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 #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 static int log_flag = 0;
  78
  79
  80 Authmethod *authmethods[] = {
  81         &method_none,
  82         &method_pubkey,
  83 #ifdef GSSAPI
  84         &method_gssapi,
  85 #endif
  86         &method_passwd,
  87         &method_kbdint,
  88         &method_hostbased,
  89         NULL
  90 };
  91
  92 /* protocol */
  93
  94 static void input_service_request(int, u_int32_t, void *);
  95 static void input_userauth_request(int, u_int32_t, void *);
  96
  97 /* helper */
  98 static Authmethod *authmethod_lookup(Authctxt *, const char *);
  99 static char *authmethods_get(Authctxt *authctxt);
 100
 101 #define MATCH_NONE      0       /* method or submethod mismatch */
 102 #define MATCH_METHOD    1       /* method matches (no submethod specified) */
 103 #define MATCH_BOTH      2       /* method and submethod match */
 104 #define MATCH_PARTIAL   3       /* method matches, submethod can't be checked */
 105 static int list_starts_with(const char *, const char *, const char *);
 106
 107 char *
 108 auth2_read_banner(void)
 109 {
 110         struct stat st;
 111         char *banner = NULL;
 112         size_t len, n;
 113         int fd;
 114
 115         if ((fd = open(options.banner, O_RDONLY)) == -1)
 116                 return (NULL);
 117         if (fstat(fd, &st) == -1) {
 118                 close(fd);
 119                 return (NULL);
 120         }
 121         if (st.st_size <= 0 || st.st_size > 1*1024*1024) {
 122                 close(fd);
 123                 return (NULL);
 124         }
 125
 126         len = (size_t)st.st_size;               /* truncate */
 127         banner = xmalloc(len + 1);
 128         n = atomicio(read, fd, banner, len);
 129         close(fd);
 130
 131         if (n != len) {
 132                 free(banner);
 133                 return (NULL);
 134         }
 135         banner[n] = '\0';
 136
 137         return (banner);
 138 }
 139
 140 void
 141 userauth_send_banner(const char *msg)
 142 {
 143         if (datafellows & SSH_BUG_BANNER)
 144                 return;
 145
 146         packet_start(SSH2_MSG_USERAUTH_BANNER);
 147         packet_put_cstring(msg);
 148         packet_put_cstring("");         /* language, unused */
 149         packet_send();
 150         debug("%s: sent", __func__);
 151 }
 152
 153 static void
 154 userauth_banner(void)
 155 {
 156         char *banner = NULL;
 157
 158         if (options.banner == NULL ||
 159             strcasecmp(options.banner, "none") == 0 ||
 160             (datafellows & SSH_BUG_BANNER) != 0)
 161                 return;
 162
 163         if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
 164                 goto done;
 165         userauth_send_banner(banner);
 166
 167 done:
 168         free(banner);
 169 }
 170
 171 /*
 172  * loop until authctxt->success == TRUE
 173  */
 174 void
 175 do_authentication2(Authctxt *authctxt)
 176 {
 177         dispatch_init(&dispatch_protocol_error);
 178         dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
 179         dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
 180 }
 181
 182 /*ARGSUSED*/
 183 static void
 184 input_service_request(int type, u_int32_t seq, void *ctxt)
 185 {
 186         Authctxt *authctxt = ctxt;
 187         u_int len;
 188         int acceptit = 0;
 189         char *service = packet_get_cstring(&len);
 190         packet_check_eom();
 191
 192         if (authctxt == NULL)
 193                 fatal("input_service_request: no authctxt");
 194
 195         if (strcmp(service, "ssh-userauth") == 0) {
 196                 if (!authctxt->success) {
 197                         acceptit = 1;
 198                         /* now we can handle user-auth requests */
 199                         dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
 200                 }
 201         }
 202         /* XXX all other service requests are denied */
 203
 204         if (acceptit) {
 205                 packet_start(SSH2_MSG_SERVICE_ACCEPT);
 206                 packet_put_cstring(service);
 207                 packet_send();
 208                 packet_write_wait();
 209         } else {
 210                 debug("bad service request %s", service);
 211                 packet_disconnect("bad service request %s", service);
 212         }
 213         free(service);
 214 }
 215
 216 /*ARGSUSED*/
 217 static void
 218 input_userauth_request(int type, u_int32_t seq, void *ctxt)
