crypto/openssh/auth.c

   1 /* $OpenBSD: auth.c,v 1.158 2022/06/03 04:47:21 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/socket.h>
  31 #include <sys/wait.h>
  32
  33 #include <netinet/in.h>
  34
  35 #include <stdlib.h>
  36 #include <errno.h>
  37 #include <fcntl.h>
  38 #ifdef HAVE_PATHS_H
  39 # include <paths.h>
  40 #endif
  41 #include <pwd.h>
  42 #ifdef HAVE_LOGIN_H
  43 #include <login.h>
  44 #endif
  45 #ifdef USE_SHADOW
  46 #include <shadow.h>
  47 #endif
  48 #include <stdarg.h>
  49 #include <stdio.h>
  50 #include <string.h>
  51 #include <unistd.h>
  52 #include <limits.h>
  53 #include <netdb.h>
  54 #include <time.h>
  55
  56 #include "xmalloc.h"
  57 #include "match.h"
  58 #include "groupaccess.h"
  59 #include "log.h"
  60 #include "sshbuf.h"
  61 #include "misc.h"
  62 #include "servconf.h"
  63 #include "sshkey.h"
  64 #include "hostfile.h"
  65 #include "auth.h"
  66 #include "auth-options.h"
  67 #include "canohost.h"
  68 #include "uidswap.h"
  69 #include "packet.h"
  70 #include "loginrec.h"
  71 #ifdef GSSAPI
  72 #include "ssh-gss.h"
  73 #endif
  74 #include "authfile.h"
  75 #include "monitor_wrap.h"
  76 #include "ssherr.h"
  77 #include "compat.h"
  78 #include "channels.h"
  79
  80 /* import */
  81 extern ServerOptions options;
  82 extern struct include_list includes;
  83 extern int use_privsep;
  84 extern struct sshbuf *loginmsg;
  85 extern struct passwd *privsep_pw;
  86 extern struct sshauthopt *auth_opts;
  87
  88 /* Debugging messages */
  89 static struct sshbuf *auth_debug;
  90
  91 /*
  92  * Check if the user is allowed to log in via ssh. If user is listed
  93  * in DenyUsers or one of user's groups is listed in DenyGroups, false
  94  * will be returned. If AllowUsers isn't empty and user isn't listed
  95  * there, or if AllowGroups isn't empty and one of user's groups isn't
  96  * listed there, false will be returned.
  97  * If the user's shell is not executable, false will be returned.
  98  * Otherwise true is returned.
  99  */
 100 int
 101 allowed_user(struct ssh *ssh, struct passwd * pw)
 102 {
 103         struct stat st;
 104         const char *hostname = NULL, *ipaddr = NULL;
 105         u_int i;
 106         int r;
 107
 108         /* Shouldn't be called if pw is NULL, but better safe than sorry... */
 109         if (!pw || !pw->pw_name)
 110                 return 0;
 111
 112         if (!options.use_pam && platform_locked_account(pw)) {
 113                 logit("User %.100s not allowed because account is locked",
 114                     pw->pw_name);
 115                 return 0;
 116         }
 117
 118         /*
 119          * Deny if shell does not exist or is not executable unless we
 120          * are chrooting.
 121          */
 122         if (options.chroot_directory == NULL ||
 123             strcasecmp(options.chroot_directory, "none") == 0) {
 124                 char *shell = xstrdup((pw->pw_shell[0] == '\0') ?
