auth.c

   1 /* $OpenBSD: auth.c,v 1.75 2006/08/03 03:34:41 deraadt 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
  77 /* Debugging messages */
  78 Buffer auth_debug;
  79 int auth_debug_init;
  80
  81 /*
  82  * Check if the user is allowed to log in via ssh. If user is listed
  83  * in DenyUsers or one of user's groups is listed in DenyGroups, false
  84  * will be returned. If AllowUsers isn't empty and user isn't listed
  85  * there, or if AllowGroups isn't empty and one of user's groups isn't
  86  * listed there, false will be returned.
  87  * If the user's shell is not executable, false will be returned.
  88  * Otherwise true is returned.
  89  */
  90 int
  91 allowed_user(struct passwd * pw)
  92 {
  93         struct stat st;
  94         const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL;
  95         char *shell;
  96         u_int i;
  97 #ifdef USE_SHADOW
  98         struct spwd *spw = NULL;
  99 #endif
 100
 101         /* Shouldn't be called if pw is NULL, but better safe than sorry... */
 102         if (!pw || !pw->pw_name)
 103                 return 0;
 104
 105 #ifdef USE_SHADOW
 106         if (!options.use_pam)
 107                 spw = getspnam(pw->pw_name);
 108 #ifdef HAS_SHADOW_EXPIRE
 109         if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw))
 110                 return 0;
 111 #endif /* HAS_SHADOW_EXPIRE */
 112 #endif /* USE_SHADOW */
 113
 114         /* grab passwd field for locked account check */
 115 #ifdef USE_SHADOW
 116         if (spw != NULL)
 117 #if defined(HAVE_LIBIAF)  &&  !defined(BROKEN_LIBIAF)
 118                 passwd = get_iaf_password(pw);
 119 #else
 120                 passwd = spw->sp_pwdp;
 121 #endif /* HAVE_LIBIAF  && !BROKEN_LIBIAF */
 122 #else
 123         passwd = pw->pw_passwd;
 124 #endif
 125
 126         /* check for locked account */
 127         if (!options.use_pam && passwd && *passwd) {
 128                 int locked = 0;
 129
 130 #ifdef LOCKED_PASSWD_STRING
 131                 if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0)
 132                          locked = 1;
 133 #endif
 134 #ifdef LOCKED_PASSWD_PREFIX
 135                 if (strncmp(passwd, LOCKED_PASSWD_PREFIX,
 136                     strlen(LOCKED_PASSWD_PREFIX)) == 0)
 137                          locked = 1;
 138 #endif
 139 #ifdef LOCKED_PASSWD_SUBSTR
 140                 if (strstr(passwd, LOCKED_PASSWD_SUBSTR))
 141                         locked = 1;
 142 #endif
 143 #if defined(HAVE_LIBIAF)  &&  !defined(BROKEN_LIBIAF)
 144                 free(passwd);
 145 #endif /* HAVE_LIBIAF  && !BROKEN_LIBIAF */
 146                 if (locked) {
 147                         logit("User %.100s not allowed because account is locked",
 148                             pw->pw_name);
 149                         return 0;
 150                 }
 151         }
 152
 153         /*
 154          * Get the shell from the password data.  An empty shell field is
 155          * legal, and means /bin/sh.
