aboutsummaryrefslogtreecommitdiff
path: root/net/sctp/input.c
blob: 3a8eb79eb78b92183824059bac7e21f7ac5e930b (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
/* SCTP kernel implementation
 * Copyright (c) 1999-2000 Cisco, Inc.
 * Copyright (c) 1999-2001 Motorola, Inc.
 * Copyright (c) 2001-2003 International Business Machines, Corp.
 * Copyright (c) 2001 Intel Corp.
 * Copyright (c) 2001 Nokia, Inc.
 * Copyright (c) 2001 La Monte H.P. Yarroll
 *
 * This file is part of the SCTP kernel implementation
 *
 * These functions handle all input from the IP layer into SCTP.
 *
 * This SCTP implementation is free software;
 * you can redistribute it and/or modify it under the terms of
 * the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This SCTP implementation 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 GNU CC; see the file COPYING.  If not, write to
 * the Free Software Foundation, 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * Please send any bug reports or fixes you make to the
 * email address(es):
 *    lksctp developers <lksctp-developers@lists.sourceforge.net>
 *
 * Or submit a bug report through the following website:
 *    http://www.sf.net/projects/lksctp
 *
 * Written or modified by:
 *    La Monte H.P. Yarroll <piggy@acm.org>
 *    Karl Knutson <karl@athena.chicago.il.us>
 *    Xingang Guo <xingang.guo@intel.com>
 *    Jon Grimm <jgrimm@us.ibm.com>
 *    Hui Huang <hui.huang@nokia.com>
 *    Daisy Chang <daisyc@us.ibm.com>
 *    Sridhar Samudrala <sri@us.ibm.com>
 *    Ardelle Fan <ardelle.fan@intel.com>
 *
 * Any bugs reported given to us we will try to fix... any fixes shared will
 * be incorporated into the next SCTP release.
 */

#include <linux/types.h>
#include <linux/list.h> /* For struct list_head */
#include <linux/socket.h>
#include <linux/ip.h>
#include <linux/time.h> /* For struct timeval */
#include <linux/slab.h>
#include <net/ip.h>
#include <net/icmp.h>
#include <net/snmp.h>
#include <net/sock.h>
#include <net/xfrm.h>
#include <net/sctp/sctp.h>
#include <net/sctp/sm.h>
#include <net/sctp/checksum.h>
#include <net/net_namespace.h>

/* Forward declarations for internal helpers. */
static int sctp_rcv_ootb(struct sk_buff *);
static struct sctp_association *__sctp_rcv_lookup(struct sk_buff *skb,
				      const union sctp_addr *laddr,
				      const union sctp_addr *paddr,
				      struct sctp_transport **transportp);
static struct sctp_endpoint *__sctp_rcv_lookup_endpoint(const union sctp_addr *laddr);
static struct sctp_association *__sctp_lookup_association(
					const union sctp_addr *local,
					const union sctp_addr *peer,
					struct sctp_transport **pt);

static int sctp_add_backlog(struct sock *sk, struct sk_buff *skb);


/* Calculate the SCTP checksum of an SCTP packet.  */
static inline int sctp_rcv_checksum(struct sk_buff *skb)
{
	struct sctphdr *sh = sctp_hdr(skb);
	__le32 cmp = sh->checksum;
	struct sk_buff *list;
	__le32 val;
	__u32 tmp = sctp_start_cksum((__u8 *)sh, skb_headlen(skb));

	skb_walk_frags(skb, list)
		tmp = sctp_update_cksum((__u8 *)list->data, skb_headlen(list),
					tmp);

	val = sctp_end_cksum(tmp);

	if (val != cmp) {
		/* CRC failure, dump it. */
		SCTP_INC_STATS_BH(SCTP_MIB_CHECKSUMERRORS);
		return -1;
	}
	return 0;
}

struct sctp_input_cb {
	union {
		struct inet_skb_parm	h4;
#if defined(CONFIG_IPV6) || defined (CONFIG_IPV6_MODULE)
		struct inet6_skb_parm	h6;
#endif
	} header;
	struct sctp_chunk *chunk;
};
#define SCTP_INPUT_CB(__skb)	((struct sctp_input_cb *)&((__skb)->cb[0]))

/*
 * This is the routine which IP calls when receiving an SCTP packet.
 */
int sctp_rcv(struct sk_buff *skb)
{
	struct sock *sk;
	struct sctp_association *asoc;
	struct sctp_endpoint *ep = NULL;
	struct sctp_ep_common *rcvr;
	struct sctp_transport *transport = NULL;
	struct sctp_chunk *chunk;
	struct sctphdr *sh;
	union sctp_addr src;
	union sctp_addr dest;
	int family;
	struct sctp_af *af;

	if (skb->pkt_type!=PACKET_HOST)
		goto discard_it;

