aboutsummaryrefslogtreecommitdiff
path: root/plugin/auth-pam/auth-pam.c
blob: 72ffa3c6bfaa90daac05d9edbcc0ff45a9e23ecc (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
/*
 *  OpenVPN -- An application to securely tunnel IP networks
 *             over a single TCP/UDP port, with support for SSL/TLS-based
 *             session authentication and key exchange,
 *             packet encryption, packet authentication, and
 *             packet compression.
 *
 *  Copyright (C) 2002-2008 OpenVPN Technologies, Inc. <sales@openvpn.net>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2
 *  as published by the Free Software Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program (see the file COPYING included with this
 *  distribution); if not, write to the Free Software Foundation, Inc.,
 *  59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

/*
 * OpenVPN plugin module to do PAM authentication using a split
 * privilege model.
 */

#if DLOPEN_PAM
#include <dlfcn.h>
#include "pamdl.h"
#else
#include <security/pam_appl.h>
#endif

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <signal.h>
#include <syslog.h>

#include "openvpn-plugin.h"

#define DEBUG(verb) ((verb) >= 4)

/* Command codes for foreground -> background communication */
#define COMMAND_VERIFY 0
#define COMMAND_EXIT   1

/* Response codes for background -> foreground communication */
#define RESPONSE_INIT_SUCCEEDED   10
#define RESPONSE_INIT_FAILED      11
#define RESPONSE_VERIFY_SUCCEEDED 12
#define RESPONSE_VERIFY_FAILED    13

/*
 * Plugin state, used by foreground
 */
struct auth_pam_context
{
  /* Foreground's socket to background process */
  int foreground_fd;

  /* Process ID of background process */
  pid_t background_pid;

  /* Verbosity level of OpenVPN */
  int verb;
};

/*
 * Name/Value pairs for conversation function.
 * Special Values:
 *
 *  "USERNAME" -- substitute client-supplied username
 *  "PASSWORD" -- substitute client-specified password
 */

#define N_NAME_VALUE 16

struct name_value {
  const char *name;
  const char *value;
};

struct name_value_list {
  int len;
  struct name_value data[N_NAME_VALUE];
};

/*
 * Used to pass the username/password
 * to the PAM conversation function.
 */
struct user_pass {
  int verb;

  char username[128];
  char password[128];

  const struct name_value_list *name_value_list;
};

/* Background process function */
static void pam_server (int fd, const char *service, int verb, const struct name_value_list *name_value_list);

/*
 * Given an environmental variable name, search
 * the envp array for its value, returning it
 * if found or NULL otherwise.
 */
static const char *
get_env (const char *name, const char *envp[])
{
  if (envp)
    {
      int i;
      const int namelen = strlen (name);
      for (i = 0; envp[i]; ++i)
	{
	  if (!strncmp (envp[i], name, namelen))
	    {
	      const char *cp = envp[i] + namelen;
	      if (*cp == '=')
		return cp + 1;
	    }
	}
    }
  return NULL;
}

/*
 * Return the length of a string array
 */
static int
string_array_len (const char *array[])
{
  int i = 0;
  if (array)
    {
      while (array[i])
	++i;
    }
  return i;
}

/*
 * Socket read/write functions.
 */

static int
recv_control (int fd)
{
  unsigned char c;
  const ssize_t size = read (fd, &c, sizeof (c));
  if (size == sizeof (c))
    return c;
  else
    {
      /*fprintf (stderr, "AUTH-PAM: DEBUG recv_control.read=%d\n", (int)size);*/
      return -1;
    }
}

static int
send_control (int fd, int code)
{
  unsigned char c = (unsigned char) code;
  const ssize_t size = write (fd, &c, sizeof (c));
  if (size == sizeof (c))
    return (int) size;
  else
    return -1;
}

static int
recv_string (int fd, char *buffer, int len)
{
  if (len > 0)
    {
      ssize_t size;
      memset (buffer, 0, len);
      size = read (fd, buffer, len);
      buffer[len-1] = 0;
      if (size >= 1)
	return (int)size;
    }
  return -1;
}

static int
send_string (int fd, const char *string)
{
  const int len = strlen (string) + 1;
  const ssize_t size = write (fd, string, len);
  if (size == len)
    return (int) size;
  else
    return -1;
}

