request(int type, u_int32_t seq, void *ctxt) 201 { 202 Authctxt *authctxt = ctxt; 203 Authmethod *m = NULL; 204 char *user, *service, *method, *style = NULL; 205 int authenticated = 0; 206 207 if (authctxt == NULL) 208 fatal("input_userauth_request: no authctxt"); 209 210 user = packet_get_cstring(NULL); 211 service = packet_get_cstring(NULL); 212 method = packet_get_cstring(NULL); 213 debug("userauth-request for user %s service %s method %s", user, service, method); 214 debug("attempt %d failures %d", authctxt->attempt, authctxt->failures); 215 216 if ((style = strchr(user, ':')) != NULL) 217 *style++ = 0; 218 219 if (authctxt->attempt++ == 0) { 220 /* setup auth context */ 221 authctxt->pw = PRIVSEP(getpwnamallow(user)); 222 if (authctxt->pw && strcmp(service, "ssh-connection")==0) { 223 authctxt->valid = 1; 224 debug2("input_userauth_request: setting up authctxt for %s", user); 225 } else { 226 logit("input_userauth_request: invalid user %s", user); 227 authctxt->pw = fakepw(); 228 } 229 setproctitle("%s%s", authctxt->valid ? user : "unknown", 230 use_privsep ? " [net]" : ""); 231 authctxt->user = xstrdup(user); 232 authctxt->service = xstrdup(service); 233 authctxt->style = style ? xstrdup(style) : NULL; 234 if (use_privsep) 235 mm_inform_authserv(service, style); 236 userauth_banner(); 237 if (auth2_setup_methods_lists(authctxt) != 0) 238 packet_disconnect("no authentication methods enabled"); 239 } else if (strcmp(user, authctxt->user) != 0 || 240 strcmp(service, authctxt->service) != 0) { 241 packet_disconnect("Change of username or service not allowed: " 242 "(%s,%s) -> (%s,%s)", 243 authctxt->user, authctxt->service, user, service); 244 } 245 /* reset state */ 246 auth2_challenge_stop(authctxt); 247 248 #ifdef GSSAPI 249 /* XXX move to auth2_gssapi_stop() */ 250 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); 251 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL); 252 #endif 253 254 authctxt->postponed = 0; 255 authctxt->server_caused_failure = 0; 256 257 /* try to authenticate user */ 258 m = authmethod_lookup(authctxt, method); 259 if (m != NULL && authctxt->failures < options.max_authtries) { 260 debug2("input_userauth_request: try method %s", method); 261 authenticated = m->userauth(authctxt); 262 } 263 userauth_finish(authctxt, authenticated, method, NULL); 264 265 free(service); 266 free(user); 267 free(method); 268 return 0; 269 } 270 271 void 272 userauth_finish(Authctxt *authctxt, int authenticated, const char *method, 273 const char *submethod) 274 { 275 char *methods; 276 int partial = 0; 277 278 if (!authctxt->valid && authenticated) 279 fatal("INTERNAL ERROR: authenticated invalid user %s", 280 authctxt->user); 281 if (authenticated && authctxt->postponed) 282 fatal("INTERNAL ERROR: authenticated and postponed"); 283 284 /* Special handling for root */ 285 if (authenticated && authctxt->pw->pw_uid == 0 && 286 !auth_root_allowed(method)) 287 authenticated = 0; 288 289 if (authenticated && options.num_auth_methods != 0) { 290 if (!auth2_update_methods_lists(authctxt, method, submethod)) { 291 authenticated = 0; 292 partial = 1; 293 } 294 } 295 296 /* Log before sending the reply */ 297 auth_log(authctxt, authenticated, partial, method, submethod); 298 299 if (authctxt->postponed) 300 return; 301 302 if (authenticated == 1) { 303 /* turn off userauth */ 304 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore); 305 packet_start(SSH2_MSG_USERAUTH_SUCCESS); 306 packet_send(); 307 packet_write_wait(); 308 /* now we can break out */ 309 authctxt->success = 1; 310 } else { 311 /* Allow initial try of "none" auth without failure penalty */ 312 if (!partial && !authctxt->server_caused_failure && 313 (authctxt->attempt > 1 || strcmp(method, "none") != 0)) 314 authctxt->failures++; 315 if (authctxt->failures >= options.max_authtries) 316 auth_maxtries_exceeded(authctxt); 317 methods = authmethods_get(authctxt); 318 debug3("%s: failure partial=%d next methods=\"%s\"", __func__, 319 partial, methods); 320 packet_start(SSH2_MSG_USERAUTH_FAILURE); 321 packet_put_cstring(methods); 322 packet_put_char(partial); 323 packet_send(); 324 packet_write_wait(); 325 free(methods); 326 } 327 } 328 329 /* 330 * Checks whether method is allowed by at least one AuthenticationMethods 331 * methods list. Returns 1 if allowed, or no methods lists configured. 332 * 0 otherwise. 333 */ 334 int 335 auth2_method_allowed(Authctxt *authctxt, const char *method, 336 const char *submethod) 337 { 338 u_int i; 339 340 /* 341 * NB. authctxt->num_auth_methods might be zero as a result of 342 * auth2_setup_methods_lists(), so check the configuration. 343 */ 344 if (options.num_auth_methods == 0) 345 return 1; 346 for (i = 0; i < authctxt->num_auth_methods; i++) { 347 if (list_starts_with(authctxt->auth_methods[i], method, 348 submethod) != MATCH_NONE) 349 return 1; 350 } 351 return 0; 352 } 353 354 static char * 355 authmethods_get(Authctxt *authctxt) 356 { 357 Buffer b; 358 char *list; 359 u_int i; 360 361 buffer_init(&b); 362 for (i = 0; authmethods[i] != NULL; i++) { 363 if (strcmp(authmethods[i]->name, "none") == 0) 364 continue; 365 if (authmethods[i]->enabled == NULL || 366 *(authmethods[i]->enabled) == 0) 367 continue; 368 if (!auth2_method_allowed(authctxt, authmethods[i]->name, 369 NULL)) 370 continue; 371 if (buffer_len(&b) > 0) 372 buffer_append(&b, ",", 1); 373 buffer_append(&b, authmethods[i]->name, 374 strlen(authmethods[i]->name)); 375 } 376 buffer_append(&b, "\0", 1); 377 list = xstrdup(buffer_ptr(&b)); 378 buffer_free(&b); 379 return list; 380 } 381 382 static Authmethod * 383 authmethod_lookup(Authctxt *authctxt, const char *name) 384 { 385 int i; 386 387 if (name != NULL) 388 for (i = 0; authmethods[i] != NULL; i++) 389 if (authmethods[i]->enabled != NULL && 390 *(authmethods[i]->enabled) != 0 && 391 strcmp(name, authmethods[i]->name) == 0 && 392 auth2_method_allowed(authctxt, 393 authmethods[i]->name, NULL)) 394 return authmethods[i]; 395 debug2("Unrecognized authentication method name: %s", 396 name ? name : "NULL"); 397 return NULL; 398 } 399 400 /* 401 * Check a comma-separated list of methods for validity. Is need_enable is 402 * non-zero, then also require that the methods are enabled. 403 * Returns 0 on success or -1 if the methods list is invalid. 404 */ 405 int 406 auth2_methods_valid(const char *_methods, int need_enable) 407 { 408 char *methods, *omethods, *method, *p; 409 u_int i, found; 410 int ret = -1; 411 412 if (*_methods == '\0') { 413 error("empty authentication method list"); 414 return -1; 415 } 416 omethods = methods = xstrdup(_methods); 417 while ((method = strsep(&methods, ",")) != NULL) { 418 for (found = i = 0; !found && authmethods[i] != NULL; i++) { 419 if ((p = strchr(method, ':')) != NULL) 420 *p = '\0'; 421 if (strcmp(method, authmethods[i]->name) != 0) 422 continue; 423 if (need_enable) { 424 if (authmethods[i]->enabled == NULL || 425 *(authmethods[i]->enabled) == 0) { 426 error("Disabled method \"%s\" in " 427 "AuthenticationMethods list \"%s\"", 428 method, _methods); 429 goto out; 430 } 431 } 432 found = 1; 433 break; 434 } 435 if (!found) { 436 error("Unknown authentication method \"%s\" in list", 437 method); 438 goto out; 439 } 440 } 441 ret = 0; 442 out: 443 free(omethods); 444 return ret; 445 } 446 447 /* 448 * Prune the AuthenticationMethods supplied in the configuration, removing 449 * any methods lists that include disabled methods. Note that this might 450 * leave authctxt->num_auth_methods == 0, even when multiple required auth 451 * has been requested. For this reason, all tests for whether multiple is 452 * enabled should consult options.num_auth_methods directly. 