	SCTP_INC_STATS_BH(SCTP_MIB_INSCTPPACKS);

	if (skb_linearize(skb))
		goto discard_it;

	sh = sctp_hdr(skb);

	/* Pull up the IP and SCTP headers. */
	__skb_pull(skb, skb_transport_offset(skb));
	if (skb->len < sizeof(struct sctphdr))
		goto discard_it;
	if (!sctp_checksum_disable && !skb_csum_unnecessary(skb) &&
		  sctp_rcv_checksum(skb) < 0)
		goto discard_it;

	skb_pull(skb, sizeof(struct sctphdr));

	/* Make sure we at least have chunk headers worth of data left. */
	if (skb->len < sizeof(struct sctp_chunkhdr))
		goto discard_it;

	family = ipver2af(ip_hdr(skb)->version);
	af = sctp_get_af_specific(family);
	if (unlikely(!af))
		goto discard_it;

	/* Initialize local addresses for lookups. */
	af->from_skb(&src, skb, 1);
	af->from_skb(&dest, skb, 0);

	/* If the packet is to or from a non-unicast address,
	 * silently discard the packet.
	 *
	 * This is not clearly defined in the RFC except in section
	 * 8.4 - OOTB handling.  However, based on the book "Stream Control
	 * Transmission Protocol" 2.1, "It is important to note that the
	 * IP address of an SCTP transport address must be a routable
	 * unicast address.  In other words, IP multicast addresses and
	 * IP broadcast addresses cannot be used in an SCTP transport
	 * address."
	 */
	if (!af->addr_valid(&src, NULL, skb) ||
	    !af->addr_valid(&dest, NULL, skb))
		goto discard_it;

	asoc = __sctp_rcv_lookup(skb, &src, &dest, &transport);

	if (!asoc)
		ep = __sctp_rcv_lookup_endpoint(&dest);

	/* Retrieve the common input handling substructure. */
	rcvr = asoc ? &asoc->base : &ep->base;
	sk = rcvr->sk;

	/*
	 * If a frame arrives on an interface and the receiving socket is
	 * bound to another interface, via SO_BINDTODEVICE, treat it as OOTB
	 */
	if (sk->sk_bound_dev_if && (sk->sk_bound_dev_if != af->skb_iif(skb)))
	{
		if (asoc) {
			sctp_association_put(asoc);
			asoc = NULL;
		} else {
			sctp_endpoint_put(ep);
			ep = NULL;
		}
		sk = sctp_get_ctl_sock();
		ep = sctp_sk(sk)->ep;
		sctp_endpoint_hold(ep);
		rcvr = &ep->base;
	}

	/*
	 * RFC 2960, 8.4 - Handle "Out of the blue" Packets.
	 * An SCTP packet is called an "out of the blue" (OOTB)
	 * packet if it is correctly formed, i.e., passed the
	 * receiver's checksum check, but the receiver is not
	 * able to identify the association to which this
	 * packet belongs.
	 */
	if (!asoc) {
		if (sctp_rcv_ootb(skb)) {
			SCTP_INC_STATS_BH(SCTP_MIB_OUTOFBLUES);
			goto discard_release;
		}
	}

	if (!xfrm_policy_check(sk, XFRM_POLICY_IN, skb, family))
		goto discard_release;
	nf_reset(skb);

	if (sk_filter(sk, skb))
		goto discard_release;

	/* Create an SCTP packet structure. */
	chunk = sctp_chunkify(skb, asoc, sk);
	if (!chunk)
		goto discard_release;
	SCTP_INPUT_CB(skb)->chunk = chunk;

	/* Remember what endpoint is to handle this packet. */
	chunk->rcvr = rcvr;

	/* Remember the SCTP header. */
	chunk->sctp_hdr = sh;

	/* Set the source and destination addresses of the incoming chunk.  */
	sctp_init_addrs(chunk, &src, &dest);

	/* Remember where we came from.  */
	chunk->transport = transport;

	/* Acquire access to the sock lock. Note: We are safe from other
	 * bottom halves on this lock, but a user may be in the lock too,
	 * so check if it is busy.
	 */
	sctp_bh_lock_sock(sk);

	if (sk != rcvr->sk) {
		/* Our cached sk is different from the rcvr->sk.  This is
		 * because migrate()/accept() may have moved the association
		 * to a new socket and released all the sockets.  So now we
		 * are holding a lock on the old socket while the user may
		 * be doing something with the new socket.  Switch our veiw
		 * of the current sk.
		 */
		sctp_bh_unlock_sock(sk);
		sk = rcvr->sk;
		sctp_bh_lock_sock(sk);
	}

	if (sock_owned_by_user(sk)) {
		if (sctp_add_backlog(sk, skb)) {
			sctp_bh_unlock_sock(sk);
			sctp_chunk_free(chunk);
			skb = NULL; /* sctp_chunk_free already freed the skb */
			goto discard_release;
		}
		SCTP_INC_STATS_BH(SCTP_MIB_IN_PKT_BACKLOG);
	} else {
		SCTP_INC_STATS_BH(SCTP_MIB_IN_PKT_SOFTIRQ);
		sctp_inq_push(&chunk->rcvr->inqueue, chunk);
	}

	sctp_bh_unlock_sock(sk);