#ifdef DO_DAEMONIZE

/*
 * Daemonize if "daemon" env var is true.
 * Preserve stderr across daemonization if
 * "daemon_log_redirect" env var is true.
 */
static void
daemonize (const char *envp[])
{
  const char *daemon_string = get_env ("daemon", envp);
  if (daemon_string && daemon_string[0] == '1')
    {
      const char *log_redirect = get_env ("daemon_log_redirect", envp);
      int fd = -1;
      if (log_redirect && log_redirect[0] == '1')
	fd = dup (2);
      if (daemon (0, 0) < 0)
	{
	  fprintf (stderr, "AUTH-PAM: daemonization failed\n");
	}
      else if (fd >= 3)
	{
	  dup2 (fd, 2);
	  close (fd);
	}
    }
}

#endif

/*
 * Close most of parent's fds.
 * Keep stdin/stdout/stderr, plus one
 * other fd which is presumed to be
 * our pipe back to parent.
 * Admittedly, a bit of a kludge,
 * but posix doesn't give us a kind
 * of FD_CLOEXEC which will stop
 * fds from crossing a fork().
 */
static void
close_fds_except (int keep)
{
  int i;
  closelog ();
  for (i = 3; i <= 100; ++i)
    {
      if (i != keep)
	close (i);
    }
}

/*
 * Usually we ignore signals, because our parent will
 * deal with them.
 */
static void
set_signals (void)
{
  signal (SIGTERM, SIG_DFL);

  signal (SIGINT, SIG_IGN);
  signal (SIGHUP, SIG_IGN);
  signal (SIGUSR1, SIG_IGN);
  signal (SIGUSR2, SIG_IGN);
  signal (SIGPIPE, SIG_IGN);
}

/*
 * Return 1 if query matches match.
 */
static int
name_value_match (const char *query, const char *match)
{
  while (!isalnum (*query))
    {
      if (*query == '\0')
	return 0;
      ++query;
    }
  return strncasecmp (match, query, strlen (match)) == 0;
}

OPENVPN_EXPORT openvpn_plugin_handle_t
openvpn_plugin_open_v1 (unsigned int *type_mask, const char *argv[], const char *envp[])
{
  pid_t pid;
  int fd[2];

  struct auth_pam_context *context;
  struct name_value_list name_value_list;

  const int base_parms = 2;

  /*
   * Allocate our context
   */
  context = (struct auth_pam_context *) calloc (1, sizeof (struct auth_pam_context));
  context->foreground_fd = -1;

  /*
   * Intercept the --auth-user-pass-verify callback.
   */
  *type_mask = OPENVPN_PLUGIN_MASK (OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY);

  /*
   * Make sure we have two string arguments: the first is the .so name,
   * the second is the PAM service type.
   */
  if (string_array_len (argv) < base_parms)
    {
      fprintf (stderr, "AUTH-PAM: need PAM service parameter\n");
      goto error;
    }

  /*
   * See if we have optional name/value pairs to match against
   * PAM module queried fields in the conversation function.
   */
  name_value_list.len = 0;
  if (string_array_len (argv) > base_parms)
    {
      const int nv_len = string_array_len (argv) - base_parms;
      int i;

      if ((nv_len & 1) == 1 || (nv_len / 2) > N_NAME_VALUE)
	{
	  fprintf (stderr, "AUTH-PAM: bad name/value list length\n");
	  goto error;
	}

      name_value_list.len = nv_len / 2;
      for (i = 0; i < name_value_list.len; ++i)
	{
	  const int base = base_parms + i * 2;
	  name_value_list.data[i].name = argv[base];
	  name_value_list.data[i].value = argv[base+1];
	}
    }

