crypto/openssh-5/auth.c

   1 /* $OpenBSD: auth.c,v 1.78 2007/09/21 08:15:29 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 #ifdef HAVE_PATHS_H
  36 # include <paths.h>
  37 #endif
  38 #include <pwd.h>
  39 #ifdef HAVE_LOGIN_H
  40 #include <login.h>
  41 #endif
  42 #ifdef USE_SHADOW
  43 #include <shadow.h>
  44 #endif
  45 #ifdef HAVE_LIBGEN_H
  46 #include <libgen.h>
  47 #endif
  48 #include <stdarg.h>
  49 #include <stdio.h>
  50 #include <string.h>
  51
  52 #include "xmalloc.h"
  53 #include "match.h"
  54 #include "groupaccess.h"
  55 #include "log.h"
  56 #include "buffer.h"
  57 #include "servconf.h"
  58 #include "key.h"
  59 #include "hostfile.h"
  60 #include "auth.h"
  61 #include "auth-options.h"
  62 #include "canohost.h"
  63 #include "uidswap.h"
  64 #include "misc.h"
  65 #include "packet.h"
  66 #include "loginrec.h"
  67 #ifdef GSSAPI
  68 #include "ssh-gss.h"
  69 #endif
  70 #include "monitor_wrap.h"
  71
  72 /* import */
  73 extern ServerOptions options;
  74 extern int use_privsep;
  75 extern Buffer loginmsg;
  76 extern struct passwd *privsep_pw;
  77
  78 /* Debugging messages */
  79 Buffer auth_debug;
  80 int auth_debug_init;
  81
  82 /*
  83  * Check if the user is allowed to log in via ssh. If user is listed
  84  * in DenyUsers or one of user's groups is listed in DenyGroups, false
  85  * will be returned. If AllowUsers isn't empty and user isn't listed
  86  * there, or if AllowGroups isn't empty and one of user's groups isn't
  87  * listed there, false will be returned.
  88  * If the user's shell is not executable, false will be returned.
  89  * Otherwise true is returned.
  90  */
  91 int
  92 allowed_user(struct passwd * pw)
  93 {
  94         struct stat st;
  95         const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL;
  96         char *shell;
  97         u_int i;
  98 #ifdef USE_SHADOW
  99         struct spwd *spw = NULL;
 100 #endif
 101
 102         /* Shouldn't be called if pw is NULL, but better safe than sorry... */
 103         if (!pw || !pw->pw_name)
 104                 return 0;
 105
 106 #ifdef USE_SHADOW
 107         if (!options.use_pam)
 108                 spw = getspnam(pw->pw_name);
 109 #ifdef HAS_SHADOW_EXPIRE
 110         if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw))
 111                 return 0;
 112 #endif /* HAS_SHADOW_EXPIRE */
 113 #endif /* USE_SHADOW */
 114
 115         /* grab passwd field for locked account check */
 116 #ifdef USE_SHADOW
 117         if (spw != NULL)
 118 #ifdef USE_LIBIAF
 119                 passwd = get_iaf_password(pw);
 120 #else
 121                 passwd = spw->sp_pwdp;
 122 #endif /* USE_LIBIAF */
 123 #else
 124         passwd = pw->pw_passwd;
 125 #endif
 126
 127         /* check for locked account */
 128         if (!options.use_pam && passwd && *passwd) {
 129                 int locked = 0;
 130
 131 #ifdef LOCKED_PASSWD_STRING
 132                 if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0)
 133                          locked = 1;
 134 #endif
 135 #ifdef LOCKED_PASSWD_PREFIX
 136                 if (strncmp(passwd, LOCKED_PASSWD_PREFIX,
 137                     strlen(LOCKED_PASSWD_PREFIX)) == 0)
 138                          locked = 1;
 139 #endif
 140 #ifdef LOCKED_PASSWD_SUBSTR
 141                 if (strstr(passwd, LOCKED_PASSWD_SUBSTR))
 142                         locked = 1;
 143 #endif
 144 #ifdef USE_LIBIAF
 145                 free(passwd);
 146 #endif /* USE_LIBIAF */
 147                 if (locked) {
 148                         logit("User %.100s not allowed because account is locked",
 149                             pw->pw_name);
 150                         return 0;
 151                 }
 152         }
 153
 154         /*
 155          * Get the shell from the password data.  An empty shell field is
 156          * legal, and means /bin/sh.
