auth.c

   1 /* $OpenBSD: auth.c,v 1.80 2008/11/04 07:58:09 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/param.h>
  31
  32 #include <netinet/in.h>
  33
  34 #include <errno.h>
  35 #include <fcntl.h>
  36 #ifdef HAVE_PATHS_H
  37 # include <paths.h>
  38 #endif
  39 #include <pwd.h>
  40 #ifdef HAVE_LOGIN_H
  41 #include <login.h>
  42 #endif
  43 #ifdef USE_SHADOW
  44 #include <shadow.h>
  45 #endif
  46 #ifdef HAVE_LIBGEN_H
  47 #include <libgen.h>
  48 #endif
  49 #include <stdarg.h>
  50 #include <stdio.h>
  51 #include <string.h>
  52 #include <unistd.h>
  53
  54 #include "xmalloc.h"
  55 #include "match.h"
  56 #include "groupaccess.h"
  57 #include "log.h"
  58 #include "buffer.h"
  59 #include "servconf.h"
  60 #include "key.h"
  61 #include "hostfile.h"
  62 #include "auth.h"
  63 #include "auth-options.h"
  64 #include "canohost.h"
  65 #include "uidswap.h"
  66 #include "misc.h"
  67 #include "packet.h"
  68 #include "loginrec.h"
  69 #ifdef GSSAPI
  70 #include "ssh-gss.h"
  71 #endif
  72 #include "monitor_wrap.h"
  73
  74 /* import */
  75 extern ServerOptions options;
  76 extern int use_privsep;
  77 extern Buffer loginmsg;
  78 extern struct passwd *privsep_pw;
  79
  80 /* Debugging messages */
  81 Buffer auth_debug;
  82 int auth_debug_init;
  83
  84 /*
  85  * Check if the user is allowed to log in via ssh. If user is listed
  86  * in DenyUsers or one of user's groups is listed in DenyGroups, false
  87  * will be returned. If AllowUsers isn't empty and user isn't listed
  88  * there, or if AllowGroups isn't empty and one of user's groups isn't
  89  * listed there, false will be returned.
  90  * If the user's shell is not executable, false will be returned.
  91  * Otherwise true is returned.
  92  */
  93 int
  94 allowed_user(struct passwd * pw)
  95 {
  96         struct stat st;
  97         const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL;
  98         char *shell;
  99         u_int i;
 100 #ifdef USE_SHADOW
 101         struct spwd *spw = NULL;
 102 #endif
 103
 104         /* Shouldn't be called if pw is NULL, but better safe than sorry... */
 105         if (!pw || !pw->pw_name)
 106                 return 0;
 107
 108 #ifdef USE_SHADOW
 109         if (!options.use_pam)
 110                 spw = getspnam(pw->pw_name);
 111 #ifdef HAS_SHADOW_EXPIRE
 112         if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw))
 113                 return 0;
 114 #endif /* HAS_SHADOW_EXPIRE */
 115 #endif /* USE_SHADOW */
 116
 117         /* grab passwd field for locked account check */
 118         passwd = pw->pw_passwd;
 119 #ifdef USE_SHADOW
 120         if (spw != NULL)
 121 #ifdef USE_LIBIAF
 122                 passwd = get_iaf_password(pw);
 123 #else
 124                 passwd = spw->sp_pwdp;
 125 #endif /* USE_LIBIAF */
 126 #endif
 127
 128         /* check for locked account */
 129         if (!options.use_pam && passwd && *passwd) {
 130                 int locked = 0;
 131
 132 #ifdef LOCKED_PASSWD_STRING
 133                 if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0)
 134                          locked = 1;
 135 #endif
 136 #ifdef LOCKED_PASSWD_PREFIX
 137                 if (strncmp(passwd, LOCKED_PASSWD_PREFIX,
 138                     strlen(LOCKED_PASSWD_PREFIX)) == 0)
 139                          locked = 1;
 140 #endif
 141 #ifdef LOCKED_PASSWD_SUBSTR
 142                 if (strstr(passwd, LOCKED_PASSWD_SUBSTR))
 143                         locked = 1;
 144 #endif
 145 #ifdef USE_LIBIAF
 146                 free(passwd);
 147 #endif /* USE_LIBIAF */
 148                 if (locked) {
 149                         logit("User %.100s not allowed because account is locked",
 150                             pw->pw_name);
 151                         return 0;
 152                 }
 153         }
 154
 155         /*
 156          * Get the shell from the password data.  An empty shell field is
 157          * legal, and means /bin/sh.