 125                     _PATH_BSHELL : pw->pw_shell); /* empty = /bin/sh */
 126
 127                 if (stat(shell, &st) == -1) {
 128                         logit("User %.100s not allowed because shell %.100s "
 129                             "does not exist", pw->pw_name, shell);
 130                         free(shell);
 131                         return 0;
 132                 }
 133                 if (S_ISREG(st.st_mode) == 0 ||
 134                     (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
 135                         logit("User %.100s not allowed because shell %.100s "
 136                             "is not executable", pw->pw_name, shell);
 137                         free(shell);
 138                         return 0;
 139                 }
 140                 free(shell);
 141         }
 142
 143         if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
 144             options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 145                 hostname = auth_get_canonical_hostname(ssh, options.use_dns);
 146                 ipaddr = ssh_remote_ipaddr(ssh);
 147         }
 148
 149         /* Return false if user is listed in DenyUsers */
 150         if (options.num_deny_users > 0) {
 151                 for (i = 0; i < options.num_deny_users; i++) {
 152                         r = match_user(pw->pw_name, hostname, ipaddr,
 153                             options.deny_users[i]);
 154                         if (r < 0) {
 155                                 fatal("Invalid DenyUsers pattern \"%.100s\"",
 156                                     options.deny_users[i]);
 157                         } else if (r != 0) {
 158                                 logit("User %.100s from %.100s not allowed "
 159                                     "because listed in DenyUsers",
 160                                     pw->pw_name, hostname);
 161                                 return 0;
 162                         }
 163                 }
 164         }
 165         /* Return false if AllowUsers isn't empty and user isn't listed there */
 166         if (options.num_allow_users > 0) {
 167                 for (i = 0; i < options.num_allow_users; i++) {
 168                         r = match_user(pw->pw_name, hostname, ipaddr,
 169                             options.allow_users[i]);
 170                         if (r < 0) {
 171                                 fatal("Invalid AllowUsers pattern \"%.100s\"",
 172                                     options.allow_users[i]);
 173                         } else if (r == 1)
 174                                 break;
 175                 }
 176                 /* i < options.num_allow_users iff we break for loop */
 177                 if (i >= options.num_allow_users) {
 178                         logit("User %.100s from %.100s not allowed because "
 179                             "not listed in AllowUsers", pw->pw_name, hostname);
 180                         return 0;
 181                 }
 182         }
 183         if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 184                 /* Get the user's group access list (primary and supplementary) */
 185                 if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
 186                         logit("User %.100s from %.100s not allowed because "
 187                             "not in any group", pw->pw_name, hostname);
 188                         return 0;
 189                 }
 190
 191                 /* Return false if one of user's groups is listed in DenyGroups */
 192                 if (options.num_deny_groups > 0)
 193                         if (ga_match(options.deny_groups,
 194                             options.num_deny_groups)) {
 195                                 ga_free();
 196                                 logit("User %.100s from %.100s not allowed "
 197                                     "because a group is listed in DenyGroups",
 198                                     pw->pw_name, hostname);
 199                                 return 0;
 200                         }
 201                 /*
 202                  * Return false if AllowGroups isn't empty and one of user's groups
 203                  * isn't listed there
 204                  */
 205                 if (options.num_allow_groups > 0)
 206                         if (!ga_match(options.allow_groups,
 207                             options.num_allow_groups)) {
 208                                 ga_free();
 209                                 logit("User %.100s from %.100s not allowed "
 210                                     "because none of user's groups are listed "
 211                                     "in AllowGroups", pw->pw_name, hostname);
 212                                 return 0;
 213                         }
 214                 ga_free();
 215         }
 216
 217 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
 218         if (!sys_auth_allowed_user(pw, loginmsg))
 219                 return 0;
 220 #endif
 221
 222         /* We found no reason not to let this user try to log on... */
 223         return 1;
 224 }
 225
 226 /*
 227  * Formats any key left in authctxt->auth_method_key for inclusion in
 228  * auth_log()'s message. Also includes authxtct->auth_method_info if present.
