aboutsummaryrefslogtreecommitdiffstats
path: root/net/dccp/feat.c
blob: b127189550f15eaf270064b8ffbe831daeed0be7 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
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
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
/*
 *  net/dccp/feat.c
 *
 *  An implementation of the DCCP protocol
 *  Andrea Bittau <a.bittau@cs.ucl.ac.uk>
 *
 *  ASSUMPTIONS
 *  -----------
 *  o Feature negotiation is coordinated with connection setup (as in TCP), wild
 *    changes of parameters of an established connection are not supported.
 *  o All currently known SP features have 1-byte quantities. If in the future
 *    extensions of RFCs 4340..42 define features with item lengths larger than
 *    one byte, a feature-specific extension of the code will be required.
 *
 *  This program 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 of the License, or (at your option) any later version.
 */

#include <linux/module.h>

#include "ccid.h"
#include "feat.h"

#define DCCP_FEAT_SP_NOAGREE (-123)

/*
 * Feature activation handlers.
 *
 * These all use an u64 argument, to provide enough room for NN/SP features. At
 * this stage the negotiated values have been checked to be within their range.
 */
static int dccp_hdlr_ccid(struct sock *sk, u64 ccid, bool rx)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct ccid *new_ccid = ccid_new(ccid, sk, rx, gfp_any());

	if (new_ccid == NULL)
		return -ENOMEM;

	if (rx) {
		ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
		dp->dccps_hc_rx_ccid = new_ccid;
	} else {
		ccid_hc_tx_delete(dp->dccps_hc_tx_ccid, sk);
		dp->dccps_hc_tx_ccid = new_ccid;
	}
	return 0;
}

static int dccp_hdlr_seq_win(struct sock *sk, u64 seq_win, bool rx)
{
	if (!rx)
		dccp_msk(sk)->dccpms_sequence_window = seq_win;
	return 0;
}

static int dccp_hdlr_ack_ratio(struct sock *sk, u64 ratio, bool rx)
{
	if (rx)
		dccp_sk(sk)->dccps_r_ack_ratio = ratio;
	else
		dccp_sk(sk)->dccps_l_ack_ratio = ratio;
	return 0;
}

static int dccp_hdlr_ackvec(struct sock *sk, u64 enable, bool rx)
{
	struct dccp_sock *dp = dccp_sk(sk);

	if (rx) {
		if (enable && dp->dccps_hc_rx_ackvec == NULL) {
			dp->dccps_hc_rx_ackvec = dccp_ackvec_alloc(gfp_any());
			if (dp->dccps_hc_rx_ackvec == NULL)
				return -ENOMEM;
		} else if (!enable) {
			dccp_ackvec_free(dp->dccps_hc_rx_ackvec);
			dp->dccps_hc_rx_ackvec = NULL;
		}
	}
	return 0;
}

static int dccp_hdlr_ndp(struct sock *sk, u64 enable, bool rx)
{
	if (!rx)
		dccp_msk(sk)->dccpms_send_ndp_count = (enable > 0);
	return 0;
}

/*
 * Minimum Checksum Coverage is located at the RX side (9.2.1). This means that
 * `rx' holds when the sending peer informs about his partial coverage via a
 * ChangeR() option. In the other case, we are the sender and the receiver
 * announces its coverage via ChangeL() options. The policy here is to honour
 * such communication by enabling the corresponding partial coverage - but only
 * if it has not been set manually before; the warning here means that all
 * packets will be dropped.
 */
static int dccp_hdlr_min_cscov(struct sock *sk, u64 cscov, bool rx)
{
	struct dccp_sock *dp = dccp_sk(sk);

	if (rx)
		dp->dccps_pcrlen = cscov;
	else {
		if (dp->dccps_pcslen == 0)
			dp->dccps_pcslen = cscov;
		else if (cscov > dp->dccps_pcslen)
			DCCP_WARN("CsCov %u too small, peer requires >= %u\n",
				  dp->dccps_pcslen, (u8)cscov);
	}
	return 0;
}

static const struct {
	u8			feat_num;		/* DCCPF_xxx */
	enum dccp_feat_type	rxtx;			/* RX or TX  */
	enum dccp_feat_type	reconciliation;		/* SP or NN  */
	u8			default_value;		/* as in 6.4 */
	int (*activation_hdlr)(struct sock *sk, u64 val, bool rx);
/*
 *    Lookup table for location and type of features (from RFC 4340/4342)
 *  +--------------------------+----+-----+----+----+---------+-----------+
 *  | Feature                  | Location | Reconc. | Initial |  Section  |
 *  |                          | RX | TX  | SP | NN |  Value  | Reference |
 *  +--------------------------+----+-----+----+----+---------+-----------+
 *  | DCCPF_CCID               |    |  X  | X  |    |   2     | 10        |
 *  | DCCPF_SHORT_SEQNOS       |    |  X  | X  |    |   0     |  7.6.1    |
 *  | DCCPF_SEQUENCE_WINDOW    |    |  X  |    | X  | 100     |  7.5.2    |
 *  | DCCPF_ECN_INCAPABLE      | X  |     | X  |    |   0     | 12.1      |
 *  | DCCPF_ACK_RATIO          |    |  X  |    | X  |   2     | 11.3      |
 *  | DCCPF_SEND_ACK_VECTOR    | X  |     | X  |    |   0     | 11.5      |
 *  | DCCPF_SEND_NDP_COUNT     |    |  X  | X  |    |   0     |  7.7.2    |
 *  | DCCPF_MIN_CSUM_COVER     | X  |     | X  |    |   0     |  9.2.1    |
 *  | DCCPF_DATA_CHECKSUM      | X  |     | X  |    |   0     |  9.3.1    |
 *  | DCCPF_SEND_LEV_RATE      | X  |     | X  |    |   0     | 4342/8.4  |
 *  +--------------------------+----+-----+----+----+---------+-----------+
 */
} dccp_feat_table[] = {
	{ DCCPF_CCID,		 FEAT_AT_TX, FEAT_SP, 2,   dccp_hdlr_ccid     },
	{ DCCPF_SHORT_SEQNOS,	 FEAT_AT_TX, FEAT_SP, 0,   NULL },
	{ DCCPF_SEQUENCE_WINDOW, FEAT_AT_TX, FEAT_NN, 100, dccp_hdlr_seq_win  },
	{ DCCPF_ECN_INCAPABLE,	 FEAT_AT_RX, FEAT_SP, 0,   NULL },
	{ DCCPF_ACK_RATIO,	 FEAT_AT_TX, FEAT_NN, 2,   dccp_hdlr_ack_ratio},
	{ DCCPF_SEND_ACK_VECTOR, FEAT_AT_RX, FEAT_SP, 0,   dccp_hdlr_ackvec   },
	{ DCCPF_SEND_NDP_COUNT,  FEAT_AT_TX, FEAT_SP, 0,   dccp_hdlr_ndp      },
	{ DCCPF_MIN_CSUM_COVER,  FEAT_AT_RX, FEAT_SP, 0,   dccp_hdlr_min_cscov},
	{ DCCPF_DATA_CHECKSUM,	 FEAT_AT_RX, FEAT_SP, 0,   NULL },
	{ DCCPF_SEND_LEV_RATE,	 FEAT_AT_RX, FEAT_SP, 0,   NULL },
};
#define DCCP_FEAT_SUPPORTED_MAX		ARRAY_SIZE(dccp_feat_table)