 156          */
 157         shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;
 158
 159         /* deny if shell does not exists or is not executable */
 160         if (stat(shell, &st) != 0) {
 161                 logit("User %.100s not allowed because shell %.100s does not exist",
 162                     pw->pw_name, shell);
 163                 return 0;
 164         }
 165         if (S_ISREG(st.st_mode) == 0 ||
 166             (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
 167                 logit("User %.100s not allowed because shell %.100s is not executable",
 168                     pw->pw_name, shell);
 169                 return 0;
 170         }
 171
 172         if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
 173             options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 174                 hostname = get_canonical_hostname(options.use_dns);
 175                 ipaddr = get_remote_ipaddr();
 176         }
 177
 178         /* Return false if user is listed in DenyUsers */
 179         if (options.num_deny_users > 0) {
 180                 for (i = 0; i < options.num_deny_users; i++)
 181                         if (match_user(pw->pw_name, hostname, ipaddr,
 182                             options.deny_users[i])) {
 183                                 logit("User %.100s from %.100s not allowed "
 184                                     "because listed in DenyUsers",
 185                                     pw->pw_name, hostname);
 186                                 return 0;
 187                         }
 188         }
 189         /* Return false if AllowUsers isn't empty and user isn't listed there */
 190         if (options.num_allow_users > 0) {
 191                 for (i = 0; i < options.num_allow_users; i++)
 192                         if (match_user(pw->pw_name, hostname, ipaddr,
 193                             options.allow_users[i]))
 194                                 break;
 195                 /* i < options.num_allow_users iff we break for loop */
 196                 if (i >= options.num_allow_users) {
 197                         logit("User %.100s from %.100s not allowed because "
 198                             "not listed in AllowUsers", pw->pw_name, hostname);
 199                         return 0;
 200                 }
 201         }
 202         if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 203                 /* Get the user's group access list (primary and supplementary) */
 204                 if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
 205                         logit("User %.100s from %.100s not allowed because "
 206                             "not in any group", pw->pw_name, hostname);
 207                         return 0;
 208                 }
 209
 210                 /* Return false if one of user's groups is listed in DenyGroups */
 211                 if (options.num_deny_groups > 0)
 212                         if (ga_match(options.deny_groups,
 213                             options.num_deny_groups)) {
 214                                 ga_free();
 215                                 logit("User %.100s from %.100s not allowed "
 216                                     "because a group is listed in DenyGroups",
 217                                     pw->pw_name, hostname);
 218                                 return 0;
 219                         }
 220                 /*
 221                  * Return false if AllowGroups isn't empty and one of user's groups
 222                  * isn't listed there
 223                  */
 224                 if (options.num_allow_groups > 0)
 225                         if (!ga_match(options.allow_groups,
 226                             options.num_allow_groups)) {
 227                                 ga_free();
 228                                 logit("User %.100s from %.100s not allowed "
 229                                     "because none of user's groups are listed "
 230                                     "in AllowGroups", pw->pw_name, hostname);
 231                                 return 0;
 232                         }
 233                 ga_free();
 234         }
 235
 236 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
 237         if (!sys_auth_allowed_user(pw, &loginmsg))
 238                 return 0;
 239 #endif
 240
 241         /* We found no reason not to let this user try to log on... */
 242         return 1;
 243 }
 244
 245 void
 246 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info)
 247 {
 248         void (*authlog) (const char *fmt,...) = verbose;
 249         char *authmsg;
 250
 251         if (use_privsep && !mm_is_monitor() && !authctxt->postponed)
 252                 return;
 253
 254         /* Raise logging level */
 255         if (authenticated == 1 ||
 256             !authctxt->valid ||
 257             authctxt->failures >= options.max_authtries / 2 ||
 258             strcmp(method, "password") == 0)
 259                 authlog = logit;
 260
 261         if (authctxt->postponed)
 262                 authmsg = "Postponed";
 263         else
 264                 authmsg = authenticated ? "Accepted" : "Failed";
 265
 266         authlog("%s %s for %s%.100s from %.200s port %d%s",
 267             authmsg,
 268             method,
 269             authctxt->valid ? "" : "invalid user ",
 270             authctxt->user,
 271             get_remote_ipaddr(),
 272             get_remote_port(),
 273             info);
 274
 275 #ifdef CUSTOM_FAILED_LOGIN
 276         if (authenticated == 0 && !authctxt->postponed &&
 277             (strcmp(method, "password") == 0 ||
 278             strncmp(method, "keyboard-interactive", 20) == 0 ||
 279             strcmp(method, "challenge-response") == 0))
 280                 record_failed_login(authctxt->user,
 281                     get_canonical_hostname(options.use_dns), "ssh");
 282 #endif
 283 #ifdef SSH_AUDIT_EVENTS
 284         if (authenticated == 0 && !authctxt->postponed)
 285                 audit_event(audit_classify_auth(method));
 286 #endif
 287 }
 288
 289 /*
 290  * Check whether root logins are disallowed.
 291  */
 292 int
 293 auth_root_allowed(char *method)
 294 {
 295         switch (options.permit_root_login) {
 296         case PERMIT_YES:
 297                 return 1;
 298         case PERMIT_NO_PASSWD:
 299                 if (strcmp(method, "password") != 0)
 300                         return 1;
 301                 break;
 302         case PERMIT_FORCED_ONLY:
 303                 if (forced_command) {
 304                         logit("Root login accepted for forced command.");
 305                         return 1;
 306                 }
 307                 break;
 308         }
 309         logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr());
 310         return 0;
 311 }
 312
 313
 314 /*
 315  * Given a template and a passwd structure, build a filename
 316  * by substituting % tokenised options. Currently, %% becomes '%',
 317  * %h becomes the home directory and %u the username.