 229  */
 230 static char *
 231 format_method_key(Authctxt *authctxt)
 232 {
 233         const struct sshkey *key = authctxt->auth_method_key;
 234         const char *methinfo = authctxt->auth_method_info;
 235         char *fp, *cafp, *ret = NULL;
 236
 237         if (key == NULL)
 238                 return NULL;
 239
 240         if (sshkey_is_cert(key)) {
 241                 fp = sshkey_fingerprint(key,
 242                     options.fingerprint_hash, SSH_FP_DEFAULT);
 243                 cafp = sshkey_fingerprint(key->cert->signature_key,
 244                     options.fingerprint_hash, SSH_FP_DEFAULT);
 245                 xasprintf(&ret, "%s %s ID %s (serial %llu) CA %s %s%s%s",
 246                     sshkey_type(key), fp == NULL ? "(null)" : fp,
 247                     key->cert->key_id,
 248                     (unsigned long long)key->cert->serial,
 249                     sshkey_type(key->cert->signature_key),
 250                     cafp == NULL ? "(null)" : cafp,
 251                     methinfo == NULL ? "" : ", ",
 252                     methinfo == NULL ? "" : methinfo);
 253                 free(fp);
 254                 free(cafp);
 255         } else {
 256                 fp = sshkey_fingerprint(key, options.fingerprint_hash,
 257                     SSH_FP_DEFAULT);
 258                 xasprintf(&ret, "%s %s%s%s", sshkey_type(key),
 259                     fp == NULL ? "(null)" : fp,
 260                     methinfo == NULL ? "" : ", ",
 261                     methinfo == NULL ? "" : methinfo);
 262                 free(fp);
 263         }
 264         return ret;
 265 }
 266
 267 void
 268 auth_log(struct ssh *ssh, int authenticated, int partial,
 269     const char *method, const char *submethod)
 270 {
 271         Authctxt *authctxt = (Authctxt *)ssh->authctxt;
 272         int level = SYSLOG_LEVEL_VERBOSE;
 273         const char *authmsg;
 274         char *extra = NULL;
 275
 276         if (use_privsep && !mm_is_monitor() && !authctxt->postponed)
 277                 return;
 278
 279         /* Raise logging level */
 280         if (authenticated == 1 ||
 281             !authctxt->valid ||
 282             authctxt->failures >= options.max_authtries / 2 ||
 283             strcmp(method, "password") == 0)
 284                 level = SYSLOG_LEVEL_INFO;
 285
 286         if (authctxt->postponed)
 287                 authmsg = "Postponed";
 288         else if (partial)
 289                 authmsg = "Partial";
 290         else
 291                 authmsg = authenticated ? "Accepted" : "Failed";
 292
 293         if ((extra = format_method_key(authctxt)) == NULL) {
 294                 if (authctxt->auth_method_info != NULL)
 295                         extra = xstrdup(authctxt->auth_method_info);
 296         }
 297
 298         do_log2(level, "%s %s%s%s for %s%.100s from %.200s port %d ssh2%s%s",
 299             authmsg,
 300             method,
 301             submethod != NULL ? "/" : "", submethod == NULL ? "" : submethod,
 302             authctxt->valid ? "" : "invalid user ",
 303             authctxt->user,
 304             ssh_remote_ipaddr(ssh),
 305             ssh_remote_port(ssh),
 306             extra != NULL ? ": " : "",
 307             extra != NULL ? extra : "");
 308
 309         free(extra);
 310
 311 #if defined(CUSTOM_FAILED_LOGIN) || defined(SSH_AUDIT_EVENTS)
 312         if (authenticated == 0 && !(authctxt->postponed || partial)) {
 313                 /* Log failed login attempt */
 314 # ifdef CUSTOM_FAILED_LOGIN
 315                 if (strcmp(method, "password") == 0 ||
 316                     strncmp(method, "keyboard-interactive", 20) == 0 ||
 317                     strcmp(method, "challenge-response") == 0)
 318                         record_failed_login(ssh, authctxt->user,
 319                             auth_get_canonical_hostname(ssh, options.use_dns), "ssh");
 320 # endif
 321 # ifdef SSH_AUDIT_EVENTS
 322                 audit_event(ssh, audit_classify_auth(method));
 323 # endif
 324         }
 325 #endif
 326 #if defined(CUSTOM_FAILED_LOGIN) && defined(WITH_AIXAUTHENTICATE)
 327         if (authenticated)
 328                 sys_auth_record_login(authctxt->user,
 329                     auth_get_canonical_hostname(ssh, options.use_dns), "ssh",
 330                     loginmsg);
 331 #endif
 332 }
 333
 334 void
 335 auth_maxtries_exceeded(struct ssh *ssh)
 336 {
 337         Authctxt *authctxt = (Authctxt *)ssh->authctxt;
 338
 339         error("maximum authentication attempts exceeded for "
 340             "%s%.100s from %.200s port %d ssh2",
 341             authctxt->valid ? "" : "invalid user ",
 342             authctxt->user,
 343             ssh_remote_ipaddr(ssh),
 344             ssh_remote_port(ssh));
 345         ssh_packet_disconnect(ssh, "Too many authentication failures");
 346         /* NOTREACHED */
 347 }
 348
 349 /*
 350  * Check whether root logins are disallowed.
