openvpn/plugin/auth-pam/auth-pam.c

   1 /*
   2  *  OpenVPN -- An application to securely tunnel IP networks
   3  *             over a single TCP/UDP port, with support for SSL/TLS-based
   4  *             session authentication and key exchange,
   5  *             packet encryption, packet authentication, and
   6  *             packet compression.
   7  *
   8  *  Copyright (C) 2002-2005 OpenVPN Solutions LLC <info@openvpn.net>
   9  *
  10  *  This program is free software; you can redistribute it and/or modify
  11  *  it under the terms of the GNU General Public License version 2
  12  *  as published by the Free Software Foundation.
  13  *
  14  *  This program is distributed in the hope that it will be useful,
  15  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  *  GNU General Public License for more details.
  18  *
  19  *  You should have received a copy of the GNU General Public License
  20  *  along with this program (see the file COPYING included with this
  21  *  distribution); if not, write to the Free Software Foundation, Inc.,
  22  *  59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  23  */
  24
  25 /*
  26  * OpenVPN plugin module to do PAM authentication using a split
  27  * privilege model.
  28  */
  29
  30 #if DLOPEN_PAM
  31 #include <dlfcn.h>
  32 #include "pamdl.h"
  33 #else
  34 #include <security/pam_appl.h>
  35 #endif
  36
  37 #include <stdio.h>
  38 #include <string.h>
  39 #include <ctype.h>
  40 #include <unistd.h>
  41 #include <stdlib.h>
  42 #include <sys/types.h>
  43 #include <sys/socket.h>
  44 #include <sys/wait.h>
  45 #include <fcntl.h>
  46 #include <signal.h>
  47 #include <syslog.h>
  48
  49 #include "openvpn-plugin.h"
  50
  51 #define DEBUG(verb) ((verb) >= 7)
  52
  53 /* Command codes for foreground -> background communication */
  54 #define COMMAND_VERIFY 0
  55 #define COMMAND_EXIT   1
  56
  57 /* Response codes for background -> foreground communication */
  58 #define RESPONSE_INIT_SUCCEEDED   10
  59 #define RESPONSE_INIT_FAILED      11
  60 #define RESPONSE_VERIFY_SUCCEEDED 12
  61 #define RESPONSE_VERIFY_FAILED    13
  62
  63 /*
  64  * Plugin state, used by foreground
  65  */
  66 struct auth_pam_context
  67 {
  68   /* Foreground's socket to background process */
  69   int foreground_fd;
  70
  71   /* Process ID of background process */
  72   pid_t background_pid;
  73
  74   /* Verbosity level of OpenVPN */
  75   int verb;
  76 };
  77
  78 /*
  79  * Name/Value pairs for conversation function.
  80  * Special Values:
  81  *
  82  *  "USERNAME" -- substitute client-supplied username
  83  *  "PASSWORD" -- substitute client-specified password
  84  */
  85
  86 #define N_NAME_VALUE 16
  87
  88 struct name_value {
  89   const char *name;
  90   const char *value;
  91 };
  92
  93 struct name_value_list {
  94   int len;
  95   struct name_value data[N_NAME_VALUE];
  96 };
  97
  98 /*
  99  * Used to pass the username/password
 100  * to the PAM conversation function.
 101  */
 102 struct user_pass {
 103   int verb;
 104
 105   char username[128];
 106   char password[128];
 107
 108   const struct name_value_list *name_value_list;
 109 };
 110
 111 /* Background process function */
 112 static void pam_server (int fd, const char *service, int verb, const struct name_value_list *name_value_list);
 113
 114 /*
 115  * Given an environmental variable name, search
 116  * the envp array for its value, returning it
 117  * if found or NULL otherwise.
