aboutsummaryrefslogtreecommitdiff
path: root/forward.c
blob: 4c0aff899fd57a3aab72794c753e8c303cafad89 (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
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
/*
 *  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) 2002-2005 OpenVPN Solutions LLC <info@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
 */

#ifdef WIN32
#include "config-win32.h"
#else
#include "config.h"
#endif

#include "syshead.h"

#include "forward.h"
#include "init.h"
#include "push.h"
#include "gremlin.h"
#include "mss.h"
#include "event.h"

#include "memdbg.h"

#include "forward-inline.h"
#include "occ-inline.h"
#include "ping-inline.h"

/* show event wait debugging info */

#ifdef ENABLE_DEBUG

const char *
wait_status_string (struct context *c, struct gc_arena *gc)
{
  struct buffer out = alloc_buf_gc (64, gc);
  buf_printf (&out, "I/O WAIT %s|%s|%s|%s %s",
	      tun_stat (c->c1.tuntap, EVENT_READ, gc),
	      tun_stat (c->c1.tuntap, EVENT_WRITE, gc),
	      socket_stat (c->c2.link_socket, EVENT_READ, gc),
	      socket_stat (c->c2.link_socket, EVENT_WRITE, gc),
	      tv_string (&c->c2.timeval, gc));
  return BSTR (&out);
}

void
show_wait_status (struct context *c)
{
  struct gc_arena gc = gc_new ();
  dmsg (D_EVENT_WAIT, "%s", wait_status_string (c, &gc));
  gc_free (&gc);
}

#endif

/*
 * In TLS mode, let TLS level respond to any control-channel
 * packets which were received, or prepare any packets for
 * transmission.
 *
 * tmp_int is purely an optimization that allows us to call
 * tls_multi_process less frequently when there's not much
 * traffic on the control-channel.
 *
 */
#if defined(USE_CRYPTO) && defined(USE_SSL)
void
check_tls_dowork (struct context *c)
{
  interval_t wakeup = BIG_TIMEOUT;

  if (interval_test (&c->c2.tmp_int))
    {
      if (tls_multi_process
	  (c->c2.tls_multi, &c->c2.to_link, &c->c2.to_link_addr,
	   get_link_socket_info (c), &wakeup))
	{
	  update_time ();
	  interval_action (&c->c2.tmp_int);
	}

      interval_future_trigger (&c->c2.tmp_int, wakeup);
    }

  interval_schedule_wakeup (&c->c2.tmp_int, &wakeup);

  if (wakeup)
    context_reschedule_sec (c, wakeup);
}
#endif

#if defined(USE_CRYPTO) && defined(USE_SSL)

void
check_tls_errors_co (struct context *c)
{
  msg (D_STREAM_ERRORS, "Fatal TLS error (check_tls_errors_co), restarting");
  c->sig->signal_received = c->c2.tls_exit_signal; /* SOFT-SIGUSR1 -- TLS error */
  c->sig->signal_text = "tls-error";
}

void
check_tls_errors_nco (struct context *c)
{
  c->sig->signal_received = c->c2.tls_exit_signal; /* SOFT-SIGUSR1 -- TLS error */
  c->sig->signal_text = "tls-error";
}

#endif

#if P2MP

/*
 * Handle incoming configuration
 * messages on the control channel.
 */
void
check_incoming_control_channel_dowork (struct context *c)
{
  const int len = tls_test_payload_len (c->c2.tls_multi);
  if (len)
    {
      struct gc_arena gc = gc_new ();
      struct buffer buf = alloc_buf_gc (len, &gc);
      if (tls_rec_payload (c->c2.tls_multi, &buf))
	{
	  /* force null termination of message */
	  buf_null_terminate (&buf);

	  /* enforce character class restrictions */
	  string_mod (BSTR (&buf), CC_PRINT, CC_CRLF, 0);

	  if (buf_string_match_head_str (&buf, "AUTH_FAILED"))
	    receive_auth_failed (c, &buf);
	  else if (buf_string_match_head_str (&buf, "PUSH_"))
	    incoming_push_message (c, &buf);
	  else
	    msg (D_PUSH_ERRORS, "WARNING: Received unknown control message: %s", BSTR (&buf));
	}
      else
	{
	  msg (D_PUSH_ERRORS, "WARNING: Receive control message failed");
	}

      gc_free (&gc);
    }
}

/*
 * Periodically resend PUSH_REQUEST until PUSH message received
 */
void
check_push_request_dowork (struct context *c)
{
  send_push_request (c);
}

#endif

/*
 * Things that need to happen immediately after connection initiation should go here.
 */
void
check_connection_established_dowork (struct context *c)
{
  if (event_timeout_trigger (&c->c2.wait_for_connect, &c->c2.timeval, ETT_DEFAULT))
    {
      if (CONNECTION_ESTABLISHED (c))
	{
#if P2MP
	  /* if --pull was specified, send a push request to server */
	  if (c->c2.tls_multi && c->options.pull)
	    {
#ifdef ENABLE_MANAGEMENT
	      if (management)
		{
		  management_set_state (management,
					OPENVPN_STATE_GET_CONFIG,
					NULL,
					0);
		}
#endif
	      send_push_request (c);

