auth.c

   1 /* $OpenBSD: auth.c,v 1.71 2006/07/12 11:34:58 dtucker 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
  31 #include <errno.h>
  32 #ifdef HAVE_PATHS_H
  33 # include <paths.h>
  34 #endif
  35 #include <pwd.h>
  36 #ifdef HAVE_LOGIN_H
  37 #include <login.h>
  38 #endif
  39 #ifdef USE_SHADOW
  40 #include <shadow.h>
  41 #endif
  42 #ifdef HAVE_LIBGEN_H
  43 #include <libgen.h>
  44 #endif
  45 #include <stdarg.h>
  46
  47 #include "xmalloc.h"
  48 #include "match.h"
  49 #include "groupaccess.h"
  50 #include "log.h"
  51 #include "servconf.h"
  52 #include "auth.h"
  53 #include "auth-options.h"
  54 #include "canohost.h"
  55 #include "buffer.h"
  56 #include "bufaux.h"
  57 #include "uidswap.h"
  58 #include "misc.h"
  59 #include "bufaux.h"
  60 #include "packet.h"
  61 #include "loginrec.h"
  62 #include "monitor_wrap.h"
  63
  64 /* import */
  65 extern ServerOptions options;
  66 extern int use_privsep;
  67 extern Buffer loginmsg;
  68
  69 /* Debugging messages */
  70 Buffer auth_debug;
  71 int auth_debug_init;
  72
  73 /*
  74  * Check if the user is allowed to log in via ssh. If user is listed
  75  * in DenyUsers or one of user's groups is listed in DenyGroups, false
  76  * will be returned. If AllowUsers isn't empty and user isn't listed
  77  * there, or if AllowGroups isn't empty and one of user's groups isn't
  78  * listed there, false will be returned.
  79  * If the user's shell is not executable, false will be returned.
  80  * Otherwise true is returned.
  81  */
  82 int
  83 allowed_user(struct passwd * pw)
  84 {
  85         struct stat st;
  86         const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL;
  87         char *shell;
  88         u_int i;
  89 #ifdef USE_SHADOW
  90         struct spwd *spw = NULL;
  91 #endif
  92
  93         /* Shouldn't be called if pw is NULL, but better safe than sorry... */
  94         if (!pw || !pw->pw_name)
  95                 return 0;
  96
  97 #ifdef USE_SHADOW
  98         if (!options.use_pam)
  99                 spw = getspnam(pw->pw_name);
 100 #ifdef HAS_SHADOW_EXPIRE
 101         if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw))
 102                 return 0;
 103 #endif /* HAS_SHADOW_EXPIRE */
 104 #endif /* USE_SHADOW */
 105
 106         /* grab passwd field for locked account check */
 107 #ifdef USE_SHADOW
 108         if (spw != NULL)
 109 #if defined(HAVE_LIBIAF)  &&  !defined(BROKEN_LIBIAF)
 110                 passwd = get_iaf_password(pw);
 111 #else
 112                 passwd = spw->sp_pwdp;
 113 #endif /* HAVE_LIBIAF  && !BROKEN_LIBIAF */
 114 #else
 115         passwd = pw->pw_passwd;
 116 #endif
 117
 118         /* check for locked account */
 119         if (!options.use_pam && passwd && *passwd) {
 120                 int locked = 0;
 121
 122 #ifdef LOCKED_PASSWD_STRING
 123                 if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0)
 124                          locked = 1;
 125 #endif
 126 #ifdef LOCKED_PASSWD_PREFIX
 127                 if (strncmp(passwd, LOCKED_PASSWD_PREFIX,
 128                     strlen(LOCKED_PASSWD_PREFIX)) == 0)
 129                          locked = 1;
 130 #endif
 131 #ifdef LOCKED_PASSWD_SUBSTR
 132                 if (strstr(passwd, LOCKED_PASSWD_SUBSTR))
 133                         locked = 1;
 134 #endif
 135 #if defined(HAVE_LIBIAF)  &&  !defined(BROKEN_LIBIAF)
 136                 free(passwd);
 137 #endif /* HAVE_LIBIAF  && !BROKEN_LIBIAF */
 138                 if (locked) {
 139                         logit("User %.100s not allowed because account is locked",
 140                             pw->pw_name);
 141                         return 0;
 142                 }
 143         }
 144
 145         /*
 146          * Get the shell from the password data.  An empty shell field is
 147          * legal, and means /bin/sh.