 157          */
 158         shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;
 159
 160         /* deny if shell does not exists or is not executable */
 161         if (stat(shell, &st) != 0) {
 162                 logit("User %.100s not allowed because shell %.100s does not exist",
 163                     pw->pw_name, shell);
 164                 return 0;
 165         }
 166         if (S_ISREG(st.st_mode) == 0 ||
 167             (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
 168                 logit("User %.100s not allowed because shell %.100s is not executable",
 169                     pw->pw_name, shell);
 170                 return 0;
 171         }
 172
 173         if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
 174             options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 175                 hostname = get_canonical_hostname(options.use_dns);
 176                 ipaddr = get_remote_ipaddr();
 177         }
 178
 179         /* Return false if user is listed in DenyUsers */
 180         if (options.num_deny_users > 0) {
 181                 for (i = 0; i < options.num_deny_users; i++)
 182                         if (match_user(pw->pw_name, hostname, ipaddr,
 183                             options.deny_users[i])) {
 184                                 logit("User %.100s from %.100s not allowed "
 185                                     "because listed in DenyUsers",
 186                                     pw->pw_name, hostname);
 187                                 return 0;
 188                         }
 189         }
 190         /* Return false if AllowUsers isn't empty and user isn't listed there */
 191         if (options.num_allow_users > 0) {
 192                 for (i = 0; i < options.num_allow_users; i++)
 193                         if (match_user(pw->pw_name, hostname, ipaddr,
 194                             options.allow_users[i]))
 195                                 break;
 196                 /* i < options.num_allow_users iff we break for loop */
 197                 if (i >= options.num_allow_users) {
 198                         logit("User %.100s from %.100s not allowed because "
 199                             "not listed in AllowUsers", pw->pw_name, hostname);
 200                         return 0;
 201                 }
 202         }
 203         if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 204                 /* Get the user's group access list (primary and supplementary) */
 205                 if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
 206                         logit("User %.100s from %.100s not allowed because "
 207                             "not in any group", pw->pw_name, hostname);
 208                         return 0;
 209                 }
 210
 211                 /* Return false if one of user's groups is listed in DenyGroups */
 212                 if (options.num_deny_groups > 0)
 213                         if (ga_match(options.deny_groups,
 214                             options.num_deny_groups)) {
 215                                 ga_free();
 216                                 logit("User %.100s from %.100s not allowed "
 217                                     "because a group is listed in DenyGroups",
 218                                     pw->pw_name, hostname);
 219                                 return 0;
 220                         }
 221                 /*
 222                  * Return false if AllowGroups isn't empty and one of user's groups
 223                  * isn't listed there
 224                  */
 225                 if (options.num_allow_groups > 0)
 226                         if (!ga_match(options.allow_groups,
 227                             options.num_allow_groups)) {
 228                                 ga_free();
 229                                 logit("User %.100s from %.100s not allowed "
 230                                     "because none of user's groups are listed "
 231                                     "in AllowGroups", pw->pw_name, hostname);
 232                                 return 0;
 233                         }
 234                 ga_free();
 235         }
 236
 237 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
 238         if (!sys_auth_allowed_user(pw, &loginmsg))
 239                 return 0;
 240 #endif
 241
 242         /* We found no reason not to let this user try to log on... */
 243         return 1;
 244 }
 245
 246 void
 247 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info)
 248 {
 249         void (*authlog) (const char *fmt,...) = verbose;
 250         char *authmsg;
 251
 252         if (use_privsep && !mm_is_monitor() && !authctxt->postponed)
 253                 return;
 254
 255         /* Raise logging level */
 256         if (authenticated == 1 ||
 257             !authctxt->valid ||
 258             authctxt->failures >= options.max_authtries / 2 ||
 259             strcmp(method, "password") == 0)
 260                 authlog = logit;
 261
 262         if (authctxt->postponed)
 263                 authmsg = "Postponed";
 264         else
 265                 authmsg = authenticated ? "Accepted" : "Failed";
 266
 267         authlog("%s %s for %s%.100s from %.200s port %d%s",
 268             authmsg,
 269             method,
 270             authctxt->valid ? "" : "invalid user ",
 271             authctxt->user,
 272             get_remote_ipaddr(),
 273             get_remote_port(),
 274             info);
 275
 276 #ifdef CUSTOM_FAILED_LOGIN
 277         if (authenticated == 0 && !authctxt->postponed &&
 278             (strcmp(method, "password") == 0 ||
 279             strncmp(method, "keyboard-interactive", 20) == 0 ||
 280             strcmp(method, "challenge-response") == 0))
 281                 record_failed_login(authctxt->user,
 282                     get_canonical_hostname(options.use_dns), "ssh");
 283 # ifdef WITH_AIXAUTHENTICATE
 284         if (authenticated)
 285                 sys_auth_record_login(authctxt->user,
 286                     get_canonical_hostname(options.use_dns), "ssh", &loginmsg);
 287 # endif
 288 #endif
 289 #ifdef SSH_AUDIT_EVENTS
 290         if (authenticated == 0 && !authctxt->postponed)
 291                 audit_event(audit_classify_auth(method));
 292 #endif
 293 }
 294
 295 /*
 296  * Check whether root logins are disallowed.