	      /* if no reply, try again in 5 sec */
	      event_timeout_init (&c->c2.push_request_interval, 5, now);
	      reset_coarse_timers (c);
	    }
	  else
#endif
	    {
	      do_up (c, false, 0);
	    }

	  event_timeout_clear (&c->c2.wait_for_connect);
	}
    }
}

/*
 * Send a string to remote over the TLS control channel.
 * Used for push/pull messages, passing username/password,
 * etc.
 */
bool
send_control_channel_string (struct context *c, const char *str, int msglevel)
{
#if defined(USE_CRYPTO) && defined(USE_SSL)

  if (c->c2.tls_multi) {
    bool stat;

    /* buffered cleartext write onto TLS control channel */
    stat = tls_send_payload (c->c2.tls_multi, (uint8_t*) str, strlen (str) + 1);

    /* reschedule tls_multi_process */
    interval_action (&c->c2.tmp_int);
    context_immediate_reschedule (c); /* ZERO-TIMEOUT */

    msg (msglevel, "SENT CONTROL [%s]: '%s' (status=%d)",
	 tls_common_name (c->c2.tls_multi, false),
	 str,
	 (int) stat);

    return stat;
  }
#endif
  return true;
}

/*
 * Add routes.
 */

static void
check_add_routes_action (struct context *c, const bool errors)
{
  do_route (&c->options, c->c1.route_list, c->c1.tuntap, c->c1.plugins, c->c2.es);
  update_time ();
  event_timeout_clear (&c->c2.route_wakeup);
  event_timeout_clear (&c->c2.route_wakeup_expire);
  initialization_sequence_completed (c, errors ? ISC_ERRORS : 0); /* client/p2p --route-delay was defined */
}

void
check_add_routes_dowork (struct context *c)
{
  if (test_routes (c->c1.route_list, c->c1.tuntap))
    {
      check_add_routes_action (c, false);
    }
  else if (event_timeout_trigger (&c->c2.route_wakeup_expire, &c->c2.timeval, ETT_DEFAULT))
    {
      check_add_routes_action (c, true);
    }
  else
    {
      msg (D_ROUTE, "Route: Waiting for TUN/TAP interface to come up...");
      if (c->c2.route_wakeup.n != 1)
	event_timeout_init (&c->c2.route_wakeup, 1, now);
    }
}

/*
 * Should we exit due to inactivity timeout?
 */
void
check_inactivity_timeout_dowork (struct context *c)
{
  msg (M_INFO, "Inactivity timeout (--inactive), exiting");
  c->sig->signal_received = SIGTERM;
  c->sig->signal_text = "inactive";
}

#if P2MP

/*
 * Schedule a SIGTERM n_seconds from now.
 */
void
schedule_exit (struct context *c, const int n_seconds)
{
  update_time ();
  reset_coarse_timers (c);
  event_timeout_init (&c->c2.scheduled_exit, n_seconds, now);
  msg (D_SCHED_EXIT, "Delayed exit in %d seconds", n_seconds);
}

/*
 * Scheduled exit?
 */
void
check_scheduled_exit_dowork (struct context *c)
{
  c->sig->signal_received = SIGTERM;
  c->sig->signal_text = "delayed-exit";
}

#endif

/*
 * Should we write timer-triggered status file.
 */
void
check_status_file_dowork (struct context *c)
{
  if (c->c1.status_output)
    print_status (c, c->c1.status_output);
}

#ifdef ENABLE_FRAGMENT
/*
 * Should we deliver a datagram fragment to remote?
 */
void
check_fragment_dowork (struct context *c)
{
  struct link_socket_info *lsi = get_link_socket_info (c);

  /* OS MTU Hint? */
  if (lsi->mtu_changed && c->c2.ipv4_tun)
    {
      frame_adjust_path_mtu (&c->c2.frame_fragment, c->c2.link_socket->mtu,
			     c->options.proto);
      lsi->mtu_changed = false;
    }

  if (fragment_outgoing_defined (c->c2.fragment))
    {
      if (!c->c2.to_link.len)
	{
	  /* encrypt a fragment for output to TCP/UDP port */
	  ASSERT (fragment_ready_to_send (c->c2.fragment, &c->c2.buf, &c->c2.frame_fragment));
	  encrypt_sign (c, false);
	}
    }

  fragment_housekeeping (c->c2.fragment, &c->c2.frame_fragment, &c->c2.timeval);
}
#endif

/*
 * Buffer reallocation, for use with null encryption.
 */
static inline void
buffer_turnover (const uint8_t *orig_buf, struct buffer *dest_stub, struct buffer *src_stub, struct buffer *storage)
{
  if (orig_buf == src_stub->data && src_stub->data != storage->data)
    {
      buf_assign (storage, src_stub);
      *dest_stub = *storage;
    }
  else
    {
      *dest_stub = *src_stub;
    }
}

/*
 * Compress, fragment, encrypt and HMAC-sign an outgoing packet.
 * Input: c->c2.buf
 * Output: c->c2.to_link
 */
void
encrypt_sign (struct context *c, bool comp_frag)
{
  struct context_buffers *b = c->c2.buffers;
  const uint8_t *orig_buf = c->c2.buf.data;