 318  *
 319  * This returns a buffer allocated by xmalloc.
 320  */
 321 static char *
 322 expand_authorized_keys(const char *filename, struct passwd *pw)
 323 {
 324         char *file, ret[MAXPATHLEN];
 325         int i;
 326
 327         file = percent_expand(filename, "h", pw->pw_dir,
 328             "u", pw->pw_name, (char *)NULL);
 329
 330         /*
 331          * Ensure that filename starts anchored. If not, be backward
 332          * compatible and prepend the '%h/'
 333          */
 334         if (*file == '/')
 335                 return (file);
 336
 337         i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file);
 338         if (i < 0 || (size_t)i >= sizeof(ret))
 339                 fatal("expand_authorized_keys: path too long");
 340         xfree(file);
 341         return (xstrdup(ret));
 342 }
 343
 344 char *
 345 authorized_keys_file(struct passwd *pw)
 346 {
 347         return expand_authorized_keys(options.authorized_keys_file, pw);
 348 }
 349
 350 char *
 351 authorized_keys_file2(struct passwd *pw)
 352 {
 353         return expand_authorized_keys(options.authorized_keys_file2, pw);
 354 }
 355
 356 /* return ok if key exists in sysfile or userfile */
 357 HostStatus
 358 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host,
 359     const char *sysfile, const char *userfile)
 360 {
 361         Key *found;
 362         char *user_hostfile;
 363         struct stat st;
 364         HostStatus host_status;
 365
 366         /* Check if we know the host and its host key. */
 367         found = key_new(key->type);
 368         host_status = check_host_in_hostfile(sysfile, host, key, found, NULL);
 369
 370         if (host_status != HOST_OK && userfile != NULL) {
 371                 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
 372                 if (options.strict_modes &&
 373                     (stat(user_hostfile, &st) == 0) &&
 374                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 375                     (st.st_mode & 022) != 0)) {
 376                         logit("Authentication refused for %.100s: "
 377                             "bad owner or modes for %.200s",
 378                             pw->pw_name, user_hostfile);
 379                 } else {
 380                         temporarily_use_uid(pw);
 381                         host_status = check_host_in_hostfile(user_hostfile,
 382                             host, key, found, NULL);
 383                         restore_uid();
 384                 }
 385                 xfree(user_hostfile);
 386         }
 387         key_free(found);
 388
 389         debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ?
 390             "ok" : "not found", host);
 391         return host_status;
 392 }
 393
 394
 395 /*
 396  * Check a given file for security. This is defined as all components
 397  * of the path to the file must be owned by either the owner of
 398  * of the file or root and no directories must be group or world writable.
 399  *
 400  * XXX Should any specific check be done for sym links ?
 401  *
 402  * Takes an open file descriptor, the file name, a uid and and
 403  * error buffer plus max size as arguments.
 404  *
 405  * Returns 0 on success and -1 on failure
 406  */
 407 int
 408 secure_filename(FILE *f, const char *file, struct passwd *pw,
 409     char *err, size_t errlen)
 410 {
 411         uid_t uid = pw->pw_uid;
 412         char buf[MAXPATHLEN], homedir[MAXPATHLEN];
 413         char *cp;
 414         int comparehome = 0;
 415         struct stat st;
 416
 417         if (realpath(file, buf) == NULL) {
 418                 snprintf(err, errlen, "realpath %s failed: %s", file,
 419                     strerror(errno));
 420                 return -1;
 421         }
 422         if (realpath(pw->pw_dir, homedir) != NULL)
 423                 comparehome = 1;
 424
 425         /* check the open file to avoid races */
 426         if (fstat(fileno(f), &st) < 0 ||
 427             (st.st_uid != 0 && st.st_uid != uid) ||
 428             (st.st_mode & 022) != 0) {
 429                 snprintf(err, errlen, "bad ownership or modes for file %s",
 430                     buf);
 431                 return -1;
 432         }
 433
 434         /* for each component of the canonical path, walking upwards */
 435         for (;;) {
 436                 if ((cp = dirname(buf)) == NULL) {
 437                         snprintf(err, errlen, "dirname() failed");
