aboutsummaryrefslogtreecommitdiffstats
path: root/net/l2tp/l2tp_core.c
blob: c64ce0a0bb03b11c3b28d3445d2abb361fee9070 (plain)
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
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
/*
 * L2TP core.
 *
 * Copyright (c) 2008,2009,2010 Katalix Systems Ltd
 *
 * This file contains some code of the original L2TPv2 pppol2tp
 * driver, which has the following copyright:
 *
 * Authors:	Martijn van Oosterhout <kleptog@svana.org>
 *		James Chapman (jchapman@katalix.com)
 * Contributors:
 *		Michal Ostrowski <mostrows@speakeasy.net>
 *		Arnaldo Carvalho de Melo <acme@xconectiva.com.br>
 *		David S. Miller (davem@redhat.com)
 *
 * 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.
 */

#include <linux/module.h>
#include <linux/string.h>
#include <linux/list.h>
#include <linux/rculist.h>
#include <linux/uaccess.h>

#include <linux/kernel.h>
#include <linux/spinlock.h>
#include <linux/kthread.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/errno.h>
#include <linux/jiffies.h>

#include <linux/netdevice.h>
#include <linux/net.h>
#include <linux/inetdevice.h>
#include <linux/skbuff.h>
#include <linux/init.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include <linux/l2tp.h>
#include <linux/hash.h>
#include <linux/sort.h>
#include <linux/file.h>
#include <linux/nsproxy.h>
#include <net/net_namespace.h>
#include <net/netns/generic.h>
#include <net/dst.h>
#include <net/ip.h>
#include <net/udp.h>
#include <net/inet_common.h>
#include <net/xfrm.h>
#include <net/protocol.h>

#include <asm/byteorder.h>
#include <asm/atomic.h>

#include "l2tp_core.h"

#define L2TP_DRV_VERSION	"V2.0"

/* L2TP header constants */
#define L2TP_HDRFLAG_T	   0x8000
#define L2TP_HDRFLAG_L	   0x4000
#define L2TP_HDRFLAG_S	   0x0800
#define L2TP_HDRFLAG_O	   0x0200
#define L2TP_HDRFLAG_P	   0x0100

#define L2TP_HDR_VER_MASK  0x000F
#define L2TP_HDR_VER_2	   0x0002
#define L2TP_HDR_VER_3	   0x0003

/* L2TPv3 default L2-specific sublayer */
#define L2TP_SLFLAG_S	   0x40000000
#define L2TP_SL_SEQ_MASK   0x00ffffff

#define L2TP_HDR_SIZE_SEQ		10
#define L2TP_HDR_SIZE_NOSEQ		6

/* Default trace flags */
#define L2TP_DEFAULT_DEBUG_FLAGS	0

#define PRINTK(_mask, _type, _lvl, _fmt, args...)			\
	do {								\
		if ((_mask) & (_type))					\
			printk(_lvl "L2TP: " _fmt, ##args);		\
	} while (0)

/* Private data stored for received packets in the skb.
 */
struct l2tp_skb_cb {
	u32			ns;
	u16			has_seq;
	u16			length;
	unsigned long		expires;
};

#define L2TP_SKB_CB(skb)	((struct l2tp_skb_cb *) &skb->cb[sizeof(struct inet_skb_parm)])

static atomic_t l2tp_tunnel_count;
static atomic_t l2tp_session_count;

/* per-net private data for this module */
static unsigned int l2tp_net_id;
struct l2tp_net {
	struct list_head l2tp_tunnel_list;
	spinlock_t l2tp_tunnel_list_lock;
	struct hlist_head l2tp_session_hlist[L2TP_HASH_SIZE_2];
	spinlock_t l2tp_session_hlist_lock;
};

static void l2tp_session_set_header_len(struct l2tp_session *session, int version);
static void l2tp_tunnel_free(struct l2tp_tunnel *tunnel);
static void l2tp_tunnel_closeall(struct l2tp_tunnel *tunnel);

static inline struct l2tp_net *l2tp_pernet(struct net *net)
{
	BUG_ON(!net);

	return net_generic(net, l2tp_net_id);
}


/* Tunnel reference counts. Incremented per session that is added to
 * the tunnel.
 */
static inline void l2tp_tunnel_inc_refcount_1(struct l2tp_tunnel *tunnel)
{
	atomic_inc(&tunnel->ref_count);
}

static inline void l2tp_tunnel_dec_refcount_1(struct l2tp_tunnel *tunnel)
{
	if (atomic_dec_and_test(&tunnel->ref_count))
		l2tp_tunnel_free(tunnel);
}
#ifdef L2TP_REFCNT_DEBUG
#define l2tp_tunnel_inc_refcount(_t) do { \
		printk(KERN_DEBUG "l2tp_tunnel_inc_refcount: %s:%d %s: cnt=%d\n", __func__, __LINE__, (_t)->name, atomic_read(&_t->ref_count)); \
		l2tp_tunnel_inc_refcount_1(_t);				\
	} while (0)
#define l2tp_tunnel_dec_refcount(_t) do { \
		printk(KERN_DEBUG "l2tp_tunnel_dec_refcount: %s:%d %s: cnt=%d\n", __func__, __LINE__, (_t)->name, atomic_read(&_t->ref_count)); \
		l2tp_tunnel_dec_refcount_1(_t);				\
	} while (0)
#else
#define l2tp_tunnel_inc_refcount(t) l2tp_tunnel_inc_refcount_1(t)
#define l2tp_tunnel_dec_refcount(t) l2tp_tunnel_dec_refcount_1(t)
#endif

/* Session hash global list for L2TPv3.
 * The session_id SHOULD be random according to RFC3931, but several
 * L2TP implementations use incrementing session_ids.  So we do a real
 * hash on the session_id, rather than a simple bitmask.
 */
static inline struct hlist_head *
l2tp_session_id_hash_2(struct l2tp_net *pn, u32 session_id)
{
	return &pn->l2tp_session_hlist[hash_32(session_id, L2TP_HASH_BITS_2)];

}

/* Lookup a session by id in the global session list
 */
static struct l2tp_session *l2tp_session_find_2(struct net *net, u32 session_id)
{
	struct l2tp_net *pn = l2tp_pernet(net);
	struct hlist_head *session_list =
		l2tp_session_id_hash_2(pn, session_id);
	struct l2tp_session *session;
	struct hlist_node *walk;

	rcu_read_lock_bh();
	hlist_for_each_entry_rcu(session, walk, session_list, global_hlist) {
		if (session->session_id == session_id) {
			rcu_read_unlock_bh();
			return session;
		}
	}
	rcu_read_unlock_bh();

	return NULL;
}

/* Session hash list.
 * The session_id SHOULD be random according to RFC2661, but several
 * L2TP implementations (Cisco and Microsoft) use incrementing
 * session_ids.  So we do a real hash on the session_id, rather than a
 * simple bitmask.
 */
static inline struct hlist_head *
l2tp_session_id_hash(struct l2tp_tunnel *tunnel, u32 session_id)
{
	return &tunnel->session_hlist[hash_32(session_id, L2TP_HASH_BITS)];
}

