summaryrefslogtreecommitdiff
path: root/package/siit/src/siit.c
blob: dddc8ef875b4f0ce3e2b2683a4baf9ee06a13f11 (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
/*
 * siit.c: the Stateless IP/ICMP Translator (SIIT) module for Linux.
 *
 *
 */

#include <linux/autoconf.h>
#include <linux/module.h>
#include <linux/version.h>
#include <linux/sched.h>
#include <linux/kernel.h>       /* printk() */
#include <linux/slab.h>

#include <linux/errno.h>        /* error codes */
#include <linux/types.h>        /* size_t */
#include <linux/interrupt.h>    /* mark_bh */
#include <linux/random.h>
#include <linux/in.h>
#include <linux/netdevice.h>    /* struct device, and other headers */
#include <linux/etherdevice.h>  /* eth_type_trans */
#include <net/ip.h>             /* struct iphdr */
#include <net/icmp.h>           /* struct icmphdr */
#include <net/ipv6.h>
#include <net/udp.h>
#include <linux/skbuff.h>
#include <linux/in6.h>
#include <linux/init.h>
#include <asm/uaccess.h>
#include <asm/checksum.h>
#if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,0)
#include <net/ip6_checksum.h>
#endif
#include <linux/in6.h>
#include "siit.h"

MODULE_AUTHOR("Dmitriy Moscalev, Grigory Klyuchnikov, Felix Fietkau");

/*
 * If tos_ignore_flag != 0, we don't copy TOS and Traffic Class
 * from origin paket and set it to 0
 */
int tos_ignore_flag = 0;

#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,0)
static inline void
skb_reset_mac_header(struct sk_buff *skb)
{
	skb->mac.raw=skb->data;
}

static struct net_device_stats *
siit_get_stats(struct net_device *dev)
{
	return netdev_priv(dev);
}

static inline void random_ether_addr(u8 *addr)
{
	get_random_bytes (addr, ETH_ALEN);
	addr [0] &= 0xfe;	/* clear multicast bit */
	addr [0] |= 0x02;	/* set local assignment bit (IEEE802) */
}


#define siit_stats(_dev) ((struct net_device_stats *)netdev_priv(_dev))
#else
#define siit_stats(_dev) (&(_dev)->stats)
#endif

/*
 * The Utility  stuff
 */

#ifdef SIIT_DEBUG
/* print dump bytes (data point data area sizeof len and message
 * before dump.
 */
static int siit_print_dump(char *data, int len, char *message)
{
	int i;
	int j = 0, k = 1;

	len = len > BUFF_SIZE ? BUFF_SIZE : len;
	printk("%s:\n", message);
	for (i=0; i < len; i++, k++) {
		if( i == len-1 || k == 16) {
			printk("%02x\n", (~(~0 << 8) & *(data+i)));
			j = 0;
			k = 0;
		}
		else if (j) {
			printk("%02x ", (~(~0 << 8) & *(data+i)));
			j--;
		}
		else {
			printk("%02x", (~(~0 << 8) & *(data+i)));
			j++;
		}
	}
	return 0;
}
#endif

/*
 * Open and close
 */
static int siit_open(struct net_device *dev)
{
	netif_start_queue(dev);
	return 0;
}


static int siit_release(struct net_device *dev)
{
	netif_stop_queue(dev); /* can't transmit any more */
	return 0;
}

/*
 * Translation IPv4 to IPv6 stuff
 *
 * ip4_ip6 (src, len, dst, include_flag)
 *
 * where
 * src - buffer with original IPv4 packet,
 * len - size of original packet,
 * dst - new buffer for IPv6 packet,
 * include_flag - if = 1, dst point to IPv4 packet that is ICMP error
 *                included IP packet, else = 0
 */

static int ip4_ip6(char *src, int len, char *dst, int include_flag)
{
	struct iphdr *ih4 = (struct iphdr *) src; /* point to current IPv4 header struct */
	struct icmphdr *icmp_hdr;   /* point to current ICMPv4 header struct */
	struct udphdr *udp_hdr;     /* point to current IPv4 UDP header struct */

	struct ipv6hdr *ih6 = (struct ipv6hdr *) dst; /* point to current IPv6 header struct */
	struct frag_hdr *ih6_frag = (struct frag_hdr *)(dst+sizeof(struct ipv6hdr));
										      /* point to current IPv6 fragment header struct */
	struct icmp6hdr *icmp6_hdr; /* point to current ICMPv6 header */

	int hdr_len = (int)(ih4->ihl * 4); /* IPv4 header length */
	int icmp_len;               /* ICMPv4 packet length */
	int plen;                   /* payload length */

	unsigned int csum;          /* need to calculate ICMPv6 and UDP checksum */
	int fl_csum = 0;            /* flag to calculate UDP checksum */
	int icmperr = 1;            /* flag to indicate ICMP error message and to need
								   translate ICMP included IP packet */
	int fr_flag = 0;            /* fragment flag, if = 0 - don't add
								   fragment header */
	__u16 new_tot_len;          /* need to calculate IPv6 total length */
	__u8 new_nexthdr;           /* next header code */
	__u16 icmp_ptr = 0;         /* Pointer field in ICMP_PARAMETERPROB */

#ifdef SIIT_DEBUG              /* print IPv4 header dump */
	siit_print_dump(src, hdr_len, "siit: ip4_ip6() (in) ip4 header dump");
#endif

	/* If DF == 1 && MF == 0 && Fragment Offset == 0
	 * or this packet is ICMP included IP packet
	 * we don't need fragment header */
	if (ntohs(ih4->frag_off) == IP_DF || include_flag ) {
		/* not fragment and we need not to add Fragment
		 * Header to IPv6 packet. */
		/* total length = total length from IPv4 packet */
		new_tot_len = ntohs(ih4->tot_len);

		if (ih4->protocol == IPPROTO_ICMP)
			new_nexthdr = NEXTHDR_ICMP;
		else
			new_nexthdr = ih4->protocol;
	}
	else {
		/* need to add Fragment Header */
		fr_flag = 1;
		/* total length = total length from IPv4 packet +
		   length of Fragment Header */
		new_tot_len = ntohs(ih4->tot_len) + sizeof(struct frag_hdr);
		/* IPv6 Header NextHeader = NEXTHDR_FRAGMENT */
		new_nexthdr = NEXTHDR_FRAGMENT;
		/* Fragment Header NextHeader copy from IPv4 packet */
		if (ih4->protocol == IPPROTO_ICMP)
			ih6_frag->nexthdr = NEXTHDR_ICMP;
		else
			ih6_frag->nexthdr = ih4->protocol;

		/* copy frag offset from IPv4 packet */
		ih6_frag->frag_off = htons((ntohs(ih4->frag_off) & IP_OFFSET) << 3);
		/* copy MF flag from IPv4 packet */
		ih6_frag->frag_off = htons((ntohs(ih6_frag->frag_off) |
									((ntohs(ih4->frag_off) & IP_MF) >> 13)));
		/* copy Identification field from IPv4 packet */
		ih6_frag->identification = htonl(ntohs(ih4->id));
		/* reserved field initialized to zero */
		ih6_frag->reserved = 0;
	}

	/* Form rest IPv6 fields */

	/*
	 * At this point we need to add checking of unxpired source
	 * route optin and if it is, send ICMPv4 "destination
	 * unreacheble/source route failes" Type 3/Code 5 and
	 * drop packet. (NOT RELEASED YET)
	 */

	/* IP version = 6 */
	ih6->version = 6;

	if (tos_ignore_flag) {
		ih6->priority = 0;
		ih6->flow_lbl[0] = 0;
	} else {
		ih6->priority = (ih4->tos & 0xf0) >> 4;
		ih6->flow_lbl[0] = (ih4->tos & 0x0f) << 4;
	}
	ih6->flow_lbl[1] = 0;
	ih6->flow_lbl[2] = 0;

	/* Hop Limit = IPv4 TTL */
	ih6->hop_limit = ih4->ttl;

	/* Translate source destination addresses,
	   for IPv6 host it's IPv4-translated IPv6 address,
	   for IPv4 host it's IPv4-mapped IPv6 address

	   !!WARNING!! Instead IPv4-mapped IPv6 addresses we use addreesses
	   with unused prefix ::ffff:ffff:0:0/96, because KAME implementation
	   doesn't support IPv4-mapped addresses in IPv6 packets and discard them.