/**
 * dccp_feat_index  -  Hash function to map feature number into array position
 * Returns consecutive array index or -1 if the feature is not understood.
 */
static int dccp_feat_index(u8 feat_num)
{
	/* The first 9 entries are occupied by the types from RFC 4340, 6.4 */
	if (feat_num > DCCPF_RESERVED && feat_num <= DCCPF_DATA_CHECKSUM)
		return feat_num - 1;

	/*
	 * Other features: add cases for new feature types here after adding
	 * them to the above table.
	 */
	switch (feat_num) {
	case DCCPF_SEND_LEV_RATE:
			return DCCP_FEAT_SUPPORTED_MAX - 1;
	}
	return -1;
}

static u8 dccp_feat_type(u8 feat_num)
{
	int idx = dccp_feat_index(feat_num);

	if (idx < 0)
		return FEAT_UNKNOWN;
	return dccp_feat_table[idx].reconciliation;
}

static int dccp_feat_default_value(u8 feat_num)
{
	int idx = dccp_feat_index(feat_num);
	/*
	 * There are no default values for unknown features, so encountering a
	 * negative index here indicates a serious problem somewhere else.
	 */
	DCCP_BUG_ON(idx < 0);

	return idx < 0 ? 0 : dccp_feat_table[idx].default_value;
}

static int __dccp_feat_activate(struct sock *sk, const int idx,
				const bool is_local, dccp_feat_val const *fval)
{
	bool rx;
	u64 val;

	if (idx < 0 || idx >= DCCP_FEAT_SUPPORTED_MAX)
		return -1;
	if (dccp_feat_table[idx].activation_hdlr == NULL)
		return 0;

	if (fval == NULL) {
		val = dccp_feat_table[idx].default_value;
	} else if (dccp_feat_table[idx].reconciliation == FEAT_SP) {
		if (fval->sp.vec == NULL) {
			/*
			 * This can happen when an empty Confirm is sent
			 * for an SP (i.e. known) feature. In this case
			 * we would be using the default anyway.
			 */
			DCCP_CRIT("Feature #%d undefined: using default", idx);
			val = dccp_feat_table[idx].default_value;
		} else {
			val = fval->sp.vec[0];
		}
	} else {
		val = fval->nn;
	}

	/* Location is RX if this is a local-RX or remote-TX feature */
	rx = (is_local == (dccp_feat_table[idx].rxtx == FEAT_AT_RX));

	return dccp_feat_table[idx].activation_hdlr(sk, val, rx);
}

/* Test for "Req'd" feature (RFC 4340, 6.4) */
static inline int dccp_feat_must_be_understood(u8 feat_num)
{
	return	feat_num == DCCPF_CCID || feat_num == DCCPF_SHORT_SEQNOS ||
		feat_num == DCCPF_SEQUENCE_WINDOW;
}

/* copy constructor, fval must not already contain allocated memory */
static int dccp_feat_clone_sp_val(dccp_feat_val *fval, u8 const *val, u8 len)
{
	fval->sp.len = len;
	if (fval->sp.len > 0) {
		fval->sp.vec = kmemdup(val, len, gfp_any());
		if (fval->sp.vec == NULL) {
			fval->sp.len = 0;
			return -ENOBUFS;
		}
	}
	return 0;
}

static void dccp_feat_val_destructor(u8 feat_num, dccp_feat_val *val)
{
	if (unlikely(val == NULL))
		return;
	if (dccp_feat_type(feat_num) == FEAT_SP)
		kfree(val->sp.vec);
	memset(val, 0, sizeof(*val));
}

static struct dccp_feat_entry *
	      dccp_feat_clone_entry(struct dccp_feat_entry const *original)
{
	struct dccp_feat_entry *new;
	u8 type = dccp_feat_type(original->feat_num);

	if (type == FEAT_UNKNOWN)
		return NULL;

	new = kmemdup(original, sizeof(struct dccp_feat_entry), gfp_any());
	if (new == NULL)
		return NULL;

	if (type == FEAT_SP && dccp_feat_clone_sp_val(&new->val,
						      original->val.sp.vec,
						      original->val.sp.len)) {
		kfree(new);
		return NULL;
	}
	return new;
}

static void dccp_feat_entry_destructor(struct dccp_feat_entry *entry)
{
	if (entry != NULL) {
		dccp_feat_val_destructor(entry->feat_num, &entry->val);
		kfree(entry);
	}
}

/*
 * List management functions
 *
 * Feature negotiation lists rely on and maintain the following invariants:
 * - each feat_num in the list is known, i.e. we know its type and default value
 * - each feat_num/is_local combination is unique (old entries are overwritten)
 * - SP values are always freshly allocated
 * - list is sorted in increasing order of feature number (faster lookup)
 */
static struct dccp_feat_entry *dccp_feat_list_lookup(struct list_head *fn_list,
						     u8 feat_num, bool is_local)
{
	struct dccp_feat_entry *entry;

	list_for_each_entry(entry, fn_list, node) {
		if (entry->feat_num == feat_num && entry->is_local == is_local)
			return entry;
		else if (entry->feat_num > feat_num)
			break;
	}
	return NULL;
}

/**
 * dccp_feat_entry_new  -  Central list update routine (called by all others)
 * @head:  list to add to
 * @feat:  feature number
 * @local: whether the local (1) or remote feature with number @feat is meant
 * This is the only constructor and serves to ensure the above invariants.
 */
static struct dccp_feat_entry *
	      dccp_feat_entry_new(struct list_head *head, u8 feat, bool local)
{
	struct dccp_feat_entry *entry;

	list_for_each_entry(entry, head, node)
		if (entry->feat_num == feat && entry->is_local == local) {
			dccp_feat_val_destructor(entry->feat_num, &entry->val);
			return entry;
		} else if (entry->feat_num > feat) {
			head = &entry->node;
			break;
		}

	entry = kmalloc(sizeof(*entry), gfp_any());
	if (entry != NULL) {
		entry->feat_num = feat;
		entry->is_local = local;
		list_add_tail(&entry->node, head);
	}
	return entry;
}