 219 {
 220         Authctxt *authctxt = ctxt;
 221         Authmethod *m = NULL;
 222         char *user, *service, *method, *style = NULL;
 223         int authenticated = 0;
 224 #ifdef HAVE_LOGIN_CAP
 225         login_cap_t *lc;
 226         const char *from_host, *from_ip;
 227
 228         from_host = get_canonical_hostname(options.use_dns);
 229         from_ip = get_remote_ipaddr();
 230 #endif
 231
 232         if (authctxt == NULL)
 233                 fatal("input_userauth_request: no authctxt");
 234
 235         user = packet_get_cstring(NULL);
 236         service = packet_get_cstring(NULL);
 237         method = packet_get_cstring(NULL);
 238         debug("userauth-request for user %s service %s method %s", user, service, method);
 239         if (!log_flag) {
 240                 logit("SSH: Server;Ltype: Authname;Remote: %s-%d;Name: %s",
 241                       get_remote_ipaddr(), get_remote_port(), user);
 242                 log_flag = 1;
 243         }
 244         debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
 245
 246         if ((style = strchr(user, ':')) != NULL)
 247                 *style++ = 0;
 248
 249         if (authctxt->attempt++ == 0) {
 250                 /* setup auth context */
 251                 authctxt->pw = PRIVSEP(getpwnamallow(user));
 252                 authctxt->user = xstrdup(user);
 253                 if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
 254                         authctxt->valid = 1;
 255                         debug2("input_userauth_request: setting up authctxt for %s", user);
 256                 } else {
 257                         logit("input_userauth_request: invalid user %s", user);
 258                         authctxt->pw = fakepw();
 259 #ifdef SSH_AUDIT_EVENTS
 260                         PRIVSEP(audit_event(SSH_INVALID_USER));
 261 #endif
 262                 }
 263 #ifdef USE_PAM
 264                 if (options.use_pam)
 265                         PRIVSEP(start_pam(authctxt));
 266 #endif
 267                 setproctitle("%s%s", authctxt->valid ? user : "unknown",
 268                     use_privsep ? " [net]" : "");
 269                 authctxt->service = xstrdup(service);
 270                 authctxt->style = style ? xstrdup(style) : NULL;
 271                 if (use_privsep)
 272                         mm_inform_authserv(service, style);
 273                 userauth_banner();
 274                 if (auth2_setup_methods_lists(authctxt) != 0)
 275                         packet_disconnect("no authentication methods enabled");
 276         } else if (strcmp(user, authctxt->user) != 0 ||
 277             strcmp(service, authctxt->service) != 0) {
 278                 packet_disconnect("Change of username or service not allowed: "
 279                     "(%s,%s) -> (%s,%s)",
 280                     authctxt->user, authctxt->service, user, service);
 281         }
 282
 283 #ifdef HAVE_LOGIN_CAP
 284         if (authctxt->pw != NULL) {
 285                 lc = login_getpwclass(authctxt->pw);
 286                 if (lc == NULL)
 287                         lc = login_getclassbyname(NULL, authctxt->pw);
 288                 if (!auth_hostok(lc, from_host, from_ip)) {
 289                         logit("Denied connection for %.200s from %.200s [%.200s].",
 290                             authctxt->pw->pw_name, from_host, from_ip);
 291                         packet_disconnect("Sorry, you are not allowed to connect.");
 292                 }
 293                 if (!auth_timeok(lc, time(NULL))) {
 294                         logit("LOGIN %.200s REFUSED (TIME) FROM %.200s",
 295                             authctxt->pw->pw_name, from_host);
 296                         packet_disconnect("Logins not available right now.");
 297                 }
 298                 login_close(lc);
 299                 lc = NULL;
 300         }
 301 #endif  /* HAVE_LOGIN_CAP */
 302
 303         /* reset state */
 304         auth2_challenge_stop(authctxt);
 305
 306 #ifdef GSSAPI
 307         /* XXX move to auth2_gssapi_stop() */
 308         dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
 309         dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
 310 #endif
 311
 312         authctxt->postponed = 0;
 313         authctxt->server_caused_failure = 0;
 314
 315         /* try to authenticate user */
 316         m = authmethod_lookup(authctxt, method);
 317         if (m != NULL && authctxt->failures < options.max_authtries) {