	/* Release the asoc/ep ref we took in the lookup calls. */
	if (asoc)
		sctp_association_put(asoc);
	else
		sctp_endpoint_put(ep);

	return 0;

discard_it:
	SCTP_INC_STATS_BH(SCTP_MIB_IN_PKT_DISCARDS);
	kfree_skb(skb);
	return 0;

discard_release:
	/* Release the asoc/ep ref we took in the lookup calls. */
	if (asoc)
		sctp_association_put(asoc);
	else
		sctp_endpoint_put(ep);

	goto discard_it;
}

/* Process the backlog queue of the socket.  Every skb on
 * the backlog holds a ref on an association or endpoint.
 * We hold this ref throughout the state machine to make
 * sure that the structure we need is still around.
 */
int sctp_backlog_rcv(struct sock *sk, struct sk_buff *skb)
{
	struct sctp_chunk *chunk = SCTP_INPUT_CB(skb)->chunk;
	struct sctp_inq *inqueue = &chunk->rcvr->inqueue;
	struct sctp_ep_common *rcvr = NULL;
	int backloged = 0;

	rcvr = chunk->rcvr;

	/* If the rcvr is dead then the association or endpoint
	 * has been deleted and we can safely drop the chunk
	 * and refs that we are holding.
	 */
	if (rcvr->dead) {
		sctp_chunk_free(chunk);
		goto done;
	}

	if (unlikely(rcvr->sk != sk)) {
		/* In this case, the association moved from one socket to
		 * another.  We are currently sitting on the backlog of the
		 * old socket, so we need to move.
		 * However, since we are here in the process context we
		 * need to take make sure that the user doesn't own
		 * the new socket when we process the packet.
		 * If the new socket is user-owned, queue the chunk to the
		 * backlog of the new socket without dropping any refs.
		 * Otherwise, we can safely push the chunk on the inqueue.
		 */

		sk = rcvr->sk;
		sctp_bh_lock_sock(sk);

		if (sock_owned_by_user(sk)) {
			if (sk_add_backlog(sk, skb))
				sctp_chunk_free(chunk);
			else
				backloged = 1;
		} else
			sctp_inq_push(inqueue, chunk);

		sctp_bh_unlock_sock(sk);

		/* If the chunk was backloged again, don't drop refs */
		if (backloged)
			return 0;
	} else {
		sctp_inq_push(inqueue, chunk);
	}

done:
	/* Release the refs we took in sctp_add_backlog */
	if (SCTP_EP_TYPE_ASSOCIATION == rcvr->type)
		sctp_association_put(sctp_assoc(rcvr));
	else if (SCTP_EP_TYPE_SOCKET == rcvr->type)
		sctp_endpoint_put(sctp_ep(rcvr));
	else
		BUG();

	return 0;
}

static int sctp_add_backlog(struct sock *sk, struct sk_buff *skb)
{
	struct sctp_chunk *chunk = SCTP_INPUT_CB(skb)->chunk;
	struct sctp_ep_common *rcvr = chunk->rcvr;
	int ret;

	ret = sk_add_backlog(sk, skb);
	if (!ret) {
		/* Hold the assoc/ep while hanging on the backlog queue.
		 * This way, we know structures we need will not disappear
		 * from us
		 */
		if (SCTP_EP_TYPE_ASSOCIATION == rcvr->type)
			sctp_association_hold(sctp_assoc(rcvr));
		else if (SCTP_EP_TYPE_SOCKET == rcvr->type)
			sctp_endpoint_hold(sctp_ep(rcvr));
		else
			BUG();
	}
	return ret;

}

/* Handle icmp frag needed error. */
void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc,
			   struct sctp_transport *t, __u32 pmtu)
{
	if (!t || (t->pathmtu <= pmtu))
		return;

	if (sock_owned_by_user(sk)) {
		asoc->pmtu_pending = 1;
		t->pmtu_pending = 1;
		return;
	}

	if (t->param_flags & SPP_PMTUD_ENABLE) {
		/* Update transports view of the MTU */
		sctp_transport_update_pmtu(t, pmtu);