 351  */
 352 int
 353 auth_root_allowed(struct ssh *ssh, const char *method)
 354 {
 355         switch (options.permit_root_login) {
 356         case PERMIT_YES:
 357                 return 1;
 358         case PERMIT_NO_PASSWD:
 359                 if (strcmp(method, "publickey") == 0 ||
 360                     strcmp(method, "hostbased") == 0 ||
 361                     strcmp(method, "gssapi-with-mic") == 0)
 362                         return 1;
 363                 break;
 364         case PERMIT_FORCED_ONLY:
 365                 if (auth_opts->force_command != NULL) {
 366                         logit("Root login accepted for forced command.");
 367                         return 1;
 368                 }
 369                 break;
 370         }
 371         logit("ROOT LOGIN REFUSED FROM %.200s port %d",
 372             ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
 373         return 0;
 374 }
 375
 376
 377 /*
 378  * Given a template and a passwd structure, build a filename
 379  * by substituting % tokenised options. Currently, %% becomes '%',
 380  * %h becomes the home directory and %u the username.
 381  *
 382  * This returns a buffer allocated by xmalloc.
 383  */
 384 char *
 385 expand_authorized_keys(const char *filename, struct passwd *pw)
 386 {
 387         char *file, uidstr[32], ret[PATH_MAX];
 388         int i;
 389
 390         snprintf(uidstr, sizeof(uidstr), "%llu",
 391             (unsigned long long)pw->pw_uid);
 392         file = percent_expand(filename, "h", pw->pw_dir,
 393             "u", pw->pw_name, "U", uidstr, (char *)NULL);
 394
 395         /*
 396          * Ensure that filename starts anchored. If not, be backward
 397          * compatible and prepend the '%h/'
 398          */
 399         if (path_absolute(file))
 400                 return (file);
 401
 402         i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file);
 403         if (i < 0 || (size_t)i >= sizeof(ret))
 404                 fatal("expand_authorized_keys: path too long");
 405         free(file);
 406         return (xstrdup(ret));
 407 }
 408
 409 char *
 410 authorized_principals_file(struct passwd *pw)
 411 {
 412         if (options.authorized_principals_file == NULL)
 413                 return NULL;
 414         return expand_authorized_keys(options.authorized_principals_file, pw);
 415 }
 416
 417 /* return ok if key exists in sysfile or userfile */
 418 HostStatus
 419 check_key_in_hostfiles(struct passwd *pw, struct sshkey *key, const char *host,
 420     const char *sysfile, const char *userfile)
 421 {
 422         char *user_hostfile;
 423         struct stat st;
 424         HostStatus host_status;
 425         struct hostkeys *hostkeys;
 426         const struct hostkey_entry *found;
 427
 428         hostkeys = init_hostkeys();
 429         load_hostkeys(hostkeys, host, sysfile, 0);
 430         if (userfile != NULL) {
 431                 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
 432                 if (options.strict_modes &&
 433                     (stat(user_hostfile, &st) == 0) &&
 434                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 435                     (st.st_mode & 022) != 0)) {
 436                         logit("Authentication refused for %.100s: "
 437                             "bad owner or modes for %.200s",
 438                             pw->pw_name, user_hostfile);
 439                         auth_debug_add("Ignored %.200s: bad ownership or modes",
 440                             user_hostfile);
 441                 } else {
 442                         temporarily_use_uid(pw);
 443                         load_hostkeys(hostkeys, host, user_hostfile, 0);
 444                         restore_uid();
 445                 }
 446                 free(user_hostfile);
 447         }
 448         host_status = check_key_in_hostkeys(hostkeys, key, &found);
 449         if (host_status == HOST_REVOKED)
 450                 error("WARNING: revoked key for %s attempted authentication",