#if P2MP_SERVER
  /*
   * Drop non-TLS outgoing packet if client-connect script/plugin
   * has not yet succeeded.
   */
  if (c->c2.context_auth != CAS_SUCCEEDED)
    c->c2.buf.len = 0;
#endif

  if (comp_frag)
    {
#ifdef USE_LZO
      /* Compress the packet. */
      if (c->options.comp_lzo)
	lzo_compress (&c->c2.buf, b->lzo_compress_buf, &c->c2.lzo_compwork, &c->c2.frame);
#endif
#ifdef ENABLE_FRAGMENT
      if (c->c2.fragment)
	fragment_outgoing (c->c2.fragment, &c->c2.buf, &c->c2.frame_fragment);
#endif
    }

#ifdef USE_CRYPTO
#ifdef USE_SSL
  /*
   * If TLS mode, get the key we will use to encrypt
   * the packet.
   */
  if (c->c2.tls_multi)
    {
      /*tls_mutex_lock (c->c2.tls_multi);*/
      tls_pre_encrypt (c->c2.tls_multi, &c->c2.buf, &c->c2.crypto_options);
    }
#endif

  /*
   * Encrypt the packet and write an optional
   * HMAC signature.
   */
  openvpn_encrypt (&c->c2.buf, b->encrypt_buf, &c->c2.crypto_options, &c->c2.frame);
#endif
  /*
   * Get the address we will be sending the packet to.
   */
  link_socket_get_outgoing_addr (&c->c2.buf, get_link_socket_info (c),
				 &c->c2.to_link_addr);
#ifdef USE_CRYPTO
#ifdef USE_SSL
  /*
   * In TLS mode, prepend the appropriate one-byte opcode
   * to the packet which identifies it as a data channel
   * packet and gives the low-permutation version of
   * the key-id to the recipient so it knows which
   * decrypt key to use.
   */
  if (c->c2.tls_multi)
    {
      tls_post_encrypt (c->c2.tls_multi, &c->c2.buf);
      /*tls_mutex_unlock (c->c2.tls_multi);*/
    }
#endif
#endif

  /* if null encryption, copy result to read_tun_buf */
  buffer_turnover (orig_buf, &c->c2.to_link, &c->c2.buf, &b->read_tun_buf);
}

/*
 * Coarse timers work to 1 second resolution.
 */
static void
process_coarse_timers (struct context *c)
{
#ifdef USE_CRYPTO
  /* flush current packet-id to file once per 60
     seconds if --replay-persist was specified */
  check_packet_id_persist_flush (c);
#endif

  /* should we update status file? */
  check_status_file (c);

  /* process connection establishment items */
  check_connection_established (c);

#if P2MP
  /* see if we should send a push_request in response to --pull */
  check_push_request (c);
#endif

  /* process --route options */
  check_add_routes (c);

  /* possibly exit due to --inactive */
  check_inactivity_timeout (c);
  if (c->sig->signal_received)
    return;

  /* restart if ping not received */
  check_ping_restart (c);
  if (c->sig->signal_received)
    return;

#if P2MP
  check_scheduled_exit (c);
  if (c->sig->signal_received)
    return;
#endif

#ifdef ENABLE_OCC
  /* Should we send an OCC_REQUEST message? */
  check_send_occ_req (c);

  /* Should we send an MTU load test? */
  check_send_occ_load_test (c);

  /* Should we send an OCC_EXIT message to remote? */
  if (c->c2.explicit_exit_notification_time_wait)
    process_explicit_exit_notification_timer_wakeup (c);
#endif

  /* Should we ping the remote? */
  check_ping_send (c);
}

static void
check_coarse_timers_dowork (struct context *c)
{
  const struct timeval save = c->c2.timeval;
  c->c2.timeval.tv_sec = BIG_TIMEOUT;
  c->c2.timeval.tv_usec = 0;
  process_coarse_timers (c);
  c->c2.coarse_timer_wakeup = now + c->c2.timeval.tv_sec; 

  dmsg (D_INTERVAL, "TIMER: coarse timer wakeup %d seconds", (int) c->c2.timeval.tv_sec);

  /* Is the coarse timeout NOT the earliest one? */
  if (c->c2.timeval.tv_sec > save.tv_sec)
    c->c2.timeval = save;
}

static inline void
check_coarse_timers (struct context *c)
{
  const time_t local_now = now;
  if (local_now >= c->c2.coarse_timer_wakeup)
    check_coarse_timers_dowork (c);
  else
    context_reschedule_sec (c, c->c2.coarse_timer_wakeup - local_now);
}

static void
check_timeout_random_component_dowork (struct context *c)
{
  const int update_interval = 10; /* seconds */
  c->c2.update_timeout_random_component = now + update_interval;
  c->c2.timeout_random_component.tv_usec = (time_t) get_random () & 0x0003FFFF;
  c->c2.timeout_random_component.tv_sec = 0;

  dmsg (D_INTERVAL, "RANDOM USEC=%d", (int) c->c2.timeout_random_component.tv_usec);
}

static inline void
check_timeout_random_component (struct context *c)
{
  if (now >= c->c2.update_timeout_random_component)
    check_timeout_random_component_dowork (c);
  if (c->c2.timeval.tv_sec >= 1)
    tv_add (&c->c2.timeval, &c->c2.timeout_random_component);
}