 318                 debug2("input_userauth_request: try method %s", method);
 319                 authenticated = m->userauth(authctxt);
 320         }
 321         userauth_finish(authctxt, authenticated, method, NULL);
 322
 323         free(service);
 324         free(user);
 325         free(method);
 326 }
 327
 328 void
 329 userauth_finish(Authctxt *authctxt, int authenticated, const char *method,
 330     const char *submethod)
 331 {
 332         char *methods;
 333         int partial = 0;
 334
 335         if (!authctxt->valid && authenticated)
 336                 fatal("INTERNAL ERROR: authenticated invalid user %s",
 337                     authctxt->user);
 338         if (authenticated && authctxt->postponed)
 339                 fatal("INTERNAL ERROR: authenticated and postponed");
 340
 341         /* Special handling for root */
 342         if (authenticated && authctxt->pw->pw_uid == 0 &&
 343             !auth_root_allowed(method)) {
 344                 authenticated = 0;
 345 #ifdef SSH_AUDIT_EVENTS
 346                 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 347 #endif
 348         }
 349
 350         if (authenticated && options.num_auth_methods != 0) {
 351                 if (!auth2_update_methods_lists(authctxt, method, submethod)) {
 352                         authenticated = 0;
 353                         partial = 1;
 354                 }
 355         }
 356
 357         /* Log before sending the reply */
 358         auth_log(authctxt, authenticated, partial, method, submethod);
 359
 360         if (authctxt->postponed)
 361                 return;
 362
 363 #ifdef USE_PAM
 364         if (options.use_pam && authenticated) {
 365                 if (!PRIVSEP(do_pam_account())) {
 366                         /* if PAM returned a message, send it to the user */
 367                         if (buffer_len(&loginmsg) > 0) {
 368                                 buffer_append(&loginmsg, "\0", 1);
 369                                 userauth_send_banner(buffer_ptr(&loginmsg));
 370                                 packet_write_wait();
 371                         }
 372                         fatal("Access denied for user %s by PAM account "
 373                             "configuration", authctxt->user);
 374                 }
 375         }
 376 #endif
 377
 378 #ifdef _UNICOS
 379         if (authenticated && cray_access_denied(authctxt->user)) {
 380                 authenticated = 0;
 381                 fatal("Access denied for user %s.", authctxt->user);
 382         }
 383 #endif /* _UNICOS */
 384
 385         if (authenticated == 1) {
 386                 /* turn off userauth */
 387                 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
 388                 packet_start(SSH2_MSG_USERAUTH_SUCCESS);
 389                 packet_send();
 390                 packet_write_wait();
 391                 /* now we can break out */
 392                 authctxt->success = 1;
 393         } else {
 394
 395                 /* Allow initial try of "none" auth without failure penalty */
 396                 if (!authctxt->server_caused_failure &&
 397                     (authctxt->attempt > 1 || strcmp(method, "none") != 0))
 398                         authctxt->failures++;
 399                 if (authctxt->failures >= options.max_authtries) {
 400 #ifdef SSH_AUDIT_EVENTS
 401                         PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
 402 #endif
 403                         auth_maxtries_exceeded(authctxt);
 404                 }
 405                 methods = authmethods_get(authctxt);
 406                 debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
 407                     partial, methods);
 408                 packet_start(SSH2_MSG_USERAUTH_FAILURE);
 409                 packet_put_cstring(methods);
 410                 packet_put_char(partial);
 411                 packet_send();
 412                 packet_write_wait();
 413                 free(methods);
 414         }
 415 }
 416
 417 /*
 418  * Checks whether method is allowed by at least one AuthenticationMethods
 419  * methods list. Returns 1 if allowed, or no methods lists configured.
 420  * 0 otherwise.
 421  */
 422 int
 423 auth2_method_allowed(Authctxt *authctxt, const char *method,
 424     const char *submethod)
 425 {
 426         u_int i;
 427
 428         /*
 429          * NB. authctxt->num_auth_methods might be zero as a result of
 430          * auth2_setup_methods_lists(), so check the configuration.