 158          */
 159         shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;
 160
 161         /* deny if shell does not exists or is not executable */
 162         if (stat(shell, &st) != 0) {
 163                 logit("User %.100s not allowed because shell %.100s does not exist",
 164                     pw->pw_name, shell);
 165                 return 0;
 166         }
 167         if (S_ISREG(st.st_mode) == 0 ||
 168             (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
 169                 logit("User %.100s not allowed because shell %.100s is not executable",
 170                     pw->pw_name, shell);
 171                 return 0;
 172         }
 173
 174         if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
 175             options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 176                 hostname = get_canonical_hostname(options.use_dns);
 177                 ipaddr = get_remote_ipaddr();
 178         }
 179
 180         /* Return false if user is listed in DenyUsers */
 181         if (options.num_deny_users > 0) {
 182                 for (i = 0; i < options.num_deny_users; i++)
 183                         if (match_user(pw->pw_name, hostname, ipaddr,
 184                             options.deny_users[i])) {
 185                                 logit("User %.100s from %.100s not allowed "
 186                                     "because listed in DenyUsers",
 187                                     pw->pw_name, hostname);
 188                                 return 0;
 189                         }
 190         }
 191         /* Return false if AllowUsers isn't empty and user isn't listed there */
 192         if (options.num_allow_users > 0) {
 193                 for (i = 0; i < options.num_allow_users; i++)
 194                         if (match_user(pw->pw_name, hostname, ipaddr,
 195                             options.allow_users[i]))
 196                                 break;
 197                 /* i < options.num_allow_users iff we break for loop */
 198                 if (i >= options.num_allow_users) {
 199                         logit("User %.100s from %.100s not allowed because "
 200                             "not listed in AllowUsers", pw->pw_name, hostname);
 201                         return 0;
 202                 }
 203         }
 204         if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 205                 /* Get the user's group access list (primary and supplementary) */
 206                 if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
 207                         logit("User %.100s from %.100s not allowed because "
 208                             "not in any group", pw->pw_name, hostname);
 209                         return 0;
 210                 }
 211
 212                 /* Return false if one of user's groups is listed in DenyGroups */
 213                 if (options.num_deny_groups > 0)
 214                         if (ga_match(options.deny_groups,
 215                             options.num_deny_groups)) {
 216                                 ga_free();
 217                                 logit("User %.100s from %.100s not allowed "
 218                                     "because a group is listed in DenyGroups",
 219                                     pw->pw_name, hostname);
 220                                 return 0;
 221                         }
 222                 /*
 223                  * Return false if AllowGroups isn't empty and one of user's groups
 224                  * isn't listed there
 225                  */
 226                 if (options.num_allow_groups > 0)
 227                         if (!ga_match(options.allow_groups,
 228                             options.num_allow_groups)) {
 229                                 ga_free();
 230                                 logit("User %.100s from %.100s not allowed "
 231                                     "because none of user's groups are listed "
 232                                     "in AllowGroups", pw->pw_name, hostname);
 233                                 return 0;
 234                         }
 235                 ga_free();
 236         }
 237
 238 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
 239         if (!sys_auth_allowed_user(pw, &loginmsg))
 240                 return 0;
 241 #endif
 242
 243         /* We found no reason not to let this user try to log on... */
 244         return 1;
 245 }
 246
 247 void
 248 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info)
 249 {
 250         void (*authlog) (const char *fmt,...) = verbose;
 251         char *authmsg;
 252
 253         if (use_privsep && !mm_is_monitor() && !authctxt->postponed)
 254                 return;
 255
 256         /* Raise logging level */
 257         if (authenticated == 1 ||
 258             !authctxt->valid ||
 259             authctxt->failures >= options.max_authtries / 2 ||
 260             strcmp(method, "password") == 0)