 148          */
 149         shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;
 150
 151         /* deny if shell does not exists or is not executable */
 152         if (stat(shell, &st) != 0) {
 153                 logit("User %.100s not allowed because shell %.100s does not exist",
 154                     pw->pw_name, shell);
 155                 return 0;
 156         }
 157         if (S_ISREG(st.st_mode) == 0 ||
 158             (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
 159                 logit("User %.100s not allowed because shell %.100s is not executable",
 160                     pw->pw_name, shell);
 161                 return 0;
 162         }
 163
 164         if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
 165             options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 166                 hostname = get_canonical_hostname(options.use_dns);
 167                 ipaddr = get_remote_ipaddr();
 168         }
 169
 170         /* Return false if user is listed in DenyUsers */
 171         if (options.num_deny_users > 0) {
 172                 for (i = 0; i < options.num_deny_users; i++)
 173                         if (match_user(pw->pw_name, hostname, ipaddr,
 174                             options.deny_users[i])) {
 175                                 logit("User %.100s from %.100s not allowed "
 176                                     "because listed in DenyUsers",
 177                                     pw->pw_name, hostname);
 178                                 return 0;
 179                         }
 180         }
 181         /* Return false if AllowUsers isn't empty and user isn't listed there */
 182         if (options.num_allow_users > 0) {
 183                 for (i = 0; i < options.num_allow_users; i++)
 184                         if (match_user(pw->pw_name, hostname, ipaddr,
 185                             options.allow_users[i]))
 186                                 break;
 187                 /* i < options.num_allow_users iff we break for loop */
 188                 if (i >= options.num_allow_users) {
 189                         logit("User %.100s from %.100s not allowed because "
 190                             "not listed in AllowUsers", pw->pw_name, hostname);
 191                         return 0;
 192                 }
 193         }
 194         if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 195                 /* Get the user's group access list (primary and supplementary) */
 196                 if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
 197                         logit("User %.100s from %.100s not allowed because "
 198                             "not in any group", pw->pw_name, hostname);
 199                         return 0;
 200                 }
 201
 202                 /* Return false if one of user's groups is listed in DenyGroups */
 203                 if (options.num_deny_groups > 0)
 204                         if (ga_match(options.deny_groups,
 205                             options.num_deny_groups)) {
 206                                 ga_free();
 207                                 logit("User %.100s from %.100s not allowed "
 208                                     "because a group is listed in DenyGroups",
 209                                     pw->pw_name, hostname);
 210                                 return 0;
 211                         }
 212                 /*
 213                  * Return false if AllowGroups isn't empty and one of user's groups
 214                  * isn't listed there
 215                  */
 216                 if (options.num_allow_groups > 0)
 217                         if (!ga_match(options.allow_groups,
 218                             options.num_allow_groups)) {
 219                                 ga_free();
 220                                 logit("User %.100s from %.100s not allowed "
 221                                     "because none of user's groups are listed "
 222                                     "in AllowGroups", pw->pw_name, hostname);
 223                                 return 0;
 224                         }
 225                 ga_free();
 226         }
 227
 228 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
 229         if (!sys_auth_allowed_user(pw, &loginmsg))
 230                 return 0;
 231 #endif
 232
 233         /* We found no reason not to let this user try to log on... */
 234         return 1;
 235 }
 236
 237 void
 238 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info)
 239 {
 240         void (*authlog) (const char *fmt,...) = verbose;
 241         char *authmsg;
 242
 243         if (use_privsep && !mm_is_monitor() && !authctxt->postponed)
 244                 return;
 245
 246         /* Raise logging level */
 247         if (authenticated == 1 ||
 248             !authctxt->valid ||
 249             authctxt->failures >= options.max_authtries / 2 ||
 250             strcmp(method, "password") == 0)
 251                 authlog = logit;
 252
 253         if (authctxt->postponed)
 254                 authmsg = "Postponed";
 255         else
 256                 authmsg = authenticated ? "Accepted" : "Failed";
 257
 258         authlog("%s %s for %s%.100s from %.200s port %d%s",
 259             authmsg,
 260             method,
 261             authctxt->valid ? "" : "invalid user ",
 262             authctxt->user,
 263             get_remote_ipaddr(),
 264             get_remote_port(),
 265             info);
 266
 267 #ifdef CUSTOM_FAILED_LOGIN
 268         if (authenticated == 0 && !authctxt->postponed &&
 269             (strcmp(method, "password") == 0 ||
 270             strncmp(method, "keyboard-interactive", 20) == 0 ||
 271             strcmp(method, "challenge-response") == 0))
 272                 record_failed_login(authctxt->user,
 273                     get_canonical_hostname(options.use_dns), "ssh");
 274 #endif
 275 #ifdef SSH_AUDIT_EVENTS
 276         if (authenticated == 0 && !authctxt->postponed)
 277                 audit_event(audit_classify_auth(method));
 278 #endif
 279 }
 280
 281 /*
 282  * Check whether root logins are disallowed.