#ifdef ENABLE_SOCKS

/*
 * Handle addition and removal of the 10-byte Socks5 header
 * in UDP packets.
 */

static inline void
socks_postprocess_incoming_link (struct context *c)
{
  if (c->c2.link_socket->socks_proxy && c->c2.link_socket->info.proto == PROTO_UDPv4)
    socks_process_incoming_udp (&c->c2.buf, &c->c2.from);
}

static inline void
socks_preprocess_outgoing_link (struct context *c,
				struct sockaddr_in **to_addr,
				int *size_delta)
{
  if (c->c2.link_socket->socks_proxy && c->c2.link_socket->info.proto == PROTO_UDPv4)
    {
      *size_delta += socks_process_outgoing_udp (&c->c2.to_link, &c->c2.to_link_addr);
      *to_addr = &c->c2.link_socket->socks_relay;
    }
}

/* undo effect of socks_preprocess_outgoing_link */
static inline void
link_socket_write_post_size_adjust (int *size,
				    int size_delta,
				    struct buffer *buf)
{
  if (size_delta > 0 && *size > size_delta)
    {
      *size -= size_delta;
      if (!buf_advance (buf, size_delta))
	*size = 0;
    }
}
#endif

/*
 * Output: c->c2.buf
 */

void
read_incoming_link (struct context *c)
{
  /*
   * Set up for recvfrom call to read datagram
   * sent to our TCP/UDP port.
   */
  int status;

  perf_push (PERF_READ_IN_LINK);

  ASSERT (!c->c2.to_tun.len);

  c->c2.buf = c->c2.buffers->read_link_buf;
  ASSERT (buf_init (&c->c2.buf, FRAME_HEADROOM_ADJ (&c->c2.frame, FRAME_HEADROOM_MARKER_READ_LINK)));
  status = link_socket_read (c->c2.link_socket, &c->c2.buf, MAX_RW_SIZE_LINK (&c->c2.frame), &c->c2.from);

  if (socket_connection_reset (c->c2.link_socket, status))
    {
      /* received a disconnect from a connection-oriented protocol */
      if (c->options.inetd)
	{
	  c->sig->signal_received = SIGTERM;
	  msg (D_STREAM_ERRORS, "Connection reset, inetd/xinetd exit [%d]", status);
	}
      else
	{
	  c->sig->signal_received = SIGUSR1; /* SOFT-SIGUSR1 -- TCP connection reset */
	  msg (D_STREAM_ERRORS, "Connection reset, restarting [%d]", status);
	}
      c->sig->signal_text = "connection-reset";
      perf_pop ();
      return;
    }

  /* check recvfrom status */
  check_status (status, "read", c->c2.link_socket, NULL);

#ifdef ENABLE_SOCKS
  /* Remove socks header if applicable */
  socks_postprocess_incoming_link (c);
#endif

  perf_pop ();
}

/*
 * Input:  c->c2.buf
 * Output: c->c2.to_tun
 */

void
process_incoming_link (struct context *c)
{
  struct gc_arena gc = gc_new ();
  bool decrypt_status;
  struct link_socket_info *lsi = get_link_socket_info (c);
  const uint8_t *orig_buf = c->c2.buf.data;

  perf_push (PERF_PROC_IN_LINK);

  if (c->c2.buf.len > 0)
    {
      c->c2.link_read_bytes += c->c2.buf.len;
      c->c2.original_recv_size = c->c2.buf.len;
    }
  else
    c->c2.original_recv_size = 0;

#ifdef ENABLE_DEBUG
  /* take action to corrupt packet if we are in gremlin test mode */
  if (c->options.gremlin) {
    if (!ask_gremlin (c->options.gremlin))
      c->c2.buf.len = 0;
    corrupt_gremlin (&c->c2.buf, c->options.gremlin);
  }
#endif

  /* log incoming packet */
#ifdef LOG_RW
  if (c->c2.log_rw)
    fprintf (stderr, "R");
#endif
  msg (D_LINK_RW, "%s READ [%d] from %s: %s",
       proto2ascii (lsi->proto, true),
       BLEN (&c->c2.buf),
       print_sockaddr (&c->c2.from, &gc),
       PROTO_DUMP (&c->c2.buf, &gc));

  /*
   * Good, non-zero length packet received.
   * Commence multi-stage processing of packet,
   * such as authenticate, decrypt, decompress.
   * If any stage fails, it sets buf.len to 0 or -1,
   * telling downstream stages to ignore the packet.
   */
  if (c->c2.buf.len > 0)
    {
      if (!link_socket_verify_incoming_addr (&c->c2.buf, lsi, &c->c2.from))
	link_socket_bad_incoming_addr (&c->c2.buf, lsi, &c->c2.from);

#ifdef USE_CRYPTO
#ifdef USE_SSL
      if (c->c2.tls_multi)
	{
	  /*
	   * If tls_pre_decrypt returns true, it means the incoming
	   * packet was a good TLS control channel packet.  If so, TLS code
	   * will deal with the packet and set buf.len to 0 so downstream
	   * stages ignore it.
	   *
	   * If the packet is a data channel packet, tls_pre_decrypt
	   * will load crypto_options with the correct encryption key
	   * and return false.
	   */
	  /*tls_mutex_lock (c->c2.tls_multi);*/
	  if (tls_pre_decrypt (c->c2.tls_multi, &c->c2.from, &c->c2.buf, &c->c2.crypto_options))
	    {
	      interval_action (&c->c2.tmp_int);

	      /* reset packet received timer if TLS packet */
	      if (c->options.ping_rec_timeout)
		event_timeout_reset (&c->c2.ping_rec_interval);
	    }
	}
#if P2MP_SERVER
      /*
       * Drop non-TLS packet if client-connect script/plugin has not
       * yet succeeded.
       */
      if (c->c2.context_auth != CAS_SUCCEEDED)
	c->c2.buf.len = 0;
#endif
#endif /* USE_SSL */