 451                     host);
 452         else if (host_status == HOST_OK)
 453                 debug_f("key for %s found at %s:%ld",
 454                     found->host, found->file, found->line);
 455         else
 456                 debug_f("key for host %s not found", host);
 457
 458         free_hostkeys(hostkeys);
 459
 460         return host_status;
 461 }
 462
 463 struct passwd *
 464 getpwnamallow(struct ssh *ssh, const char *user)
 465 {
 466 #ifdef HAVE_LOGIN_CAP
 467         extern login_cap_t *lc;
 468 #ifdef BSD_AUTH
 469         auth_session_t *as;
 470 #endif
 471 #endif
 472         struct passwd *pw;
 473         struct connection_info *ci;
 474         u_int i;
 475
 476         ci = get_connection_info(ssh, 1, options.use_dns);
 477         ci->user = user;
 478         parse_server_match_config(&options, &includes, ci);
 479         log_change_level(options.log_level);
 480         log_verbose_reset();
 481         for (i = 0; i < options.num_log_verbose; i++)
 482                 log_verbose_add(options.log_verbose[i]);
 483         process_permitopen(ssh, &options);
 484
 485 #if defined(_AIX) && defined(HAVE_SETAUTHDB)
 486         aix_setauthdb(user);
 487 #endif
 488
 489         pw = getpwnam(user);
 490
 491 #if defined(_AIX) && defined(HAVE_SETAUTHDB)
 492         aix_restoreauthdb();
 493 #endif
 494         if (pw == NULL) {
 495                 logit("Invalid user %.100s from %.100s port %d",
 496                     user, ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
 497 #ifdef CUSTOM_FAILED_LOGIN
 498                 record_failed_login(ssh, user,
 499                     auth_get_canonical_hostname(ssh, options.use_dns), "ssh");
 500 #endif
 501 #ifdef SSH_AUDIT_EVENTS
 502                 audit_event(ssh, SSH_INVALID_USER);
 503 #endif /* SSH_AUDIT_EVENTS */
 504                 return (NULL);
 505         }
 506         if (!allowed_user(ssh, pw))
 507                 return (NULL);
 508 #ifdef HAVE_LOGIN_CAP
 509         if ((lc = login_getpwclass(pw)) == NULL) {
 510                 debug("unable to get login class: %s", user);
 511                 return (NULL);
 512         }
 513 #ifdef BSD_AUTH
 514         if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
 515             auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
 516                 debug("Approval failure for %s", user);
 517                 pw = NULL;
 518         }
 519         if (as != NULL)
 520                 auth_close(as);
 521 #endif
 522 #endif
 523         if (pw != NULL)
 524                 return (pwcopy(pw));
 525         return (NULL);
 526 }
 527
 528 /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */
 529 int
 530 auth_key_is_revoked(struct sshkey *key)
 531 {
 532         char *fp = NULL;
 533         int r;
 534
 535         if (options.revoked_keys_file == NULL)
 536                 return 0;
 537         if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
 538             SSH_FP_DEFAULT)) == NULL) {
 539                 r = SSH_ERR_ALLOC_FAIL;
 540                 error_fr(r, "fingerprint key");
 541                 goto out;
 542         }
 543
 544         r = sshkey_check_revoked(key, options.revoked_keys_file);
 545         switch (r) {
 546         case 0:
 547                 break; /* not revoked */
 548         case SSH_ERR_KEY_REVOKED:
 549                 error("Authentication key %s %s revoked by file %s",
 550                     sshkey_type(key), fp, options.revoked_keys_file);
 551                 goto out;
 552         default:
 553                 error_r(r, "Error checking authentication key %s %s in "
 554                     "revoked keys file %s", sshkey_type(key), fp,
 555                     options.revoked_keys_file);
 556                 goto out;
 557         }
 558
 559         /* Success */
 560         r = 0;
 561
 562  out:
 563         free(fp);
 564         return r == 0 ? 0 : 1;
 565 }
 566
 567 void
 568 auth_debug_add(const char *fmt,...)