 297  */
 298 int
 299 auth_root_allowed(char *method)
 300 {
 301         switch (options.permit_root_login) {
 302         case PERMIT_YES:
 303                 return 1;
 304         case PERMIT_NO_PASSWD:
 305                 if (strcmp(method, "password") != 0)
 306                         return 1;
 307                 break;
 308         case PERMIT_FORCED_ONLY:
 309                 if (forced_command) {
 310                         logit("Root login accepted for forced command.");
 311                         return 1;
 312                 }
 313                 break;
 314         }
 315         logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr());
 316         return 0;
 317 }
 318
 319
 320 /*
 321  * Given a template and a passwd structure, build a filename
 322  * by substituting % tokenised options. Currently, %% becomes '%',
 323  * %h becomes the home directory and %u the username.
 324  *
 325  * This returns a buffer allocated by xmalloc.
 326  */
 327 static char *
 328 expand_authorized_keys(const char *filename, struct passwd *pw)
 329 {
 330         char *file, ret[MAXPATHLEN];
 331         int i;
 332
 333         file = percent_expand(filename, "h", pw->pw_dir,
 334             "u", pw->pw_name, (char *)NULL);
 335
 336         /*
 337          * Ensure that filename starts anchored. If not, be backward
 338          * compatible and prepend the '%h/'
 339          */
 340         if (*file == '/')
 341                 return (file);
 342
 343         i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file);
 344         if (i < 0 || (size_t)i >= sizeof(ret))
 345                 fatal("expand_authorized_keys: path too long");
 346         xfree(file);
 347         return (xstrdup(ret));
 348 }
 349
 350 char *
 351 authorized_keys_file(struct passwd *pw)
 352 {
 353         return expand_authorized_keys(options.authorized_keys_file, pw);
 354 }
 355
 356 char *
 357 authorized_keys_file2(struct passwd *pw)
 358 {
 359         return expand_authorized_keys(options.authorized_keys_file2, pw);
 360 }
 361
 362 /* return ok if key exists in sysfile or userfile */
 363 HostStatus
 364 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host,
 365     const char *sysfile, const char *userfile)
 366 {
 367         Key *found;
 368         char *user_hostfile;
 369         struct stat st;
 370         HostStatus host_status;
 371
 372         /* Check if we know the host and its host key. */
 373         found = key_new(key->type);
 374         host_status = check_host_in_hostfile(sysfile, host, key, found, NULL);
 375
 376         if (host_status != HOST_OK && userfile != NULL) {
 377                 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
 378                 if (options.strict_modes &&
 379                     (stat(user_hostfile, &st) == 0) &&
 380                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 381                     (st.st_mode & 022) != 0)) {
 382                         logit("Authentication refused for %.100s: "
 383                             "bad owner or modes for %.200s",
 384                             pw->pw_name, user_hostfile);
 385                 } else {
 386                         temporarily_use_uid(pw);
 387                         host_status = check_host_in_hostfile(user_hostfile,
 388                             host, key, found, NULL);
 389                         restore_uid();
 390                 }
 391                 xfree(user_hostfile);
 392         }
 393         key_free(found);
 394
 395         debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ?
 396             "ok" : "not found", host);
 397         return host_status;
 398 }
 399
 400
 401 /*
 402  * Check a given file for security. This is defined as all components
 403  * of the path to the file must be owned by either the owner of
 404  * of the file or root and no directories must be group or world writable.
 405  *
 406  * XXX Should any specific check be done for sym links ?
 407  *
 408  * Takes an open file descriptor, the file name, a uid and and
 409  * error buffer plus max size as arguments.
