crypto/openssh/auth2.c

   1 /* $OpenBSD: auth2.c,v 1.132 2014/07/15 15:54:14 millert 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 void input_service_request(int, u_int32_t, void *);
  91 static void 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 ||
 155             strcasecmp(options.banner, "none") == 0 ||
 156             (datafellows & SSH_BUG_BANNER) != 0)
 157                 return;
 158
 159         if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
 160                 goto done;
 161         userauth_send_banner(banner);
 162
 163 done:
 164         free(banner);
 165 }
 166
 167 /*
 168  * loop until authctxt->success == TRUE
 169  */
 170 void
 171 do_authentication2(Authctxt *authctxt)
 172 {
 173         dispatch_init(&dispatch_protocol_error);
 174         dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
 175         dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
 176 }
 177
 178 /*ARGSUSED*/
 179 static void
 180 input_service_request(int type, u_int32_t seq, void *ctxt)
 181 {
 182         Authctxt *authctxt = ctxt;
 183         u_int len;
 184         int acceptit = 0;
 185         char *service = packet_get_cstring(&len);
 186         packet_check_eom();
 187
 188         if (authctxt == NULL)
 189                 fatal("input_service_request: no authctxt");
 190
 191         if (strcmp(service, "ssh-userauth") == 0) {
 192                 if (!authctxt->success) {
 193                         acceptit = 1;
 194                         /* now we can handle user-auth requests */
 195                         dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
 196                 }
 197         }
 198         /* XXX all other service requests are denied */
 199
 200         if (acceptit) {
 201                 packet_start(SSH2_MSG_SERVICE_ACCEPT);
 202                 packet_put_cstring(service);
 203                 packet_send();
 204                 packet_write_wait();
 205         } else {
 206                 debug("bad service request %s", service);
 207                 packet_disconnect("bad service request %s", service);
 208         }
 209         free(service);
 210 }
 211
 212 /*ARGSUSED*/
 213 static void
 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 }
 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 (!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