 118  */
 119 static const char *
 120 get_env (const char *name, const char *envp[])
 121 {
 122   if (envp)
 123     {
 124       int i;
 125       const int namelen = strlen (name);
 126       for (i = 0; envp[i]; ++i)
 127         {
 128           if (!strncmp (envp[i], name, namelen))
 129             {
 130               const char *cp = envp[i] + namelen;
 131               if (*cp == '=')
 132                 return cp + 1;
 133             }
 134         }
 135     }
 136   return NULL;
 137 }
 138
 139 /*
 140  * Return the length of a string array
 141  */
 142 static int
 143 string_array_len (const char *array[])
 144 {
 145   int i = 0;
 146   if (array)
 147     {
 148       while (array[i])
 149         ++i;
 150     }
 151   return i;
 152 }
 153
 154 /*
 155  * Socket read/write functions.
 156  */
 157
 158 static int
 159 recv_control (int fd)
 160 {
 161   unsigned char c;
 162   const ssize_t size = read (fd, &c, sizeof (c));
 163   if (size == sizeof (c))
 164     return c;
 165   else
 166     {
 167       /*fprintf (stderr, "AUTH-PAM: DEBUG recv_control.read=%d\n", (int)size);*/
 168       return -1;
 169     }
 170 }
 171
 172 static int
 173 send_control (int fd, int code)
 174 {
 175   unsigned char c = (unsigned char) code;
 176   const ssize_t size = write (fd, &c, sizeof (c));
 177   if (size == sizeof (c))
 178     return (int) size;
 179   else
 180     return -1;
 181 }
 182
 183 static int
 184 recv_string (int fd, char *buffer, int len)
 185 {
 186   if (len > 0)
 187     {
 188       ssize_t size;
 189       memset (buffer, 0, len);
 190       size = read (fd, buffer, len);
 191       buffer[len-1] = 0;
 192       if (size >= 1)
 193         return (int)size;
 194     }
 195   return -1;
 196 }
 197
 198 static int
 199 send_string (int fd, const char *string)
 200 {
 201   const int len = strlen (string) + 1;
 202   const ssize_t size = write (fd, string, len);
 203   if (size == len)
 204     return (int) size;
 205   else
 206     return -1;
 207 }
 208
 209 /*
 210  * Daemonize if "daemon" env var is true.
 211  * Preserve stderr across daemonization if
 212  * "daemon_log_redirect" env var is true.
 213  */
 214 static void
 215 daemonize (const char *envp[])
 216 {
 217   const char *daemon_string = get_env ("daemon", envp);
 218   if (daemon_string && daemon_string[0] == '1')
 219     {
 220       const char *log_redirect = get_env ("daemon_log_redirect", envp);
 221       int fd = -1;
 222       if (log_redirect && log_redirect[0] == '1')
 223         fd = dup (2);
 224       if (daemon (0, 0) < 0)
 225         {
 226           fprintf (stderr, "AUTH-PAM: daemonization failed\n");
 227         }
 228       else if (fd >= 3)
 229         {
 230           dup2 (fd, 2);
 231           close (fd);
 232         }
 233     }
 234 }
 235
 236 /*
 237  * Close most of parent's fds.
 238  * Keep stdin/stdout/stderr, plus one
 239  * other fd which is presumed to be
 240  * our pipe back to parent.
 241  * Admittedly, a bit of a kludge,
 242  * but posix doesn't give us a kind
 243  * of FD_CLOEXEC which will stop
 244  * fds from crossing a fork().
 245  */
 246 static void
 247 close_fds_except (int keep)
 248 {
 249   int i;
 250   closelog ();
 251   for (i = 3; i <= 100; ++i)
 252     {
 253       if (i != keep)
 254         close (i);
 255     }
 256 }
 257
 258 /*
 259  * Usually we ignore signals, because our parent will
 260  * deal with them.
 261  */
 262 static void
 263 set_signals (void)
 264 {
 265   signal (SIGTERM, SIG_DFL);
 266
 267   signal (SIGINT, SIG_IGN);
 268   signal (SIGHUP, SIG_IGN);
 269   signal (SIGUSR1, SIG_IGN);
 270   signal (SIGUSR2, SIG_IGN);
 271   signal (SIGPIPE, SIG_IGN);
 272 }
 273
 274 /*
 275  * Return 1 if query matches match.