      /* authenticate and decrypt the incoming packet */
      decrypt_status = openvpn_decrypt (&c->c2.buf, c->c2.buffers->decrypt_buf, &c->c2.crypto_options, &c->c2.frame);

#ifdef USE_SSL
      if (c->c2.tls_multi)
	{
	  /*tls_mutex_unlock (c->c2.tls_multi);*/
	}
#endif
      
      if (!decrypt_status && link_socket_connection_oriented (c->c2.link_socket))
	{
	  /* decryption errors are fatal in TCP mode */
	  c->sig->signal_received = SIGUSR1; /* SOFT-SIGUSR1 -- decryption error in TCP mode */
	  c->sig->signal_text = "decryption-error";
	  msg (D_STREAM_ERRORS, "Fatal decryption error (process_incoming_link), restarting");
	  goto done;
	}

#endif /* USE_CRYPTO */

#ifdef ENABLE_FRAGMENT
      if (c->c2.fragment)
	fragment_incoming (c->c2.fragment, &c->c2.buf, &c->c2.frame_fragment);
#endif

#ifdef USE_LZO
      /* decompress the incoming packet */
      if (c->options.comp_lzo)
	lzo_decompress (&c->c2.buf, c->c2.buffers->lzo_decompress_buf, &c->c2.lzo_compwork, &c->c2.frame);
#endif
      /*
       * Set our "official" outgoing address, since
       * if buf.len is non-zero, we know the packet
       * authenticated.  In TLS mode we do nothing
       * because TLS mode takes care of source address
       * authentication.
       *
       * Also, update the persisted version of our packet-id.
       */
      if (!TLS_MODE (c))
	link_socket_set_outgoing_addr (&c->c2.buf, lsi, &c->c2.from, NULL, c->c2.es);

      /* reset packet received timer */
      if (c->options.ping_rec_timeout && c->c2.buf.len > 0)
	event_timeout_reset (&c->c2.ping_rec_interval);

      /* increment authenticated receive byte count */
      if (c->c2.buf.len > 0)
	{
	  c->c2.link_read_bytes_auth += c->c2.buf.len;
	  c->c2.max_recv_size_local = max_int (c->c2.original_recv_size, c->c2.max_recv_size_local);
	}

      /* Did we just receive an openvpn ping packet? */
      if (is_ping_msg (&c->c2.buf))
	{
	  dmsg (D_PACKET_CONTENT, "RECEIVED PING PACKET");
	  c->c2.buf.len = 0; /* drop packet */
	}

#ifdef ENABLE_OCC
      /* Did we just receive an OCC packet? */
      if (is_occ_msg (&c->c2.buf))
	process_received_occ_msg (c);
#endif

      buffer_turnover (orig_buf, &c->c2.to_tun, &c->c2.buf, &c->c2.buffers->read_link_buf);

      /* to_tun defined + unopened tuntap can cause deadlock */
      if (!tuntap_defined (c->c1.tuntap))
	c->c2.to_tun.len = 0;
    }
  else
    {
      buf_reset (&c->c2.to_tun);
    }
 done:
  perf_pop ();
  gc_free (&gc);
}

/*
 * Output: c->c2.buf
 */

void
read_incoming_tun (struct context *c)
{
  perf_push (PERF_READ_IN_TUN);

  /*
   * Setup for read() call on TUN/TAP device.
   */
  ASSERT (!c->c2.to_link.len);

  c->c2.buf = c->c2.buffers->read_tun_buf;
#ifdef TUN_PASS_BUFFER
  read_tun_buffered (c->c1.tuntap, &c->c2.buf, MAX_RW_SIZE_TUN (&c->c2.frame));
#else
  ASSERT (buf_init (&c->c2.buf, FRAME_HEADROOM (&c->c2.frame)));
  ASSERT (buf_safe (&c->c2.buf, MAX_RW_SIZE_TUN (&c->c2.frame)));
  c->c2.buf.len = read_tun (c->c1.tuntap, BPTR (&c->c2.buf), MAX_RW_SIZE_TUN (&c->c2.frame));
#endif

  /* Was TUN/TAP interface stopped? */
  if (tuntap_stop (c->c2.buf.len))
    {
      c->sig->signal_received = SIGTERM;
      c->sig->signal_text = "tun-stop";
      msg (M_INFO, "TUN/TAP interface has been stopped, exiting");
      perf_pop ();
      return;		  
    }

  /* Check the status return from read() */
  check_status (c->c2.buf.len, "read from TUN/TAP", NULL, c->c1.tuntap);

  perf_pop ();
}

/*
 * Input:  c->c2.buf
 * Output: c->c2.to_link
 */

void
process_incoming_tun (struct context *c)
{
  struct gc_arena gc = gc_new ();

  perf_push (PERF_PROC_IN_TUN);

  if (c->c2.buf.len > 0)
    c->c2.tun_read_bytes += c->c2.buf.len;