 261                 authlog = logit;
 262
 263         if (authctxt->postponed)
 264                 authmsg = "Postponed";
 265         else
 266                 authmsg = authenticated ? "Accepted" : "Failed";
 267
 268         authlog("%s %s for %s%.100s from %.200s port %d%s",
 269             authmsg,
 270             method,
 271             authctxt->valid ? "" : "invalid user ",
 272             authctxt->user,
 273             get_remote_ipaddr(),
 274             get_remote_port(),
 275             info);
 276
 277 #ifdef CUSTOM_FAILED_LOGIN
 278         if (authenticated == 0 && !authctxt->postponed &&
 279             (strcmp(method, "password") == 0 ||
 280             strncmp(method, "keyboard-interactive", 20) == 0 ||
 281             strcmp(method, "challenge-response") == 0))
 282                 record_failed_login(authctxt->user,
 283                     get_canonical_hostname(options.use_dns), "ssh");
 284 # ifdef WITH_AIXAUTHENTICATE
 285         if (authenticated)
 286                 sys_auth_record_login(authctxt->user,
 287                     get_canonical_hostname(options.use_dns), "ssh", &loginmsg);
 288 # endif
 289 #endif
 290 #ifdef SSH_AUDIT_EVENTS
 291         if (authenticated == 0 && !authctxt->postponed)
 292                 audit_event(audit_classify_auth(method));
 293 #endif
 294 }
 295
 296 /*
 297  * Check whether root logins are disallowed.
 298  */
 299 int
 300 auth_root_allowed(char *method)
 301 {
 302         switch (options.permit_root_login) {
 303         case PERMIT_YES:
 304                 return 1;
 305         case PERMIT_NO_PASSWD:
 306                 if (strcmp(method, "password") != 0)
 307                         return 1;
 308                 break;
 309         case PERMIT_FORCED_ONLY:
 310                 if (forced_command) {
 311                         logit("Root login accepted for forced command.");
 312                         return 1;
 313                 }
 314                 break;
 315         }
 316         logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr());
 317         return 0;
 318 }
 319
 320
 321 /*
 322  * Given a template and a passwd structure, build a filename
 323  * by substituting % tokenised options. Currently, %% becomes '%',
 324  * %h becomes the home directory and %u the username.
 325  *
 326  * This returns a buffer allocated by xmalloc.
 327  */
 328 static char *
 329 expand_authorized_keys(const char *filename, struct passwd *pw)
 330 {
 331         char *file, ret[MAXPATHLEN];
 332         int i;
 333
 334         file = percent_expand(filename, "h", pw->pw_dir,
 335             "u", pw->pw_name, (char *)NULL);
 336
 337         /*
 338          * Ensure that filename starts anchored. If not, be backward
 339          * compatible and prepend the '%h/'
 340          */
 341         if (*file == '/')
 342                 return (file);
 343
 344         i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file);
 345         if (i < 0 || (size_t)i >= sizeof(ret))
 346                 fatal("expand_authorized_keys: path too long");
 347         xfree(file);
 348         return (xstrdup(ret));
 349 }
 350
 351 char *
 352 authorized_keys_file(struct passwd *pw)
 353 {
 354         return expand_authorized_keys(options.authorized_keys_file, pw);
 355 }
 356
 357 char *
 358 authorized_keys_file2(struct passwd *pw)
 359 {
 360         return expand_authorized_keys(options.authorized_keys_file2, pw);
 361 }
 362
 363 /* return ok if key exists in sysfile or userfile */
 364 HostStatus
 365 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host,
 366     const char *sysfile, const char *userfile)
 367 {
 368         Key *found;
 369         char *user_hostfile;
 370         struct stat st;
 371         HostStatus host_status;
 372
 373         /* Check if we know the host and its host key. */
 374         found = key_new(key->type);
 375         host_status = check_host_in_hostfile(sysfile, host, key, found, NULL);
 376
 377         if (host_status != HOST_OK && userfile != NULL) {
 378                 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
 379                 if (options.strict_modes &&
 380                     (stat(user_hostfile, &st) == 0) &&
 381                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 382                     (st.st_mode & 022) != 0)) {
 383                         logit("Authentication refused for %.100s: "
 384                             "bad owner or modes for %.200s",
 385                             pw->pw_name, user_hostfile);
 386                 } else {
 387                         temporarily_use_uid(pw);
 388                         host_status = check_host_in_hostfile(user_hostfile,
 389                             host, key, found, NULL);
 390                         restore_uid();
 391                 }
 392                 xfree(user_hostfile);
 393         }
 394         key_free(found);
 395
 396         debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ?