 431          */
 432         if (options.num_auth_methods == 0)
 433                 return 1;
 434         for (i = 0; i < authctxt->num_auth_methods; i++) {
 435                 if (list_starts_with(authctxt->auth_methods[i], method,
 436                     submethod) != MATCH_NONE)
 437                         return 1;
 438         }
 439         return 0;
 440 }
 441
 442 static char *
 443 authmethods_get(Authctxt *authctxt)
 444 {
 445         Buffer b;
 446         char *list;
 447         u_int i;
 448
 449         buffer_init(&b);
 450         for (i = 0; authmethods[i] != NULL; i++) {
 451                 if (strcmp(authmethods[i]->name, "none") == 0)
 452                         continue;
 453                 if (authmethods[i]->enabled == NULL ||
 454                     *(authmethods[i]->enabled) == 0)
 455                         continue;
 456                 if (!auth2_method_allowed(authctxt, authmethods[i]->name,
 457                     NULL))
 458                         continue;
 459                 if (buffer_len(&b) > 0)
 460                         buffer_append(&b, ",", 1);
 461                 buffer_append(&b, authmethods[i]->name,
 462                     strlen(authmethods[i]->name));
 463         }
 464         buffer_append(&b, "\0", 1);
 465         list = xstrdup(buffer_ptr(&b));
 466         buffer_free(&b);
 467         return list;
 468 }
 469
 470 static Authmethod *
 471 authmethod_lookup(Authctxt *authctxt, const char *name)
 472 {
 473         int i;
 474
 475         if (name != NULL)
 476                 for (i = 0; authmethods[i] != NULL; i++)
 477                         if (authmethods[i]->enabled != NULL &&
 478                             *(authmethods[i]->enabled) != 0 &&
 479                             strcmp(name, authmethods[i]->name) == 0 &&
 480                             auth2_method_allowed(authctxt,
 481                             authmethods[i]->name, NULL))
 482                                 return authmethods[i];
 483         debug2("Unrecognized authentication method name: %s",
 484             name ? name : "NULL");
 485         return NULL;
 486 }
 487
 488 /*
 489  * Check a comma-separated list of methods for validity. Is need_enable is
 490  * non-zero, then also require that the methods are enabled.
 491  * Returns 0 on success or -1 if the methods list is invalid.
 492  */
 493 int
 494 auth2_methods_valid(const char *_methods, int need_enable)
 495 {
 496         char *methods, *omethods, *method, *p;
 497         u_int i, found;
 498         int ret = -1;
 499
 500         if (*_methods == '\0') {
 501                 error("empty authentication method list");
 502                 return -1;
 503         }
 504         omethods = methods = xstrdup(_methods);
 505         while ((method = strsep(&methods, ",")) != NULL) {
 506                 for (found = i = 0; !found && authmethods[i] != NULL; i++) {
 507                         if ((p = strchr(method, ':')) != NULL)
 508                                 *p = '\0';
 509                         if (strcmp(method, authmethods[i]->name) != 0)
 510                                 continue;
 511                         if (need_enable) {
 512                                 if (authmethods[i]->enabled == NULL ||
 513                                     *(authmethods[i]->enabled) == 0) {
 514                                         error("Disabled method \"%s\" in "
 515                                             "AuthenticationMethods list \"%s\"",
 516                                             method, _methods);
 517                                         goto out;
 518                                 }
 519                         }
 520                         found = 1;
 521                         break;
 522                 }
 523                 if (!found) {
 524                         error("Unknown authentication method \"%s\" in list",
 525                             method);
 526                         goto out;
 527                 }
 528         }
 529         ret = 0;
 530  out:
 531         free(omethods);
 532         return ret;
 533 }
 534
 535 /*
 536  * Prune the AuthenticationMethods supplied in the configuration, removing
 537  * any methods lists that include disabled methods. Note that this might
 538  * leave authctxt->num_auth_methods == 0, even when multiple required auth
 539  * has been requested. For this reason, all tests for whether multiple is
 540  * enabled should consult options.num_auth_methods directly.