		/* Update association pmtu. */
		sctp_assoc_sync_pmtu(asoc);
	}

	/* Retransmit with the new pmtu setting.
	 * Normally, if PMTU discovery is disabled, an ICMP Fragmentation
	 * Needed will never be sent, but if a message was sent before
	 * PMTU discovery was disabled that was larger than the PMTU, it
	 * would not be fragmented, so it must be re-transmitted fragmented.
	 */
	sctp_retransmit(&asoc->outqueue, t, SCTP_RTXR_PMTUD);
}

/*
 * SCTP Implementer's Guide, 2.37 ICMP handling procedures
 *
 * ICMP8) If the ICMP code is a "Unrecognized next header type encountered"
 *        or a "Protocol Unreachable" treat this message as an abort
 *        with the T bit set.
 *
 * This function sends an event to the state machine, which will abort the
 * association.
 *
 */
void sctp_icmp_proto_unreachable(struct sock *sk,
			   struct sctp_association *asoc,
			   struct sctp_transport *t)
{
	SCTP_DEBUG_PRINTK("%s\n",  __func__);

	if (sock_owned_by_user(sk)) {
		if (timer_pending(&t->proto_unreach_timer))
			return;
		else {
			if (!mod_timer(&t->proto_unreach_timer,
						jiffies + (HZ/20)))
				sctp_association_hold(asoc);
		}
			
	} else {
		if (timer_pending(&t->proto_unreach_timer) &&
		    del_timer(&t->proto_unreach_timer))
			sctp_association_put(asoc);

		sctp_do_sm(SCTP_EVENT_T_OTHER,
			   SCTP_ST_OTHER(SCTP_EVENT_ICMP_PROTO_UNREACH),
			   asoc->state, asoc->ep, asoc, t,
			   GFP_ATOMIC);
	}
}

/* Common lookup code for icmp/icmpv6 error handler. */
struct sock *sctp_err_lookup(int family, struct sk_buff *skb,
			     struct sctphdr *sctphdr,
			     struct sctp_association **app,
			     struct sctp_transport **tpp)
{
	union sctp_addr saddr;
	union sctp_addr daddr;
	struct sctp_af *af;
	struct sock *sk = NULL;
	struct sctp_association *asoc;
	struct sctp_transport *transport = NULL;
	struct sctp_init_chunk *chunkhdr;
	__u32 vtag = ntohl(sctphdr->vtag);
	int len = skb->len - ((void *)sctphdr - (void *)skb->data);

	*app = NULL; *tpp = NULL;

	af = sctp_get_af_specific(family);
	if (unlikely(!af)) {
		return NULL;
	}

	/* Initialize local addresses for lookups. */
	af->from_skb(&saddr, skb, 1);
	af->from_skb(&daddr, skb, 0);

	/* Look for an association that matches the incoming ICMP error
	 * packet.
	 */
	asoc = __sctp_lookup_association(&saddr, &daddr, &transport);
	if (!asoc)
		return NULL;

	sk = asoc->base.sk;

	/* RFC 4960, Appendix C. ICMP Handling
	 *
	 * ICMP6) An implementation MUST validate that the Verification Tag
	 * contained in the ICMP message matches the Verification Tag of
	 * the peer.  If the Verification Tag is not 0 and does NOT
	 * match, discard the ICMP message.  If it is 0 and the ICMP
	 * message contains enough bytes to verify that the chunk type is
	 * an INIT chunk and that the Initiate Tag matches the tag of the
	 * peer, continue with ICMP7.  If the ICMP message is too short
	 * or the chunk type or the Initiate Tag does not match, silently
	 * discard the packet.
	 */
	if (vtag == 0) {
		chunkhdr = (struct sctp_init_chunk *)((void *)sctphdr
				+ sizeof(struct sctphdr));
		if (len < sizeof(struct sctphdr) + sizeof(sctp_chunkhdr_t)
			  + sizeof(__be32) ||
		    chunkhdr->chunk_hdr.type != SCTP_CID_INIT ||
		    ntohl(chunkhdr->init_hdr.init_tag) != asoc->c.my_vtag) {
			goto out;
		}
	} else if (vtag != asoc->c.peer_vtag) {
		goto out;
	}

	sctp_bh_lock_sock(sk);

	/* If too many ICMPs get dropped on busy
	 * servers this needs to be solved differently.
	 */
	if (sock_owned_by_user(sk))
		NET_INC_STATS_BH(&init_net, LINUX_MIB_LOCKDROPPEDICMPS);

	*app = asoc;
	*tpp = transport;
	return sk;

out:
	if (asoc)
		sctp_association_put(asoc);
	return NULL;
}

/* Common cleanup code for icmp/icmpv6 error handler. */
void sctp_err_finish(struct sock *sk, struct sctp_association *asoc)
{
	sctp_bh_unlock_sock(sk);
	if (asoc)
		sctp_association_put(asoc);
}