#ifdef LOG_RW
  if (c->c2.log_rw)
    fprintf (stderr, "r");
#endif

  /* Show packet content */
  dmsg (D_TUN_RW, "TUN READ [%d]: %s md5=%s",
       BLEN (&c->c2.buf),
       format_hex (BPTR (&c->c2.buf), BLEN (&c->c2.buf), 80, &gc),
       MD5SUM (BPTR (&c->c2.buf), BLEN (&c->c2.buf), &gc));

  if (c->c2.buf.len > 0)
    {
      /*
       * The --passtos and --mssfix options require
       * us to examine the IPv4 header.
       */
      process_ipv4_header (c, PIPV4_PASSTOS|PIPV4_MSSFIX, &c->c2.buf);
      encrypt_sign (c, true);
    }
  else
    {
      buf_reset (&c->c2.to_link);
    }
  perf_pop ();
  gc_free (&gc);
}

void
process_ipv4_header (struct context *c, unsigned int flags, struct buffer *buf)
{
  if (!c->options.mssfix)
    flags &= ~PIPV4_MSSFIX;
#if PASSTOS_CAPABILITY
  if (!c->options.passtos)
    flags &= ~PIPV4_PASSTOS;
#endif

  if (buf->len > 0)
    {
      /*
       * The --passtos and --mssfix options require
       * us to examine the IPv4 header.
       */
#if PASSTOS_CAPABILITY
      if (flags & (PIPV4_PASSTOS|PIPV4_MSSFIX))
#else
      if (flags & PIPV4_MSSFIX)
#endif
	{
	  struct buffer ipbuf = *buf;
	  if (is_ipv4 (TUNNEL_TYPE (c->c1.tuntap), &ipbuf))
	    {
#if PASSTOS_CAPABILITY
	      /* extract TOS from IP header */
	      if (flags & PIPV4_PASSTOS)
		link_socket_extract_tos (c->c2.link_socket, &ipbuf);
#endif
			  
	      /* possibly alter the TCP MSS */
	      if (flags & PIPV4_MSSFIX)
		mss_fixup (&ipbuf, MTU_TO_MSS (TUN_MTU_SIZE_DYNAMIC (&c->c2.frame)));
	    }
	}
    }
}

/*
 * Input: c->c2.to_link
 */

void
process_outgoing_link (struct context *c)
{
  struct gc_arena gc = gc_new ();

  perf_push (PERF_PROC_OUT_LINK);

  if (c->c2.to_link.len > 0 && c->c2.to_link.len <= EXPANDED_SIZE (&c->c2.frame))
    {
      /*
       * Setup for call to send/sendto which will send
       * packet to remote over the TCP/UDP port.
       */
      int size = 0;
      ASSERT (addr_defined (&c->c2.to_link_addr));

#ifdef ENABLE_DEBUG
      /* In gremlin-test mode, we may choose to drop this packet */
      if (!c->options.gremlin || ask_gremlin (c->options.gremlin))
#endif
	{
	  /*
	   * Let the traffic shaper know how many bytes
	   * we wrote.
	   */
#ifdef HAVE_GETTIMEOFDAY
	  if (c->options.shaper)
	    shaper_wrote_bytes (&c->c2.shaper, BLEN (&c->c2.to_link)
				+ datagram_overhead (c->options.proto));
#endif
	  /*
	   * Let the pinger know that we sent a packet.
	   */
	  if (c->options.ping_send_timeout)
	    event_timeout_reset (&c->c2.ping_send_interval);

#if PASSTOS_CAPABILITY
	  /* Set TOS */
	  link_socket_set_tos (c->c2.link_socket);
#endif

	  /* Log packet send */
#ifdef LOG_RW
	  if (c->c2.log_rw)
	    fprintf (stderr, "W");
#endif
	  msg (D_LINK_RW, "%s WRITE [%d] to %s: %s",
	       proto2ascii (c->c2.link_socket->info.proto, true),
	       BLEN (&c->c2.to_link),
	       print_sockaddr (&c->c2.to_link_addr, &gc),
	       PROTO_DUMP (&c->c2.to_link, &gc));

	  /* Packet send complexified by possible Socks5 usage */
	  {
	    struct sockaddr_in *to_addr = &c->c2.to_link_addr;
#ifdef ENABLE_SOCKS
	    int size_delta = 0;
#endif

#ifdef ENABLE_SOCKS
	    /* If Socks5 over UDP, prepend header */
	    socks_preprocess_outgoing_link (c, &to_addr, &size_delta);
#endif
	    /* Send packet */
	    size = link_socket_write (c->c2.link_socket, &c->c2.to_link, to_addr);

#ifdef ENABLE_SOCKS
	    /* Undo effect of prepend */
	    link_socket_write_post_size_adjust (&size, size_delta, &c->c2.to_link);
#endif
	  }

	  if (size > 0)
	    {
	      c->c2.max_send_size_local = max_int (size, c->c2.max_send_size_local);
	      c->c2.link_write_bytes += size;
	    }
	}

      /* Check return status */
      check_status (size, "write", c->c2.link_socket, NULL);

      if (size > 0)
	{
	  /* Did we write a different size packet than we intended? */
	  if (size != BLEN (&c->c2.to_link))
	    msg (D_LINK_ERRORS,
		 "TCP/UDP packet was truncated/expanded on write to %s (tried=%d,actual=%d)",
		 print_sockaddr (&c->c2.to_link_addr, &gc),
		 BLEN (&c->c2.to_link),
		 size);
	}
    }
  else
    {
      if (c->c2.to_link.len > 0)
	msg (D_LINK_ERRORS, "TCP/UDP packet too large on write to %s (tried=%d,max=%d)",
	     print_sockaddr (&c->c2.to_link_addr, &gc),
	     c->c2.to_link.len,
	     EXPANDED_SIZE (&c->c2.frame));
    }

  buf_reset (&c->c2.to_link);

  perf_pop ();
  gc_free (&gc);
}

/*
 * Input: c->c2.to_tun
 */

void
process_outgoing_tun (struct context *c)
{
  struct gc_arena gc = gc_new ();

  perf_push (PERF_PROC_OUT_TUN);