	*/

	if (include_flag) {
		/*
		   It's ICMP included IP packet and there is a diffirence
		   in src/dst addresses then src/dst in normal direction
		 */

		/*
		   Source address
		   is IPv4-translated IPv6 address because packet traveled
		   from IPv6 to IPv4 area
		*/
		ih6->saddr.in6_u.u6_addr32[0] = 0;
		ih6->saddr.in6_u.u6_addr32[1] = 0;
		ih6->saddr.in6_u.u6_addr32[2] = htonl(TRANSLATED_PREFIX); /* to network order bytes */
		ih6->saddr.in6_u.u6_addr32[3] = ih4->saddr;

		/*
		   Destination address
		   is IPv4-mapped address (but it's not IPv4- mapped, we use
		   prefix ::ffff:ffff:0:0/96
		 */
		ih6->daddr.in6_u.u6_addr32[0] = 0;
		ih6->daddr.in6_u.u6_addr32[1] = 0;
		ih6->daddr.in6_u.u6_addr32[2] = htonl(MAPPED_PREFIX); /* to network order bytes */
		ih6->daddr.in6_u.u6_addr32[3] = ih4->daddr;
	}
	else {

		/*
		   This is normal case (packet isn't included IP packet)

		   Source address
		   is IPv4-mapped address (but it's not IPv4- mapped, we use
		   prefix ::ffff:ffff:0:0/96)
		*/
		ih6->saddr.in6_u.u6_addr32[0] = 0;
		ih6->saddr.in6_u.u6_addr32[1] = 0;
		ih6->saddr.in6_u.u6_addr32[2] = htonl(MAPPED_PREFIX); /* to network order bytes */
		ih6->saddr.in6_u.u6_addr32[3] = ih4->saddr;

		/* Destination address
		   is is IPv4-translated IPv6 address
		 */
		ih6->daddr.in6_u.u6_addr32[0] = 0;
		ih6->daddr.in6_u.u6_addr32[1] = 0;
		ih6->daddr.in6_u.u6_addr32[2] = htonl(TRANSLATED_PREFIX); /* to network order bytes */
		ih6->daddr.in6_u.u6_addr32[3] = ih4->daddr;
	}

	/* Payload Length */
	plen = new_tot_len - hdr_len; /* Payload length = IPv4 total len - IPv4 header len */
	ih6->payload_len = htons(plen);

	/* Next Header */
	ih6->nexthdr = new_nexthdr; /* Next Header */

	/* Process ICMP protocols data */

	switch (ih4->protocol) {
	case IPPROTO_ICMP:
		if ( (ntohs(ih4->frag_off) & IP_OFFSET) != 0 || (ntohs(ih4->frag_off) & IP_MF) != 0 ) {
			PDEBUG("ip4_ip6(): don't translate ICMPv4 fragments - packet dropped.\n");
			return -1;
		}

		icmp_hdr = (struct icmphdr *) (src+hdr_len); /* point to ICMPv4 header */
		csum = 0;
		icmp_len =  ntohs(ih4->tot_len) - hdr_len; /* ICMPv4 packet length */
		icmp6_hdr = (struct icmp6hdr *)(dst+sizeof(struct ipv6hdr)
									    +fr_flag*sizeof(struct frag_hdr)); /* point to ICMPv6 header */

		if (include_flag) {
			/* ICMPv4 packet cannot be included in ICMPv4 Error message */
			/* !!! May be it's WRONG !!! ICMPv4 QUERY packet can be included
			   in ICMPv4 Error message */
			PDEBUG("ip4_ip6(): It's included ICMPv4 in ICMPv4 Error message - packet dropped.\n");
			return -1;
		}

		/* Check ICMPv4 Type field */
		switch (icmp_hdr->type) {
		/* ICMP Error messages */
		/* Destination Unreachable (Type 3) */
		case ICMP_DEST_UNREACH:
			icmp6_hdr->icmp6_type = ICMPV6_DEST_UNREACH; /* to Type 1 */
			icmp6_hdr->icmp6_unused = 0;
			switch (icmp_hdr->code)
			{
			case ICMP_NET_UNREACH: /* Code 0 */
			case ICMP_HOST_UNREACH: /* Code 1 */
			case ICMP_SR_FAILED: /* Code 5 */
			case ICMP_NET_UNKNOWN: /* Code 6 */
			case ICMP_HOST_UNKNOWN: /* Code 7 */
			case ICMP_HOST_ISOLATED: /* Code 8 */
			case ICMP_NET_UNR_TOS: /* Code 11 */
			case ICMP_HOST_UNR_TOS: /* Code 12 */
				icmp6_hdr->icmp6_code = ICMPV6_NOROUTE; /* to Code 0 */
				break;
			case ICMP_PROT_UNREACH: /* Code 2 */
				icmp6_hdr->icmp6_type = ICMPV6_PARAMPROB; /* to Type 4 */
				icmp6_hdr->icmp6_code = ICMPV6_UNK_NEXTHDR; /* to Code 1 */
				/* Set pointer filed to 6, it's octet offset IPv6 Next Header field */
				icmp6_hdr->icmp6_pointer = htonl(6);
				break;
			case ICMP_PORT_UNREACH: /* Code 3 */
				icmp6_hdr->icmp6_code = ICMPV6_PORT_UNREACH; /* to Code 4 */
				break;
			case ICMP_FRAG_NEEDED: /* Code 4 */
				icmp6_hdr->icmp6_type = ICMPV6_PKT_TOOBIG; /* to Type 2 */
				icmp6_hdr->icmp6_code = 0;
				/* Correct MTU  */
				if (icmp_hdr->un.frag.mtu == 0)
					/* we use minimum MTU for IPv4 PMTUv4 RFC1191, section 5;
					   IPv6 implementation wouldn't accept Path MTU < 1280,
					   but it records info correctly to always include
					   a fragment header */
					icmp6_hdr->icmp6_mtu = htonl(576);
				else
					/* needs to adjusted for difference between IPv4/IPv6 headers
					 * SIIT RFC2765, section 3.3,
					 * we assume that difference is 20 bytes */
					icmp6_hdr->icmp6_mtu = htonl(ntohs(icmp_hdr->un.frag.mtu)+IP4_IP6_HDR_DIFF);