/* Lookup a session by id
 */
struct l2tp_session *l2tp_session_find(struct net *net, struct l2tp_tunnel *tunnel, u32 session_id)
{
	struct hlist_head *session_list;
	struct l2tp_session *session;
	struct hlist_node *walk;

	/* In L2TPv3, session_ids are unique over all tunnels and we
	 * sometimes need to look them up before we know the
	 * tunnel.
	 */
	if (tunnel == NULL)
		return l2tp_session_find_2(net, session_id);

	session_list = l2tp_session_id_hash(tunnel, session_id);
	read_lock_bh(&tunnel->hlist_lock);
	hlist_for_each_entry(session, walk, session_list, hlist) {
		if (session->session_id == session_id) {
			read_unlock_bh(&tunnel->hlist_lock);
			return session;
		}
	}
	read_unlock_bh(&tunnel->hlist_lock);

	return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_session_find);

struct l2tp_session *l2tp_session_find_nth(struct l2tp_tunnel *tunnel, int nth)
{
	int hash;
	struct hlist_node *walk;
	struct l2tp_session *session;
	int count = 0;

	read_lock_bh(&tunnel->hlist_lock);
	for (hash = 0; hash < L2TP_HASH_SIZE; hash++) {
		hlist_for_each_entry(session, walk, &tunnel->session_hlist[hash], hlist) {
			if (++count > nth) {
				read_unlock_bh(&tunnel->hlist_lock);
				return session;
			}
		}
	}

	read_unlock_bh(&tunnel->hlist_lock);

	return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_session_find_nth);

/* Lookup a session by interface name.
 * This is very inefficient but is only used by management interfaces.
 */
struct l2tp_session *l2tp_session_find_by_ifname(struct net *net, char *ifname)
{
	struct l2tp_net *pn = l2tp_pernet(net);
	int hash;
	struct hlist_node *walk;
	struct l2tp_session *session;

	rcu_read_lock_bh();
	for (hash = 0; hash < L2TP_HASH_SIZE_2; hash++) {
		hlist_for_each_entry_rcu(session, walk, &pn->l2tp_session_hlist[hash], global_hlist) {
			if (!strcmp(session->ifname, ifname)) {
				rcu_read_unlock_bh();
				return session;
			}
		}
	}

	rcu_read_unlock_bh();

	return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_session_find_by_ifname);

/* Lookup a tunnel by id
 */
struct l2tp_tunnel *l2tp_tunnel_find(struct net *net, u32 tunnel_id)
{
	struct l2tp_tunnel *tunnel;
	struct l2tp_net *pn = l2tp_pernet(net);

	rcu_read_lock_bh();
	list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {
		if (tunnel->tunnel_id == tunnel_id) {
			rcu_read_unlock_bh();
			return tunnel;
		}
	}
	rcu_read_unlock_bh();

	return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_find);

struct l2tp_tunnel *l2tp_tunnel_find_nth(struct net *net, int nth)
{
	struct l2tp_net *pn = l2tp_pernet(net);
	struct l2tp_tunnel *tunnel;
	int count = 0;

	rcu_read_lock_bh();
	list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {
		if (++count > nth) {
			rcu_read_unlock_bh();
			return tunnel;
		}
	}

	rcu_read_unlock_bh();

	return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_find_nth);

/*****************************************************************************
 * Receive data handling
 *****************************************************************************/

/* Queue a skb in order. We come here only if the skb has an L2TP sequence
 * number.
 */
static void l2tp_recv_queue_skb(struct l2tp_session *session, struct sk_buff *skb)
{
	struct sk_buff *skbp;
	struct sk_buff *tmp;
	u32 ns = L2TP_SKB_CB(skb)->ns;

	spin_lock_bh(&session->reorder_q.lock);
	skb_queue_walk_safe(&session->reorder_q, skbp, tmp) {
		if (L2TP_SKB_CB(skbp)->ns > ns) {
			__skb_queue_before(&session->reorder_q, skbp, skb);
			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
			       "%s: pkt %hu, inserted before %hu, reorder_q len=%d\n",
			       session->name, ns, L2TP_SKB_CB(skbp)->ns,
			       skb_queue_len(&session->reorder_q));
			session->stats.rx_oos_packets++;
			goto out;
		}
	}

	__skb_queue_tail(&session->reorder_q, skb);

out:
	spin_unlock_bh(&session->reorder_q.lock);
}

/* Dequeue a single skb.
 */
static void l2tp_recv_dequeue_skb(struct l2tp_session *session, struct sk_buff *skb)
{
	struct l2tp_tunnel *tunnel = session->tunnel;
	int length = L2TP_SKB_CB(skb)->length;

	/* We're about to requeue the skb, so return resources
	 * to its current owner (a socket receive buffer).
	 */
	skb_orphan(skb);

	tunnel->stats.rx_packets++;
	tunnel->stats.rx_bytes += length;
	session->stats.rx_packets++;
	session->stats.rx_bytes += length;

	if (L2TP_SKB_CB(skb)->has_seq) {
		/* Bump our Nr */
		session->nr++;
		if (tunnel->version == L2TP_HDR_VER_2)
			session->nr &= 0xffff;
		else
			session->nr &= 0xffffff;

		PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
		       "%s: updated nr to %hu\n", session->name, session->nr);
	}

	/* call private receive handler */
	if (session->recv_skb != NULL)
		(*session->recv_skb)(session, skb, L2TP_SKB_CB(skb)->length);
	else
		kfree_skb(skb);

	if (session->deref)
		(*session->deref)(session);
}

/* Dequeue skbs from the session's reorder_q, subject to packet order.
 * Skbs that have been in the queue for too long are simply discarded.
 */
static void l2tp_recv_dequeue(struct l2tp_session *session)
{
	struct sk_buff *skb;
	struct sk_buff *tmp;

	/* If the pkt at the head of the queue has the nr that we
	 * expect to send up next, dequeue it and any other
	 * in-sequence packets behind it.
	 */
	spin_lock_bh(&session->reorder_q.lock);
	skb_queue_walk_safe(&session->reorder_q, skb, tmp) {
		if (time_after(jiffies, L2TP_SKB_CB(skb)->expires)) {
			session->stats.rx_seq_discards++;
			session->stats.rx_errors++;
			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
			       "%s: oos pkt %u len %d discarded (too old), "
			       "waiting for %u, reorder_q_len=%d\n",
			       session->name, L2TP_SKB_CB(skb)->ns,
			       L2TP_SKB_CB(skb)->length, session->nr,
			       skb_queue_len(&session->reorder_q));
			__skb_unlink(skb, &session->reorder_q);
			kfree_skb(skb);
			if (session->deref)
				(*session->deref)(session);
			continue;
		}

		if (L2TP_SKB_CB(skb)->has_seq) {
			if (L2TP_SKB_CB(skb)->ns != session->nr) {
				PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
				       "%s: holding oos pkt %u len %d, "
				       "waiting for %u, reorder_q_len=%d\n",
				       session->name, L2TP_SKB_CB(skb)->ns,
				       L2TP_SKB_CB(skb)->length, session->nr,
				       skb_queue_len(&session->reorder_q));
				goto out;
			}
		}
		__skb_unlink(skb, &session->reorder_q);