  /*
   * Get verbosity level from environment
   */
  {
    const char *verb_string = get_env ("verb", envp);
    if (verb_string)
      context->verb = atoi (verb_string);
  }

  /*
   * Make a socket for foreground and background processes
   * to communicate.
   */
  if (socketpair (PF_UNIX, SOCK_DGRAM, 0, fd) == -1)
    {
      fprintf (stderr, "AUTH-PAM: socketpair call failed\n");
      goto error;
    }

  /*
   * Fork off the privileged process.  It will remain privileged
   * even after the foreground process drops its privileges.
   */
  pid = fork ();

  if (pid)
    {
      int status;

      /*
       * Foreground Process
       */

      context->background_pid = pid;

      /* close our copy of child's socket */
      close (fd[1]);

      /* don't let future subprocesses inherit child socket */
      if (fcntl (fd[0], F_SETFD, FD_CLOEXEC) < 0)
	fprintf (stderr, "AUTH-PAM: Set FD_CLOEXEC flag on socket file descriptor failed\n");

      /* wait for background child process to initialize */
      status = recv_control (fd[0]);
      if (status == RESPONSE_INIT_SUCCEEDED)
	{
	  context->foreground_fd = fd[0];
	  return (openvpn_plugin_handle_t) context;
	}
    }
  else
    {
      /*
       * Background Process
       */

      /* close all parent fds except our socket back to parent */
      close_fds_except (fd[1]);

      /* Ignore most signals (the parent will receive them) */
      set_signals ();

#ifdef DO_DAEMONIZE
      /* Daemonize if --daemon option is set. */
      daemonize (envp);
#endif

      /* execute the event loop */
      pam_server (fd[1], argv[1], context->verb, &name_value_list);

      close (fd[1]);

      exit (0);
      return 0; /* NOTREACHED */
    }

 error:
  if (context)
    free (context);
  return NULL;
}

OPENVPN_EXPORT int
openvpn_plugin_func_v1 (openvpn_plugin_handle_t handle, const int type, const char *argv[], const char *envp[])
{
  struct auth_pam_context *context = (struct auth_pam_context *) handle;

  if (type == OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY && context->foreground_fd >= 0)
    {
      /* get username/password from envp string array */
      const char *username = get_env ("username", envp);
      const char *password = get_env ("password", envp);

      if (username && strlen (username) > 0 && password)
	{
	  if (send_control (context->foreground_fd, COMMAND_VERIFY) == -1
	      || send_string (context->foreground_fd, username) == -1
	      || send_string (context->foreground_fd, password) == -1)
	    {
	      fprintf (stderr, "AUTH-PAM: Error sending auth info to background process\n");
	    }
	  else
	    {
	      const int status = recv_control (context->foreground_fd);
	      if (status == RESPONSE_VERIFY_SUCCEEDED)
		return OPENVPN_PLUGIN_FUNC_SUCCESS;
	      if (status == -1)
		fprintf (stderr, "AUTH-PAM: Error receiving auth confirmation from background process\n");
	    }
	}
    }
  return OPENVPN_PLUGIN_FUNC_ERROR;
}

OPENVPN_EXPORT void
openvpn_plugin_close_v1 (openvpn_plugin_handle_t handle)
{
  struct auth_pam_context *context = (struct auth_pam_context *) handle;

  if (DEBUG (context->verb))
    fprintf (stderr, "AUTH-PAM: close\n");

  if (context->foreground_fd >= 0)
    {
      /* tell background process to exit */
      if (send_control (context->foreground_fd, COMMAND_EXIT) == -1)
	fprintf (stderr, "AUTH-PAM: Error signaling background process to exit\n");

      /* wait for background process to exit */
      if (context->background_pid > 0)
	waitpid (context->background_pid, NULL, 0);

      close (context->foreground_fd);
      context->foreground_fd = -1;
    }

  free (context);
}

OPENVPN_EXPORT void
openvpn_plugin_abort_v1 (openvpn_plugin_handle_t handle)
{
  struct auth_pam_context *context = (struct auth_pam_context *) handle;