				break;
			case ICMP_NET_ANO: /* Code 9 */
			case ICMP_HOST_ANO: /* Code 10 */
				icmp6_hdr->icmp6_code = ICMPV6_ADM_PROHIBITED; /* to Code 1 */
				break;
			default: /* discard any other Code */
				PDEBUG("ip4_ip6(): Unknown ICMPv4 Type %d Code %d - packet dropped.\n",
					   ICMP_DEST_UNREACH, icmp_hdr->code);
				return -1;
			}
			break;
			/* Time Exceeded (Type 11) */
		case ICMP_TIME_EXCEEDED:
			icmp6_hdr->icmp6_type = ICMPV6_TIME_EXCEED;
			icmp6_hdr->icmp6_code = icmp_hdr->code;
			break;
			/* Parameter Problem (Type 12) */
		case ICMP_PARAMETERPROB:
			icmp6_hdr->icmp6_type = ICMPV6_PARAMPROB;
			icmp6_hdr->icmp6_code = icmp_hdr->code;

			icmp_ptr = ntohs(icmp_hdr->un.echo.id) >> 8;
			switch (icmp_ptr) {
			case 0:
				icmp6_hdr->icmp6_pointer = 0; /* IPv4 Version -> IPv6 Version */
				break;
			case 2:
				icmp6_hdr->icmp6_pointer = __constant_htonl(4); /* IPv4 length -> IPv6 Payload Length */
				break;
			case 8:
				icmp6_hdr->icmp6_pointer = __constant_htonl(7); /* IPv4 TTL -> IPv6 Hop Limit */
				break;
			case 9:
				icmp6_hdr->icmp6_pointer = __constant_htonl(6); /* IPv4 Protocol -> IPv6 Next Header */
				break;
			case 12:
				icmp6_hdr->icmp6_pointer = __constant_htonl(8); /* IPv4 Src Addr -> IPv6 Src Addr */
				break;
			case 16:
				icmp6_hdr->icmp6_pointer = __constant_htonl(24); /* IPv4 Dst Addr -> IPv6 Dst Addr */
				break;
			default:
				icmp6_hdr->icmp6_pointer = 0xffffffff; /* set to all ones in any other cases */
				break;
			}
			break;
		case ICMP_ECHO:
			icmperr = 0;
			icmp6_hdr->icmp6_type = ICMPV6_ECHO_REQUEST;
			icmp6_hdr->icmp6_code = 0;
			/* Copy rest ICMP data to new IPv6 packet without changing */
			memcpy(((char *)icmp6_hdr)+4, ((char *)icmp_hdr)+4, len - hdr_len - 4);
			break;

		case ICMP_ECHOREPLY:
			icmperr = 0;
			icmp6_hdr->icmp6_type = ICMPV6_ECHO_REPLY;
			icmp6_hdr->icmp6_code = 0;
			/* Copy rest ICMP data to new IPv6 packet without changing */
			memcpy(((char *)icmp6_hdr)+4, ((char *)icmp_hdr)+4, len - hdr_len - 4);
			break;

			/* Discard any other ICMP messages */
		default:
			PDEBUG("ip4_ip6(): Unknown ICMPv4 packet Type %x - packet dropped.\n", icmp_hdr->type);
			return -1;
		}

		/* Now if it's ICMPv4 Error message we must translate included IP packet */

		if (icmperr) {
			/* Call our ip4_ip6() to translate included IP packet */
			if (ip4_ip6(src+hdr_len+sizeof(struct icmphdr), len - hdr_len - sizeof(struct icmphdr),
						dst+sizeof(struct ipv6hdr)+fr_flag*sizeof(struct frag_hdr)
						+sizeof(struct icmp6hdr), 1) == -1) {
				PDEBUG("ip4_ip6(): Uncorrect translation of ICMPv4 Error message - packet dropped.\n");
				return -1;
			}
			/* correct ICMPv6 packet length for diffirence between IPv4 and IPv6 headers
			   in included IP packet
			   */
			icmp_len += 20;
			/* and correct Payload length for diffirence between IPv4 and IPv6 headers */
			plen += 20;
			ih6->payload_len = htons(plen);
		}

		/* Calculate ICMPv6 checksum */

		icmp6_hdr->icmp6_cksum = 0;
		csum = 0;

		csum = csum_partial((u_char *)icmp6_hdr, icmp_len, csum);
		icmp6_hdr->icmp6_cksum = csum_ipv6_magic(&ih6->saddr, &ih6->daddr, icmp_len,
									         IPPROTO_ICMPV6, csum);
		break;

	/* Process TCP protocols data */
	case IPPROTO_TCP:
		/* Copy TCP data to new IPv6 packet without changing */
		memcpy(dst+sizeof(struct ipv6hdr)+fr_flag*sizeof(struct frag_hdr),
				   src+hdr_len, len - hdr_len);
		break;

	/* Process UDP protocols data */
	case IPPROTO_UDP:
		udp_hdr = (struct udphdr *)(src+hdr_len);
		if ((ntohs(ih4->frag_off) & IP_OFFSET) == 0) {
			if ((ntohs(ih4->frag_off) & IP_MF) != 0) {
				/* It's a first fragment */
				if (udp_hdr->check == 0) {
					/* System management event */
					printk("siit: First fragment of UDP with zero checksum - packet droped\n");
					printk("siit: addr: %x src port: %d dst port: %d\n",
						   htonl(ih4->saddr), htons(udp_hdr->source), htons(udp_hdr->dest));
					return -1;
				}
			}
			else if (udp_hdr->check == 0)
				fl_csum = 1;
		}

		/* Copy UDP data to new IPv6 packet */
		udp_hdr = (struct udphdr *)(dst+sizeof(struct ipv6hdr)
									+ fr_flag*sizeof(struct frag_hdr));
		memcpy((char *)udp_hdr, src+hdr_len, len - hdr_len);

		/* Calculate UDP checksum if UDP checksum in IPv4 packet was ZERO
		   and if it isn't included IP packet
		 */
		if (fl_csum && (!include_flag)) {
			udp_hdr->check = 0;
			csum = 0;
			csum = csum_partial((unsigned char *)udp_hdr, plen - fr_flag*sizeof(struct frag_hdr), csum);
			udp_hdr->check = csum_ipv6_magic(&ih6->saddr, &ih6->daddr, plen -
										     fr_flag*sizeof(struct frag_hdr), IPPROTO_UDP, csum);
		}
		break;

	/* Discard packets with any other protocol */
	default:
		PDEBUG("ip4_ip6(): Unknown upper protocol - packet dropped.\n");
		return -1;
	}

#ifdef SIIT_DEBUG
	siit_print_dump(dst, sizeof(struct ipv6hdr), "siit: ip4_ip6(): (out) ipv6 header dump");
#endif

	return 0;
}

/*
 * Translation IPv6 to IPv4 stuff
 *
 * ip6_ip4(src, len, dst, include_flag)
 *
 * where
 * src - buffer with original IPv6 packet,
 * len - size of original packet,
 * dst - new buffer for IPv4 packet,
 * include_flag - if = 1, dst point to IPv6 packet that is ICMP error
 *                included IP packet, else = 0
 *
 */

static int ip6_ip4(char *src, int len, char *dst, int include_flag)
{
	struct ipv6hdr *ip6_hdr;    /* point to current IPv6 header struct */
	struct iphdr *ip_hdr;       /* point to current IPv4 header struct */
	int opts_len = 0;           /* to sum Option Headers length */
	int icmperr = 1;            /* if = 1, indicate that packet is ICMP Error message, else = 0 */
	int ntot_len = 0;           /* to calculate IPv6 Total Length field */
	int real_len;
	int len_delta;
	int ip6_payload_len;
	int inc_opts_len = 0;       /* to sum Option Headers length in ICMP included IP packet */
	__u8 next_hdr;              /* Next Header */