		/* Process the skb. We release the queue lock while we
		 * do so to let other contexts process the queue.
		 */
		spin_unlock_bh(&session->reorder_q.lock);
		l2tp_recv_dequeue_skb(session, skb);
		spin_lock_bh(&session->reorder_q.lock);
	}

out:
	spin_unlock_bh(&session->reorder_q.lock);
}

static inline int l2tp_verify_udp_checksum(struct sock *sk,
					   struct sk_buff *skb)
{
	struct udphdr *uh = udp_hdr(skb);
	u16 ulen = ntohs(uh->len);
	struct inet_sock *inet;
	__wsum psum;

	if (sk->sk_no_check || skb_csum_unnecessary(skb) || !uh->check)
		return 0;

	inet = inet_sk(sk);
	psum = csum_tcpudp_nofold(inet->inet_saddr, inet->inet_daddr, ulen,
				  IPPROTO_UDP, 0);

	if ((skb->ip_summed == CHECKSUM_COMPLETE) &&
	    !csum_fold(csum_add(psum, skb->csum)))
		return 0;

	skb->csum = psum;

	return __skb_checksum_complete(skb);
}

/* Do receive processing of L2TP data frames. We handle both L2TPv2
 * and L2TPv3 data frames here.
 *
 * L2TPv2 Data Message Header
 *
 *  0                   1                   2                   3
 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |T|L|x|x|S|x|O|P|x|x|x|x|  Ver  |          Length (opt)         |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |           Tunnel ID           |           Session ID          |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |             Ns (opt)          |             Nr (opt)          |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |      Offset Size (opt)        |    Offset pad... (opt)
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *
 * Data frames are marked by T=0. All other fields are the same as
 * those in L2TP control frames.
 *
 * L2TPv3 Data Message Header
 *
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                      L2TP Session Header                      |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                      L2-Specific Sublayer                     |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                        Tunnel Payload                      ...
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *
 * L2TPv3 Session Header Over IP
 *
 *  0                   1                   2                   3
 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                           Session ID                          |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |               Cookie (optional, maximum 64 bits)...
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *                                                                 |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *
 * L2TPv3 L2-Specific Sublayer Format
 *
 *  0                   1                   2                   3
 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |x|S|x|x|x|x|x|x|              Sequence Number                  |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *
 * Cookie value, sublayer format and offset (pad) are negotiated with
 * the peer when the session is set up. Unlike L2TPv2, we do not need
 * to parse the packet header to determine if optional fields are
 * present.
 *
 * Caller must already have parsed the frame and determined that it is
 * a data (not control) frame before coming here. Fields up to the
 * session-id have already been parsed and ptr points to the data
 * after the session-id.
 */
void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
		      unsigned char *ptr, unsigned char *optr, u16 hdrflags,
		      int length, int (*payload_hook)(struct sk_buff *skb))
{
	struct l2tp_tunnel *tunnel = session->tunnel;
	int offset;
	u32 ns, nr;

	/* The ref count is increased since we now hold a pointer to
	 * the session. Take care to decrement the refcnt when exiting
	 * this function from now on...
	 */
	l2tp_session_inc_refcount(session);
	if (session->ref)
		(*session->ref)(session);

	/* Parse and check optional cookie */
	if (session->peer_cookie_len > 0) {
		if (memcmp(ptr, &session->peer_cookie[0], session->peer_cookie_len)) {
			PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_INFO,
			       "%s: cookie mismatch (%u/%u). Discarding.\n",
			       tunnel->name, tunnel->tunnel_id, session->session_id);
			session->stats.rx_cookie_discards++;
			goto discard;
		}
		ptr += session->peer_cookie_len;
	}

	/* Handle the optional sequence numbers. Sequence numbers are
	 * in different places for L2TPv2 and L2TPv3.
	 *
	 * If we are the LAC, enable/disable sequence numbers under
	 * the control of the LNS.  If no sequence numbers present but
	 * we were expecting them, discard frame.
	 */
	ns = nr = 0;
	L2TP_SKB_CB(skb)->has_seq = 0;
	if (tunnel->version == L2TP_HDR_VER_2) {
		if (hdrflags & L2TP_HDRFLAG_S) {
			ns = ntohs(*(__be16 *) ptr);
			ptr += 2;
			nr = ntohs(*(__be16 *) ptr);
			ptr += 2;

			/* Store L2TP info in the skb */
			L2TP_SKB_CB(skb)->ns = ns;
			L2TP_SKB_CB(skb)->has_seq = 1;

			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
			       "%s: recv data ns=%u, nr=%u, session nr=%u\n",
			       session->name, ns, nr, session->nr);
		}
	} else if (session->l2specific_type == L2TP_L2SPECTYPE_DEFAULT) {
		u32 l2h = ntohl(*(__be32 *) ptr);

		if (l2h & 0x40000000) {
			ns = l2h & 0x00ffffff;

			/* Store L2TP info in the skb */
			L2TP_SKB_CB(skb)->ns = ns;
			L2TP_SKB_CB(skb)->has_seq = 1;

			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
			       "%s: recv data ns=%u, session nr=%u\n",
			       session->name, ns, session->nr);
		}
	}

	/* Advance past L2-specific header, if present */
	ptr += session->l2specific_len;

	if (L2TP_SKB_CB(skb)->has_seq) {
		/* Received a packet with sequence numbers. If we're the LNS,
		 * check if we sre sending sequence numbers and if not,
		 * configure it so.
		 */
		if ((!session->lns_mode) && (!session->send_seq)) {
			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_INFO,
			       "%s: requested to enable seq numbers by LNS\n",
			       session->name);
			session->send_seq = -1;
			l2tp_session_set_header_len(session, tunnel->version);
		}
	} else {
		/* No sequence numbers.
		 * If user has configured mandatory sequence numbers, discard.
		 */
		if (session->recv_seq) {
			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_WARNING,
			       "%s: recv data has no seq numbers when required. "
			       "Discarding\n", session->name);
			session->stats.rx_seq_discards++;
			goto discard;
		}