/**
 * dccp_feat_push_change  -  Add/overwrite a Change option in the list
 * @fn_list: feature-negotiation list to update
 * @feat: one of %dccp_feature_numbers
 * @local: whether local (1) or remote (0) @feat_num is meant
 * @needs_mandatory: whether to use Mandatory feature negotiation options
 * @fval: pointer to NN/SP value to be inserted (will be copied)
 */
static int dccp_feat_push_change(struct list_head *fn_list, u8 feat, u8 local,
				 u8 mandatory, dccp_feat_val *fval)
{
	struct dccp_feat_entry *new = dccp_feat_entry_new(fn_list, feat, local);

	if (new == NULL)
		return -ENOMEM;

	new->feat_num	     = feat;
	new->is_local	     = local;
	new->state	     = FEAT_INITIALISING;
	new->needs_confirm   = 0;
	new->empty_confirm   = 0;
	new->val	     = *fval;
	new->needs_mandatory = mandatory;

	return 0;
}

/**
 * dccp_feat_push_confirm  -  Add a Confirm entry to the FN list
 * @fn_list: feature-negotiation list to add to
 * @feat: one of %dccp_feature_numbers
 * @local: whether local (1) or remote (0) @feat_num is being confirmed
 * @fval: pointer to NN/SP value to be inserted or NULL
 * Returns 0 on success, a Reset code for further processing otherwise.
 */
static int dccp_feat_push_confirm(struct list_head *fn_list, u8 feat, u8 local,
				  dccp_feat_val *fval)
{
	struct dccp_feat_entry *new = dccp_feat_entry_new(fn_list, feat, local);

	if (new == NULL)
		return DCCP_RESET_CODE_TOO_BUSY;

	new->feat_num	     = feat;
	new->is_local	     = local;
	new->state	     = FEAT_STABLE;	/* transition in 6.6.2 */
	new->needs_confirm   = 1;
	new->empty_confirm   = (fval == NULL);
	new->val.nn	     = 0;		/* zeroes the whole structure */
	if (!new->empty_confirm)
		new->val     = *fval;
	new->needs_mandatory = 0;

	return 0;
}

static int dccp_push_empty_confirm(struct list_head *fn_list, u8 feat, u8 local)
{
	return dccp_feat_push_confirm(fn_list, feat, local, NULL);
}

static inline void dccp_feat_list_pop(struct dccp_feat_entry *entry)
{
	list_del(&entry->node);
	dccp_feat_entry_destructor(entry);
}

void dccp_feat_list_purge(struct list_head *fn_list)
{
	struct dccp_feat_entry *entry, *next;

	list_for_each_entry_safe(entry, next, fn_list, node)
		dccp_feat_entry_destructor(entry);
	INIT_LIST_HEAD(fn_list);
}
EXPORT_SYMBOL_GPL(dccp_feat_list_purge);

/* generate @to as full clone of @from - @to must not contain any nodes */
int dccp_feat_clone_list(struct list_head const *from, struct list_head *to)
{
	struct dccp_feat_entry *entry, *new;

	INIT_LIST_HEAD(to);
	list_for_each_entry(entry, from, node) {
		new = dccp_feat_clone_entry(entry);
		if (new == NULL)
			goto cloning_failed;
		list_add_tail(&new->node, to);
	}
	return 0;

cloning_failed:
	dccp_feat_list_purge(to);
	return -ENOMEM;
}

/**
 * dccp_feat_valid_nn_length  -  Enforce length constraints on NN options
 * Length is between 0 and %DCCP_OPTVAL_MAXLEN. Used for outgoing packets only,
 * incoming options are accepted as long as their values are valid.
 */
static u8 dccp_feat_valid_nn_length(u8 feat_num)
{
	if (feat_num == DCCPF_ACK_RATIO)	/* RFC 4340, 11.3 and 6.6.8 */
		return 2;
	if (feat_num == DCCPF_SEQUENCE_WINDOW)	/* RFC 4340, 7.5.2 and 6.5  */
		return 6;
	return 0;
}

static u8 dccp_feat_is_valid_nn_val(u8 feat_num, u64 val)
{
	switch (feat_num) {
	case DCCPF_ACK_RATIO:
		return val <= DCCPF_ACK_RATIO_MAX;
	case DCCPF_SEQUENCE_WINDOW:
		return val >= DCCPF_SEQ_WMIN && val <= DCCPF_SEQ_WMAX;
	}
	return 0;	/* feature unknown - so we can't tell */
}

/* check that SP values are within the ranges defined in RFC 4340 */
static u8 dccp_feat_is_valid_sp_val(u8 feat_num, u8 val)
{
	switch (feat_num) {
	case DCCPF_CCID:
		return val == DCCPC_CCID2 || val == DCCPC_CCID3;
	/* Type-check Boolean feature values: */
	case DCCPF_SHORT_SEQNOS:
	case DCCPF_ECN_INCAPABLE:
	case DCCPF_SEND_ACK_VECTOR:
	case DCCPF_SEND_NDP_COUNT:
	case DCCPF_DATA_CHECKSUM:
	case DCCPF_SEND_LEV_RATE:
		return val < 2;
	case DCCPF_MIN_CSUM_COVER:
		return val < 16;
	}
	return 0;			/* feature unknown */
}

static u8 dccp_feat_sp_list_ok(u8 feat_num, u8 const *sp_list, u8 sp_len)
{
	if (sp_list == NULL || sp_len < 1)
		return 0;
	while (sp_len--)
		if (!dccp_feat_is_valid_sp_val(feat_num, *sp_list++))
			return 0;
	return 1;
}

/**
 * dccp_feat_insert_opts  -  Generate FN options from current list state
 * @skb: next sk_buff to be sent to the peer
 * @dp: for client during handshake and general negotiation
 * @dreq: used by the server only (all Changes/Confirms in LISTEN/RESPOND)
 */
int dccp_feat_insert_opts(struct dccp_sock *dp, struct dccp_request_sock *dreq,
			  struct sk_buff *skb)
{
	struct list_head *fn = dreq ? &dreq->dreq_featneg : &dp->dccps_featneg;
	struct dccp_feat_entry *pos, *next;
	u8 opt, type, len, *ptr, nn_in_nbo[DCCP_OPTVAL_MAXLEN];
	bool rpt;

	/* put entries into @skb in the order they appear in the list */
	list_for_each_entry_safe_reverse(pos, next, fn, node) {
		opt  = dccp_feat_genopt(pos);
		type = dccp_feat_type(pos->feat_num);
		rpt  = false;

		if (pos->empty_confirm) {
			len = 0;
			ptr = NULL;
		} else {
			if (type == FEAT_SP) {
				len = pos->val.sp.len;
				ptr = pos->val.sp.vec;
				rpt = pos->needs_confirm;
			} else if (type == FEAT_NN) {
				len = dccp_feat_valid_nn_length(pos->feat_num);
				ptr = nn_in_nbo;
				dccp_encode_value_var(pos->val.nn, ptr, len);
			} else {
				DCCP_BUG("unknown feature %u", pos->feat_num);
				return -1;
			}
		}

		if (dccp_insert_fn_opt(skb, opt, pos->feat_num, ptr, len, rpt))
			return -1;
		if (pos->needs_mandatory && dccp_insert_option_mandatory(skb))
			return -1;
		/*
		 * Enter CHANGING after transmitting the Change option (6.6.2).
		 */
		if (pos->state == FEAT_INITIALISING)
			pos->state = FEAT_CHANGING;
	}
	return 0;
}