#ifdef SIIT_DEBUG
	siit_print_dump(src, sizeof(struct ipv6hdr), "siit: ip6_ip4(): (in) ipv6 header dump");
#endif

	if ( (len_delta = len - sizeof(struct ipv6hdr)) >= 0)
	{
		ip6_hdr = (struct ipv6hdr *)src;
		ip_hdr = (struct iphdr *)dst;

		real_len = sizeof(struct iphdr);

		/* Check validation of Saddr & Daddr? is a packet to fall under our translation? */
		if (include_flag) { /* It's ICMP included IP packet,
							   about process include_flag see comment in ip4_ip6() */
			if (ip6_hdr->saddr.s6_addr32[2] != htonl(MAPPED_PREFIX)) {
				PDEBUG("ip6_ip4(): Included IP packet Src addr isn't mapped addr: %x%x%x%x, packet dropped.\n",
					   ip6_hdr->saddr.s6_addr32[0], ip6_hdr->saddr.s6_addr32[1],
					   ip6_hdr->saddr.s6_addr32[2], ip6_hdr->saddr.s6_addr32[3]);
				return -1;
			}
			if ( ip6_hdr->daddr.s6_addr32[2] != htonl(TRANSLATED_PREFIX)) {
				PDEBUG("ip6_ip4(): Included IP packet Dst addr isn't translated addr: %x%x%x%x, packet dropped.\n",
					   ip6_hdr->daddr.s6_addr32[0], ip6_hdr->daddr.s6_addr32[1],
					   ip6_hdr->daddr.s6_addr32[2], ip6_hdr->daddr.s6_addr32[3]);
				return -1;
			}
		}
		else { /* It's normal IP packet (not included in ICMP) */
			if (ip6_hdr->saddr.s6_addr32[2] != htonl(TRANSLATED_PREFIX)) {
				PDEBUG("ip6_ip4(): Src addr isn't translated addr: %x%x%x%x, packet dropped.\n",
					   ip6_hdr->saddr.s6_addr32[0], ip6_hdr->saddr.s6_addr32[1],
					   ip6_hdr->saddr.s6_addr32[2], ip6_hdr->saddr.s6_addr32[3]);
				return -1;
			}
			if ( ip6_hdr->daddr.s6_addr32[2] != htonl(MAPPED_PREFIX)) {
				PDEBUG("ip6_ip4(): Dst addr isn't mapped addr: %x%x%x%x, packet dropped.\n",
					   ip6_hdr->daddr.s6_addr32[0], ip6_hdr->daddr.s6_addr32[1],
					   ip6_hdr->daddr.s6_addr32[2], ip6_hdr->daddr.s6_addr32[3]);
				return -1;
			}
		}

		/* Set IPv4 Fragment Offset and ID to 0
		   before process any Option Headers */
		ip_hdr->frag_off = 0;
		ip_hdr->id = 0;

		/*
		 * We process only Fragment Header. Any other options headers
		 * are ignored, i.e. there is no attempt to translate them.
		 * However, the Total Length field and the Protocol field would
		 * have to be adjusted to "skip" these extension headers.
		 */

		next_hdr = ip6_hdr->nexthdr;

		/* Hop_by_Hop options header (ip6_hdr->nexthdr = 0). It must
		 * appear only in IPv6 header's Next Header field.
		 */
		if (next_hdr == NEXTHDR_HOP) {
			if ( (len_delta - sizeof(struct ipv6_opt_hdr)) >= 0)
			{
				struct ipv6_opt_hdr *ip6h =
					(struct ipv6_opt_hdr *)(src+sizeof(struct ipv6hdr) + opts_len);
				if ( (len_delta -= ip6h->hdrlen*8 + 8) >= 0)
				{
					opts_len += ip6h->hdrlen*8 + 8;  /* See  RFC 2460 page 11:
							Hdr Ext Len  8-bit unsigned integer.  Length of the Hop-by-
										 Hop Options header in 8-octet units, not
										 including the first 8 octets.
							*/
					next_hdr = ip6h->nexthdr;
				}
				else
				{
					PDEBUG("ip6_ip4(): hop_by_hop header error, packet droped");
					/* Generate ICMP Parameter Problem */
					return -1;
				}
			}
		}

		if (len_delta > 0)
		{
			while(next_hdr != NEXTHDR_ICMP && next_hdr != NEXTHDR_TCP
				  && next_hdr != NEXTHDR_UDP)
			{
				/* Destination options header */
				if (next_hdr == NEXTHDR_DEST)
				{
					if ( (len_delta - sizeof(struct ipv6_opt_hdr)) >= 0)
					{
						struct ipv6_opt_hdr *ip6d =
							(struct ipv6_opt_hdr *)(src + sizeof(struct ipv6hdr) + opts_len);
						if ( (len_delta -= ip6d->hdrlen*8 + 8) >= 0)
						{
							opts_len += ip6d->hdrlen*8 + 8;
							next_hdr = ip6d->nexthdr;
						}
					}
					else
					{
						PDEBUG("ip6_ip4(): destination header error, packet droped");
						/* Generate ICMP Parameter Problem */
						return -1;
					}
				}
				/* Routing options header */
				else if (next_hdr == NEXTHDR_ROUTING)
				{
					if ( (len_delta - sizeof(struct ipv6_rt_hdr)) >= 0)
					{
						struct ipv6_rt_hdr *ip6rt =
							(struct ipv6_rt_hdr *)(src+sizeof(struct ipv6hdr) + opts_len);
						/* RFC 2765 SIIT, 4.1:
						   If a routing header with a non-zero Segments Left field is present
						   then the packet MUST NOT be translated, and an ICMPv6 "parameter
						   problem/ erroneous header field encountered" (Type 4/Code 0) error
						   message, with the Pointer field indicating the first byte of the
						   Segments Left field, SHOULD be returned to the sender.
						   */
						if (ip6rt->segments_left != 0) {
							/* Build ICMPv6 "Parameter Problem/Erroneous Header
							   Field Encountered" & drop the packet */
							/* !!! We don't send ICMPv6 "Parameter Problem" !!! */
							PDEBUG("ip6_ip4(): routing header type != 0\n");
							return -1;
						}
						if ( (len_delta -= ip6rt->hdrlen*8 + 8) >= 0)
						{
							opts_len += ip6rt->hdrlen*8 + 8;
							next_hdr = ip6rt->nexthdr;
						}
						else
						{
							PDEBUG("ip6_ip4(): routing header error, packet droped");
							/* Generate ICMP Parameter Problem */
							return -1;
						}
					}
				}
				/* Fragment options header */
				else if (next_hdr == NEXTHDR_FRAGMENT)
				{
					if ( (len_delta -= sizeof(struct frag_hdr)) >= 0)
					{
						struct frag_hdr *ip6f =
							(struct frag_hdr *)(src+sizeof(struct ipv6hdr)+opts_len);

						opts_len += sizeof(struct frag_hdr);      /* Frag Header Length = 8 */
						ip_hdr->id = htons(ntohl(ip6f->identification)); /* ID field */
						ip_hdr->frag_off = htons((ntohs(ip6f->frag_off) & IP6F_OFF_MASK) >> 3);
										                                   /* fragment offset */
						ip_hdr->frag_off = htons(ntohs(ip_hdr->frag_off) |
										         ((ntohs(ip6f->frag_off) & IP6F_MORE_FRAG) << 13));
										                                  /* more fragments flag */
						next_hdr = ip6f->nexthdr;
					}
					else
					{
						PDEBUG("ip6_ip4(): fragment header error, packet droped");
						/* Generate ICMP Parameter Problem */
						return -1;
					}
				}
				/* No Next Header */
				else if (next_hdr == NEXTHDR_NONE)
				{
					/* RFC 2460 IPv6 Specification, 4.7
					   4.7 No Next Header