 569 {
 570         char buf[1024];
 571         va_list args;
 572         int r;
 573
 574         if (auth_debug == NULL)
 575                 return;
 576
 577         va_start(args, fmt);
 578         vsnprintf(buf, sizeof(buf), fmt, args);
 579         va_end(args);
 580         if ((r = sshbuf_put_cstring(auth_debug, buf)) != 0)
 581                 fatal_fr(r, "sshbuf_put_cstring");
 582 }
 583
 584 void
 585 auth_debug_send(struct ssh *ssh)
 586 {
 587         char *msg;
 588         int r;
 589
 590         if (auth_debug == NULL)
 591                 return;
 592         while (sshbuf_len(auth_debug) != 0) {
 593                 if ((r = sshbuf_get_cstring(auth_debug, &msg, NULL)) != 0)
 594                         fatal_fr(r, "sshbuf_get_cstring");
 595                 ssh_packet_send_debug(ssh, "%s", msg);
 596                 free(msg);
 597         }
 598 }
 599
 600 void
 601 auth_debug_reset(void)
 602 {
 603         if (auth_debug != NULL)
 604                 sshbuf_reset(auth_debug);
 605         else if ((auth_debug = sshbuf_new()) == NULL)
 606                 fatal_f("sshbuf_new failed");
 607 }
 608
 609 struct passwd *
 610 fakepw(void)
 611 {
 612         static int done = 0;
 613         static struct passwd fake;
 614         const char hashchars[] = "./ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 615             "abcdefghijklmnopqrstuvwxyz0123456789"; /* from bcrypt.c */
 616         char *cp;
 617
 618         if (done)
 619                 return (&fake);
 620
 621         memset(&fake, 0, sizeof(fake));
 622         fake.pw_name = "NOUSER";
 623         fake.pw_passwd = xstrdup("$2a$10$"
 624             "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx");
 625         for (cp = fake.pw_passwd + 7; *cp != '\0'; cp++)
 626                 *cp = hashchars[arc4random_uniform(sizeof(hashchars) - 1)];
 627 #ifdef HAVE_STRUCT_PASSWD_PW_GECOS
 628         fake.pw_gecos = "NOUSER";
 629 #endif
 630         fake.pw_uid = privsep_pw == NULL ? (uid_t)-1 : privsep_pw->pw_uid;
 631         fake.pw_gid = privsep_pw == NULL ? (gid_t)-1 : privsep_pw->pw_gid;
 632 #ifdef HAVE_STRUCT_PASSWD_PW_CLASS
 633         fake.pw_class = "";
 634 #endif
 635         fake.pw_dir = "/nonexist";
 636         fake.pw_shell = "/nonexist";
 637         done = 1;
 638
 639         return (&fake);
 640 }
 641
 642 /*
 643  * Returns the remote DNS hostname as a string. The returned string must not
 644  * be freed. NB. this will usually trigger a DNS query the first time it is
 645  * called.
 646  * This function does additional checks on the hostname to mitigate some
 647  * attacks on based on conflation of hostnames and IP addresses.