/**
 * __feat_register_nn  -  Register new NN value on socket
 * @fn: feature-negotiation list to register with
 * @feat: an NN feature from %dccp_feature_numbers
 * @mandatory: use Mandatory option if 1
 * @nn_val: value to register (restricted to 4 bytes)
 * Note that NN features are local by definition (RFC 4340, 6.3.2).
 */
static int __feat_register_nn(struct list_head *fn, u8 feat,
			      u8 mandatory, u64 nn_val)
{
	dccp_feat_val fval = { .nn = nn_val };

	if (dccp_feat_type(feat) != FEAT_NN ||
	    !dccp_feat_is_valid_nn_val(feat, nn_val))
		return -EINVAL;

	/* Don't bother with default values, they will be activated anyway. */
	if (nn_val - (u64)dccp_feat_default_value(feat) == 0)
		return 0;

	return dccp_feat_push_change(fn, feat, 1, mandatory, &fval);
}

/**
 * __feat_register_sp  -  Register new SP value/list on socket
 * @fn: feature-negotiation list to register with
 * @feat: an SP feature from %dccp_feature_numbers
 * @is_local: whether the local (1) or the remote (0) @feat is meant
 * @mandatory: use Mandatory option if 1
 * @sp_val: SP value followed by optional preference list
 * @sp_len: length of @sp_val in bytes
 */
static int __feat_register_sp(struct list_head *fn, u8 feat, u8 is_local,
			      u8 mandatory, u8 const *sp_val, u8 sp_len)
{
	dccp_feat_val fval;

	if (dccp_feat_type(feat) != FEAT_SP ||
	    !dccp_feat_sp_list_ok(feat, sp_val, sp_len))
		return -EINVAL;

	/* Avoid negotiating alien CCIDs by only advertising supported ones */
	if (feat == DCCPF_CCID && !ccid_support_check(sp_val, sp_len))
		return -EOPNOTSUPP;

	if (dccp_feat_clone_sp_val(&fval, sp_val, sp_len))
		return -ENOMEM;

	return dccp_feat_push_change(fn, feat, is_local, mandatory, &fval);
}

/**
 * dccp_feat_register_sp  -  Register requests to change SP feature values
 * @sk: client or listening socket
 * @feat: one of %dccp_feature_numbers
 * @is_local: whether the local (1) or remote (0) @feat is meant
 * @list: array of preferred values, in descending order of preference
 * @len: length of @list in bytes
 */
int dccp_feat_register_sp(struct sock *sk, u8 feat, u8 is_local,
			  u8 const *list, u8 len)
{	 /* any changes must be registered before establishing the connection */
	if (sk->sk_state != DCCP_CLOSED)
		return -EISCONN;
	if (dccp_feat_type(feat) != FEAT_SP)
		return -EINVAL;
	return __feat_register_sp(&dccp_sk(sk)->dccps_featneg, feat, is_local,
				  0, list, len);
}

/* Analogous to dccp_feat_register_sp(), but for non-negotiable values */
int dccp_feat_register_nn(struct sock *sk, u8 feat, u64 val)
{
	/* any changes must be registered before establishing the connection */
	if (sk->sk_state != DCCP_CLOSED)
		return -EISCONN;
	if (dccp_feat_type(feat) != FEAT_NN)
		return -EINVAL;
	return __feat_register_nn(&dccp_sk(sk)->dccps_featneg, feat, 0, val);
}

/*
 *	Tracking features whose value depend on the choice of CCID
 *
 * This is designed with an extension in mind so that a list walk could be done
 * before activating any features. However, the existing framework was found to
 * work satisfactorily up until now, the automatic verification is left open.
 * When adding new CCIDs, add a corresponding dependency table here.
 */
static const struct ccid_dependency *dccp_feat_ccid_deps(u8 ccid, bool is_local)
{
	static const struct ccid_dependency ccid2_dependencies[2][2] = {
		/*
		 * CCID2 mandates Ack Vectors (RFC 4341, 4.): as CCID is a TX
		 * feature and Send Ack Vector is an RX feature, `is_local'
		 * needs to be reversed.
		 */
		{	/* Dependencies of the receiver-side (remote) CCID2 */
			{
				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
				.is_local	= true,
				.is_mandatory	= true,
				.val		= 1
			},
			{ 0, 0, 0, 0 }
		},
		{	/* Dependencies of the sender-side (local) CCID2 */
			{
				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
				.is_local	= false,
				.is_mandatory	= true,
				.val		= 1
			},
			{ 0, 0, 0, 0 }
		}
	};
	static const struct ccid_dependency ccid3_dependencies[2][5] = {
		{	/*
			 * Dependencies of the receiver-side CCID3
			 */
			{	/* locally disable Ack Vectors */
				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
				.is_local	= true,
				.is_mandatory	= false,
				.val		= 0
			},
			{	/* see below why Send Loss Event Rate is on */
				.dependent_feat	= DCCPF_SEND_LEV_RATE,
				.is_local	= true,
				.is_mandatory	= true,
				.val		= 1
			},
			{	/* NDP Count is needed as per RFC 4342, 6.1.1 */
				.dependent_feat	= DCCPF_SEND_NDP_COUNT,
				.is_local	= false,
				.is_mandatory	= true,
				.val		= 1
			},
			{ 0, 0, 0, 0 },
		},
		{	/*
			 * CCID3 at the TX side: we request that the HC-receiver
			 * will not send Ack Vectors (they will be ignored, so
			 * Mandatory is not set); we enable Send Loss Event Rate
			 * (Mandatory since the implementation does not support
			 * the Loss Intervals option of RFC 4342, 8.6).
			 * The last two options are for peer's information only.
			*/
			{
				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
				.is_local	= false,
				.is_mandatory	= false,
				.val		= 0
			},
			{
				.dependent_feat	= DCCPF_SEND_LEV_RATE,
				.is_local	= false,
				.is_mandatory	= true,
				.val		= 1
			},
			{	/* this CCID does not support Ack Ratio */
				.dependent_feat	= DCCPF_ACK_RATIO,
				.is_local	= true,
				.is_mandatory	= false,
				.val		= 0
			},
			{	/* tell receiver we are sending NDP counts */
				.dependent_feat	= DCCPF_SEND_NDP_COUNT,
				.is_local	= true,
				.is_mandatory	= false,
				.val		= 1
			},
			{ 0, 0, 0, 0 }
		}
	};
	switch (ccid) {
	case DCCPC_CCID2:
		return ccid2_dependencies[is_local];
	case DCCPC_CCID3:
		return ccid3_dependencies[is_local];
	default:
		return NULL;
	}
}