					   The value 59 in the Next Header field of an IPv6 header or any
					   extension header indicates that there is nothing following that
					   header.  If the Payload Length field of the IPv6 header indicates the
					   presence of octets past the end of a header whose Next Header field
					   contains 59, those octets must be ignored, and passed on unchanged if
					   the packet is forwarded.
					   */
					break;
				}
				else if (next_hdr == NEXTHDR_ESP || next_hdr == NEXTHDR_AUTH)
				{
					PDEBUG("ip6_ip4(): cannot translate AUTH or ESP extention header, packet dropped\n");
					return -1;
				}
				else if (next_hdr == NEXTHDR_IPV6)
				{
					PDEBUG("ip6_ip4(): cannot translate IPv6-IPv6 packet, packet dropped\n");
					return -1;
				}
				else if (next_hdr == 0)
				{
					/* As say RFC 2460 (IPv6 Spec) we should discard the packet and send an
					   ICMP Parameter Problem message to the source of the packet, with an
					   ICMP Code value of 1 ("unrecognized Next Header type encountered")
					   and the ICMP Pointer field containing the offset of the unrecognized
					   value within the original packet
					   */
					/* NOT IMPLEMENTED */
					PDEBUG("ip6_ip4(): NEXTHDR in extention header = 0, packet dropped\n");
					return -1;
				}
				else
				{
					PDEBUG("ip6_ip4(): cannot translate extention header = %d, packet dropped\n", next_hdr);
					return -1;
				}
			}
		}
	}
	else
	{
	   PDEBUG("ip6_ip4(): error packet len, packet dropped.\n");
	   return -1;
	}

	/* Building ipv4 packet */

	ip_hdr->version = IPVERSION;
	ip_hdr->ihl = 5;

	/* TOS see comment about TOS in ip4_ip6() */
	if (tos_ignore_flag)
		ip_hdr->tos = 0;
	else {
		ip_hdr->tos = ip6_hdr->priority << 4;
		ip_hdr->tos = ip_hdr->tos | (ip6_hdr->flow_lbl[0] >> 4);
	}

	/* IPv4 Total Len = IPv6 Payload Len +
	   IPv4 Header Len (without options) - Options Headers Len */
	ip6_payload_len = ntohs(ip6_hdr->payload_len);

	if (ip6_payload_len == 0)
		ntot_len = 0;
	else
		ntot_len = ip6_payload_len + IP4_IP6_HDR_DIFF - opts_len;

	ip_hdr->tot_len = htons(ntot_len);

	/* IPv4 TTL = IPv6 Hop Limit */
	ip_hdr->ttl = ip6_hdr->hop_limit;

	/* IPv4 Protocol = Next Header that will point to upper layer protocol */
	ip_hdr->protocol = next_hdr;

	/* IPv4 Src addr = last 4 bytes from IPv6 Src addr */
	ip_hdr->saddr = ip6_hdr->saddr.s6_addr32[3];
	/* IPv4 Dst addr = last 4 bytes from IPv6 Dst addr */
	ip_hdr->daddr = ip6_hdr->daddr.s6_addr32[3];

	/* Calculate IPv4 header checksum */
	ip_hdr->check = 0;
	ip_hdr->check = ip_fast_csum((unsigned char *)ip_hdr, ip_hdr->ihl);

	if (len_delta > 0)
	{
		/* PROCESS ICMP */

		if (next_hdr == NEXTHDR_ICMP)
		{
			struct icmp6hdr *icmp6_hdr;
			struct icmphdr *icmp_hdr;

			if ((len_delta -= sizeof(struct icmp6hdr)) >= 0)
			{
				icmp6_hdr = (struct icmp6hdr *)(src + sizeof(struct ipv6hdr) + opts_len);
				icmp_hdr = (struct icmphdr *)(dst + sizeof(struct iphdr));

				real_len += len_delta + sizeof(struct icmphdr);

				/* There is diffirent between ICMPv4/ICMPv6 protocol codes
				   IPPROTO_ICMP = 1
				   IPPROTO_ICMPV6 = 58        */
				ip_hdr->protocol = IPPROTO_ICMP;

				if (include_flag) {
					/* !!! Warnig !!! We discard ICMP packets with any ICMP as included
					   in ICMP Error. But ICMP Error messages can include ICMP Query message
					   */
					if (icmp6_hdr->icmp6_type != ICMPV6_ECHO_REQUEST)
					{
						PDEBUG("ip6_ip4(): included ICMPv6 in ICMPv6 Error message, packet dropped\n");
						return -1;
					}
				}

			/* Translate ICMPv6 to ICMPv4 */
				switch (icmp6_hdr->icmp6_type)
				{
/* ICMP Error messages */
			/* Destination Unreachable (Type 1) */
				case ICMPV6_DEST_UNREACH: /* Type 1 */
					icmp_hdr->type = ICMP_DEST_UNREACH; /* to Type 3 */
					icmp_hdr->un.echo.id = 0;
					icmp_hdr->un.echo.sequence = 0;
					switch (icmp6_hdr->icmp6_code)
					{
					case ICMPV6_NOROUTE: /* Code 0 */
					case ICMPV6_NOT_NEIGHBOUR: /* Code 2 */
					case ICMPV6_ADDR_UNREACH: /* Code 3  */
						icmp_hdr->code = ICMP_HOST_UNREACH; /* To Code 1 */
						break;
					case ICMPV6_ADM_PROHIBITED: /* Code 1 */
						icmp_hdr->code = ICMP_HOST_ANO; /* To Code 10 */
						break;
					case ICMPV6_PORT_UNREACH: /* Code 4 */
						icmp_hdr->code = ICMP_PORT_UNREACH; /* To Code 3 */