 283  */
 284 int
 285 auth_root_allowed(char *method)
 286 {
 287         switch (options.permit_root_login) {
 288         case PERMIT_YES:
 289                 return 1;
 290         case PERMIT_NO_PASSWD:
 291                 if (strcmp(method, "password") != 0)
 292                         return 1;
 293                 break;
 294         case PERMIT_FORCED_ONLY:
 295                 if (forced_command) {
 296                         logit("Root login accepted for forced command.");
 297                         return 1;
 298                 }
 299                 break;
 300         }
 301         logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr());
 302         return 0;
 303 }
 304
 305
 306 /*
 307  * Given a template and a passwd structure, build a filename
 308  * by substituting % tokenised options. Currently, %% becomes '%',
 309  * %h becomes the home directory and %u the username.
 310  *
 311  * This returns a buffer allocated by xmalloc.
 312  */
 313 static char *
 314 expand_authorized_keys(const char *filename, struct passwd *pw)
 315 {
 316         char *file, ret[MAXPATHLEN];
 317         int i;
 318
 319         file = percent_expand(filename, "h", pw->pw_dir,
 320             "u", pw->pw_name, (char *)NULL);
 321
 322         /*
 323          * Ensure that filename starts anchored. If not, be backward
 324          * compatible and prepend the '%h/'
 325          */
 326         if (*file == '/')
 327                 return (file);
 328
 329         i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file);
 330         if (i < 0 || (size_t)i >= sizeof(ret))
 331                 fatal("expand_authorized_keys: path too long");
 332         xfree(file);
 333         return (xstrdup(ret));
 334 }
 335
 336 char *
 337 authorized_keys_file(struct passwd *pw)
 338 {
 339         return expand_authorized_keys(options.authorized_keys_file, pw);
 340 }
 341
 342 char *
 343 authorized_keys_file2(struct passwd *pw)
 344 {
 345         return expand_authorized_keys(options.authorized_keys_file2, pw);
 346 }
 347
 348 /* return ok if key exists in sysfile or userfile */
 349 HostStatus
 350 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host,
 351     const char *sysfile, const char *userfile)
 352 {
 353         Key *found;
 354         char *user_hostfile;
 355         struct stat st;
 356         HostStatus host_status;
 357
 358         /* Check if we know the host and its host key. */
 359         found = key_new(key->type);
 360         host_status = check_host_in_hostfile(sysfile, host, key, found, NULL);
 361
 362         if (host_status != HOST_OK && userfile != NULL) {
 363                 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
 364                 if (options.strict_modes &&
 365                     (stat(user_hostfile, &st) == 0) &&
 366                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 367                     (st.st_mode & 022) != 0)) {
 368                         logit("Authentication refused for %.100s: "
 369                             "bad owner or modes for %.200s",
 370                             pw->pw_name, user_hostfile);
 371                 } else {
 372                         temporarily_use_uid(pw);
 373                         host_status = check_host_in_hostfile(user_hostfile,
 374                             host, key, found, NULL);
 375                         restore_uid();
 376                 }
 377                 xfree(user_hostfile);
 378         }
 379         key_free(found);
 380
 381         debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ?
 382             "ok" : "not found", host);
 383         return host_status;
 384 }
 385
 386
 387 /*
 388  * Check a given file for security. This is defined as all components
 389  * of the path to the file must be owned by either the owner of
 390  * of the file or root and no directories must be group or world writable.
 391  *
 392  * XXX Should any specific check be done for sym links ?
 393  *
 394  * Takes an open file descriptor, the file name, a uid and and
 395  * error buffer plus max size as arguments.