  /* tell background process to exit */
  if (context->foreground_fd >= 0)
    {
      send_control (context->foreground_fd, COMMAND_EXIT);
      close (context->foreground_fd);
      context->foreground_fd = -1;
    }
}

/*
 * PAM conversation function
 */
static int
my_conv (int n, const struct pam_message **msg_array,
	 struct pam_response **response_array, void *appdata_ptr)
{
  const struct user_pass *up = ( const struct user_pass *) appdata_ptr;
  struct pam_response *aresp;
  int i;
  int ret = PAM_SUCCESS;

  *response_array = NULL;

  if (n <= 0 || n > PAM_MAX_NUM_MSG)
    return (PAM_CONV_ERR);
  if ((aresp = calloc (n, sizeof *aresp)) == NULL)
    return (PAM_BUF_ERR);

  /* loop through each PAM-module query */
  for (i = 0; i < n; ++i)
    {
      const struct pam_message *msg = msg_array[i];
      aresp[i].resp_retcode = 0;
      aresp[i].resp = NULL;

      if (DEBUG (up->verb))
	{
	  fprintf (stderr, "AUTH-PAM: BACKGROUND: my_conv[%d] query='%s' style=%d\n",
		   i,
		   msg->msg ? msg->msg : "NULL",
		   msg->msg_style);
	}

      if (up->name_value_list && up->name_value_list->len > 0)
	{
	  /* use name/value list match method */
	  const struct name_value_list *list = up->name_value_list;
	  int j;

	  /* loop through name/value pairs */
	  for (j = 0; j < list->len; ++j)
	    {
	      const char *match_name = list->data[j].name;
	      const char *match_value = list->data[j].value;

	      if (name_value_match (msg->msg, match_name))
		{
		  /* found name/value match */
		  const char *return_value = NULL;

		  if (DEBUG (up->verb))
		    fprintf (stderr, "AUTH-PAM: BACKGROUND: name match found, query/match-string ['%s', '%s'] = '%s'\n",
			     msg->msg,
			     match_name,
			     match_value);

		  if (!strcmp (match_value, "USERNAME"))
		    return_value = up->username;
		  else if (!strcmp (match_value, "PASSWORD"))
		    return_value = up->password;
		  else
		    return_value = match_value;

		  aresp[i].resp = strdup (return_value);
		  if (aresp[i].resp == NULL)
		    ret = PAM_CONV_ERR;
		  break;
		}
	    }

	  if (j == list->len)
	    ret = PAM_CONV_ERR;
	}
      else
	{
	  /* use PAM_PROMPT_ECHO_x hints */
	  switch (msg->msg_style)
	    {
	    case PAM_PROMPT_ECHO_OFF:
	      aresp[i].resp = strdup (up->password);
	      if (aresp[i].resp == NULL)
		ret = PAM_CONV_ERR;
	      break;

	    case PAM_PROMPT_ECHO_ON:
	      aresp[i].resp = strdup (up->username);
	      if (aresp[i].resp == NULL)
		ret = PAM_CONV_ERR;
	      break;

	    case PAM_ERROR_MSG:
	    case PAM_TEXT_INFO:
	      break;

	    default:
	      ret = PAM_CONV_ERR;
	      break;
	    }
	}
    }

  if (ret == PAM_SUCCESS)
    *response_array = aresp;
  return ret;
}

/*
 * Return 1 if authenticated and 0 if failed.
 * Called once for every username/password
 * to be authenticated.
 */
static int
pam_auth (const char *service, const struct user_pass *up)
{
  struct pam_conv conv;
  pam_handle_t *pamh = NULL;
  int status = PAM_SUCCESS;
  int ret = 0;
  const int name_value_list_provided = (up->name_value_list && up->name_value_list->len > 0);