/*
 * This routine is called by the ICMP module when it gets some
 * sort of error condition.  If err < 0 then the socket should
 * be closed and the error returned to the user.  If err > 0
 * it's just the icmp type << 8 | icmp code.  After adjustment
 * header points to the first 8 bytes of the sctp header.  We need
 * to find the appropriate port.
 *
 * The locking strategy used here is very "optimistic". When
 * someone else accesses the socket the ICMP is just dropped
 * and for some paths there is no check at all.
 * A more general error queue to queue errors for later handling
 * is probably better.
 *
 */
void sctp_v4_err(struct sk_buff *skb, __u32 info)
{
	struct iphdr *iph = (struct iphdr *)skb->data;
	const int ihlen = iph->ihl * 4;
	const int type = icmp_hdr(skb)->type;
	const int code = icmp_hdr(skb)->code;
	struct sock *sk;
	struct sctp_association *asoc = NULL;
	struct sctp_transport *transport;
	struct inet_sock *inet;
	sk_buff_data_t saveip, savesctp;
	int err;

	if (skb->len < ihlen + 8) {
		ICMP_INC_STATS_BH(&init_net, ICMP_MIB_INERRORS);
		return;
	}

	/* Fix up skb to look at the embedded net header. */
	saveip = skb->network_header;
	savesctp = skb->transport_header;
	skb_reset_network_header(skb);
	skb_set_transport_header(skb, ihlen);
	sk = sctp_err_lookup(AF_INET, skb, sctp_hdr(skb), &asoc, &transport);
	/* Put back, the original values. */
	skb->network_header = saveip;
	skb->transport_header = savesctp;
	if (!sk) {
		ICMP_INC_STATS_BH(&init_net, ICMP_MIB_INERRORS);
		return;
	}
	/* Warning:  The sock lock is held.  Remember to call
	 * sctp_err_finish!
	 */

	switch (type) {
	case ICMP_PARAMETERPROB:
		err = EPROTO;
		break;
	case ICMP_DEST_UNREACH:
		if (code > NR_ICMP_UNREACH)
			goto out_unlock;

		/* PMTU discovery (RFC1191) */
		if (ICMP_FRAG_NEEDED == code) {
			sctp_icmp_frag_needed(sk, asoc, transport, info);
			goto out_unlock;
		}
		else {
			if (ICMP_PROT_UNREACH == code) {
				sctp_icmp_proto_unreachable(sk, asoc,
							    transport);
				goto out_unlock;
			}
		}
		err = icmp_err_convert[code].errno;
		break;
	case ICMP_TIME_EXCEEDED:
		/* Ignore any time exceeded errors due to fragment reassembly
		 * timeouts.
		 */
		if (ICMP_EXC_FRAGTIME == code)
			goto out_unlock;

		err = EHOSTUNREACH;
		break;
	default:
		goto out_unlock;
	}

	inet = inet_sk(sk);
	if (!sock_owned_by_user(sk) && inet->recverr) {
		sk->sk_err = err;
		sk->sk_error_report(sk);
	} else {  /* Only an error on timeout */
		sk->sk_err_soft = err;
	}

out_unlock:
	sctp_err_finish(sk, asoc);
}

/*
 * RFC 2960, 8.4 - Handle "Out of the blue" Packets.
 *
 * This function scans all the chunks in the OOTB packet to determine if
 * the packet should be discarded right away.  If a response might be needed
 * for this packet, or, if further processing is possible, the packet will
 * be queued to a proper inqueue for the next phase of handling.
 *
 * Output:
 * Return 0 - If further processing is needed.
 * Return 1 - If the packet can be discarded right away.
 */
static int sctp_rcv_ootb(struct sk_buff *skb)
{
	sctp_chunkhdr_t *ch;
	__u8 *ch_end;

	ch = (sctp_chunkhdr_t *) skb->data;

	/* Scan through all the chunks in the packet.  */
	do {
		/* Break out if chunk length is less then minimal. */
		if (ntohs(ch->length) < sizeof(sctp_chunkhdr_t))
			break;

		ch_end = ((__u8 *)ch) + WORD_ROUND(ntohs(ch->length));
		if (ch_end > skb_tail_pointer(skb))
			break;

		/* RFC 8.4, 2) If the OOTB packet contains an ABORT chunk, the
		 * receiver MUST silently discard the OOTB packet and take no
		 * further action.
		 */
		if (SCTP_CID_ABORT == ch->type)
			goto discard;

		/* RFC 8.4, 6) If the packet contains a SHUTDOWN COMPLETE
		 * chunk, the receiver should silently discard the packet
		 * and take no further action.
		 */
		if (SCTP_CID_SHUTDOWN_COMPLETE == ch->type)
			goto discard;