453 */ 454 int 455 auth2_setup_methods_lists(Authctxt *authctxt) 456 { 457 u_int i; 458 459 if (options.num_auth_methods == 0) 460 return 0; 461 debug3("%s: checking methods", __func__); 462 authctxt->auth_methods = xcalloc(options.num_auth_methods, 463 sizeof(*authctxt->auth_methods)); 464 authctxt->num_auth_methods = 0; 465 for (i = 0; i < options.num_auth_methods; i++) { 466 if (auth2_methods_valid(options.auth_methods[i], 1) != 0) { 467 logit("Authentication methods list \"%s\" contains " 468 "disabled method, skipping", 469 options.auth_methods[i]); 470 continue; 471 } 472 debug("authentication methods list %d: %s", 473 authctxt->num_auth_methods, options.auth_methods[i]); 474 authctxt->auth_methods[authctxt->num_auth_methods++] = 475 xstrdup(options.auth_methods[i]); 476 } 477 if (authctxt->num_auth_methods == 0) { 478 error("No AuthenticationMethods left after eliminating " 479 "disabled methods"); 480 return -1; 481 } 482 return 0; 483 } 484 485 static int 486 list_starts_with(const char *methods, const char *method, 487 const char *submethod) 488 { 489 size_t l = strlen(method); 490 int match; 491 const char *p; 492 493 if (strncmp(methods, method, l) != 0) 494 return MATCH_NONE; 495 p = methods + l; 496 match = MATCH_METHOD; 497 if (*p == ':') { 498 if (!submethod) 499 return MATCH_PARTIAL; 500 l = strlen(submethod); 501 p += 1; 502 if (strncmp(submethod, p, l)) 503 return MATCH_NONE; 504 p += l; 505 match = MATCH_BOTH; 506 } 507 if (*p != ',' && *p != '\0') 508 return MATCH_NONE; 509 return match; 510 } 511 512 /* 513 * Remove method from the start of a comma-separated list of methods. 514 * Returns 0 if the list of methods did not start with that method or 1 515 * if it did. 516 */ 517 static int 518 remove_method(char **methods, const char *method, const char *submethod) 519 { 520 char *omethods = *methods, *p; 521 size_t l = strlen(method); 522 int match; 523 524 match = list_starts_with(omethods, method, submethod); 525 if (match != MATCH_METHOD && match != MATCH_BOTH) 526 return 0; 527 p = omethods + l; 528 if (submethod && match == MATCH_BOTH) 529 p += 1 + strlen(submethod); /* include colon */ 530 if (*p == ',') 531 p++; 532 *methods = xstrdup(p); 533 free(omethods); 534 return 1; 535 } 536 537 /* 538 * Called after successful authentication. Will remove the successful method 539 * from the start of each list in which it occurs. If it was the last method 540 * in any list, then authentication is deemed successful. 541 * Returns 1 if the method completed any authentication list or 0 otherwise. 542 */ 543 int 544 auth2_update_methods_lists(Authctxt *authctxt, const char *method, 545 const char *submethod) 546 { 547 u_int i, found = 0; 548 549 debug3("%s: updating methods list after \"%s\"", __func__, method); 550 for (i = 0; i < authctxt->num_auth_methods; i++) { 551 if (!remove_method(&(authctxt->auth_methods[i]), method, 552 submethod)) 553 continue; 554 found = 1; 555 if (*authctxt->auth_methods[i] == '\0') { 556 debug2("authentication methods list %d complete", i); 557 return 1; 558 } 559 debug3("authentication methods list %d remaining: \"%s\"", 560 i, authctxt->auth_methods[i]); 561 } 562 /* This should not happen, but would be bad if it did */ 563 if (!found) 564 fatal("%s: method not in AuthenticationMethods", __func__); 565 return 0; 566 } 567 568 569