 438                         return -1;
 439                 }
 440                 strlcpy(buf, cp, sizeof(buf));
 441
 442                 debug3("secure_filename: checking '%s'", buf);
 443                 if (stat(buf, &st) < 0 ||
 444                     (st.st_uid != 0 && st.st_uid != uid) ||
 445                     (st.st_mode & 022) != 0) {
 446                         snprintf(err, errlen,
 447                             "bad ownership or modes for directory %s", buf);
 448                         return -1;
 449                 }
 450
 451                 /* If are passed the homedir then we can stop */
 452                 if (comparehome && strcmp(homedir, buf) == 0) {
 453                         debug3("secure_filename: terminating check at '%s'",
 454                             buf);
 455                         break;
 456                 }
 457                 /*
 458                  * dirname should always complete with a "/" path,
 459                  * but we can be paranoid and check for "." too
 460                  */
 461                 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0))
 462                         break;
 463         }
 464         return 0;
 465 }
 466
 467 struct passwd *
 468 getpwnamallow(const char *user)
 469 {
 470 #ifdef HAVE_LOGIN_CAP
 471         extern login_cap_t *lc;
 472 #ifdef BSD_AUTH
 473         auth_session_t *as;
 474 #endif
 475 #endif
 476         struct passwd *pw;
 477
 478         parse_server_match_config(&options, user,
 479             get_canonical_hostname(options.use_dns), get_remote_ipaddr());
 480
 481         pw = getpwnam(user);
 482         if (pw == NULL) {
 483                 logit("Invalid user %.100s from %.100s",
 484                     user, get_remote_ipaddr());
 485 #ifdef CUSTOM_FAILED_LOGIN
 486                 record_failed_login(user,
 487                     get_canonical_hostname(options.use_dns), "ssh");
 488 #endif
 489 #ifdef SSH_AUDIT_EVENTS
 490                 audit_event(SSH_INVALID_USER);
 491 #endif /* SSH_AUDIT_EVENTS */
 492                 return (NULL);
 493         }
 494         if (!allowed_user(pw))
 495                 return (NULL);
 496 #ifdef HAVE_LOGIN_CAP
 497         if ((lc = login_getclass(pw->pw_class)) == NULL) {
 498                 debug("unable to get login class: %s", user);
 499                 return (NULL);
 500         }
 501 #ifdef BSD_AUTH
 502         if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
 503             auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
 504                 debug("Approval failure for %s", user);
 505                 pw = NULL;
 506         }
 507         if (as != NULL)
 508                 auth_close(as);
 509 #endif
 510 #endif
 511         if (pw != NULL)
 512                 return (pwcopy(pw));
 513         return (NULL);
 514 }
 515
 516 void
 517 auth_debug_add(const char *fmt,...)
 518 {
 519         char buf[1024];
 520         va_list args;
 521
 522         if (!auth_debug_init)
 523                 return;
 524
 525         va_start(args, fmt);
 526         vsnprintf(buf, sizeof(buf), fmt, args);
 527         va_end(args);
 528         buffer_put_cstring(&auth_debug, buf);
 529 }
 530
 531 void
 532 auth_debug_send(void)
 533 {
 534         char *msg;
 535
 536         if (!auth_debug_init)
 537                 return;
 538         while (buffer_len(&auth_debug)) {
 539                 msg = buffer_get_string(&auth_debug, NULL);
 540                 packet_send_debug("%s", msg);
 541                 xfree(msg);
 542         }
 543 }
 544
 545 void
 546 auth_debug_reset(void)
 547 {
 548         if (auth_debug_init)
 549                 buffer_clear(&auth_debug);
 550         else {
 551                 buffer_init(&auth_debug);
 552                 auth_debug_init = 1;
 553         }
 554 }
 555
 556 struct passwd *
 557 fakepw(void)
 558 {
 559         static struct passwd fake;
 560
 561         memset(&fake, 0, sizeof(fake));
 562         fake.pw_name = "NOUSER";
 563         fake.pw_passwd =
 564             "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK";
 565         fake.pw_gecos = "NOUSER";
 566         fake.pw_uid = (uid_t)-1;
 567         fake.pw_gid = (gid_t)-1;
 568 #ifdef HAVE_PW_CLASS_IN_PASSWD
 569         fake.pw_class = "";
 570 #endif
 571         fake.pw_dir = "/nonexist";
 572         fake.pw_shell = "/nonexist";
 573
 574         return (&fake);
 575 }