/**
 * dccp_feat_propagate_ccid - Resolve dependencies of features on choice of CCID
 * @fn: feature-negotiation list to update
 * @id: CCID number to track
 * @is_local: whether TX CCID (1) or RX CCID (0) is meant
 * This function needs to be called after registering all other features.
 */
static int dccp_feat_propagate_ccid(struct list_head *fn, u8 id, bool is_local)
{
	const struct ccid_dependency *table = dccp_feat_ccid_deps(id, is_local);
	int i, rc = (table == NULL);

	for (i = 0; rc == 0 && table[i].dependent_feat != DCCPF_RESERVED; i++)
		if (dccp_feat_type(table[i].dependent_feat) == FEAT_SP)
			rc = __feat_register_sp(fn, table[i].dependent_feat,
						    table[i].is_local,
						    table[i].is_mandatory,
						    &table[i].val, 1);
		else
			rc = __feat_register_nn(fn, table[i].dependent_feat,
						    table[i].is_mandatory,
						    table[i].val);
	return rc;
}

/**
 * dccp_feat_finalise_settings  -  Finalise settings before starting negotiation
 * @dp: client or listening socket (settings will be inherited)
 * This is called after all registrations (socket initialisation, sysctls, and
 * sockopt calls), and before sending the first packet containing Change options
 * (ie. client-Request or server-Response), to ensure internal consistency.
 */
int dccp_feat_finalise_settings(struct dccp_sock *dp)
{
	struct list_head *fn = &dp->dccps_featneg;
	struct dccp_feat_entry *entry;
	int i = 2, ccids[2] = { -1, -1 };

	/*
	 * Propagating CCIDs:
	 * 1) not useful to propagate CCID settings if this host advertises more
	 *    than one CCID: the choice of CCID  may still change - if this is
	 *    the client, or if this is the server and the client sends
	 *    singleton CCID values.
	 * 2) since is that propagate_ccid changes the list, we defer changing
	 *    the sorted list until after the traversal.
	 */
	list_for_each_entry(entry, fn, node)
		if (entry->feat_num == DCCPF_CCID && entry->val.sp.len == 1)
			ccids[entry->is_local] = entry->val.sp.vec[0];
	while (i--)
		if (ccids[i] > 0 && dccp_feat_propagate_ccid(fn, ccids[i], i))
			return -1;
	return 0;
}

/**
 * dccp_feat_server_ccid_dependencies  -  Resolve CCID-dependent features
 * It is the server which resolves the dependencies once the CCID has been
 * fully negotiated. If no CCID has been negotiated, it uses the default CCID.
 */
int dccp_feat_server_ccid_dependencies(struct dccp_request_sock *dreq)
{
	struct list_head *fn = &dreq->dreq_featneg;
	struct dccp_feat_entry *entry;
	u8 is_local, ccid;

	for (is_local = 0; is_local <= 1; is_local++) {
		entry = dccp_feat_list_lookup(fn, DCCPF_CCID, is_local);

		if (entry != NULL && !entry->empty_confirm)
			ccid = entry->val.sp.vec[0];
		else
			ccid = dccp_feat_default_value(DCCPF_CCID);

		if (dccp_feat_propagate_ccid(fn, ccid, is_local))
			return -1;
	}
	return 0;
}

static int dccp_feat_update_ccid(struct sock *sk, u8 type, u8 new_ccid_nr)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct dccp_minisock *dmsk = dccp_msk(sk);
	/* figure out if we are changing our CCID or the peer's */
	const int rx = type == DCCPO_CHANGE_R;
	const u8 ccid_nr = rx ? dmsk->dccpms_rx_ccid : dmsk->dccpms_tx_ccid;
	struct ccid *new_ccid;

	/* Check if nothing is being changed. */
	if (ccid_nr == new_ccid_nr)
		return 0;

	new_ccid = ccid_new(new_ccid_nr, sk, rx, GFP_ATOMIC);
	if (new_ccid == NULL)
		return -ENOMEM;

	if (rx) {
		ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
		dp->dccps_hc_rx_ccid = new_ccid;
		dmsk->dccpms_rx_ccid = new_ccid_nr;
	} else {
		ccid_hc_tx_delete(dp->dccps_hc_tx_ccid, sk);
		dp->dccps_hc_tx_ccid = new_ccid;
		dmsk->dccpms_tx_ccid = new_ccid_nr;
	}

	return 0;
}

static int dccp_feat_update(struct sock *sk, u8 type, u8 feat, u8 val)
{
	dccp_feat_debug(type, feat, val);

	switch (feat) {
	case DCCPF_CCID:
		return dccp_feat_update_ccid(sk, type, val);
	default:
		dccp_pr_debug("UNIMPLEMENTED: %s(%d, ...)\n",
			      dccp_feat_typename(type), feat);
		break;
	}
	return 0;
}

/* Select the first entry in @servlist that also occurs in @clilist (6.3.1) */
static int dccp_feat_preflist_match(u8 *servlist, u8 slen, u8 *clilist, u8 clen)
{
	u8 c, s;

	for (s = 0; s < slen; s++)
		for (c = 0; c < clen; c++)
			if (servlist[s] == clilist[c])
				return servlist[s];
	return -1;
}

/**
 * dccp_feat_prefer  -  Move preferred entry to the start of array
 * Reorder the @array_len elements in @array so that @preferred_value comes
 * first. Returns >0 to indicate that @preferred_value does occur in @array.
 */
static u8 dccp_feat_prefer(u8 preferred_value, u8 *array, u8 array_len)
{
	u8 i, does_occur = 0;

	if (array != NULL) {
		for (i = 0; i < array_len; i++)
			if (array[i] == preferred_value) {
				array[i] = array[0];
				does_occur++;
			}
		if (does_occur)
			array[0] = preferred_value;
	}
	return does_occur;
}

/**
 * dccp_feat_reconcile  -  Reconcile SP preference lists
 *  @fval: SP list to reconcile into
 *  @arr: received SP preference list
 *  @len: length of @arr in bytes
 *  @is_server: whether this side is the server (and @fv is the server's list)
 *  @reorder: whether to reorder the list in @fv after reconciling with @arr
 * When successful, > 0 is returned and the reconciled list is in @fval.
 * A value of 0 means that negotiation failed (no shared entry).
 */
static int dccp_feat_reconcile(dccp_feat_val *fv, u8 *arr, u8 len,
			       bool is_server, bool reorder)
{
	int rc;

	if (!fv->sp.vec || !arr) {
		DCCP_CRIT("NULL feature value or array");
		return 0;
	}

	if (is_server)
		rc = dccp_feat_preflist_match(fv->sp.vec, fv->sp.len, arr, len);
	else
		rc = dccp_feat_preflist_match(arr, len, fv->sp.vec, fv->sp.len);

	if (!reorder)
		return rc;
	if (rc < 0)
		return 0;