		/* RFC 4460, 2.11.2
		 * This will discard packets with INIT chunk bundled as
		 * subsequent chunks in the packet.  When INIT is first,
		 * the normal INIT processing will discard the chunk.
		 */
		if (SCTP_CID_INIT == ch->type && (void *)ch != skb->data)
			goto discard;

		ch = (sctp_chunkhdr_t *) ch_end;
	} while (ch_end < skb_tail_pointer(skb));

	return 0;

discard:
	return 1;
}

/* Insert endpoint into the hash table.  */
static void __sctp_hash_endpoint(struct sctp_endpoint *ep)
{
	struct sctp_ep_common *epb;
	struct sctp_hashbucket *head;

	epb = &ep->base;

	epb->hashent = sctp_ep_hashfn(epb->bind_addr.port);
	head = &sctp_ep_hashtable[epb->hashent];

	sctp_write_lock(&head->lock);
	hlist_add_head(&epb->node, &head->chain);
	sctp_write_unlock(&head->lock);
}

/* Add an endpoint to the hash. Local BH-safe. */
void sctp_hash_endpoint(struct sctp_endpoint *ep)
{
	sctp_local_bh_disable();
	__sctp_hash_endpoint(ep);
	sctp_local_bh_enable();
}

/* Remove endpoint from the hash table.  */
static void __sctp_unhash_endpoint(struct sctp_endpoint *ep)
{
	struct sctp_hashbucket *head;
	struct sctp_ep_common *epb;

	epb = &ep->base;

	if (hlist_unhashed(&epb->node))
		return;

	epb->hashent = sctp_ep_hashfn(epb->bind_addr.port);

	head = &sctp_ep_hashtable[epb->hashent];

	sctp_write_lock(&head->lock);
	__hlist_del(&epb->node);
	sctp_write_unlock(&head->lock);
}

/* Remove endpoint from the hash.  Local BH-safe. */
void sctp_unhash_endpoint(struct sctp_endpoint *ep)
{
	sctp_local_bh_disable();
	__sctp_unhash_endpoint(ep);
	sctp_local_bh_enable();
}

/* Look up an endpoint. */
static struct sctp_endpoint *__sctp_rcv_lookup_endpoint(const union sctp_addr *laddr)
{
	struct sctp_hashbucket *head;
	struct sctp_ep_common *epb;
	struct sctp_endpoint *ep;
	struct hlist_node *node;
	int hash;

	hash = sctp_ep_hashfn(ntohs(laddr->v4.sin_port));
	head = &sctp_ep_hashtable[hash];
	read_lock(&head->lock);
	sctp_for_each_hentry(epb, node, &head->chain) {
		ep = sctp_ep(epb);
		if (sctp_endpoint_is_match(ep, laddr))
			goto hit;
	}

	ep = sctp_sk((sctp_get_ctl_sock()))->ep;

hit:
	sctp_endpoint_hold(ep);
	read_unlock(&head->lock);
	return ep;
}

/* Insert association into the hash table.  */
static void __sctp_hash_established(struct sctp_association *asoc)
{
	struct sctp_ep_common *epb;
	struct sctp_hashbucket *head;

	epb = &asoc->base;

	/* Calculate which chain this entry will belong to. */
	epb->hashent = sctp_assoc_hashfn(epb->bind_addr.port, asoc->peer.port);

	head = &sctp_assoc_hashtable[epb->hashent];

	sctp_write_lock(&head->lock);
	hlist_add_head(&epb->node, &head->chain);
	sctp_write_unlock(&head->lock);
}

/* Add an association to the hash. Local BH-safe. */
void sctp_hash_established(struct sctp_association *asoc)
{
	if (asoc->temp)
		return;

	sctp_local_bh_disable();
	__sctp_hash_established(asoc);
	sctp_local_bh_enable();
}

/* Remove association from the hash table.  */
static void __sctp_unhash_established(struct sctp_association *asoc)
{
	struct sctp_hashbucket *head;
	struct sctp_ep_common *epb;

	epb = &asoc->base;

	epb->hashent = sctp_assoc_hashfn(epb->bind_addr.port,
					 asoc->peer.port);

	head = &sctp_assoc_hashtable[epb->hashent];

	sctp_write_lock(&head->lock);
	__hlist_del(&epb->node);
	sctp_write_unlock(&head->lock);
}

/* Remove association from the hash table.  Local BH-safe. */
void sctp_unhash_established(struct sctp_association *asoc)
{
	if (asoc->temp)
		return;

	sctp_local_bh_disable();
	__sctp_unhash_established(asoc);
	sctp_local_bh_enable();
}

/* Look up an association. */
static struct sctp_association *__sctp_lookup_association(
					const union sctp_addr *local,
					const union sctp_addr *peer,
					struct sctp_transport **pt)
{
	struct sctp_hashbucket *head;
	struct sctp_ep_common *epb;
	struct sctp_association *asoc;
	struct sctp_transport *transport;
	struct hlist_node *node;
	int hash;