		/* If we're the LAC and we're sending sequence numbers, the
		 * LNS has requested that we no longer send sequence numbers.
		 * If we're the LNS and we're sending sequence numbers, the
		 * LAC is broken. Discard the frame.
		 */
		if ((!session->lns_mode) && (session->send_seq)) {
			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_INFO,
			       "%s: requested to disable seq numbers by LNS\n",
			       session->name);
			session->send_seq = 0;
			l2tp_session_set_header_len(session, tunnel->version);
		} else if (session->send_seq) {
			PRINTK(session->debug, L2TP_MSG_SEQ, KERN_WARNING,
			       "%s: recv data has no seq numbers when required. "
			       "Discarding\n", session->name);
			session->stats.rx_seq_discards++;
			goto discard;
		}
	}

	/* Session data offset is handled differently for L2TPv2 and
	 * L2TPv3. For L2TPv2, there is an optional 16-bit value in
	 * the header. For L2TPv3, the offset is negotiated using AVPs
	 * in the session setup control protocol.
	 */
	if (tunnel->version == L2TP_HDR_VER_2) {
		/* If offset bit set, skip it. */
		if (hdrflags & L2TP_HDRFLAG_O) {
			offset = ntohs(*(__be16 *)ptr);
			ptr += 2 + offset;
		}
	} else
		ptr += session->offset;

	offset = ptr - optr;
	if (!pskb_may_pull(skb, offset))
		goto discard;

	__skb_pull(skb, offset);

	/* If caller wants to process the payload before we queue the
	 * packet, do so now.
	 */
	if (payload_hook)
		if ((*payload_hook)(skb))
			goto discard;

	/* Prepare skb for adding to the session's reorder_q.  Hold
	 * packets for max reorder_timeout or 1 second if not
	 * reordering.
	 */
	L2TP_SKB_CB(skb)->length = length;
	L2TP_SKB_CB(skb)->expires = jiffies +
		(session->reorder_timeout ? session->reorder_timeout : HZ);

	/* Add packet to the session's receive queue. Reordering is done here, if
	 * enabled. Saved L2TP protocol info is stored in skb->sb[].
	 */
	if (L2TP_SKB_CB(skb)->has_seq) {
		if (session->reorder_timeout != 0) {
			/* Packet reordering enabled. Add skb to session's
			 * reorder queue, in order of ns.
			 */
			l2tp_recv_queue_skb(session, skb);
		} else {
			/* Packet reordering disabled. Discard out-of-sequence
			 * packets
			 */
			if (L2TP_SKB_CB(skb)->ns != session->nr) {
				session->stats.rx_seq_discards++;
				PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
				       "%s: oos pkt %u len %d discarded, "
				       "waiting for %u, reorder_q_len=%d\n",
				       session->name, L2TP_SKB_CB(skb)->ns,
				       L2TP_SKB_CB(skb)->length, session->nr,
				       skb_queue_len(&session->reorder_q));
				goto discard;
			}
			skb_queue_tail(&session->reorder_q, skb);
		}
	} else {
		/* No sequence numbers. Add the skb to the tail of the
		 * reorder queue. This ensures that it will be
		 * delivered after all previous sequenced skbs.
		 */
		skb_queue_tail(&session->reorder_q, skb);
	}

	/* Try to dequeue as many skbs from reorder_q as we can. */
	l2tp_recv_dequeue(session);

	l2tp_session_dec_refcount(session);

	return;

discard:
	session->stats.rx_errors++;
	kfree_skb(skb);

	if (session->deref)
		(*session->deref)(session);

	l2tp_session_dec_refcount(session);
}
EXPORT_SYMBOL(l2tp_recv_common);

/* Internal UDP receive frame. Do the real work of receiving an L2TP data frame
 * here. The skb is not on a list when we get here.
 * Returns 0 if the packet was a data packet and was successfully passed on.
 * Returns 1 if the packet was not a good data packet and could not be
 * forwarded.  All such packets are passed up to userspace to deal with.
 */
static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb,
			      int (*payload_hook)(struct sk_buff *skb))
{
	struct l2tp_session *session = NULL;
	unsigned char *ptr, *optr;
	u16 hdrflags;
	u32 tunnel_id, session_id;
	int offset;
	u16 version;
	int length;

	if (tunnel->sock && l2tp_verify_udp_checksum(tunnel->sock, skb))
		goto discard_bad_csum;

	/* UDP always verifies the packet length. */
	__skb_pull(skb, sizeof(struct udphdr));

	/* Short packet? */
	if (!pskb_may_pull(skb, L2TP_HDR_SIZE_SEQ)) {
		PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_INFO,
		       "%s: recv short packet (len=%d)\n", tunnel->name, skb->len);
		goto error;
	}

	/* Point to L2TP header */
	optr = ptr = skb->data;

	/* Trace packet contents, if enabled */
	if (tunnel->debug & L2TP_MSG_DATA) {
		length = min(32u, skb->len);
		if (!pskb_may_pull(skb, length))
			goto error;

		printk(KERN_DEBUG "%s: recv: ", tunnel->name);

		offset = 0;
		do {
			printk(" %02X", ptr[offset]);
		} while (++offset < length);

		printk("\n");
	}

	/* Get L2TP header flags */
	hdrflags = ntohs(*(__be16 *) ptr);

	/* Check protocol version */
	version = hdrflags & L2TP_HDR_VER_MASK;
	if (version != tunnel->version) {
		PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_INFO,
		       "%s: recv protocol version mismatch: got %d expected %d\n",
		       tunnel->name, version, tunnel->version);
		goto error;
	}

	/* Get length of L2TP packet */
	length = skb->len;

	/* If type is control packet, it is handled by userspace. */
	if (hdrflags & L2TP_HDRFLAG_T) {
		PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_DEBUG,
		       "%s: recv control packet, len=%d\n", tunnel->name, length);
		goto error;
	}

	/* Skip flags */
	ptr += 2;

	if (tunnel->version == L2TP_HDR_VER_2) {
		/* If length is present, skip it */
		if (hdrflags & L2TP_HDRFLAG_L)
			ptr += 2;

		/* Extract tunnel and session ID */
		tunnel_id = ntohs(*(__be16 *) ptr);
		ptr += 2;
		session_id = ntohs(*(__be16 *) ptr);
		ptr += 2;
	} else {
		ptr += 2;	/* skip reserved bits */
		tunnel_id = tunnel->tunnel_id;
		session_id = ntohl(*(__be32 *) ptr);
		ptr += 4;
	}

	/* Find the session context */
	session = l2tp_session_find(tunnel->l2tp_net, tunnel, session_id);
	if (!session || !session->recv_skb) {
		/* Not found? Pass to userspace to deal with */
		PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_INFO,
		       "%s: no session found (%u/%u). Passing up.\n",
		       tunnel->name, tunnel_id, session_id);
		goto error;
	}

	l2tp_recv_common(session, skb, ptr, optr, hdrflags, length, payload_hook);

	return 0;

discard_bad_csum:
	LIMIT_NETDEBUG("%s: UDP: bad checksum\n", tunnel->name);
	UDP_INC_STATS_USER(tunnel->l2tp_net, UDP_MIB_INERRORS, 0);
	tunnel->stats.rx_errors++;
	kfree_skb(skb);

	return 0;

error:
	/* Put UDP header back */
	__skb_push(skb, sizeof(struct udphdr));

	return 1;
}

/* UDP encapsulation receive handler. See net/ipv4/udp.c.
 * Return codes:
 * 0 : success.
 * <0: error
 * >0: skb should be passed up to userspace as UDP.
 */
int l2tp_udp_encap_recv(struct sock *sk, struct sk_buff *skb)
{
	struct l2tp_tunnel *tunnel;

	tunnel = l2tp_sock_to_tunnel(sk);
	if (tunnel == NULL)
		goto pass_up;

	PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_DEBUG,
	       "%s: received %d bytes\n", tunnel->name, skb->len);

	if (l2tp_udp_recv_core(tunnel, skb, tunnel->recv_payload_hook))
		goto pass_up_put;

	sock_put(sk);
	return 0;

pass_up_put:
	sock_put(sk);
pass_up:
	return 1;
}
EXPORT_SYMBOL_GPL(l2tp_udp_encap_recv);

/************************************************************************
 * Transmit handling
 ***********************************************************************/

/* Build an L2TP header for the session into the buffer provided.
 */
static int l2tp_build_l2tpv2_header(struct l2tp_session *session, void *buf)
{
	struct l2tp_tunnel *tunnel = session->tunnel;
	__be16 *bufp = buf;
	__be16 *optr = buf;
	u16 flags = L2TP_HDR_VER_2;
	u32 tunnel_id = tunnel->peer_tunnel_id;
	u32 session_id = session->peer_session_id;

	if (session->send_seq)
		flags |= L2TP_HDRFLAG_S;

	/* Setup L2TP header. */
	*bufp++ = htons(flags);
	*bufp++ = htons(tunnel_id);
	*bufp++ = htons(session_id);
	if (session->send_seq) {
		*bufp++ = htons(session->ns);
		*bufp++ = 0;
		session->ns++;
		session->ns &= 0xffff;
		PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
		       "%s: updated ns to %u\n", session->name, session->ns);
	}

	return bufp - optr;
}

static int l2tp_build_l2tpv3_header(struct l2tp_session *session, void *buf)
{
	struct l2tp_tunnel *tunnel = session->tunnel;
	char *bufp = buf;
	char *optr = bufp;

	/* Setup L2TP header. The header differs slightly for UDP and
	 * IP encapsulations. For UDP, there is 4 bytes of flags.
	 */
	if (tunnel->encap == L2TP_ENCAPTYPE_UDP) {
		u16 flags = L2TP_HDR_VER_3;
		*((__be16 *) bufp) = htons(flags);
		bufp += 2;
		*((__be16 *) bufp) = 0;
		bufp += 2;
	}

	*((__be32 *) bufp) = htonl(session->peer_session_id);
	bufp += 4;
	if (session->cookie_len) {
		memcpy(bufp, &session->cookie[0], session->cookie_len);
		bufp += session->cookie_len;
	}
	if (session->l2specific_len) {
		if (session->l2specific_type == L2TP_L2SPECTYPE_DEFAULT) {
			u32 l2h = 0;
			if (session->send_seq) {
				l2h = 0x40000000 | session->ns;
				session->ns++;
				session->ns &= 0xffffff;
				PRINTK(session->debug, L2TP_MSG_SEQ, KERN_DEBUG,
				       "%s: updated ns to %u\n", session->name, session->ns);
			}

			*((__be32 *) bufp) = htonl(l2h);
		}
		bufp += session->l2specific_len;
	}
	if (session->offset)
		bufp += session->offset;

	return bufp - optr;
}

static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb,
			  size_t data_len)
{
	struct l2tp_tunnel *tunnel = session->tunnel;
	unsigned int len = skb->len;
	int error;

	/* Debug */
	if (session->send_seq)
		PRINTK(session->debug, L2TP_MSG_DATA, KERN_DEBUG,
		       "%s: send %Zd bytes, ns=%u\n", session->name,
		       data_len, session->ns - 1);
	else
		PRINTK(session->debug, L2TP_MSG_DATA, KERN_DEBUG,
		       "%s: send %Zd bytes\n", session->name, data_len);

	if (session->debug & L2TP_MSG_DATA) {
		int i;
		int uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
		unsigned char *datap = skb->data + uhlen;

		printk(KERN_DEBUG "%s: xmit:", session->name);
		for (i = 0; i < (len - uhlen); i++) {
			printk(" %02X", *datap++);
			if (i == 31) {
				printk(" ...");
				break;
			}
		}
		printk("\n");
	}

	/* Queue the packet to IP for output */
	skb->local_df = 1;
	error = ip_queue_xmit(skb);

	/* Update stats */
	if (error >= 0) {
		tunnel->stats.tx_packets++;
		tunnel->stats.tx_bytes += len;
		session->stats.tx_packets++;
		session->stats.tx_bytes += len;
	} else {
		tunnel->stats.tx_errors++;
		session->stats.tx_errors++;
	}

	return 0;
}

/* Automatically called when the skb is freed.
 */
static void l2tp_sock_wfree(struct sk_buff *skb)
{
	sock_put(skb->sk);
}

/* For data skbs that we transmit, we associate with the tunnel socket
 * but don't do accounting.
 */
static inline void l2tp_skb_set_owner_w(struct sk_buff *skb, struct sock *sk)
{
	sock_hold(sk);
	skb->sk = sk;
	skb->destructor = l2tp_sock_wfree;
}

/* If caller requires the skb to have a ppp header, the header must be
 * inserted in the skb data before calling this function.
 */
int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len)
{
	int data_len = skb->len;
	struct l2tp_tunnel *tunnel = session->tunnel;
	struct sock *sk = tunnel->sock;
	struct udphdr *uh;
	struct inet_sock *inet;
	__wsum csum;
	int old_headroom;
	int new_headroom;
	int headroom;
	int uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
	int udp_len;

	/* Check that there's enough headroom in the skb to insert IP,
	 * UDP and L2TP headers. If not enough, expand it to
	 * make room. Adjust truesize.
	 */
	headroom = NET_SKB_PAD + sizeof(struct iphdr) +
		uhlen + hdr_len;
	old_headroom = skb_headroom(skb);
	if (skb_cow_head(skb, headroom))
		goto abort;

	new_headroom = skb_headroom(skb);
	skb_orphan(skb);
	skb->truesize += new_headroom - old_headroom;

	/* Setup L2TP header */
	session->build_header(session, __skb_push(skb, hdr_len));

	/* Reset skb netfilter state */
	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
	IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED |
			      IPSKB_REROUTED);
	nf_reset(skb);