 276  */
 277 static int
 278 name_value_match (const char *query, const char *match)
 279 {
 280   while (!isalnum (*query))
 281     {
 282       if (*query == '\0')
 283         return 0;
 284       ++query;
 285     }
 286   return strncasecmp (match, query, strlen (match)) == 0;
 287 }
 288
 289 OPENVPN_EXPORT openvpn_plugin_handle_t
 290 openvpn_plugin_open_v1 (unsigned int *type_mask, const char *argv[], const char *envp[])
 291 {
 292   pid_t pid;
 293   int fd[2];
 294
 295   struct auth_pam_context *context;
 296   struct name_value_list name_value_list;
 297
 298   const int base_parms = 2;
 299
 300   /*
 301    * Allocate our context
 302    */
 303   context = (struct auth_pam_context *) calloc (1, sizeof (struct auth_pam_context));
 304   context->foreground_fd = -1;
 305
 306   /*
 307    * Intercept the --auth-user-pass-verify callback.
 308    */
 309   *type_mask = OPENVPN_PLUGIN_MASK (OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY);
 310
 311   /*
 312    * Make sure we have two string arguments: the first is the .so name,
 313    * the second is the PAM service type.
 314    */
 315   if (string_array_len (argv) < base_parms)
 316     {
 317       fprintf (stderr, "AUTH-PAM: need PAM service parameter\n");
 318       goto error;
 319     }
 320
 321   /*
 322    * See if we have optional name/value pairs to match against
 323    * PAM module queried fields in the conversation function.
 324    */
 325   name_value_list.len = 0;
 326   if (string_array_len (argv) > base_parms)
 327     {
 328       const int nv_len = string_array_len (argv) - base_parms;
 329       int i;
 330
 331       if ((nv_len & 1) == 1 || (nv_len / 2) > N_NAME_VALUE)
 332         {
 333           fprintf (stderr, "AUTH-PAM: bad name/value list length\n");
 334           goto error;
 335         }
 336
 337       name_value_list.len = nv_len / 2;
 338       for (i = 0; i < name_value_list.len; ++i)
 339         {
 340           const int base = base_parms + i * 2;
 341           name_value_list.data[i].name = argv[base];
 342           name_value_list.data[i].value = argv[base+1];
 343         }
 344     }
 345
 346   /*
 347    * Get verbosity level from environment
 348    */
 349   {
 350     const char *verb_string = get_env ("verb", envp);
 351     if (verb_string)
 352       context->verb = atoi (verb_string);
 353   }
 354
 355   /*
 356    * Make a socket for foreground and background processes
 357    * to communicate.
 358    */
 359   if (socketpair (PF_UNIX, SOCK_DGRAM, 0, fd) == -1)
 360     {
 361       fprintf (stderr, "AUTH-PAM: socketpair call failed\n");
 362       goto error;
 363     }
 364
 365   /*
 366    * Fork off the privileged process.  It will remain privileged
 367    * even after the foreground process drops its privileges.