 396  *
 397  * Returns 0 on success and -1 on failure
 398  */
 399 int
 400 secure_filename(FILE *f, const char *file, struct passwd *pw,
 401     char *err, size_t errlen)
 402 {
 403         uid_t uid = pw->pw_uid;
 404         char buf[MAXPATHLEN], homedir[MAXPATHLEN];
 405         char *cp;
 406         int comparehome = 0;
 407         struct stat st;
 408
 409         if (realpath(file, buf) == NULL) {
 410                 snprintf(err, errlen, "realpath %s failed: %s", file,
 411                     strerror(errno));
 412                 return -1;
 413         }
 414         if (realpath(pw->pw_dir, homedir) != NULL)
 415                 comparehome = 1;
 416
 417         /* check the open file to avoid races */
 418         if (fstat(fileno(f), &st) < 0 ||
 419             (st.st_uid != 0 && st.st_uid != uid) ||
 420             (st.st_mode & 022) != 0) {
 421                 snprintf(err, errlen, "bad ownership or modes for file %s",
 422                     buf);
 423                 return -1;
 424         }
 425
 426         /* for each component of the canonical path, walking upwards */
 427         for (;;) {
 428                 if ((cp = dirname(buf)) == NULL) {
 429                         snprintf(err, errlen, "dirname() failed");
 430                         return -1;
 431                 }
 432                 strlcpy(buf, cp, sizeof(buf));
 433
 434                 debug3("secure_filename: checking '%s'", buf);
 435                 if (stat(buf, &st) < 0 ||
 436                     (st.st_uid != 0 && st.st_uid != uid) ||
 437                     (st.st_mode & 022) != 0) {
 438                         snprintf(err, errlen,
 439                             "bad ownership or modes for directory %s", buf);
 440                         return -1;
 441                 }
 442
 443                 /* If are passed the homedir then we can stop */
 444                 if (comparehome && strcmp(homedir, buf) == 0) {
 445                         debug3("secure_filename: terminating check at '%s'",
 446                             buf);
 447                         break;
 448                 }
 449                 /*
 450                  * dirname should always complete with a "/" path,
 451                  * but we can be paranoid and check for "." too
 452                  */
 453                 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0))
 454                         break;
 455         }
 456         return 0;
 457 }
 458
 459 struct passwd *
 460 getpwnamallow(const char *user)
 461 {
 462 #ifdef HAVE_LOGIN_CAP
 463         extern login_cap_t *lc;
 464 #ifdef BSD_AUTH
 465         auth_session_t *as;
 466 #endif
 467 #endif
 468         struct passwd *pw;
 469
 470         parse_server_match_config(&options, user,
 471             get_canonical_hostname(options.use_dns), get_remote_ipaddr());
 472
 473         pw = getpwnam(user);
 474         if (pw == NULL) {
 475                 logit("Invalid user %.100s from %.100s",
 476                     user, get_remote_ipaddr());
 477 #ifdef CUSTOM_FAILED_LOGIN
 478                 record_failed_login(user,
 479                     get_canonical_hostname(options.use_dns), "ssh");
 480 #endif
 481 #ifdef SSH_AUDIT_EVENTS
 482                 audit_event(SSH_INVALID_USER);
 483 #endif /* SSH_AUDIT_EVENTS */
 484                 return (NULL);
 485         }
 486         if (!allowed_user(pw))
 487                 return (NULL);
 488 #ifdef HAVE_LOGIN_CAP
 489         if ((lc = login_getclass(pw->pw_class)) == NULL) {
 490                 debug("unable to get login class: %s", user);
 491                 return (NULL);
 492         }
 493 #ifdef BSD_AUTH
 494         if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
 495             auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
 496                 debug("Approval failure for %s", user);
 497                 pw = NULL;
 498         }
 499         if (as != NULL)
 500                 auth_close(as);
 501 #endif
 502 #endif
 503         if (pw != NULL)
 504                 return (pwcopy(pw));
 505         return (NULL);
 506 }
 507
 508 void
 509 auth_debug_add(const char *fmt,...)
 510 {
 511         char buf[1024];
 512         va_list args;
 513
 514         if (!auth_debug_init)
 515                 return;
 516
 517         va_start(args, fmt);
 518         vsnprintf(buf, sizeof(buf), fmt, args);
 519         va_end(args);
 520         buffer_put_cstring(&auth_debug, buf);
 521 }
 522
 523 void
 524 auth_debug_send(void)
 525 {
 526         char *msg;
 527
 528         if (!auth_debug_init)
 529                 return;
 530         while (buffer_len(&auth_debug)) {
 531                 msg = buffer_get_string(&auth_debug, NULL);
 532                 packet_send_debug("%s", msg);
 533                 xfree(msg);
 534         }
 535 }
 536
 537 void
 538 auth_debug_reset(void)
 539 {
 540         if (auth_debug_init)
 541                 buffer_clear(&auth_debug);
 542         else {
 543                 buffer_init(&auth_debug);
 544                 auth_debug_init = 1;
 545         }
 546 }
 547
 548 struct passwd *
 549 fakepw(void)
 550 {
 551         static struct passwd fake;
 552
 553         memset(&fake, 0, sizeof(fake));
 554         fake.pw_name = "NOUSER";
 555         fake.pw_passwd =
 556             "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK";
 557         fake.pw_gecos = "NOUSER";
 558         fake.pw_uid = (uid_t)-1;
 559         fake.pw_gid = (gid_t)-1;
 560 #ifdef HAVE_PW_CLASS_IN_PASSWD
 561         fake.pw_class = "";
 562 #endif
 563         fake.pw_dir = "/nonexist";
 564         fake.pw_shell = "/nonexist";
 565
 566         return (&fake);
 567 }