	/* Optimize here for direct hit, only listening connections can
	 * have wildcards anyways.
	 */
	hash = sctp_assoc_hashfn(ntohs(local->v4.sin_port), ntohs(peer->v4.sin_port));
	head = &sctp_assoc_hashtable[hash];
	read_lock(&head->lock);
	sctp_for_each_hentry(epb, node, &head->chain) {
		asoc = sctp_assoc(epb);
		transport = sctp_assoc_is_match(asoc, local, peer);
		if (transport)
			goto hit;
	}

	read_unlock(&head->lock);

	return NULL;

hit:
	*pt = transport;
	sctp_association_hold(asoc);
	read_unlock(&head->lock);
	return asoc;
}

/* Look up an association. BH-safe. */
SCTP_STATIC
struct sctp_association *sctp_lookup_association(const union sctp_addr *laddr,
						 const union sctp_addr *paddr,
					    struct sctp_transport **transportp)
{
	struct sctp_association *asoc;

	sctp_local_bh_disable();
	asoc = __sctp_lookup_association(laddr, paddr, transportp);
	sctp_local_bh_enable();

	return asoc;
}

/* Is there an association matching the given local and peer addresses? */
int sctp_has_association(const union sctp_addr *laddr,
			 const union sctp_addr *paddr)
{
	struct sctp_association *asoc;
	struct sctp_transport *transport;

	if ((asoc = sctp_lookup_association(laddr, paddr, &transport))) {
		sctp_association_put(asoc);
		return 1;
	}

	return 0;
}

/*
 * SCTP Implementors Guide, 2.18 Handling of address
 * parameters within the INIT or INIT-ACK.
 *
 * D) When searching for a matching TCB upon reception of an INIT
 *    or INIT-ACK chunk the receiver SHOULD use not only the
 *    source address of the packet (containing the INIT or
 *    INIT-ACK) but the receiver SHOULD also use all valid
 *    address parameters contained within the chunk.
 *
 * 2.18.3 Solution description
 *
 * This new text clearly specifies to an implementor the need
 * to look within the INIT or INIT-ACK. Any implementation that
 * does not do this, may not be able to establish associations
 * in certain circumstances.
 *
 */
static struct sctp_association *__sctp_rcv_init_lookup(struct sk_buff *skb,
	const union sctp_addr *laddr, struct sctp_transport **transportp)
{
	struct sctp_association *asoc;
	union sctp_addr addr;
	union sctp_addr *paddr = &addr;
	struct sctphdr *sh = sctp_hdr(skb);
	union sctp_params params;
	sctp_init_chunk_t *init;
	struct sctp_transport *transport;
	struct sctp_af *af;

	/*
	 * This code will NOT touch anything inside the chunk--it is
	 * strictly READ-ONLY.
	 *
	 * RFC 2960 3  SCTP packet Format
	 *
	 * Multiple chunks can be bundled into one SCTP packet up to
	 * the MTU size, except for the INIT, INIT ACK, and SHUTDOWN
	 * COMPLETE chunks.  These chunks MUST NOT be bundled with any
	 * other chunk in a packet.  See Section 6.10 for more details
	 * on chunk bundling.
	 */

	/* Find the start of the TLVs and the end of the chunk.  This is
	 * the region we search for address parameters.
	 */
	init = (sctp_init_chunk_t *)skb->data;

	/* Walk the parameters looking for embedded addresses. */
	sctp_walk_params(params, init, init_hdr.params) {

		/* Note: Ignoring hostname addresses. */
		af = sctp_get_af_specific(param_type2af(params.p->type));
		if (!af)
			continue;

		af->from_addr_param(paddr, params.addr, sh->source, 0);

		asoc = __sctp_lookup_association(laddr, paddr, &transport);
		if (asoc)
			return asoc;
	}

	return NULL;
}

/* ADD-IP, Section 5.2
 * When an endpoint receives an ASCONF Chunk from the remote peer
 * special procedures may be needed to identify the association the
 * ASCONF Chunk is associated with. To properly find the association
 * the following procedures SHOULD be followed:
 *
 * D2) If the association is not found, use the address found in the
 * Address Parameter TLV combined with the port number found in the
 * SCTP common header. If found proceed to rule D4.
 *
 * D2-ext) If more than one ASCONF Chunks are packed together, use the
 * address found in the ASCONF Address Parameter TLV of each of the
 * subsequent ASCONF Chunks. If found, proceed to rule D4.
 */
static struct sctp_association *__sctp_rcv_asconf_lookup(
					sctp_chunkhdr_t *ch,
					const union sctp_addr *laddr,
					__be16 peer_port,
					struct sctp_transport **transportp)
{
	sctp_addip_chunk_t *asconf = (struct sctp_addip_chunk *)ch;
	struct sctp_af *af;
	union sctp_addr_param *param;
	union sctp_addr paddr;