 648  */
 649
 650 static char *
 651 remote_hostname(struct ssh *ssh)
 652 {
 653         struct sockaddr_storage from;
 654         socklen_t fromlen;
 655         struct addrinfo hints, *ai, *aitop;
 656         char name[NI_MAXHOST], ntop2[NI_MAXHOST];
 657         const char *ntop = ssh_remote_ipaddr(ssh);
 658
 659         /* Get IP address of client. */
 660         fromlen = sizeof(from);
 661         memset(&from, 0, sizeof(from));
 662         if (getpeername(ssh_packet_get_connection_in(ssh),
 663             (struct sockaddr *)&from, &fromlen) == -1) {
 664                 debug("getpeername failed: %.100s", strerror(errno));
 665                 return xstrdup(ntop);
 666         }
 667
 668         ipv64_normalise_mapped(&from, &fromlen);
 669         if (from.ss_family == AF_INET6)
 670                 fromlen = sizeof(struct sockaddr_in6);
 671
 672         debug3("Trying to reverse map address %.100s.", ntop);
 673         /* Map the IP address to a host name. */
 674         if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name),
 675             NULL, 0, NI_NAMEREQD) != 0) {
 676                 /* Host name not found.  Use ip address. */
 677                 return xstrdup(ntop);
 678         }
 679
 680         /*
 681          * if reverse lookup result looks like a numeric hostname,
 682          * someone is trying to trick us by PTR record like following:
 683          *      1.1.1.10.in-addr.arpa.  IN PTR  2.3.4.5
 684          */
 685         memset(&hints, 0, sizeof(hints));
 686         hints.ai_socktype = SOCK_DGRAM; /*dummy*/
 687         hints.ai_flags = AI_NUMERICHOST;
 688         if (getaddrinfo(name, NULL, &hints, &ai) == 0) {
 689                 logit("Nasty PTR record \"%s\" is set up for %s, ignoring",
 690                     name, ntop);
 691                 freeaddrinfo(ai);
 692                 return xstrdup(ntop);
 693         }
 694
 695         /* Names are stored in lowercase. */
 696         lowercase(name);
 697
 698         /*
 699          * Map it back to an IP address and check that the given
 700          * address actually is an address of this host.  This is
 701          * necessary because anyone with access to a name server can
 702          * define arbitrary names for an IP address. Mapping from
 703          * name to IP address can be trusted better (but can still be
 704          * fooled if the intruder has access to the name server of
 705          * the domain).
 706          */
 707         memset(&hints, 0, sizeof(hints));
 708         hints.ai_family = from.ss_family;
 709         hints.ai_socktype = SOCK_STREAM;
 710         if (getaddrinfo(name, NULL, &hints, &aitop) != 0) {
 711                 logit("reverse mapping checking getaddrinfo for %.700s "
 712                     "[%s] failed.", name, ntop);
 713                 return xstrdup(ntop);
 714         }
 715         /* Look for the address from the list of addresses. */
 716         for (ai = aitop; ai; ai = ai->ai_next) {
 717                 if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop2,
 718                     sizeof(ntop2), NULL, 0, NI_NUMERICHOST) == 0 &&
 719                     (strcmp(ntop, ntop2) == 0))
 720                                 break;
 721         }
 722         freeaddrinfo(aitop);
 723         /* If we reached the end of the list, the address was not there. */
 724         if (ai == NULL) {
 725                 /* Address not found for the host name. */
 726                 logit("Address %.100s maps to %.600s, but this does not "
 727                     "map back to the address.", ntop, name);
 728                 return xstrdup(ntop);
 729         }
 730         return xstrdup(name);
 731 }
 732
 733 /*
 734  * Return the canonical name of the host in the other side of the current
 735  * connection.  The host name is cached, so it is efficient to call this
 736  * several times.