	/* Get routing info from the tunnel socket */
	skb_dst_drop(skb);
	skb_dst_set(skb, dst_clone(__sk_dst_get(sk)));

	switch (tunnel->encap) {
	case L2TP_ENCAPTYPE_UDP:
		/* Setup UDP header */
		inet = inet_sk(sk);
		__skb_push(skb, sizeof(*uh));
		skb_reset_transport_header(skb);
		uh = udp_hdr(skb);
		uh->source = inet->inet_sport;
		uh->dest = inet->inet_dport;
		udp_len = uhlen + hdr_len + data_len;
		uh->len = htons(udp_len);
		uh->check = 0;

		/* Calculate UDP checksum if configured to do so */
		if (sk->sk_no_check == UDP_CSUM_NOXMIT)
			skb->ip_summed = CHECKSUM_NONE;
		else if ((skb_dst(skb) && skb_dst(skb)->dev) &&
			 (!(skb_dst(skb)->dev->features & NETIF_F_V4_CSUM))) {
			skb->ip_summed = CHECKSUM_COMPLETE;
			csum = skb_checksum(skb, 0, udp_len, 0);
			uh->check = csum_tcpudp_magic(inet->inet_saddr,
						      inet->inet_daddr,
						      udp_len, IPPROTO_UDP, csum);
			if (uh->check == 0)
				uh->check = CSUM_MANGLED_0;
		} else {
			skb->ip_summed = CHECKSUM_PARTIAL;
			skb->csum_start = skb_transport_header(skb) - skb->head;
			skb->csum_offset = offsetof(struct udphdr, check);
			uh->check = ~csum_tcpudp_magic(inet->inet_saddr,
						       inet->inet_daddr,
						       udp_len, IPPROTO_UDP, 0);
		}
		break;

	case L2TP_ENCAPTYPE_IP:
		break;
	}

	l2tp_skb_set_owner_w(skb, sk);

	l2tp_xmit_core(session, skb, data_len);

abort:
	return 0;
}
EXPORT_SYMBOL_GPL(l2tp_xmit_skb);

/*****************************************************************************
 * Tinnel and session create/destroy.
 *****************************************************************************/

/* Tunnel socket destruct hook.
 * The tunnel context is deleted only when all session sockets have been
 * closed.
 */
static void l2tp_tunnel_destruct(struct sock *sk)
{
	struct l2tp_tunnel *tunnel;

	tunnel = sk->sk_user_data;
	if (tunnel == NULL)
		goto end;

	PRINTK(tunnel->debug, L2TP_MSG_CONTROL, KERN_INFO,
	       "%s: closing...\n", tunnel->name);

	/* Close all sessions */
	l2tp_tunnel_closeall(tunnel);

	switch (tunnel->encap) {
	case L2TP_ENCAPTYPE_UDP:
		/* No longer an encapsulation socket. See net/ipv4/udp.c */
		(udp_sk(sk))->encap_type = 0;
		(udp_sk(sk))->encap_rcv = NULL;
		break;
	case L2TP_ENCAPTYPE_IP:
		break;
	}

	/* Remove hooks into tunnel socket */
	tunnel->sock = NULL;
	sk->sk_destruct = tunnel->old_sk_destruct;
	sk->sk_user_data = NULL;

	/* Call the original destructor */
	if (sk->sk_destruct)
		(*sk->sk_destruct)(sk);

	/* We're finished with the socket */
	l2tp_tunnel_dec_refcount(tunnel);

end:
	return;
}

/* When the tunnel is closed, all the attached sessions need to go too.
 */
static void l2tp_tunnel_closeall(struct l2tp_tunnel *tunnel)
{
	int hash;
	struct hlist_node *walk;
	struct hlist_node *tmp;
	struct l2tp_session *session;

	BUG_ON(tunnel == NULL);

	PRINTK(tunnel->debug, L2TP_MSG_CONTROL, KERN_INFO,
	       "%s: closing all sessions...\n", tunnel->name);

	write_lock_bh(&tunnel->hlist_lock);
	for (hash = 0; hash < L2TP_HASH_SIZE; hash++) {
again:
		hlist_for_each_safe(walk, tmp, &tunnel->session_hlist[hash]) {
			session = hlist_entry(walk, struct l2tp_session, hlist);

			PRINTK(session->debug, L2TP_MSG_CONTROL, KERN_INFO,
			       "%s: closing session\n", session->name);

			hlist_del_init(&session->hlist);

			/* Since we should hold the sock lock while
			 * doing any unbinding, we need to release the
			 * lock we're holding before taking that lock.
			 * Hold a reference to the sock so it doesn't
			 * disappear as we're jumping between locks.
			 */
			if (session->ref != NULL)
				(*session->ref)(session);

			write_unlock_bh(&tunnel->hlist_lock);

			if (tunnel->version != L2TP_HDR_VER_2) {
				struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);

				spin_lock_bh(&pn->l2tp_session_hlist_lock);
				hlist_del_init_rcu(&session->global_hlist);
				spin_unlock_bh(&pn->l2tp_session_hlist_lock);
				synchronize_rcu();
			}

			if (session->session_close != NULL)
				(*session->session_close)(session);

			if (session->deref != NULL)
				(*session->deref)(session);

			write_lock_bh(&tunnel->hlist_lock);

			/* Now restart from the beginning of this hash
			 * chain.  We always remove a session from the
			 * list so we are guaranteed to make forward
			 * progress.
			 */
			goto again;
		}
	}
	write_unlock_bh(&tunnel->hlist_lock);
}

/* Really kill the tunnel.
 * Come here only when all sessions have been cleared from the tunnel.
 */
static void l2tp_tunnel_free(struct l2tp_tunnel *tunnel)
{
	struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);

	BUG_ON(atomic_read(&tunnel->ref_count) != 0);
	BUG_ON(tunnel->sock != NULL);

	PRINTK(tunnel->debug, L2TP_MSG_CONTROL, KERN_INFO,
	       "%s: free...\n", tunnel->name);

	/* Remove from tunnel list */
	spin_lock_bh(&pn->l2tp_tunnel_list_lock);
	list_del_rcu(&tunnel->list);
	spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
	synchronize_rcu();

	atomic_dec(&l2tp_tunnel_count);
	kfree(tunnel);
}

/* Create a socket for the tunnel, if one isn't set up by
 * userspace. This is used for static tunnels where there is no
 * managing L2TP daemon.
 */
static int l2tp_tunnel_sock_create(u32 tunnel_id, u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg, struct socket **sockp)
{
	int err = -EINVAL;
	struct sockaddr_in udp_addr;
	struct sockaddr_l2tpip ip_addr;
	struct socket *sock = NULL;

	switch (cfg->encap) {
	case L2TP_ENCAPTYPE_UDP:
		err = sock_create(AF_INET, SOCK_DGRAM, 0, sockp);
		if (err < 0)
			goto out;

		sock = *sockp;

		memset(&udp_addr, 0, sizeof(udp_addr));
		udp_addr.sin_family = AF_INET;
		udp_addr.sin_addr = cfg->local_ip;
		udp_addr.sin_port = htons(cfg->local_udp_port);
		err = kernel_bind(sock, (struct sockaddr *) &udp_addr, sizeof(udp_addr));
		if (err < 0)
			goto out;