 541  */
 542 int
 543 auth2_setup_methods_lists(Authctxt *authctxt)
 544 {
 545         u_int i;
 546
 547         if (options.num_auth_methods == 0)
 548                 return 0;
 549         debug3("%s: checking methods", __func__);
 550         authctxt->auth_methods = xcalloc(options.num_auth_methods,
 551             sizeof(*authctxt->auth_methods));
 552         authctxt->num_auth_methods = 0;
 553         for (i = 0; i < options.num_auth_methods; i++) {
 554                 if (auth2_methods_valid(options.auth_methods[i], 1) != 0) {
 555                         logit("Authentication methods list \"%s\" contains "
 556                             "disabled method, skipping",
 557                             options.auth_methods[i]);
 558                         continue;
 559                 }
 560                 debug("authentication methods list %d: %s",
 561                     authctxt->num_auth_methods, options.auth_methods[i]);
 562                 authctxt->auth_methods[authctxt->num_auth_methods++] =
 563                     xstrdup(options.auth_methods[i]);
 564         }
 565         if (authctxt->num_auth_methods == 0) {
 566                 error("No AuthenticationMethods left after eliminating "
 567                     "disabled methods");
 568                 return -1;
 569         }
 570         return 0;
 571 }
 572
 573 static int
 574 list_starts_with(const char *methods, const char *method,
 575     const char *submethod)
 576 {
 577         size_t l = strlen(method);
 578         int match;
 579         const char *p;
 580
 581         if (strncmp(methods, method, l) != 0)
 582                 return MATCH_NONE;
 583         p = methods + l;
 584         match = MATCH_METHOD;
 585         if (*p == ':') {
 586                 if (!submethod)
 587                         return MATCH_PARTIAL;
 588                 l = strlen(submethod);
 589                 p += 1;
 590                 if (strncmp(submethod, p, l))
 591                         return MATCH_NONE;
 592                 p += l;
 593                 match = MATCH_BOTH;
 594         }
 595         if (*p != ',' && *p != '\0')
 596                 return MATCH_NONE;
 597         return match;
 598 }
 599
 600 /*
 601  * Remove method from the start of a comma-separated list of methods.
 602  * Returns 0 if the list of methods did not start with that method or 1
 603  * if it did.
 604  */
 605 static int
 606 remove_method(char **methods, const char *method, const char *submethod)
 607 {
 608         char *omethods = *methods, *p;
 609         size_t l = strlen(method);
 610         int match;
 611
 612         match = list_starts_with(omethods, method, submethod);
 613         if (match != MATCH_METHOD && match != MATCH_BOTH)
 614                 return 0;
 615         p = omethods + l;
 616         if (submethod && match == MATCH_BOTH)
 617                 p += 1 + strlen(submethod); /* include colon */
 618         if (*p == ',')
 619                 p++;
 620         *methods = xstrdup(p);
 621         free(omethods);
 622         return 1;
 623 }
 624
 625 /*
 626  * Called after successful authentication. Will remove the successful method
 627  * from the start of each list in which it occurs. If it was the last method
 628  * in any list, then authentication is deemed successful.
 629  * Returns 1 if the method completed any authentication list or 0 otherwise.
 630  */
 631 int
 632 auth2_update_methods_lists(Authctxt *authctxt, const char *method,
 633     const char *submethod)
 634 {
 635         u_int i, found = 0;
 636
 637         debug3("%s: updating methods list after \"%s\"", __func__, method);
 638         for (i = 0; i < authctxt->num_auth_methods; i++) {
 639                 if (!remove_method(&(authctxt->auth_methods[i]), method,
 640                     submethod))
 641                         continue;
 642                 found = 1;
 643                 if (*authctxt->auth_methods[i] == '\0') {
 644                         debug2("authentication methods list %d complete", i);
 645                         return 1;
 646                 }
 647                 debug3("authentication methods list %d remaining: \"%s\"",
 648                     i, authctxt->auth_methods[i]);
 649         }
 650         /* This should not happen, but would be bad if it did */
 651         if (!found)
 652                 fatal("%s: method not in AuthenticationMethods", __func__);
 653         return 0;
 654 }
 655
 656