 737  */
 738
 739 const char *
 740 auth_get_canonical_hostname(struct ssh *ssh, int use_dns)
 741 {
 742         static char *dnsname;
 743
 744         if (!use_dns)
 745                 return ssh_remote_ipaddr(ssh);
 746         else if (dnsname != NULL)
 747                 return dnsname;
 748         else {
 749                 dnsname = remote_hostname(ssh);
 750                 return dnsname;
 751         }
 752 }
 753
 754 /* These functions link key/cert options to the auth framework */
 755
 756 /* Log sshauthopt options locally and (optionally) for remote transmission */
 757 void
 758 auth_log_authopts(const char *loc, const struct sshauthopt *opts, int do_remote)
 759 {
 760         int do_env = options.permit_user_env && opts->nenv > 0;
 761         int do_permitopen = opts->npermitopen > 0 &&
 762             (options.allow_tcp_forwarding & FORWARD_LOCAL) != 0;
 763         int do_permitlisten = opts->npermitlisten > 0 &&
 764             (options.allow_tcp_forwarding & FORWARD_REMOTE) != 0;
 765         size_t i;
 766         char msg[1024], buf[64];
 767
 768         snprintf(buf, sizeof(buf), "%d", opts->force_tun_device);
 769         /* Try to keep this alphabetically sorted */
 770         snprintf(msg, sizeof(msg), "key options:%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s",
 771             opts->permit_agent_forwarding_flag ? " agent-forwarding" : "",
 772             opts->force_command == NULL ? "" : " command",
 773             do_env ?  " environment" : "",
 774             opts->valid_before == 0 ? "" : "expires",
 775             opts->no_require_user_presence ? " no-touch-required" : "",
 776             do_permitopen ?  " permitopen" : "",
 777             do_permitlisten ?  " permitlisten" : "",
 778             opts->permit_port_forwarding_flag ? " port-forwarding" : "",
 779             opts->cert_principals == NULL ? "" : " principals",
 780             opts->permit_pty_flag ? " pty" : "",
 781             opts->require_verify ? " uv" : "",
 782             opts->force_tun_device == -1 ? "" : " tun=",
 783             opts->force_tun_device == -1 ? "" : buf,
 784             opts->permit_user_rc ? " user-rc" : "",
 785             opts->permit_x11_forwarding_flag ? " x11-forwarding" : "");
 786
 787         debug("%s: %s", loc, msg);
 788         if (do_remote)
 789                 auth_debug_add("%s: %s", loc, msg);
 790
 791         if (options.permit_user_env) {
 792                 for (i = 0; i < opts->nenv; i++) {
 793                         debug("%s: environment: %s", loc, opts->env[i]);
 794                         if (do_remote) {
 795                                 auth_debug_add("%s: environment: %s",
 796                                     loc, opts->env[i]);
 797                         }
 798                 }
 799         }
 800
 801         /* Go into a little more details for the local logs. */
 802         if (opts->valid_before != 0) {
 803                 format_absolute_time(opts->valid_before, buf, sizeof(buf));
 804                 debug("%s: expires at %s", loc, buf);
 805         }
 806         if (opts->cert_principals != NULL) {
 807                 debug("%s: authorized principals: \"%s\"",
 808                     loc, opts->cert_principals);
 809         }
 810         if (opts->force_command != NULL)
 811                 debug("%s: forced command: \"%s\"", loc, opts->force_command);
 812         if (do_permitopen) {
 813                 for (i = 0; i < opts->npermitopen; i++) {
 814                         debug("%s: permitted open: %s",
 815                             loc, opts->permitopen[i]);
 816                 }
 817         }
 818         if (do_permitlisten) {
 819                 for (i = 0; i < opts->npermitlisten; i++) {
 820                         debug("%s: permitted listen: %s",
 821                             loc, opts->permitlisten[i]);
 822                 }
 823         }
 824 }
 825
 826 /* Activate a new set of key/cert options; merging with what is there. */
 827 int
 828 auth_activate_options(struct ssh *ssh, struct sshauthopt *opts)
 829 {
 830         struct sshauthopt *old = auth_opts;
 831         const char *emsg = NULL;
 832
 833         debug_f("setting new authentication options");
 834         if ((auth_opts = sshauthopt_merge(old, opts, &emsg)) == NULL) {
 835                 error("Inconsistent authentication options: %s", emsg);
 836                 return -1;
 837         }
 838         return 0;
 839 }
 840
 841 /* Disable forwarding, etc for the session */
 842 void
 843 auth_restrict_session(struct ssh *ssh)
 844 {
 845         struct sshauthopt *restricted;
 846
 847         debug_f("restricting session");
 848
 849         /* A blank sshauthopt defaults to permitting nothing */
 850         if ((restricted = sshauthopt_new()) == NULL)
 851                 fatal_f("sshauthopt_new failed");
 852         restricted->permit_pty_flag = 1;
 853         restricted->restricted = 1;
 854
 855         if (auth_activate_options(ssh, restricted) != 0)
 856                 fatal_f("failed to restrict session");
 857         sshauthopt_free(restricted);
 858 }