	/* Skip over the ADDIP header and find the Address parameter */
	param = (union sctp_addr_param *)(asconf + 1);

	af = sctp_get_af_specific(param_type2af(param->p.type));
	if (unlikely(!af))
		return NULL;

	af->from_addr_param(&paddr, param, peer_port, 0);

	return __sctp_lookup_association(laddr, &paddr, transportp);
}


/* SCTP-AUTH, Section 6.3:
*    If the receiver does not find a STCB for a packet containing an AUTH
*    chunk as the first chunk and not a COOKIE-ECHO chunk as the second
*    chunk, it MUST use the chunks after the AUTH chunk to look up an existing
*    association.
*
* This means that any chunks that can help us identify the association need
* to be looked at to find this association.
*/
static struct sctp_association *__sctp_rcv_walk_lookup(struct sk_buff *skb,
				      const union sctp_addr *laddr,
				      struct sctp_transport **transportp)
{
	struct sctp_association *asoc = NULL;
	sctp_chunkhdr_t *ch;
	int have_auth = 0;
	unsigned int chunk_num = 1;
	__u8 *ch_end;

	/* Walk through the chunks looking for AUTH or ASCONF chunks
	 * to help us find the association.
	 */
	ch = (sctp_chunkhdr_t *) skb->data;
	do {
		/* Break out if chunk length is less then minimal. */
		if (ntohs(ch->length) < sizeof(sctp_chunkhdr_t))
			break;

		ch_end = ((__u8 *)ch) + WORD_ROUND(ntohs(ch->length));
		if (ch_end > skb_tail_pointer(skb))
			break;

		switch(ch->type) {
		    case SCTP_CID_AUTH:
			    have_auth = chunk_num;
			    break;

		    case SCTP_CID_COOKIE_ECHO:
			    /* If a packet arrives containing an AUTH chunk as
			     * a first chunk, a COOKIE-ECHO chunk as the second
			     * chunk, and possibly more chunks after them, and
			     * the receiver does not have an STCB for that
			     * packet, then authentication is based on
			     * the contents of the COOKIE- ECHO chunk.
			     */
			    if (have_auth == 1 && chunk_num == 2)
				    return NULL;
			    break;

		    case SCTP_CID_ASCONF:
			    if (have_auth || sctp_addip_noauth)
				    asoc = __sctp_rcv_asconf_lookup(ch, laddr,
							sctp_hdr(skb)->source,
							transportp);
		    default:
			    break;
		}

		if (asoc)
			break;

		ch = (sctp_chunkhdr_t *) ch_end;
		chunk_num++;
	} while (ch_end < skb_tail_pointer(skb));

	return asoc;
}

/*
 * There are circumstances when we need to look inside the SCTP packet
 * for information to help us find the association.   Examples
 * include looking inside of INIT/INIT-ACK chunks or after the AUTH
 * chunks.
 */
static struct sctp_association *__sctp_rcv_lookup_harder(struct sk_buff *skb,
				      const union sctp_addr *laddr,
				      struct sctp_transport **transportp)
{
	sctp_chunkhdr_t *ch;

	ch = (sctp_chunkhdr_t *) skb->data;

	/* The code below will attempt to walk the chunk and extract
	 * parameter information.  Before we do that, we need to verify
	 * that the chunk length doesn't cause overflow.  Otherwise, we'll
	 * walk off the end.
	 */
	if (WORD_ROUND(ntohs(ch->length)) > skb->len)
		return NULL;

	/* If this is INIT/INIT-ACK look inside the chunk too. */
	switch (ch->type) {
	case SCTP_CID_INIT:
	case SCTP_CID_INIT_ACK:
		return __sctp_rcv_init_lookup(skb, laddr, transportp);
		break;

	default:
		return __sctp_rcv_walk_lookup(skb, laddr, transportp);
		break;
	}


	return NULL;
}

/* Lookup an association for an inbound skb. */
static struct sctp_association *__sctp_rcv_lookup(struct sk_buff *skb,
				      const union sctp_addr *paddr,
				      const union sctp_addr *laddr,
				      struct sctp_transport **transportp)
{
	struct sctp_association *asoc;

	asoc = __sctp_lookup_association(laddr, paddr, transportp);

	/* Further lookup for INIT/INIT-ACK packets.
	 * SCTP Implementors Guide, 2.18 Handling of address
	 * parameters within the INIT or INIT-ACK.
	 */
	if (!asoc)
		asoc = __sctp_rcv_lookup_harder(skb, laddr, transportp);

	return asoc;
}