  /* Initialize PAM */
  conv.conv = my_conv;
  conv.appdata_ptr = (void *)up;
  status = pam_start (service, name_value_list_provided ? NULL : up->username, &conv, &pamh);
  if (status == PAM_SUCCESS)
    {
      /* Call PAM to verify username/password */
      status = pam_authenticate(pamh, 0);
      if (status == PAM_SUCCESS)
	status = pam_acct_mgmt (pamh, 0);
      if (status == PAM_SUCCESS)
	ret = 1;

      /* Output error message if failed */
      if (!ret)
	{
	  fprintf (stderr, "AUTH-PAM: BACKGROUND: user '%s' failed to authenticate: %s\n",
		   up->username,
		   pam_strerror (pamh, status));
	}

      /* Close PAM */
      pam_end (pamh, status);      
    }

  return ret;
}

/*
 * Background process -- runs with privilege.
 */
static void
pam_server (int fd, const char *service, int verb, const struct name_value_list *name_value_list)
{
  struct user_pass up;
  int command;
#if DLOPEN_PAM
  static const char pam_so[] = "libpam.so";
#endif

  /*
   * Do initialization
   */
  if (DEBUG (verb))
    fprintf (stderr, "AUTH-PAM: BACKGROUND: INIT service='%s'\n", service);

#if DLOPEN_PAM
  /*
   * Load PAM shared object
   */
  if (!dlopen_pam (pam_so))
    {
      fprintf (stderr, "AUTH-PAM: BACKGROUND: could not load PAM lib %s: %s\n", pam_so, dlerror());
      send_control (fd, RESPONSE_INIT_FAILED);
      goto done;
    }
#endif

  /*
   * Tell foreground that we initialized successfully
   */
  if (send_control (fd, RESPONSE_INIT_SUCCEEDED) == -1)
    {
      fprintf (stderr, "AUTH-PAM: BACKGROUND: write error on response socket [1]\n");
      goto done;
    }

  /*
   * Event loop
   */
  while (1)
    {
      memset (&up, 0, sizeof (up));
      up.verb = verb;
      up.name_value_list = name_value_list;

      /* get a command from foreground process */
      command = recv_control (fd);

      if (DEBUG (verb))
	fprintf (stderr, "AUTH-PAM: BACKGROUND: received command code: %d\n", command);

      switch (command)
	{
	case COMMAND_VERIFY:
	  if (recv_string (fd, up.username, sizeof (up.username)) == -1
	      || recv_string (fd, up.password, sizeof (up.password)) == -1)
	    {
	      fprintf (stderr, "AUTH-PAM: BACKGROUND: read error on command channel: code=%d, exiting\n",
		       command);
	      goto done;
	    }

	  if (DEBUG (verb))
	    {
#if 0
	      fprintf (stderr, "AUTH-PAM: BACKGROUND: USER/PASS: %s/%s\n",
		       up.username, up.password);
#else
	      fprintf (stderr, "AUTH-PAM: BACKGROUND: USER: %s\n", up.username);
#endif
	    }

	  if (pam_auth (service, &up)) /* Succeeded */
	    {
	      if (send_control (fd, RESPONSE_VERIFY_SUCCEEDED) == -1)
		{
		  fprintf (stderr, "AUTH-PAM: BACKGROUND: write error on response socket [2]\n");
		  goto done;
		}
	    }
	  else /* Failed */
	    {
	      if (send_control (fd, RESPONSE_VERIFY_FAILED) == -1)
		{
		  fprintf (stderr, "AUTH-PAM: BACKGROUND: write error on response socket [3]\n");
		  goto done;
		}
	    }
	  break;

	case COMMAND_EXIT:
	  goto done;

	case -1:
	  fprintf (stderr, "AUTH-PAM: BACKGROUND: read error on command channel\n");
	  goto done;

	default:
	  fprintf (stderr, "AUTH-PAM: BACKGROUND: unknown command code: code=%d, exiting\n",
		   command);
	  goto done;
	}
    }
 done:

#if DLOPEN_PAM
  dlclose_pam ();
#endif
  if (DEBUG (verb))
    fprintf (stderr, "AUTH-PAM: BACKGROUND: EXIT\n");

  return;
}