  /*
   * Set up for write() call to TUN/TAP
   * device.
   */
  ASSERT (c->c2.to_tun.len > 0);

  /*
   * The --mssfix option requires
   * us to examine the IPv4 header.
   */
  process_ipv4_header (c, PIPV4_MSSFIX, &c->c2.to_tun);

  if (c->c2.to_tun.len <= MAX_RW_SIZE_TUN (&c->c2.frame))
    {
      /*
       * Write to TUN/TAP device.
       */
      int size;

#ifdef LOG_RW
      if (c->c2.log_rw)
	fprintf (stderr, "w");
#endif
      dmsg (D_TUN_RW, "TUN WRITE [%d]: %s md5=%s",
	   BLEN (&c->c2.to_tun),
	   format_hex (BPTR (&c->c2.to_tun), BLEN (&c->c2.to_tun), 80, &gc),
	   MD5SUM (BPTR (&c->c2.to_tun), BLEN (&c->c2.to_tun), &gc));

#ifdef TUN_PASS_BUFFER
      size = write_tun_buffered (c->c1.tuntap, &c->c2.to_tun);
#else
      size = write_tun (c->c1.tuntap, BPTR (&c->c2.to_tun), BLEN (&c->c2.to_tun));
#endif

      if (size > 0)
	c->c2.tun_write_bytes += size;
      check_status (size, "write to TUN/TAP", NULL, c->c1.tuntap);

      /* check written packet size */
      if (size > 0)
	{
	  /* Did we write a different size packet than we intended? */
	  if (size != BLEN (&c->c2.to_tun))
	    msg (D_LINK_ERRORS,
		 "TUN/TAP packet was destructively fragmented on write to %s (tried=%d,actual=%d)",
		 c->c1.tuntap->actual_name,
		 BLEN (&c->c2.to_tun),
		 size);
	}
    }
  else
    {
      /*
       * This should never happen, probably indicates some kind
       * of MTU mismatch.
       */
      msg (D_LINK_ERRORS, "tun packet too large on write (tried=%d,max=%d)",
	   c->c2.to_tun.len,
	   MAX_RW_SIZE_TUN (&c->c2.frame));
    }

  /*
   * Putting the --inactive timeout reset here, ensures that we will timeout
   * if the remote goes away, even if we are trying to send data to the
   * remote and failing.
   */
  register_activity (c);

  buf_reset (&c->c2.to_tun);

  perf_pop ();
  gc_free (&gc);
}

void
pre_select (struct context *c)
{
  /* make sure current time (now) is updated on function entry */

  /*
   * Start with an effectively infinite timeout, then let it
   * reduce to a timeout that reflects the component which
   * needs the earliest service.
   */
  c->c2.timeval.tv_sec = BIG_TIMEOUT;
  c->c2.timeval.tv_usec = 0;

#if defined(WIN32)
  if (check_debug_level (D_TAP_WIN32_DEBUG))
    {
      c->c2.timeval.tv_sec = 1;
      if (tuntap_defined (c->c1.tuntap))
	tun_show_debug (c->c1.tuntap);
    }
#endif

  /* check coarse timers? */
  check_coarse_timers (c);
  if (c->sig->signal_received)
    return;

  /* Does TLS need service? */
  check_tls (c);

  /* In certain cases, TLS errors will require a restart */
  check_tls_errors (c);
  if (c->sig->signal_received)
    return;

  /* check for incoming configuration info on the control channel */
  check_incoming_control_channel (c);

#ifdef ENABLE_OCC
  /* Should we send an OCC message? */
  check_send_occ_msg (c);
#endif

#ifdef ENABLE_FRAGMENT
  /* Should we deliver a datagram fragment to remote? */
  check_fragment (c);
#endif

  /* Update random component of timeout */
  check_timeout_random_component (c);
}

/*
 * Wait for I/O events.  Used for both TCP & UDP sockets
 * in point-to-point mode and for UDP sockets in
 * point-to-multipoint mode.
 */

void
io_wait_dowork (struct context *c, const unsigned int flags)
{
  unsigned int socket = 0;
  unsigned int tuntap = 0;
  struct event_set_return esr[4];

  /* These shifts all depend on EVENT_READ and EVENT_WRITE */
  static const int socket_shift = 0;     /* depends on SOCKET_READ and SOCKET_WRITE */
  static const int tun_shift = 2;        /* depends on TUN_READ and TUN_WRITE */
  static const int err_shift = 4;        /* depends on ES_ERROR */
#ifdef ENABLE_MANAGEMENT
  static const int management_shift = 6; /* depends on MANAGEMENT_READ and MANAGEMENT_WRITE */
#endif

  /*
   * Decide what kind of events we want to wait for.
   */
  event_reset (c->c2.event_set);

  /*
   * On win32 we use the keyboard or an event object as a source
   * of asynchronous signals.
   */
  if (flags & IOW_WAIT_SIGNAL)
    wait_signal (c->c2.event_set, (void*)&err_shift);