 410  *
 411  * Returns 0 on success and -1 on failure
 412  */
 413 int
 414 secure_filename(FILE *f, const char *file, struct passwd *pw,
 415     char *err, size_t errlen)
 416 {
 417         uid_t uid = pw->pw_uid;
 418         char buf[MAXPATHLEN], homedir[MAXPATHLEN];
 419         char *cp;
 420         int comparehome = 0;
 421         struct stat st;
 422
 423         if (realpath(file, buf) == NULL) {
 424                 snprintf(err, errlen, "realpath %s failed: %s", file,
 425                     strerror(errno));
 426                 return -1;
 427         }
 428         if (realpath(pw->pw_dir, homedir) != NULL)
 429                 comparehome = 1;
 430
 431         /* check the open file to avoid races */
 432         if (fstat(fileno(f), &st) < 0 ||
 433             (st.st_uid != 0 && st.st_uid != uid) ||
 434             (st.st_mode & 022) != 0) {
 435                 snprintf(err, errlen, "bad ownership or modes for file %s",
 436                     buf);
 437                 return -1;
 438         }
 439
 440         /* for each component of the canonical path, walking upwards */
 441         for (;;) {
 442                 if ((cp = dirname(buf)) == NULL) {
 443                         snprintf(err, errlen, "dirname() failed");
 444                         return -1;
 445                 }
 446                 strlcpy(buf, cp, sizeof(buf));
 447
 448                 debug3("secure_filename: checking '%s'", buf);
 449                 if (stat(buf, &st) < 0 ||
 450                     (st.st_uid != 0 && st.st_uid != uid) ||
 451                     (st.st_mode & 022) != 0) {
 452                         snprintf(err, errlen,
 453                             "bad ownership or modes for directory %s", buf);
 454                         return -1;
 455                 }
 456
 457                 /* If are passed the homedir then we can stop */
 458                 if (comparehome && strcmp(homedir, buf) == 0) {
 459                         debug3("secure_filename: terminating check at '%s'",
 460                             buf);
 461                         break;
 462                 }
 463                 /*
 464                  * dirname should always complete with a "/" path,
 465                  * but we can be paranoid and check for "." too
 466                  */
 467                 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0))
 468                         break;
 469         }
 470         return 0;
 471 }
 472
 473 struct passwd *
 474 getpwnamallow(const char *user)
 475 {
 476 #ifdef HAVE_LOGIN_CAP
 477         extern login_cap_t *lc;
 478 #ifdef BSD_AUTH
 479         auth_session_t *as;
 480 #endif
 481 #endif
 482         struct passwd *pw;
 483
 484         parse_server_match_config(&options, user,
 485             get_canonical_hostname(options.use_dns), get_remote_ipaddr());
 486
 487         pw = getpwnam(user);
 488         if (pw == NULL) {
 489                 logit("Invalid user %.100s from %.100s",
 490                     user, get_remote_ipaddr());
 491 #ifdef CUSTOM_FAILED_LOGIN
 492                 record_failed_login(user,
 493                     get_canonical_hostname(options.use_dns), "ssh");
 494 #endif
 495 #ifdef SSH_AUDIT_EVENTS
 496                 audit_event(SSH_INVALID_USER);
 497 #endif /* SSH_AUDIT_EVENTS */
 498                 return (NULL);
 499         }
 500         if (!allowed_user(pw))
 501                 return (NULL);
 502 #ifdef HAVE_LOGIN_CAP
 503         if ((lc = login_getclass(pw->pw_class)) == NULL) {
 504                 debug("unable to get login class: %s", user);
 505                 return (NULL);
 506         }
 507 #ifdef BSD_AUTH
 508         if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
 509             auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
 510                 debug("Approval failure for %s", user);
 511                 pw = NULL;
 512         }
 513         if (as != NULL)
 514                 auth_close(as);
 515 #endif
 516 #endif
 517         if (pw != NULL)
 518                 return (pwcopy(pw));
 519         return (NULL);
 520 }
 521
 522 void
 523 auth_debug_add(const char *fmt,...)
 524 {
 525         char buf[1024];
 526         va_list args;
 527
 528         if (!auth_debug_init)
 529                 return;
 530
 531         va_start(args, fmt);
 532         vsnprintf(buf, sizeof(buf), fmt, args);
 533         va_end(args);
 534         buffer_put_cstring(&auth_debug, buf);
 535 }
 536
 537 void
 538 auth_debug_send(void)
 539 {
 540         char *msg;
 541
 542         if (!auth_debug_init)
 543                 return;
 544         while (buffer_len(&auth_debug)) {
 545                 msg = buffer_get_string(&auth_debug, NULL);
 546                 packet_send_debug("%s", msg);
 547                 xfree(msg);
 548         }
 549 }
 550
 551 void
 552 auth_debug_reset(void)
 553 {
 554         if (auth_debug_init)
 555                 buffer_clear(&auth_debug);
 556         else {
 557                 buffer_init(&auth_debug);
 558                 auth_debug_init = 1;
 559         }
 560 }
 561
 562 struct passwd *
 563 fakepw(void)
 564 {
 565         static struct passwd fake;
 566
 567         memset(&fake, 0, sizeof(fake));
 568         fake.pw_name = "NOUSER";
 569         fake.pw_passwd =
 570             "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK";
 571         fake.pw_gecos = "NOUSER";
 572         fake.pw_uid = privsep_pw == NULL ? (uid_t)-1 : privsep_pw->pw_uid;
 573         fake.pw_gid = privsep_pw == NULL ? (gid_t)-1 : privsep_pw->pw_gid;
 574 #ifdef HAVE_PW_CLASS_IN_PASSWD
 575         fake.pw_class = "";
 576 #endif
 577         fake.pw_dir = "/nonexist";
 578         fake.pw_shell = "/nonexist";
 579
 580         return (&fake);
 581 }