		udp_addr.sin_family = AF_INET;
		udp_addr.sin_addr = cfg->peer_ip;
		udp_addr.sin_port = htons(cfg->peer_udp_port);
		err = kernel_connect(sock, (struct sockaddr *) &udp_addr, sizeof(udp_addr), 0);
		if (err < 0)
			goto out;

		if (!cfg->use_udp_checksums)
			sock->sk->sk_no_check = UDP_CSUM_NOXMIT;

		break;

	case L2TP_ENCAPTYPE_IP:
		err = sock_create(AF_INET, SOCK_DGRAM, IPPROTO_L2TP, sockp);
		if (err < 0)
			goto out;

		sock = *sockp;

		memset(&ip_addr, 0, sizeof(ip_addr));
		ip_addr.l2tp_family = AF_INET;
		ip_addr.l2tp_addr = cfg->local_ip;
		ip_addr.l2tp_conn_id = tunnel_id;
		err = kernel_bind(sock, (struct sockaddr *) &ip_addr, sizeof(ip_addr));
		if (err < 0)
			goto out;

		ip_addr.l2tp_family = AF_INET;
		ip_addr.l2tp_addr = cfg->peer_ip;
		ip_addr.l2tp_conn_id = peer_tunnel_id;
		err = kernel_connect(sock, (struct sockaddr *) &ip_addr, sizeof(ip_addr), 0);
		if (err < 0)
			goto out;

		break;

	default:
		goto out;
	}

out:
	if ((err < 0) && sock) {
		sock_release(sock);
		*sockp = NULL;
	}

	return err;
}

int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg, struct l2tp_tunnel **tunnelp)
{
	struct l2tp_tunnel *tunnel = NULL;
	int err;
	struct socket *sock = NULL;
	struct sock *sk = NULL;
	struct l2tp_net *pn;
	enum l2tp_encap_type encap = L2TP_ENCAPTYPE_UDP;

	/* Get the tunnel socket from the fd, which was opened by
	 * the userspace L2TP daemon. If not specified, create a
	 * kernel socket.
	 */
	if (fd < 0) {
		err = l2tp_tunnel_sock_create(tunnel_id, peer_tunnel_id, cfg, &sock);
		if (err < 0)
			goto err;
	} else {
		err = -EBADF;
		sock = sockfd_lookup(fd, &err);
		if (!sock) {
			printk(KERN_ERR "tunl %hu: sockfd_lookup(fd=%d) returned %d\n",
			       tunnel_id, fd, err);
			goto err;
		}
	}

	sk = sock->sk;

	if (cfg != NULL)
		encap = cfg->encap;

	/* Quick sanity checks */
	switch (encap) {
	case L2TP_ENCAPTYPE_UDP:
		err = -EPROTONOSUPPORT;
		if (sk->sk_protocol != IPPROTO_UDP) {
			printk(KERN_ERR "tunl %hu: fd %d wrong protocol, got %d, expected %d\n",
			       tunnel_id, fd, sk->sk_protocol, IPPROTO_UDP);
			goto err;
		}
		break;
	case L2TP_ENCAPTYPE_IP:
		err = -EPROTONOSUPPORT;
		if (sk->sk_protocol != IPPROTO_L2TP) {
			printk(KERN_ERR "tunl %hu: fd %d wrong protocol, got %d, expected %d\n",
			       tunnel_id, fd, sk->sk_protocol, IPPROTO_L2TP);
			goto err;
		}
		break;
	}

	/* Check if this socket has already been prepped */
	tunnel = (struct l2tp_tunnel *)sk->sk_user_data;
	if (tunnel != NULL) {
		/* This socket has already been prepped */
		err = -EBUSY;
		goto err;
	}

	tunnel = kzalloc(sizeof(struct l2tp_tunnel), GFP_KERNEL);
	if (tunnel == NULL) {
		err = -ENOMEM;
		goto err;
	}

	tunnel->version = version;
	tunnel->tunnel_id = tunnel_id;
	tunnel->peer_tunnel_id = peer_tunnel_id;
	tunnel->debug = L2TP_DEFAULT_DEBUG_FLAGS;

	tunnel->magic = L2TP_TUNNEL_MAGIC;
	sprintf(&tunnel->name[0], "tunl %u", tunnel_id);
	rwlock_init(&tunnel->hlist_lock);

	/* The net we belong to */
	tunnel->l2tp_net = net;
	pn = l2tp_pernet(net);

	if (cfg != NULL)
		tunnel->debug = cfg->debug;

	/* Mark socket as an encapsulation socket. See net/ipv4/udp.c */
	tunnel->encap = encap;
	if (encap == L2TP_ENCAPTYPE_UDP) {
		/* Mark socket as an encapsulation socket. See net/ipv4/udp.c */
		udp_sk(sk)->encap_type = UDP_ENCAP_L2TPINUDP;
		udp_sk(sk)->encap_rcv = l2tp_udp_encap_recv;
	}

	sk->sk_user_data = tunnel;

	/* Hook on the tunnel socket destructor so that we can cleanup
	 * if the tunnel socket goes away.
	 */
	tunnel->old_sk_destruct = sk->sk_destruct;
	sk->sk_destruct = &l2tp_tunnel_destruct;
	tunnel->sock = sk;
	sk->sk_allocation = GFP_ATOMIC;

	/* Add tunnel to our list */
	INIT_LIST_HEAD(&tunnel->list);
	spin_lock_bh(&pn->l2tp_tunnel_list_lock);
	list_add_rcu(&tunnel->list, &pn->l2tp_tunnel_list);
	spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
	synchronize_rcu();
	atomic_inc(&l2tp_tunnel_count);

	/* Bump the reference count. The tunnel context is deleted
	 * only when this drops to zero.
	 */
	l2tp_tunnel_inc_refcount(tunnel);

	err = 0;
err:
	if (tunnelp)
		*tunnelp = tunnel;

	/* If tunnel's socket was created by the kernel, it doesn't
	 *  have a file.
	 */
	if (sock && sock->file)
		sockfd_put(sock);

	return err;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_create);

/* This function is used by the netlink TUNNEL_DELETE command.
 */
int l2tp_tunnel_delete(struct l2tp_tunnel *tunnel)
{
	int err = 0;
	struct socket *sock = tunnel->sock ? tunnel->sock->sk_socket : NULL;

	/* Force the tunnel socket to close. This will eventually
	 * cause the tunnel to be deleted via the normal socket close
	 * mechanisms when userspace closes the tunnel socket.
	 */
	if (sock != NULL) {
		err = inet_shutdown(sock, 2);

		/* If the tunnel's socket was created by the kernel,
		 * close the socket here since the socket was not
		 * created by userspace.
		 */
		if (sock->file == NULL)
			err = inet_release(sock);
	}

	return err;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_delete);