						break;
					default:            /* discard any other codes */
						PDEBUG("ip6_ip4(): Unknown ICMPv6 Type %d Code %d - packet dropped.\n",
							   ICMPV6_DEST_UNREACH, icmp6_hdr->icmp6_code);
						return -1;
					}
					break;
			/* Packet Too Big (Type 2) */
				case ICMPV6_PKT_TOOBIG: /* Type 2 */
					icmp_hdr->type = ICMP_DEST_UNREACH; /* to Type 3  */
					icmp_hdr->code = ICMP_FRAG_NEEDED; /*  to Code 4 */
					/* Change MTU, RFC 2765 (SIIT), 4.2:
					   The MTU field needs to be adjusted for the difference between
					   the IPv4 and IPv6 header sizes taking into account whether or
					   not the packet in error includes a Fragment header.
					   */
					/* !!! Don't implement !!! */
					icmp_hdr->un.frag.mtu = (__u16) icmp6_hdr->icmp6_mtu;
					break;
			/* Time Exceeded (Type 3) */
				case ICMPV6_TIME_EXCEED:
					icmp_hdr->type = ICMP_TIME_EXCEEDED; /* to Type 11 */
					icmp_hdr->code = icmp6_hdr->icmp6_code; /* Code unchanged */
					break;
			/* Parameter Problem (Type 4) */
				case ICMPV6_PARAMPROB:
					switch (icmp6_hdr->icmp6_code) {
					case ICMPV6_UNK_NEXTHDR: /* Code 1 */
						icmp_hdr->type = ICMP_DEST_UNREACH; /* to Type 3 */
						icmp_hdr->code = ICMP_PROT_UNREACH; /* to Code 2 */
						break;
					default: /* if Code != 1 */
						icmp_hdr->type = ICMP_PARAMETERPROB; /* to Type 12 */
						icmp_hdr->code = 0; /* to Code 0 */
						/* Update Pointer field
						   RFC 2765 (SIIT), 4.2:
						   The Pointer needs to be updated to point to the corresponding
						   field in the translated include IP header.
						   */
						switch (ntohl(icmp6_hdr->icmp6_pointer))
						{
						case 0: /* IPv6 Version -> IPv4 Version */
							icmp_hdr->un.echo.id = 0;
							break;
						case 4: /* IPv6 PayloadLength -> IPv4 Total Length */
							icmp_hdr->un.echo.id = 0x0002; /* 2 */
							break;
						case 6: /* IPv6 Next Header-> IPv4 Protocol */
							icmp_hdr->un.echo.id = 0x0009; /* 9 */
							break;
						case 7: /* IPv6 Hop Limit -> IPv4 TTL */
							icmp_hdr->un.echo.id = 0x0008; /* 8 */
							break;
						case 8: /* IPv6 Src addr -> IPv4 Src addr */
							icmp_hdr->un.echo.id = 0x000c; /* 12 */
							break;
						case 24: /* IPv6 Dst addr -> IPv4 Dst addr*/
							icmp_hdr->un.echo.id = 0x0010; /* 16 */
							break;
						default: /* set all ones in other cases */
							icmp_hdr->un.echo.id = 0xff;
							break;
						}
						break;
					}
					break;

/* End of ICMP Error messages */

			/* Echo Request and Echo Reply (Type 128 and 129)  */
				case ICMPV6_ECHO_REQUEST:
					icmperr = 0;        /* not error ICMP message */
					icmp_hdr->type = ICMP_ECHO; /* to Type 8 */
					icmp_hdr->code = 0; /* to Code 0 */
					icmp_hdr->un.echo.id = icmp6_hdr->icmp6_identifier;
					icmp_hdr->un.echo.sequence = icmp6_hdr->icmp6_sequence;
					/* copy rest of ICMP data to result packet */
					if (len_delta > 0)
						memcpy(((char *)icmp_hdr) + sizeof(struct icmphdr),
							   ((char *)icmp6_hdr) + sizeof(struct icmp6hdr), len_delta);
					break;
				case ICMPV6_ECHO_REPLY:
					icmperr = 0;        /* not error ICMP message */
					icmp_hdr->type = ICMP_ECHOREPLY; /* to Type 0 */
					icmp_hdr->code = 0; /* to Code 0 */
					icmp_hdr->un.echo.id = icmp6_hdr->icmp6_identifier;
					icmp_hdr->un.echo.sequence = icmp6_hdr->icmp6_sequence;
					/* copy rest of ICMP data */
					if (len_delta > 0)
						memcpy(((char *)icmp_hdr) + sizeof(struct icmphdr),
							   ((char *)icmp6_hdr) + sizeof(struct icmp6hdr), len_delta);
					break;
				default:
					/* Unknown error messages. Silently drop. */
					PDEBUG("ip6_ip4(): unknown ICMPv6 Type %d, packet dropped.\n", icmp6_hdr->icmp6_type);
					return -1;
				}

				if (icmperr)
				{
					/* If ICMP Error message, we translate IP included packet*/
					if (len_delta >= sizeof(struct ipv6hdr))
					{
						if((inc_opts_len = ip6_ip4((char *)icmp6_hdr + sizeof(struct icmp6hdr), len_delta,
										           (char *)icmp_hdr + sizeof(struct icmphdr), 1)) == -1) {
							PDEBUG("ip6_ip4(): incorrect translation of ICMPv6 Error message, packet dropped\n");
							return -1;
						}
						/* correct IPv4 Total Len that = old Total Len
						   - Options Headers Len in included IP packet
						   - diffirence between IPv6 Header Len and IPv4 Header Len
						   */
						if (ntot_len != 0)
							ip_hdr->tot_len = htons(ntot_len - inc_opts_len - IP4_IP6_HDR_DIFF);
						real_len = real_len - inc_opts_len - IP4_IP6_HDR_DIFF;
					}
					else if (len_delta > 0)
					{
						/* May be it need set 0x0 to rest area in result IPv4 packet,
						 * but we copy rest data unchanged
						 */
						memcpy(((char *)icmp_hdr) + sizeof(struct icmphdr),
							   ((char *)icmp6_hdr) + sizeof(struct icmp6hdr), len_delta);
					}
				}

				/* Calculate IPv4 Header checksum */
				ip_hdr->check = 0;
				ip_hdr->check = ip_fast_csum((unsigned char *)ip_hdr, ip_hdr->ihl);

				/* Calculate ICMPv4 checksum */
				if (ntot_len != 0)
				{
					icmp_hdr->checksum = 0;
					icmp_hdr->checksum = ip_compute_csum((unsigned char *)icmp_hdr, ntohs(ip_hdr->tot_len)
										             - sizeof(struct iphdr));
				}
			}
			else
			{
				PDEBUG("ip6_ip4(): error length ICMP packet, packet dropped.\n");
				return -1;
			}

		}
		/* PROCESS TCP and UDP (and rest data) */

		else {
			real_len += len_delta;
			/* we copy rest data to IPv4 packet without changing */
			memcpy(dst+sizeof(struct iphdr), src + sizeof(struct ipv6hdr) + opts_len, len_delta);
		}
	}

	if (include_flag)           /* if it's included IP packet */
		return opts_len;        /* return options headers length */
	else
		return real_len; /* result packet len */
}

/*
 * ip4_fragment(skb, len, hdr_len, dev, eth_h)
 * to fragment original IPv4 packet if result IPv6 packet will be > 1280
 */

static int ip4_fragment(struct sk_buff *skb, int len, int hdr_len, struct net_device *dev, struct ethhdr *eth_h)
{
	struct sk_buff *skb2 = NULL;       /* pointer to new struct sk_buff for transleded packet */
	char buff[FRAG_BUFF_SIZE+hdr_len]; /* buffer to form new fragment packet */
	char *cur_ptr = skb->data+hdr_len; /* pointter to current packet data with len = frag_len */
	struct iphdr *ih4 = (struct iphdr *) skb->data;
	struct iphdr *new_ih4 = (struct iphdr *) buff; /* point to new IPv4 hdr */
	struct ethhdr *new_eth_h;   /* point to ether hdr, need to set hard header data in fragment */
	int data_len = len - hdr_len; /* origin packet data len */
	int rest_len = data_len;    /* rest data to fragment */
	int frag_len = 0;           /* current fragment len */
	int last_frag = 0;          /* last fragment flag, if = 1, it's last fragment */
	int flag_last_mf = 0;
	__u16 new_id = 0;           /* to generate identification field */
	__u16 frag_offset = 0;      /* fragment offset */
	unsigned int csum;
	unsigned short udp_len;