 368    */
 369   pid = fork ();
 370
 371   if (pid)
 372     {
 373       int status;
 374
 375       /*
 376        * Foreground Process
 377        */
 378
 379       context->background_pid = pid;
 380
 381       /* close our copy of child's socket */
 382       close (fd[1]);
 383
 384       /* don't let future subprocesses inherit child socket */
 385       if (fcntl (fd[0], F_SETFD, FD_CLOEXEC) < 0)
 386         fprintf (stderr, "AUTH-PAM: Set FD_CLOEXEC flag on socket file descriptor failed\n");
 387
 388       /* wait for background child process to initialize */
 389       status = recv_control (fd[0]);
 390       if (status == RESPONSE_INIT_SUCCEEDED)
 391         {
 392           context->foreground_fd = fd[0];
 393           return (openvpn_plugin_handle_t) context;
 394         }
 395     }
 396   else
 397     {
 398       /*
 399        * Background Process
 400        */
 401
 402       /* close all parent fds except our socket back to parent */
 403       close_fds_except (fd[1]);
 404
 405       /* Ignore most signals (the parent will receive them) */
 406       set_signals ();
 407
 408       /* Daemonize if --daemon option is set. */
 409       daemonize (envp);
 410
 411       /* execute the event loop */
 412       pam_server (fd[1], argv[1], context->verb, &name_value_list);
 413
 414       close (fd[1]);
 415
 416       exit (0);
 417       return 0; /* NOTREACHED */
 418     }
 419
 420  error:
 421   if (context)
 422     free (context);
 423   return NULL;
 424 }
 425
 426 OPENVPN_EXPORT int
 427 openvpn_plugin_func_v1 (openvpn_plugin_handle_t handle, const int type, const char *argv[], const char *envp[])
 428 {
 429   struct auth_pam_context *context = (struct auth_pam_context *) handle;
 430
 431   if (type == OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY && context->foreground_fd >= 0)
 432     {
 433       /* get username/password from envp string array */
 434       const char *username = get_env ("username", envp);
 435       const char *password = get_env ("password", envp);
 436
 437       if (username && strlen (username) > 0 && password)
 438         {
 439           if (send_control (context->foreground_fd, COMMAND_VERIFY) == -1
 440               || send_string (context->foreground_fd, username) == -1
 441               || send_string (context->foreground_fd, password) == -1)
 442             {
 443               fprintf (stderr, "AUTH-PAM: Error sending auth info to background process\n");
 444             }
 445           else
 446             {
 447               const int status = recv_control (context->foreground_fd);
 448               if (status == RESPONSE_VERIFY_SUCCEEDED)
 449                 return OPENVPN_PLUGIN_FUNC_SUCCESS;
 450               if (status == -1)
 451                 fprintf (stderr, "AUTH-PAM: Error receiving auth confirmation from background process\n");
 452             }
 453         }
 454     }
 455   return OPENVPN_PLUGIN_FUNC_ERROR;
 456 }
 457
 458 OPENVPN_EXPORT void
 459 openvpn_plugin_close_v1 (openvpn_plugin_handle_t handle)
 460 {
 461   struct auth_pam_context *context = (struct auth_pam_context *) handle;
 462
 463   if (DEBUG (context->verb))
 464     fprintf (stderr, "AUTH-PAM: close\n");
 465
 466   if (context->foreground_fd >= 0)
 467     {
 468       /* tell background process to exit */
 469       if (send_control (context->foreground_fd, COMMAND_EXIT) == -1)
 470         fprintf (stderr, "AUTH-PAM: Error signaling background process to exit\n");
 471
 472       /* wait for background process to exit */
 473       if (context->background_pid > 0)
 474         waitpid (context->background_pid, NULL, 0);
 475
 476       close (context->foreground_fd);
 477       context->foreground_fd = -1;
 478     }
 479
 480   free (context);
 481 }
 482
 483 OPENVPN_EXPORT void
 484 openvpn_plugin_abort_v1 (openvpn_plugin_handle_t handle)
 485 {
 486   struct auth_pam_context *context = (struct auth_pam_context *) handle;
 487
 488   /* tell background process to exit */
 489   if (context->foreground_fd >= 0)
 490     {
 491       send_control (context->foreground_fd, COMMAND_EXIT);
 492       close (context->foreground_fd);
 493       context->foreground_fd = -1;
 494     }
 495 }
 496
 497 /*
 498  * PAM conversation function
 499  */
 500 static int
 501 my_conv (int n, const struct pam_message **msg_array,
 502          struct pam_response **response_array, void *appdata_ptr)
 503 {
 504   const struct user_pass *up = ( const struct user_pass *) appdata_ptr;
 505   struct pam_response *aresp;
 506   int i;
 507   int ret = PAM_SUCCESS;
 508
 509   *response_array = NULL;