	/*
	 * Reorder list: used for activating features and in dccp_insert_fn_opt.
	 */
	return dccp_feat_prefer(rc, fv->sp.vec, fv->sp.len);
}

#ifdef __this_is_the_old_framework_and_will_be_removed_later_in_a_subsequent_patch
static int dccp_feat_reconcile(struct sock *sk, struct dccp_opt_pend *opt,
			       u8 *rpref, u8 rlen)
{
	struct dccp_sock *dp = dccp_sk(sk);
	u8 *spref, slen, *res = NULL;
	int i, j, rc, agree = 1;

	BUG_ON(rpref == NULL);

	/* check if we are the black sheep */
	if (dp->dccps_role == DCCP_ROLE_CLIENT) {
		spref = rpref;
		slen  = rlen;
		rpref = opt->dccpop_val;
		rlen  = opt->dccpop_len;
	} else {
		spref = opt->dccpop_val;
		slen  = opt->dccpop_len;
	}
	/*
	 * Now we have server preference list in spref and client preference in
	 * rpref
	 */
	BUG_ON(spref == NULL);
	BUG_ON(rpref == NULL);

	/* FIXME sanity check vals */

	/* Are values in any order?  XXX Lame "algorithm" here */
	for (i = 0; i < slen; i++) {
		for (j = 0; j < rlen; j++) {
			if (spref[i] == rpref[j]) {
				res = &spref[i];
				break;
			}
		}
		if (res)
			break;
	}

	/* we didn't agree on anything */
	if (res == NULL) {
		/* confirm previous value */
		switch (opt->dccpop_feat) {
		case DCCPF_CCID:
			/* XXX did i get this right? =P */
			if (opt->dccpop_type == DCCPO_CHANGE_L)
				res = &dccp_msk(sk)->dccpms_tx_ccid;
			else
				res = &dccp_msk(sk)->dccpms_rx_ccid;
			break;

		default:
			DCCP_BUG("Fell through, feat=%d", opt->dccpop_feat);
			/* XXX implement res */
			return -EFAULT;
		}

		dccp_pr_debug("Don't agree... reconfirming %d\n", *res);
		agree = 0; /* this is used for mandatory options... */
	}

	/* need to put result and our preference list */
	rlen = 1 + opt->dccpop_len;
	rpref = kmalloc(rlen, GFP_ATOMIC);
	if (rpref == NULL)
		return -ENOMEM;

	*rpref = *res;
	memcpy(&rpref[1], opt->dccpop_val, opt->dccpop_len);

	/* put it in the "confirm queue" */
	if (opt->dccpop_sc == NULL) {
		opt->dccpop_sc = kmalloc(sizeof(*opt->dccpop_sc), GFP_ATOMIC);
		if (opt->dccpop_sc == NULL) {
			kfree(rpref);
			return -ENOMEM;
		}
	} else {
		/* recycle the confirm slot */
		BUG_ON(opt->dccpop_sc->dccpoc_val == NULL);
		kfree(opt->dccpop_sc->dccpoc_val);
		dccp_pr_debug("recycling confirm slot\n");
	}
	memset(opt->dccpop_sc, 0, sizeof(*opt->dccpop_sc));

	opt->dccpop_sc->dccpoc_val = rpref;
	opt->dccpop_sc->dccpoc_len = rlen;

	/* update the option on our side [we are about to send the confirm] */
	rc = dccp_feat_update(sk, opt->dccpop_type, opt->dccpop_feat, *res);
	if (rc) {
		kfree(opt->dccpop_sc->dccpoc_val);
		kfree(opt->dccpop_sc);
		opt->dccpop_sc = NULL;
		return rc;
	}

	dccp_pr_debug("Will confirm %d\n", *rpref);

	/* say we want to change to X but we just got a confirm X, suppress our
	 * change
	 */
	if (!opt->dccpop_conf) {
		if (*opt->dccpop_val == *res)
			opt->dccpop_conf = 1;
		dccp_pr_debug("won't ask for change of same feature\n");
	}

	return agree ? 0 : DCCP_FEAT_SP_NOAGREE; /* used for mandatory opts */
}

static int dccp_feat_sp(struct sock *sk, u8 type, u8 feature, u8 *val, u8 len)
{
	struct dccp_minisock *dmsk = dccp_msk(sk);
	struct dccp_opt_pend *opt;
	int rc = 1;
	u8 t;

	/*
	 * We received a CHANGE.  We gotta match it against our own preference
	 * list.  If we got a CHANGE_R it means it's a change for us, so we need
	 * to compare our CHANGE_L list.
	 */
	if (type == DCCPO_CHANGE_L)
		t = DCCPO_CHANGE_R;
	else
		t = DCCPO_CHANGE_L;

	/* find our preference list for this feature */
	list_for_each_entry(opt, &dmsk->dccpms_pending, dccpop_node) {
		if (opt->dccpop_type != t || opt->dccpop_feat != feature)
			continue;

		/* find the winner from the two preference lists */
		rc = dccp_feat_reconcile(sk, opt, val, len);
		break;
	}

	/* We didn't deal with the change.  This can happen if we have no
	 * preference list for the feature.  In fact, it just shouldn't
	 * happen---if we understand a feature, we should have a preference list
	 * with at least the default value.
	 */
	BUG_ON(rc == 1);

	return rc;
}

static int dccp_feat_nn(struct sock *sk, u8 type, u8 feature, u8 *val, u8 len)
{
	struct dccp_opt_pend *opt;
	struct dccp_minisock *dmsk = dccp_msk(sk);
	u8 *copy;
	int rc;

	/* NN features must be Change L (sec. 6.3.2) */
	if (type != DCCPO_CHANGE_L) {
		dccp_pr_debug("received %s for NN feature %d\n",
				dccp_feat_typename(type), feature);
		return -EFAULT;
	}

	/* XXX sanity check opt val */

	/* copy option so we can confirm it */
	opt = kzalloc(sizeof(*opt), GFP_ATOMIC);
	if (opt == NULL)
		return -ENOMEM;

	copy = kmemdup(val, len, GFP_ATOMIC);
	if (copy == NULL) {
		kfree(opt);
		return -ENOMEM;
	}

	opt->dccpop_type = DCCPO_CONFIRM_R; /* NN can only confirm R */
	opt->dccpop_feat = feature;
	opt->dccpop_val	 = copy;
	opt->dccpop_len	 = len;