#ifdef SIIT_DEBUG
	printk("siit: it's DF == 0 and result IPv6 packet will be > 1280\n");
	siit_print_dump(skb->data, hdr_len, "siit: (orig) ipv4_hdr dump");
#endif

	if ((ntohs(ih4->frag_off) & IP_MF) == 0 )
		/* it's a case we'll clear MF flag in our last packet */
		flag_last_mf = 1;

	if (ih4->protocol == IPPROTO_UDP) {
		if ( (ntohs(ih4->frag_off) & IP_OFFSET) == 0) {
			struct udphdr *udp_hdr = (struct udphdr *)((char *)ih4 + hdr_len);
			if (!flag_last_mf) {
				if (udp_hdr->check == 0) {
					/* it's a first fragment with ZERO checksum and we drop packet */
					printk("siit: First fragment of UDP with zero checksum - packet droped\n");
					printk("siit: addr: %x src port: %d dst port: %d\n",
						   htonl(ih4->saddr), htons(udp_hdr->source), htons(udp_hdr->dest));
					return -1;
				}
			}
			else if (udp_hdr->check == 0) {
				/* Calculate UDP checksum only if it's not fragment */
				udp_len = ntohs(udp_hdr->len);
				csum = 0;
				csum = csum_partial((unsigned char *)udp_hdr, udp_len, csum);
				udp_hdr->check = csum_tcpudp_magic(ih4->saddr, ih4->daddr, udp_len, IPPROTO_UDP, csum);
			}
		}
	}

	frag_offset = ntohs(ih4->frag_off) & IP_OFFSET;

	new_id = ih4->id;

	while(1) {
		if (rest_len <= FRAG_BUFF_SIZE) {
			/* it's last fragmen */
			frag_len = rest_len; /* rest data */
			last_frag = 1;
		}
		else
			frag_len = FRAG_BUFF_SIZE;

		/* copy IP header to buffer */
		memcpy(buff, skb->data, hdr_len);
		/* copy data to buffer with len = frag_len */
		memcpy(buff + hdr_len, cur_ptr, frag_len);

		/* set id field in new IPv4 header*/
		new_ih4->id = new_id;

		/* is it last fragmet */
		if(last_frag && flag_last_mf)
			/* clear MF flag */
			new_ih4->frag_off = htons(frag_offset & (~IP_MF));
		else
			/* set MF flag */
			new_ih4->frag_off = htons(frag_offset | IP_MF);

		/* change packet total length */
		new_ih4->tot_len = htons(frag_len+hdr_len);

		/* rebuild the header checksum (IP needs it) */
		new_ih4->check = 0;
		new_ih4->check = ip_fast_csum((unsigned char *)new_ih4,new_ih4->ihl);

		/* Allocate new sk_buff to compose translated packet */
		skb2 = dev_alloc_skb(frag_len+hdr_len+dev->hard_header_len+IP4_IP6_HDR_DIFF+IP6_FRAGMENT_SIZE);
		if (!skb2) {
			printk(KERN_DEBUG "%s: alloc_skb failure - packet dropped.\n", dev->name);
			dev_kfree_skb(skb2);
			return -1;
		}
		/* allocate skb->data portion for IP header len, fragment data len and ether header len
		 * and copy to head ether header from origin skb
		 */
		memcpy(skb_put(skb2, frag_len+hdr_len+dev->hard_header_len+IP4_IP6_HDR_DIFF+IP6_FRAGMENT_SIZE), (char *) eth_h,
			   dev->hard_header_len);
		/* correct ether header data, ether protocol field to ETH_P_IPV6 */
		new_eth_h = (struct ethhdr *)skb2->data;
		new_eth_h->h_proto = htons(ETH_P_IPV6);

		/* reset the mac header */
		skb_reset_mac_header(skb2);

		/* pull ether header from new skb->data */
		skb_pull(skb2, dev->hard_header_len);
		/* set skb protocol to IPV6 */
		skb2->protocol = htons(ETH_P_IPV6);

		/* call translation function */
		if ( ip4_ip6(buff, frag_len+hdr_len, skb2->data, 0) == -1) {
			dev_kfree_skb(skb2);
			return -1;
		}

		/*
		 * Set needed fields in new sk_buff
		 */
		skb2->dev = dev;
		skb2->ip_summed = CHECKSUM_UNNECESSARY;
		skb2->pkt_type = PACKET_HOST;

		/* Add transmit statistic */
		siit_stats(dev)->tx_packets++;
		siit_stats(dev)->tx_bytes += skb2->len;

		/* send packet to upper layer */
		netif_rx(skb2);

		/* exit if it was last fragment */
		if (last_frag)
			break;

		/* correct current data pointer */
		cur_ptr += frag_len;
		/* rest data len */
		rest_len -= frag_len;
		/* current fragment offset */
		frag_offset = (frag_offset*8 + frag_len)/8;
	}

	return 0;
}
/*
 * Transmit a packet (called by the kernel)
 *
 * siit_xmit(skb, dev)
 *
 * where
 * skb - pointer to struct sk_buff with incomed packet
 * dev - pointer to struct device on which packet revieved
 *
 * Statistic:
 * for all incoming packes:
 *            stats.rx_bytes+=skb->len
 *            stats.rx_packets++
 * for packets we can't transle:
 *            stats.tx_errors++
 * device busy:
 *            stats.tx_errors++
 * for packets we can't allocate sk_buff:
 *            stats.tx_dropped++
 * for outgoing packes:
 *            stats.tx_packets++
 *            stats.tx_bytes+=skb2->len !!! But we don't set skb2->len !!!
 */

static int siit_xmit(struct sk_buff *skb, struct net_device *dev)
{
	struct sk_buff *skb2 = NULL;/* pointer to new struct sk_buff for transleded packet */
	struct ethhdr *eth_h;       /* pointer to incoming Ether header */
	int len;                    /* original packets length */
	int new_packet_len;
	int skb_delta = 0;          /* delta size for allocate new skb */
	char new_packet_buff[2048];

	/* Check pointer to sk_buff and device structs */
	if (skb == NULL || dev == NULL)
		return -EINVAL;

	/* Add receive statistic */
	siit_stats(dev)->rx_bytes += skb->len;
	siit_stats(dev)->rx_packets++;

	dev->trans_start = jiffies;

	/* Upper layer (IP) protocol forms sk_buff for outgoing packet
	 * and sets IP header + Ether header too. IP layer sets outgoing
	 * device in sk_buff->dev.
	 * In function (from linux/net/core/dev.c) ther is a call to
	 * device transmit function (dev->hard_start_xmit):
	 *
	 *    dev_queue_xmit(struct sk_buff *skb)
	 *    {
	 *    ...
	 *          device *dev = skb->dev;
	 *    ...
	 *          dev->hard_start_xmit(skb, dev);
	 *    ...
	 *    }
	 * We save pointer to ether header in eth_h and skb_pull ether header
	 * from data field of skb_buff
	 */

	eth_h = (struct ethhdr *)skb->data; /* point to incoming packet Ether Header */

#ifdef SIIT_DEBUG
	siit_print_dump(skb->data, ETH_HLEN, "siit: eth_hdr dump");
#endif

	/* Remove hardware header from origin sk_buff */
	skb_pull(skb,dev->hard_header_len);

	/*
	 * Process IPv4 paket
	 */
	if (ntohs(skb->protocol) == ETH_P_IP) {
		int hdr_len;            /* IPv4 header length */
		int data_len;           /* IPv4 data length */
		struct iphdr *ih4;      /* pointer to IPv4 header */
		struct icmphdr *icmp_hdr;   /* point to current ICMPv4 header struct */

		ih4 = (struct iphdr *)skb->data; /* point to incoming packet's IPv4 header */

		/* Check IPv4 Total Length */
		if (skb->len != ntohs(ih4->tot_len)) {
			PDEBUG("siit_xmit(): Different skb_len %x and ip4 tot_len %x - packet dropped.\n",
				   skb->len, ih4->tot_len);
			siit_stats(dev)->tx_errors++;
			dev_kfree_skb(skb);
			return 0;
		}

		len = skb->len;     /* packet's total len */
		hdr_len = (int)(ih4->ihl * 4); /* packet's header len */
		data_len = len - hdr_len; /* packet's data len */