 510
 511   if (n <= 0 || n > PAM_MAX_NUM_MSG)
 512     return (PAM_CONV_ERR);
 513   if ((aresp = calloc (n, sizeof *aresp)) == NULL)
 514     return (PAM_BUF_ERR);
 515
 516   /* loop through each PAM-module query */
 517   for (i = 0; i < n; ++i)
 518     {
 519       const struct pam_message *msg = msg_array[i];
 520       aresp[i].resp_retcode = 0;
 521       aresp[i].resp = NULL;
 522
 523       if (DEBUG (up->verb))
 524         {
 525           fprintf (stderr, "AUTH-PAM: BACKGROUND: my_conv[%d] query='%s' style=%d\n",
 526                    i,
 527                    msg->msg ? msg->msg : "NULL",
 528                    msg->msg_style);
 529         }
 530
 531       if (up->name_value_list && up->name_value_list->len > 0)
 532         {
 533           /* use name/value list match method */
 534           const struct name_value_list *list = up->name_value_list;
 535           int j;
 536
 537           /* loop through name/value pairs */
 538           for (j = 0; j < list->len; ++j)
 539             {
 540               const char *match_name = list->data[j].name;
 541               const char *match_value = list->data[j].value;
 542
 543               if (name_value_match (msg->msg, match_name))
 544                 {
 545                   /* found name/value match */
 546                   const char *return_value = NULL;
 547
 548                   if (DEBUG (up->verb))
 549                     fprintf (stderr, "AUTH-PAM: BACKGROUND: name match found, query/match-string ['%s', '%s'] = '%s'\n",
 550                              msg->msg,
 551                              match_name,
 552                              match_value);
 553
 554                   if (!strcmp (match_value, "USERNAME"))
 555                     return_value = up->username;
 556                   else if (!strcmp (match_value, "PASSWORD"))
 557                     return_value = up->password;
 558                   else
 559                     return_value = match_value;
 560
 561                   aresp[i].resp = strdup (return_value);
 562                   if (aresp[i].resp == NULL)
 563                     ret = PAM_CONV_ERR;
 564                   break;
 565                 }
 566             }
 567
 568           if (j == list->len)
 569             ret = PAM_CONV_ERR;
 570         }
 571       else
 572         {
 573           /* use PAM_PROMPT_ECHO_x hints */
 574           switch (msg->msg_style)
 575             {
 576             case PAM_PROMPT_ECHO_OFF:
 577               aresp[i].resp = strdup (up->password);
 578               if (aresp[i].resp == NULL)
 579                 ret = PAM_CONV_ERR;
 580               break;
 581
 582             case PAM_PROMPT_ECHO_ON:
 583               aresp[i].resp = strdup (up->username);
 584               if (aresp[i].resp == NULL)
 585                 ret = PAM_CONV_ERR;
 586               break;
 587
 588             case PAM_ERROR_MSG:
 589             case PAM_TEXT_INFO:
 590               break;
 591
 592             default:
 593               ret = PAM_CONV_ERR;
 594               break;
 595             }
 596         }
 597     }
 598
 599   if (ret == PAM_SUCCESS)
 600     *response_array = aresp;
 601   return ret;
 602 }
 603
 604 /*
 605  * Return 1 if authenticated and 0 if failed.
 606  * Called once for every username/password
 607  * to be authenticated.
 608  */
 609 static int
 610 pam_auth (const char *service, const struct user_pass *up)
 611 {
 612   struct pam_conv conv;
 613   pam_handle_t *pamh = NULL;
 614   int status = PAM_SUCCESS;
 615   int ret = 0;
 616   const int name_value_list_provided = (up->name_value_list && up->name_value_list->len > 0);
 617
 618   /* Initialize PAM */
 619   conv.conv = my_conv;
 620   conv.appdata_ptr = (void *)up;
 621   status = pam_start (service, name_value_list_provided ? NULL : up->username, &conv, &pamh);
 622   if (status == PAM_SUCCESS)
 623     {
 624       /* Call PAM to verify username/password */
 625       status = pam_authenticate(pamh, 0);
 626       if (status == PAM_SUCCESS)
 627         status = pam_acct_mgmt (pamh, 0);
 628       if (status == PAM_SUCCESS)
 629         ret = 1;
 630
 631       /* Output error message if failed */
 632       if (!ret)
 633         {
 634           fprintf (stderr, "AUTH-PAM: BACKGROUND: user '%s' failed to authenticate: %s\n",
 635                    up->username,
 636                    pam_strerror (pamh, status));
 637         }
 638
 639       /* Close PAM */
 640       pam_end (pamh, status);
 641     }
 642
 643   return ret;
 644 }
 645
 646 /*
 647  * Background process -- runs with privilege.