 397             "ok" : "not found", host);
 398         return host_status;
 399 }
 400
 401
 402 /*
 403  * Check a given file for security. This is defined as all components
 404  * of the path to the file must be owned by either the owner of
 405  * of the file or root and no directories must be group or world writable.
 406  *
 407  * XXX Should any specific check be done for sym links ?
 408  *
 409  * Takes an open file descriptor, the file name, a uid and and
 410  * error buffer plus max size as arguments.
 411  *
 412  * Returns 0 on success and -1 on failure
 413  */
 414 static int
 415 secure_filename(FILE *f, const char *file, struct passwd *pw,
 416     char *err, size_t errlen)
 417 {
 418         uid_t uid = pw->pw_uid;
 419         char buf[MAXPATHLEN], homedir[MAXPATHLEN];
 420         char *cp;
 421         int comparehome = 0;
 422         struct stat st;
 423
 424         if (realpath(file, buf) == NULL) {
 425                 snprintf(err, errlen, "realpath %s failed: %s", file,
 426                     strerror(errno));
 427                 return -1;
 428         }
 429         if (realpath(pw->pw_dir, homedir) != NULL)
 430                 comparehome = 1;
 431
 432         /* check the open file to avoid races */
 433         if (fstat(fileno(f), &st) < 0 ||
 434             (st.st_uid != 0 && st.st_uid != uid) ||
 435             (st.st_mode & 022) != 0) {
 436                 snprintf(err, errlen, "bad ownership or modes for file %s",
 437                     buf);
 438                 return -1;
 439         }
 440
 441         /* for each component of the canonical path, walking upwards */
 442         for (;;) {
 443                 if ((cp = dirname(buf)) == NULL) {
 444                         snprintf(err, errlen, "dirname() failed");
 445                         return -1;
 446                 }
 447                 strlcpy(buf, cp, sizeof(buf));
 448
 449                 debug3("secure_filename: checking '%s'", buf);
 450                 if (stat(buf, &st) < 0 ||
 451                     (st.st_uid != 0 && st.st_uid != uid) ||
 452                     (st.st_mode & 022) != 0) {
 453                         snprintf(err, errlen,
 454                             "bad ownership or modes for directory %s", buf);
 455                         return -1;
 456                 }
 457
 458                 /* If are passed the homedir then we can stop */
 459                 if (comparehome && strcmp(homedir, buf) == 0) {
 460                         debug3("secure_filename: terminating check at '%s'",
 461                             buf);
 462                         break;
 463                 }
 464                 /*
 465                  * dirname should always complete with a "/" path,
 466                  * but we can be paranoid and check for "." too
 467                  */
 468                 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0))
 469                         break;
 470         }
 471         return 0;
 472 }
 473
 474 FILE *
 475 auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes)
 476 {
 477         char line[1024];
 478         struct stat st;
 479         int fd;
 480         FILE *f;
 481
 482         /*
 483          * Open the file containing the authorized keys
 484          * Fail quietly if file does not exist
 485          */
 486         if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1)
 487                 return NULL;
 488
 489         if (fstat(fd, &st) < 0) {
 490                 close(fd);
 491                 return NULL;
 492         }
 493         if (!S_ISREG(st.st_mode)) {
 494                 logit("User %s authorized keys %s is not a regular file",
 495                     pw->pw_name, file);
 496                 close(fd);
 497                 return NULL;