	/* change feature */
	rc = dccp_feat_update(sk, type, feature, *val);
	if (rc) {
		kfree(opt->dccpop_val);
		kfree(opt);
		return rc;
	}

	dccp_feat_debug(type, feature, *copy);

	list_add_tail(&opt->dccpop_node, &dmsk->dccpms_conf);

	return 0;
}

static void dccp_feat_empty_confirm(struct dccp_minisock *dmsk,
				    u8 type, u8 feature)
{
	/* XXX check if other confirms for that are queued and recycle slot */
	struct dccp_opt_pend *opt = kzalloc(sizeof(*opt), GFP_ATOMIC);

	if (opt == NULL) {
		/* XXX what do we do?  Ignoring should be fine.  It's a change
		 * after all =P
		 */
		return;
	}

	switch (type) {
	case DCCPO_CHANGE_L:
		opt->dccpop_type = DCCPO_CONFIRM_R;
		break;
	case DCCPO_CHANGE_R:
		opt->dccpop_type = DCCPO_CONFIRM_L;
		break;
	default:
		DCCP_WARN("invalid type %d\n", type);
		kfree(opt);
		return;
	}
	opt->dccpop_feat = feature;
	opt->dccpop_val	 = NULL;
	opt->dccpop_len	 = 0;

	/* change feature */
	dccp_pr_debug("Empty %s(%d)\n", dccp_feat_typename(type), feature);

	list_add_tail(&opt->dccpop_node, &dmsk->dccpms_conf);
}

static void dccp_feat_flush_confirm(struct sock *sk)
{
	struct dccp_minisock *dmsk = dccp_msk(sk);
	/* Check if there is anything to confirm in the first place */
	int yes = !list_empty(&dmsk->dccpms_conf);

	if (!yes) {
		struct dccp_opt_pend *opt;

		list_for_each_entry(opt, &dmsk->dccpms_pending, dccpop_node) {
			if (opt->dccpop_conf) {
				yes = 1;
				break;
			}
		}
	}

	if (!yes)
		return;

	/* OK there is something to confirm... */
	/* XXX check if packet is in flight?  Send delayed ack?? */
	if (sk->sk_state == DCCP_OPEN)
		dccp_send_ack(sk);
}

int dccp_feat_change_recv(struct sock *sk, u8 type, u8 feature, u8 *val, u8 len)
{
	int rc;

	/* Ignore Change requests other than during connection setup */
	if (sk->sk_state != DCCP_LISTEN && sk->sk_state != DCCP_REQUESTING)
		return 0;
	dccp_feat_debug(type, feature, *val);

	/* figure out if it's SP or NN feature */
	switch (feature) {
	/* deal with SP features */
	case DCCPF_CCID:
		/* XXX Obsoleted by next patch
		rc = dccp_feat_sp(sk, type, feature, val, len); */
		break;

	/* deal with NN features */
	case DCCPF_ACK_RATIO:
		/* XXX Obsoleted by next patch
		rc = dccp_feat_nn(sk, type, feature, val, len); */
		break;

	/* XXX implement other features */
	default:
		dccp_pr_debug("UNIMPLEMENTED: not handling %s(%d, ...)\n",
			      dccp_feat_typename(type), feature);
		rc = -EFAULT;
		break;
	}

	/* check if there were problems changing features */
	if (rc) {
		/* If we don't agree on SP, we sent a confirm for old value.
		 * However we propagate rc to caller in case option was
		 * mandatory
		 */
		if (rc != DCCP_FEAT_SP_NOAGREE)
			dccp_feat_empty_confirm(dccp_msk(sk), type, feature);
	}

	/* generate the confirm [if required] */
	dccp_feat_flush_confirm(sk);

	return rc;
}

EXPORT_SYMBOL_GPL(dccp_feat_change_recv);

int dccp_feat_confirm_recv(struct sock *sk, u8 type, u8 feature,
			   u8 *val, u8 len)
{
	u8 t;
	struct dccp_opt_pend *opt;
	struct dccp_minisock *dmsk = dccp_msk(sk);
	int found = 0;
	int all_confirmed = 1;

	/* Ignore Confirm options other than during connection setup */
	if (sk->sk_state != DCCP_LISTEN && sk->sk_state != DCCP_REQUESTING)
		return 0;
	dccp_feat_debug(type, feature, *val);

	/* locate our change request */
	switch (type) {
	case DCCPO_CONFIRM_L: t = DCCPO_CHANGE_R; break;
	case DCCPO_CONFIRM_R: t = DCCPO_CHANGE_L; break;
	default:	      DCCP_WARN("invalid type %d\n", type);
			      return 1;

	}
	/* XXX sanity check feature value */

	list_for_each_entry(opt, &dmsk->dccpms_pending, dccpop_node) {
		if (!opt->dccpop_conf && opt->dccpop_type == t &&
		    opt->dccpop_feat == feature) {
			found = 1;
			dccp_pr_debug("feature %d found\n", opt->dccpop_feat);

			/* XXX do sanity check */

			opt->dccpop_conf = 1;

			/* We got a confirmation---change the option */
			dccp_feat_update(sk, opt->dccpop_type,
					 opt->dccpop_feat, *val);

			/* XXX check the return value of dccp_feat_update */
			break;
		}

		if (!opt->dccpop_conf)
			all_confirmed = 0;
	}

	if (!found)
		dccp_pr_debug("%s(%d, ...) never requested\n",
			      dccp_feat_typename(type), feature);
	return 0;
}

EXPORT_SYMBOL_GPL(dccp_feat_confirm_recv);
#endif	/* (later) */

void dccp_feat_clean(struct dccp_minisock *dmsk)
{
	struct dccp_opt_pend *opt, *next;

	list_for_each_entry_safe(opt, next, &dmsk->dccpms_pending,
				 dccpop_node) {
		BUG_ON(opt->dccpop_val == NULL);
		kfree(opt->dccpop_val);

		if (opt->dccpop_sc != NULL) {
			BUG_ON(opt->dccpop_sc->dccpoc_val == NULL);
			kfree(opt->dccpop_sc->dccpoc_val);
			kfree(opt->dccpop_sc);
		}

		kfree(opt);
	}
	INIT_LIST_HEAD(&dmsk->dccpms_pending);

	list_for_each_entry_safe(opt, next, &dmsk->dccpms_conf, dccpop_node) {
		BUG_ON(opt == NULL);
		if (opt->dccpop_val != NULL)
			kfree(opt->dccpop_val);
		kfree(opt);
	}
	INIT_LIST_HEAD(&dmsk->dccpms_conf);
}

EXPORT_SYMBOL_GPL(dccp_feat_clean);

/* this is to be called only when a listening sock creates its child.  It is
 * assumed by the function---the confirm is not duplicated, but rather it is
 * "passed on".
 */
int dccp_feat_clone(struct sock *oldsk, struct sock *newsk)
{
	struct dccp_minisock *olddmsk = dccp_msk(oldsk);
	struct dccp_minisock *newdmsk = dccp_msk(newsk);
	struct dccp_opt_pend *opt;
	int rc = 0;