  /*
   * If outgoing data (for TCP/UDP port) pending, wait for ready-to-send
   * status from TCP/UDP port. Otherwise, wait for incoming data on
   * TUN/TAP device.
   */
  if (flags & IOW_TO_LINK)
    {
      if (flags & IOW_SHAPER)
	{
	  /*
	   * If sending this packet would put us over our traffic shaping
	   * quota, don't send -- instead compute the delay we must wait
	   * until it will be OK to send the packet.
	   */
#ifdef HAVE_GETTIMEOFDAY
	  int delay = 0;

	  /* set traffic shaping delay in microseconds */
	  if (c->options.shaper)
	    delay = max_int (delay, shaper_delay (&c->c2.shaper));
	  
	  if (delay < 1000)
	    {
	      socket |= EVENT_WRITE;
	    }
	  else
	    {
	      shaper_soonest_event (&c->c2.timeval, delay);
	    }
#else /* HAVE_GETTIMEOFDAY */
	  socket |= EVENT_WRITE;
#endif /* HAVE_GETTIMEOFDAY */
	}
      else
	{
	  socket |= EVENT_WRITE;
	}
    }
  else if (!((flags & IOW_FRAG) && TO_LINK_FRAG (c)))
    {
      if (flags & IOW_READ_TUN)
	tuntap |= EVENT_READ;
    }

  /*
   * If outgoing data (for TUN/TAP device) pending, wait for ready-to-send status
   * from device.  Otherwise, wait for incoming data on TCP/UDP port.
   */
  if (flags & IOW_TO_TUN)
    {
      tuntap |= EVENT_WRITE;
    }
  else
    {
      if (flags & IOW_READ_LINK)
	socket |= EVENT_READ;
    }

  /*
   * outgoing bcast buffer waiting to be sent?
   */
  if (flags & IOW_MBUF)
    socket |= EVENT_WRITE;

  /*
   * Force wait on TUN input, even if also waiting on TCP/UDP output
   */
  if (flags & IOW_READ_TUN_FORCE)
    tuntap |= EVENT_READ;

  /*
   * Configure event wait based on socket, tuntap flags.
   */
  socket_set (c->c2.link_socket, c->c2.event_set, socket, (void*)&socket_shift, NULL);
  tun_set (c->c1.tuntap, c->c2.event_set, tuntap, (void*)&tun_shift, NULL);

#ifdef ENABLE_MANAGEMENT
  if (management)
    management_socket_set (management, c->c2.event_set, (void*)&management_shift, NULL);
#endif

  /*
   * Possible scenarios:
   *  (1) tcp/udp port has data available to read
   *  (2) tcp/udp port is ready to accept more data to write
   *  (3) tun dev has data available to read
   *  (4) tun dev is ready to accept more data to write
   *  (5) we received a signal (handler sets signal_received)
   *  (6) timeout (tv) expired
   */

  c->c2.event_set_status = ES_ERROR;

  if (!c->sig->signal_received)
    {
      if (!(flags & IOW_CHECK_RESIDUAL) || !socket_read_residual (c->c2.link_socket))
	{
	  int status;

#ifdef ENABLE_DEBUG
	  if (check_debug_level (D_EVENT_WAIT))
	    show_wait_status (c);
#endif

	  /*
	   * Wait for something to happen.
	   */
	  status = event_wait (c->c2.event_set, &c->c2.timeval, esr, SIZE(esr));

	  check_status (status, "event_wait", NULL, NULL);

	  if (status > 0)
	    {
	      int i;
	      c->c2.event_set_status = 0;
	      for (i = 0; i < status; ++i)
		{
		  const struct event_set_return *e = &esr[i];
		  c->c2.event_set_status |= ((e->rwflags & 3) << *((int*)e->arg));
		}
	    }
	  else if (status == 0)
	    {
	      c->c2.event_set_status = ES_TIMEOUT;
	    }
	}
      else
	{
	  c->c2.event_set_status = SOCKET_READ;
	}
    }

  /* 'now' should always be a reasonably up-to-date timestamp */
  update_time ();

  /* set signal_received if a signal was received */
  if (c->c2.event_set_status & ES_ERROR)
    get_signal (&c->sig->signal_received);

  dmsg (D_EVENT_WAIT, "I/O WAIT status=0x%04x", c->c2.event_set_status);
}

void
process_io (struct context *c)
{
  const unsigned int status = c->c2.event_set_status;

#ifdef ENABLE_MANAGEMENT
  if (status & (MANAGEMENT_READ|MANAGEMENT_WRITE))
    {
      ASSERT (management);
      management_io (management);
    }
#endif

  /* TCP/UDP port ready to accept write */
  if (status & SOCKET_WRITE)
    {
      process_outgoing_link (c);
    }
  /* TUN device ready to accept write */
  else if (status & TUN_WRITE)
    {
      process_outgoing_tun (c);
    }
  /* Incoming data on TCP/UDP port */
  else if (status & SOCKET_READ)
    {
      read_incoming_link (c);
      if (!IS_SIG (c))
	process_incoming_link (c);
    }
  /* Incoming data on TUN device */
  else if (status & TUN_READ)
    {
      read_incoming_tun (c);
      if (!IS_SIG (c))
	process_incoming_tun (c);
    }
}