		/* If DF == 0 */
		if ( (ntohs(ih4->frag_off) & IP_DF) == 0 ) {
			/* If result IPv6 packet will be > 1280
			   we need to fragment original IPv4 packet
			*/
			if ( data_len > FRAG_BUFF_SIZE ) {
				/* call function that fragment packet and translate to IPv6 each fragment
				 * and send to upper layer
				 */
				if ( ip4_fragment(skb, len, hdr_len, dev, eth_h) == -1) {
					siit_stats(dev)->tx_errors++;
				}
				/* Free incoming skb */
				dev_kfree_skb(skb);
				/* Device can accept a new packet */

				return 0;

			}
		}
		/* If DF == 1 && MF == 0 && Fragment Offset == 0
		 * we don't include fragment header
		 */
		if ( ntohs(ih4->frag_off) == IP_DF )
			skb_delta = IP4_IP6_HDR_DIFF; /* delta is +20 */
		else
			skb_delta = IP4_IP6_HDR_DIFF + IP6_FRAGMENT_SIZE; /* delta is +20 and +8 */

		/* If it's ICMP, check is it included IP packet in it */
		if ( ih4->protocol == IPPROTO_ICMP) {
			icmp_hdr = (struct icmphdr *) (skb->data+hdr_len); /* point to ICMPv4 header */
			if ( icmp_hdr->type != ICMP_ECHO && icmp_hdr->type != ICMP_ECHOREPLY) {
				/*
				 * It's ICMP Error that has included IP packet
				 * we'll add only +20 because we don't include Fragment Header
				 * into translated included IP packet
				 */
				skb_delta += IP4_IP6_HDR_DIFF;
			}
		}

		/* Allocate new sk_buff to compose translated packet */
		skb2 = dev_alloc_skb(len+dev->hard_header_len+skb_delta);
		if (!skb2) {
			printk(KERN_DEBUG "%s: alloc_skb failure - packet dropped.\n", dev->name);
			dev_kfree_skb(skb);
			siit_stats(dev)->rx_dropped++;

			return 0;
		}
		/* allocate skb->data portion = IPv4 packet len + ether header len
		 * + skb_delta (max = two times (diffirence between IPv4 header and
		 * IPv6 header + Frag Header), second for included packet,
		 * and copy to head of skb->data ether header from origin skb
		 */
		memcpy(skb_put(skb2, len+dev->hard_header_len+skb_delta), (char *)eth_h, dev->hard_header_len);
		/* correct ether header data, ether protocol field to ETH_P_IPV6 */
		eth_h = (struct ethhdr *)skb2->data;
		eth_h->h_proto = htons(ETH_P_IPV6);
		skb_reset_mac_header(skb2);
		/* remove ether header from new skb->data,
		 * NOTE! data will rest, pointer to data and data len will change
		 */
		skb_pull(skb2,dev->hard_header_len);
		/* set skb protocol to IPV6 */
		skb2->protocol = htons(ETH_P_IPV6);

		/* call translation function */
		if (ip4_ip6(skb->data, len, skb2->data, 0) == -1 ) {
			dev_kfree_skb(skb);
			dev_kfree_skb(skb2);
			siit_stats(dev)->rx_errors++;

			return 0;
		}
	}
	/*
	 * IPv6 paket
	 */
	else if (ntohs(skb->protocol) == ETH_P_IPV6) {

#ifdef SIIT_DEBUG
		siit_print_dump(skb->data, sizeof(struct ipv6hdr), "siit: (in) ip6_hdr dump");
#endif
		/* packet len = skb->data len*/
		len = skb->len;

		/* call translation function */
		if ((new_packet_len = ip6_ip4(skb->data, len, new_packet_buff, 0)) == -1 )
		{
			PDEBUG("siit_xmit(): error translation ipv6->ipv4, packet dropped.\n");
			siit_stats(dev)->rx_dropped++;
			goto end;
		}

		/* Allocate new sk_buff to compose translated packet */
		skb2 = dev_alloc_skb(new_packet_len + dev->hard_header_len);
		if (!skb2) {
			printk(KERN_DEBUG "%s: alloc_skb failure, packet dropped.\n", dev->name);
			siit_stats(dev)->rx_dropped++;
			goto end;
		}
		memcpy(skb_put(skb2, new_packet_len + dev->hard_header_len), (char *)eth_h, dev->hard_header_len);
		eth_h = (struct ethhdr *)skb2->data;
		eth_h->h_proto = htons(ETH_P_IP);
		skb_reset_mac_header(skb2);
		skb_pull(skb2, dev->hard_header_len);
		memcpy(skb2->data, new_packet_buff, new_packet_len);
		skb2->protocol = htons(ETH_P_IP);
	}
	else {
		PDEBUG("siit_xmit(): unsupported protocol family %x, packet dropped.\n", skb->protocol);
		goto end;
	}

	/*
	 * Set needed fields in new sk_buff
	 */
	skb2->pkt_type = PACKET_HOST;
	skb2->dev = dev;
	skb2->ip_summed = CHECKSUM_UNNECESSARY;

	/* Add transmit statistic */
	siit_stats(dev)->tx_packets++;
	siit_stats(dev)->tx_bytes += skb2->len;

	/* Send packet to upper layer protocol */
	netif_rx(skb2);

end:
	dev_kfree_skb(skb);

	return 0;
}

#if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,0)
static bool header_ops_init = false;
static struct header_ops siit_header_ops ____cacheline_aligned;
#endif

/*
 * The init function initialize of the SIIT device..
 * It is invoked by register_netdev()
 */
static void
siit_init(struct net_device *dev)
{
	ether_setup(dev);    /* assign some of the fields */
	random_ether_addr(dev->dev_addr);

	/*
	 * Assign device function.
	 */
	dev->open            = siit_open;
	dev->stop            = siit_release;
	dev->hard_start_xmit = siit_xmit;
	dev->flags           |= IFF_NOARP;     /* ARP not used */
	dev->tx_queue_len = 10;

#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,0)
	dev->hard_header_cache = NULL;        /* Disable caching */
	memset(netdev_priv(dev), 0, sizeof(struct net_device_stats));
	dev->get_stats = siit_get_stats;
#else
	if (!header_ops_init) {
		memcpy(&siit_header_ops, dev->header_ops, sizeof(struct header_ops));
		siit_header_ops.cache = NULL;
	}
	dev->header_ops = &siit_header_ops;
#endif
}

/*
 * Finally, the module stuff
 */
static struct net_device *siit_dev = NULL;

int init_module(void)
{
	int res = -ENOMEM;
	int priv_size;

#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,0)
	priv_size = sizeof(struct net_device_stats);
#else
	priv_size = sizeof(struct header_ops);
#endif
	siit_dev = alloc_netdev(priv_size, "siit%d", siit_init);
	if (!siit_dev)
		goto err_alloc;

	res = register_netdev(siit_dev);
	if (res)
		goto err_register;

	return 0;

err_register:
	free_netdev(siit_dev);
err_alloc:
	printk(KERN_ERR "Error creating siit device: %d\n", res);
	return res;
}

void cleanup_module(void)
{
	unregister_netdev(siit_dev);
	free_netdev(siit_dev);
}