 498         }
 499         unset_nonblock(fd);
 500         if ((f = fdopen(fd, "r")) == NULL) {
 501                 close(fd);
 502                 return NULL;
 503         }
 504         if (options.strict_modes &&
 505             secure_filename(f, file, pw, line, sizeof(line)) != 0) {
 506                 fclose(f);
 507                 logit("Authentication refused: %s", line);
 508                 return NULL;
 509         }
 510
 511         return f;
 512 }
 513
 514 struct passwd *
 515 getpwnamallow(const char *user)
 516 {
 517 #ifdef HAVE_LOGIN_CAP
 518         extern login_cap_t *lc;
 519 #ifdef BSD_AUTH
 520         auth_session_t *as;
 521 #endif
 522 #endif
 523         struct passwd *pw;
 524
 525         parse_server_match_config(&options, user,
 526             get_canonical_hostname(options.use_dns), get_remote_ipaddr());
 527
 528         pw = getpwnam(user);
 529         if (pw == NULL) {
 530                 logit("Invalid user %.100s from %.100s",
 531                     user, get_remote_ipaddr());
 532 #ifdef CUSTOM_FAILED_LOGIN
 533                 record_failed_login(user,
 534                     get_canonical_hostname(options.use_dns), "ssh");
 535 #endif
 536 #ifdef SSH_AUDIT_EVENTS
 537                 audit_event(SSH_INVALID_USER);
 538 #endif /* SSH_AUDIT_EVENTS */
 539                 return (NULL);
 540         }
 541         if (!allowed_user(pw))
 542                 return (NULL);
 543 #ifdef HAVE_LOGIN_CAP
 544         if ((lc = login_getclass(pw->pw_class)) == NULL) {
 545                 debug("unable to get login class: %s", user);
 546                 return (NULL);
 547         }
 548 #ifdef BSD_AUTH
 549         if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
 550             auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
 551                 debug("Approval failure for %s", user);
 552                 pw = NULL;
 553         }
 554         if (as != NULL)
 555                 auth_close(as);
 556 #endif
 557 #endif
 558         if (pw != NULL)
 559                 return (pwcopy(pw));
 560         return (NULL);
 561 }
 562
 563 void
 564 auth_debug_add(const char *fmt,...)
 565 {
 566         char buf[1024];
 567         va_list args;
 568
 569         if (!auth_debug_init)
 570                 return;
 571
 572         va_start(args, fmt);
 573         vsnprintf(buf, sizeof(buf), fmt, args);
 574         va_end(args);
 575         buffer_put_cstring(&auth_debug, buf);
 576 }
 577
 578 void
 579 auth_debug_send(void)
 580 {
 581         char *msg;
 582
 583         if (!auth_debug_init)
 584                 return;
 585         while (buffer_len(&auth_debug)) {
 586                 msg = buffer_get_string(&auth_debug, NULL);
 587                 packet_send_debug("%s", msg);
 588                 xfree(msg);
 589         }
 590 }
 591
 592 void
 593 auth_debug_reset(void)
 594 {
 595         if (auth_debug_init)
 596                 buffer_clear(&auth_debug);
 597         else {
 598                 buffer_init(&auth_debug);
 599                 auth_debug_init = 1;
 600         }
 601 }
 602
 603 struct passwd *
 604 fakepw(void)
 605 {
 606         static struct passwd fake;
 607
 608         memset(&fake, 0, sizeof(fake));
 609         fake.pw_name = "NOUSER";
 610         fake.pw_passwd =
 611             "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK";
 612         fake.pw_gecos = "NOUSER";
 613         fake.pw_uid = privsep_pw == NULL ? (uid_t)-1 : privsep_pw->pw_uid;
 614         fake.pw_gid = privsep_pw == NULL ? (gid_t)-1 : privsep_pw->pw_gid;
 615 #ifdef HAVE_PW_CLASS_IN_PASSWD
 616         fake.pw_class = "";
 617 #endif
 618         fake.pw_dir = "/nonexist";
 619         fake.pw_shell = "/nonexist";
 620
 621         return (&fake);
 622 }