 648  */
 649 static void
 650 pam_server (int fd, const char *service, int verb, const struct name_value_list *name_value_list)
 651 {
 652   struct user_pass up;
 653   int command;
 654 #if DLOPEN_PAM
 655   static const char pam_so[] = "libpam.so";
 656 #endif
 657
 658   /*
 659    * Do initialization
 660    */
 661   if (DEBUG (verb))
 662     fprintf (stderr, "AUTH-PAM: BACKGROUND: INIT service='%s'\n", service);
 663
 664 #if DLOPEN_PAM
 665   /*
 666    * Load PAM shared object
 667    */
 668   if (!dlopen_pam (pam_so))
 669     {
 670       fprintf (stderr, "AUTH-PAM: BACKGROUND: could not load PAM lib %s: %s\n", pam_so, dlerror());
 671       send_control (fd, RESPONSE_INIT_FAILED);
 672       goto done;
 673     }
 674 #endif
 675
 676   /*
 677    * Tell foreground that we initialized successfully
 678    */
 679   if (send_control (fd, RESPONSE_INIT_SUCCEEDED) == -1)
 680     {
 681       fprintf (stderr, "AUTH-PAM: BACKGROUND: write error on response socket [1]\n");
 682       goto done;
 683     }
 684
 685   /*
 686    * Event loop
 687    */
 688   while (1)
 689     {
 690       memset (&up, 0, sizeof (up));
 691       up.verb = verb;
 692       up.name_value_list = name_value_list;
 693
 694       /* get a command from foreground process */
 695       command = recv_control (fd);
 696
 697       if (DEBUG (verb))
 698         fprintf (stderr, "AUTH-PAM: BACKGROUND: received command code: %d\n", command);
 699
 700       switch (command)
 701         {
 702         case COMMAND_VERIFY:
 703           if (recv_string (fd, up.username, sizeof (up.username)) == -1
 704               || recv_string (fd, up.password, sizeof (up.password)) == -1)
 705             {
 706               fprintf (stderr, "AUTH-PAM: BACKGROUND: read error on command channel: code=%d, exiting\n",
 707                        command);
 708               goto done;
 709             }
 710
 711           if (DEBUG (verb))
 712             fprintf (stderr, "AUTH-PAM: BACKGROUND: USER/PASS: %s/%s\n",
 713                      up.username, up.password);
 714
 715           if (pam_auth (service, &up)) /* Succeeded */
 716             {
 717               if (send_control (fd, RESPONSE_VERIFY_SUCCEEDED) == -1)
 718                 {
 719                   fprintf (stderr, "AUTH-PAM: BACKGROUND: write error on response socket [2]\n");
 720                   goto done;
 721                 }
 722             }
 723           else /* Failed */
 724             {
 725               if (send_control (fd, RESPONSE_VERIFY_FAILED) == -1)
 726                 {
 727                   fprintf (stderr, "AUTH-PAM: BACKGROUND: write error on response socket [3]\n");
 728                   goto done;
 729                 }
 730             }
 731           break;
 732
 733         case COMMAND_EXIT:
 734           goto done;
 735
 736         case -1:
 737           fprintf (stderr, "AUTH-PAM: BACKGROUND: read error on command channel\n");
 738           goto done;
 739
 740         default:
 741           fprintf (stderr, "AUTH-PAM: BACKGROUND: unknown command code: code=%d, exiting\n",
 742                    command);
 743           goto done;
 744         }
 745     }
 746  done:
 747
 748 #if DLOPEN_PAM
 749   dlclose_pam ();
 750 #endif
 751   if (DEBUG (verb))
 752     fprintf (stderr, "AUTH-PAM: BACKGROUND: EXIT\n");
 753
 754   return;
 755 }