/* Really kill the session.
 */
void l2tp_session_free(struct l2tp_session *session)
{
	struct l2tp_tunnel *tunnel;

	BUG_ON(atomic_read(&session->ref_count) != 0);

	tunnel = session->tunnel;
	if (tunnel != NULL) {
		BUG_ON(tunnel->magic != L2TP_TUNNEL_MAGIC);

		/* Delete the session from the hash */
		write_lock_bh(&tunnel->hlist_lock);
		hlist_del_init(&session->hlist);
		write_unlock_bh(&tunnel->hlist_lock);

		/* Unlink from the global hash if not L2TPv2 */
		if (tunnel->version != L2TP_HDR_VER_2) {
			struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);

			spin_lock_bh(&pn->l2tp_session_hlist_lock);
			hlist_del_init_rcu(&session->global_hlist);
			spin_unlock_bh(&pn->l2tp_session_hlist_lock);
			synchronize_rcu();
		}

		if (session->session_id != 0)
			atomic_dec(&l2tp_session_count);

		sock_put(tunnel->sock);

		/* This will delete the tunnel context if this
		 * is the last session on the tunnel.
		 */
		session->tunnel = NULL;
		l2tp_tunnel_dec_refcount(tunnel);
	}

	kfree(session);

	return;
}
EXPORT_SYMBOL_GPL(l2tp_session_free);

/* This function is used by the netlink SESSION_DELETE command and by
   pseudowire modules.
 */
int l2tp_session_delete(struct l2tp_session *session)
{
	if (session->session_close != NULL)
		(*session->session_close)(session);

	l2tp_session_dec_refcount(session);

	return 0;
}
EXPORT_SYMBOL_GPL(l2tp_session_delete);


/* We come here whenever a session's send_seq, cookie_len or
 * l2specific_len parameters are set.
 */
static void l2tp_session_set_header_len(struct l2tp_session *session, int version)
{
	if (version == L2TP_HDR_VER_2) {
		session->hdr_len = 6;
		if (session->send_seq)
			session->hdr_len += 4;
	} else {
		session->hdr_len = 4 + session->cookie_len + session->l2specific_len + session->offset;
		if (session->tunnel->encap == L2TP_ENCAPTYPE_UDP)
			session->hdr_len += 4;
	}

}

struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunnel, u32 session_id, u32 peer_session_id, struct l2tp_session_cfg *cfg)
{
	struct l2tp_session *session;

	session = kzalloc(sizeof(struct l2tp_session) + priv_size, GFP_KERNEL);
	if (session != NULL) {
		session->magic = L2TP_SESSION_MAGIC;
		session->tunnel = tunnel;

		session->session_id = session_id;
		session->peer_session_id = peer_session_id;
		session->nr = 1;

		sprintf(&session->name[0], "sess %u/%u",
			tunnel->tunnel_id, session->session_id);

		skb_queue_head_init(&session->reorder_q);

		INIT_HLIST_NODE(&session->hlist);
		INIT_HLIST_NODE(&session->global_hlist);

		/* Inherit debug options from tunnel */
		session->debug = tunnel->debug;

		if (cfg) {
			session->pwtype = cfg->pw_type;
			session->debug = cfg->debug;
			session->mtu = cfg->mtu;
			session->mru = cfg->mru;
			session->send_seq = cfg->send_seq;
			session->recv_seq = cfg->recv_seq;
			session->lns_mode = cfg->lns_mode;
			session->reorder_timeout = cfg->reorder_timeout;
			session->offset = cfg->offset;
			session->l2specific_type = cfg->l2specific_type;
			session->l2specific_len = cfg->l2specific_len;
			session->cookie_len = cfg->cookie_len;
			memcpy(&session->cookie[0], &cfg->cookie[0], cfg->cookie_len);
			session->peer_cookie_len = cfg->peer_cookie_len;
			memcpy(&session->peer_cookie[0], &cfg->peer_cookie[0], cfg->peer_cookie_len);
		}

		if (tunnel->version == L2TP_HDR_VER_2)
			session->build_header = l2tp_build_l2tpv2_header;
		else
			session->build_header = l2tp_build_l2tpv3_header;

		l2tp_session_set_header_len(session, tunnel->version);

		/* Bump the reference count. The session context is deleted
		 * only when this drops to zero.
		 */
		l2tp_session_inc_refcount(session);
		l2tp_tunnel_inc_refcount(tunnel);

		/* Ensure tunnel socket isn't deleted */
		sock_hold(tunnel->sock);

		/* Add session to the tunnel's hash list */
		write_lock_bh(&tunnel->hlist_lock);
		hlist_add_head(&session->hlist,
			       l2tp_session_id_hash(tunnel, session_id));
		write_unlock_bh(&tunnel->hlist_lock);

		/* And to the global session list if L2TPv3 */
		if (tunnel->version != L2TP_HDR_VER_2) {
			struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);

			spin_lock_bh(&pn->l2tp_session_hlist_lock);
			hlist_add_head_rcu(&session->global_hlist,
					   l2tp_session_id_hash_2(pn, session_id));
			spin_unlock_bh(&pn->l2tp_session_hlist_lock);
			synchronize_rcu();
		}

		/* Ignore management session in session count value */
		if (session->session_id != 0)
			atomic_inc(&l2tp_session_count);
	}

	return session;
}
EXPORT_SYMBOL_GPL(l2tp_session_create);

/*****************************************************************************
 * Init and cleanup
 *****************************************************************************/

static __net_init int l2tp_init_net(struct net *net)
{
	struct l2tp_net *pn = net_generic(net, l2tp_net_id);
	int hash;

	INIT_LIST_HEAD(&pn->l2tp_tunnel_list);
	spin_lock_init(&pn->l2tp_tunnel_list_lock);

	for (hash = 0; hash < L2TP_HASH_SIZE_2; hash++)
		INIT_HLIST_HEAD(&pn->l2tp_session_hlist[hash]);

	spin_lock_init(&pn->l2tp_session_hlist_lock);

	return 0;
}

static struct pernet_operations l2tp_net_ops = {
	.init = l2tp_init_net,
	.id   = &l2tp_net_id,
	.size = sizeof(struct l2tp_net),
};

static int __init l2tp_init(void)
{
	int rc = 0;

	rc = register_pernet_device(&l2tp_net_ops);
	if (rc)
		goto out;

	printk(KERN_INFO "L2TP core driver, %s\n", L2TP_DRV_VERSION);

out:
	return rc;
}

static void __exit l2tp_exit(void)
{
	unregister_pernet_device(&l2tp_net_ops);
}

module_init(l2tp_init);
module_exit(l2tp_exit);

MODULE_AUTHOR("James Chapman <jchapman@katalix.com>");
MODULE_DESCRIPTION("L2TP core");
MODULE_LICENSE("GPL");
MODULE_VERSION(L2TP_DRV_VERSION);