aboutsummaryrefslogblamecommitdiff
path: root/plugin/down-root/down-root.c
blob: e3b92f19415ea70d38ddfe02135a47eb22890f7c (plain) (tree)
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






                                                                         
                                                                          






























































































































































































































































































































































































































































































































































                                                                                                                   
/*
 *  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 privileged down-script execution.
 */

#include <stdio.h>
#include <string.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) >= 7)

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

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

/* Background process function */
static void down_root_server (const int fd, char *command, const char *argv[], const char *envp[], const int verb);

/*
 * Plugin state, used by foreground
 */
struct down_root_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;

  /* down command */
  char *command;
};

/*
 * 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
    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;
}

/*
 * 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, "DOWN-ROOT: daemonization failed\n");
	}
      else if (fd >= 3)
	{
	  dup2 (fd, 2);
	  close (fd);
	}
    }
}

/*
 * 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);
}

/*
 * convert system() return into a success/failure value
 */
int
system_ok (int stat)
{
#ifdef WIN32
  return stat == 0;
#else
  return stat != -1 && WIFEXITED (stat) && WEXITSTATUS (stat) == 0;
#endif
}

static char *
build_command_line (const char *argv[])
{
  int size = 0;
  int n = 0;
  int i;
  char *string;

  /* precompute size */
  if (argv)
    {
      for (i = 0; argv[i]; ++i)
	{
	  size += (strlen (argv[i]) + 1); /* string length plus trailing space */
	  ++n;
	}
    }
  ++size;                                 /* for null terminator */

  /* allocate memory */
  string = (char *) malloc (size);
  if (!string)
    {
      fprintf (stderr, "DOWN-ROOT: out of memory\n");
      exit (1);
    }
  string[0] = '\0';

  /* build string */
  for (i = 0; i < n; ++i)
    {
      strcat (string, argv[i]);
      if (i + 1 < n)
	strcat (string, " ");
    }
  return string;
}

static void
free_context (struct down_root_context *context)
{
  if (context)
    {
      if (context->command)
	free (context->command);
      free (context);
    }
}

OPENVPN_EXPORT openvpn_plugin_handle_t
openvpn_plugin_open_v1 (unsigned int *type_mask, const char *argv[], const char *envp[])
{
  struct down_root_context *context;

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

  /*
   * Intercept the --up and --down callbacks
   */
  *type_mask = OPENVPN_PLUGIN_MASK (OPENVPN_PLUGIN_UP) | OPENVPN_PLUGIN_MASK (OPENVPN_PLUGIN_DOWN);

  /*
   * Make sure we have two string arguments: the first is the .so name,
   * the second is the script command.
   */
  if (string_array_len (argv) < 2)
    {
      fprintf (stderr, "DOWN-ROOT: need down script command\n");
      goto error;
    }

  /*
   * Save our argument in context
   */
  context->command = build_command_line (&argv[1]);

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

  return (openvpn_plugin_handle_t) context;

 error:
  free_context (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 down_root_context *context = (struct down_root_context *) handle;

  if (type == OPENVPN_PLUGIN_UP && context->foreground_fd == -1) /* fork off a process to hold onto root */
    {
      pid_t pid;
      int fd[2];

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

	  /* Daemonize if --daemon option is set. */
	  daemonize (envp);

	  /* execute the event loop */
	  down_root_server (fd[1], context->command, argv, envp, context->verb);

	  close (fd[1]);
	  exit (0);
	  return 0; /* NOTREACHED */
	}
    }
  else if (type == OPENVPN_PLUGIN_DOWN && context->foreground_fd >= 0)
    {
      if (send_control (context->foreground_fd, COMMAND_RUN_SCRIPT) == -1)
	{
	  fprintf (stderr, "DOWN-ROOT: Error sending script execution signal to background process\n");
	}
      else
	{
	  const int status = recv_control (context->foreground_fd);
	  if (status == RESPONSE_SCRIPT_SUCCEEDED)
	    return OPENVPN_PLUGIN_FUNC_SUCCESS;
	  if (status == -1)
	    fprintf (stderr, "DOWN-ROOT: Error receiving script execution confirmation from background process\n");
	}
    }
  return OPENVPN_PLUGIN_FUNC_ERROR;
}

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

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

  if (context->foreground_fd >= 0)
    {
      /* tell background process to exit */
      if (send_control (context->foreground_fd, COMMAND_EXIT) == -1)
	fprintf (stderr, "DOWN-ROOT: 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 (context);
}

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

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

/*
 * Background process -- runs with privilege.
 */
static void
down_root_server (const int fd, char *command, const char *argv[], const char *envp[], const int verb)
{
  const char *p[3];
  char *command_line = NULL;
  char *argv_cat = NULL;
  int i;

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

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

  /*
   * Build command line
   */
  if (string_array_len (argv) >= 2)
    argv_cat = build_command_line (&argv[1]);
  else
    argv_cat = build_command_line (NULL);
  p[0] = command;
  p[1] = argv_cat;
  p[2] = NULL;
  command_line = build_command_line (p);

  /*
   * Save envp in environment
   */
  for (i = 0; envp[i]; ++i)
    {
      putenv ((char *)envp[i]);
    }

  /*
   * Event loop
   */
  while (1)
    {
      int command_code;
      int status;

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

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

      switch (command_code)
	{
	case COMMAND_RUN_SCRIPT:
	  status = system (command_line);
	  if (system_ok (status)) /* Succeeded */
	    {
	      if (send_control (fd, RESPONSE_SCRIPT_SUCCEEDED) == -1)
		{
		  fprintf (stderr, "DOWN-ROOT: BACKGROUND: write error on response socket [2]\n");
		  goto done;
		}
	    }
	  else /* Failed */
	    {
	      if (send_control (fd, RESPONSE_SCRIPT_FAILED) == -1)
		{
		  fprintf (stderr, "DOWN-ROOT: BACKGROUND: write error on response socket [3]\n");
		  goto done;
		}
	    }
	  break;

	case COMMAND_EXIT:
	  goto done;

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

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

 done:
  if (argv_cat)
    free (argv_cat);
  if (command_line)
    free (command_line);
  if (DEBUG (verb))
    fprintf (stderr, "DOWN-ROOT: BACKGROUND: EXIT\n");

  return;
}