	INIT_LIST_HEAD(&newdmsk->dccpms_pending);
	INIT_LIST_HEAD(&newdmsk->dccpms_conf);

	list_for_each_entry(opt, &olddmsk->dccpms_pending, dccpop_node) {
		struct dccp_opt_pend *newopt;
		/* copy the value of the option */
		u8 *val = kmemdup(opt->dccpop_val, opt->dccpop_len, GFP_ATOMIC);

		if (val == NULL)
			goto out_clean;

		newopt = kmemdup(opt, sizeof(*newopt), GFP_ATOMIC);
		if (newopt == NULL) {
			kfree(val);
			goto out_clean;
		}

		/* insert the option */
		newopt->dccpop_val = val;
		list_add_tail(&newopt->dccpop_node, &newdmsk->dccpms_pending);

		/* XXX what happens with backlogs and multiple connections at
		 * once...
		 */
		/* the master socket no longer needs to worry about confirms */
		opt->dccpop_sc = NULL; /* it's not a memleak---new socket has it */

		/* reset state for a new socket */
		opt->dccpop_conf = 0;
	}

	/* XXX not doing anything about the conf queue */

out:
	return rc;

out_clean:
	dccp_feat_clean(newdmsk);
	rc = -ENOMEM;
	goto out;
}

EXPORT_SYMBOL_GPL(dccp_feat_clone);

/**
 * dccp_feat_change_recv  -  Process incoming ChangeL/R options
 * @fn: feature-negotiation list to update
 * @is_mandatory: whether the Change was preceded by a Mandatory option
 * @opt: %DCCPO_CHANGE_L or %DCCPO_CHANGE_R
 * @feat: one of %dccp_feature_numbers
 * @val: NN value or SP value/preference list
 * @len: length of @val in bytes
 * @server: whether this node is the server (1) or the client (0)
 */
static u8 dccp_feat_change_recv(struct list_head *fn, u8 is_mandatory, u8 opt,
				u8 feat, u8 *val, u8 len, const bool server)
{
	u8 defval, type = dccp_feat_type(feat);
	const bool local = (opt == DCCPO_CHANGE_R);
	struct dccp_feat_entry *entry;
	dccp_feat_val fval;

	if (len == 0 || type == FEAT_UNKNOWN)		/* 6.1 and 6.6.8 */
		goto unknown_feature_or_value;

	/*
	 *	Negotiation of NN features: Change R is invalid, so there is no
	 *	simultaneous negotiation; hence we do not look up in the list.
	 */
	if (type == FEAT_NN) {
		if (local || len > sizeof(fval.nn))
			goto unknown_feature_or_value;

		/* 6.3.2: "The feature remote MUST accept any valid value..." */
		fval.nn = dccp_decode_value_var(val, len);
		if (!dccp_feat_is_valid_nn_val(feat, fval.nn))
			goto unknown_feature_or_value;

		return dccp_feat_push_confirm(fn, feat, local, &fval);
	}

	/*
	 *	Unidirectional/simultaneous negotiation of SP features (6.3.1)
	 */
	entry = dccp_feat_list_lookup(fn, feat, local);
	if (entry == NULL) {
		/*
		 * No particular preferences have been registered. We deal with
		 * this situation by assuming that all valid values are equally
		 * acceptable, and apply the following checks:
		 * - if the peer's list is a singleton, we accept a valid value;
		 * - if we are the server, we first try to see if the peer (the
		 *   client) advertises the default value. If yes, we use it,
		 *   otherwise we accept the preferred value;
		 * - else if we are the client, we use the first list element.
		 */
		if (dccp_feat_clone_sp_val(&fval, val, 1))
			return DCCP_RESET_CODE_TOO_BUSY;

		if (len > 1 && server) {
			defval = dccp_feat_default_value(feat);
			if (dccp_feat_preflist_match(&defval, 1, val, len) > -1)
				fval.sp.vec[0] = defval;
		} else if (!dccp_feat_is_valid_sp_val(feat, fval.sp.vec[0])) {
			kfree(fval.sp.vec);
			goto unknown_feature_or_value;
		}

		/* Treat unsupported CCIDs like invalid values */
		if (feat == DCCPF_CCID && !ccid_support_check(fval.sp.vec, 1)) {
			kfree(fval.sp.vec);
			goto not_valid_or_not_known;
		}

		return dccp_feat_push_confirm(fn, feat, local, &fval);

	} else if (entry->state == FEAT_UNSTABLE) {	/* 6.6.2 */
		return 0;
	}

	if (dccp_feat_reconcile(&entry->val, val, len, server, true)) {
		entry->empty_confirm = 0;
	} else if (is_mandatory) {
		return DCCP_RESET_CODE_MANDATORY_ERROR;
	} else if (entry->state == FEAT_INITIALISING) {
		/*
		 * Failed simultaneous negotiation (server only): try to `save'
		 * the connection by checking whether entry contains the default
		 * value for @feat. If yes, send an empty Confirm to signal that
		 * the received Change was not understood - which implies using
		 * the default value.
		 * If this also fails, we use Reset as the last resort.
		 */
		WARN_ON(!server);
		defval = dccp_feat_default_value(feat);
		if (!dccp_feat_reconcile(&entry->val, &defval, 1, server, true))
			return DCCP_RESET_CODE_OPTION_ERROR;
		entry->empty_confirm = 1;
	}
	entry->needs_confirm   = 1;
	entry->needs_mandatory = 0;
	entry->state	       = FEAT_STABLE;
	return 0;

unknown_feature_or_value:
	if (!is_mandatory)
		return dccp_push_empty_confirm(fn, feat, local);

not_valid_or_not_known:
	return is_mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
			    : DCCP_RESET_CODE_OPTION_ERROR;
}

/**
 * dccp_feat_confirm_recv  -  Process received Confirm options
 * @fn: feature-negotiation list to update
 * @is_mandatory: whether @opt was preceded by a Mandatory option
 * @opt: %DCCPO_CONFIRM_L or %DCCPO_CONFIRM_R
 * @feat: one of %dccp_feature_numbers
 * @val: NN value or SP value/preference list
 * @len: length of @val in bytes
 * @server: whether this node is server (1) or client (0)
 */
static u8 dccp_feat_confirm_recv(struct list_head *fn, u8 is_mandatory, u8 opt,
				 u8 feat, u8 *val, u8 len, const bool server)
{
	u8 *plist, plen, type = dccp_feat_type(feat);
	const bool local = (opt == DCCPO_CONFIRM_R);
	struct dccp_feat_entry *entry = dccp_feat_list_lookup(fn, feat, local);

	if (entry == NULL) {	/* nothing queued: ignore or handle error */
		if (is_mandatory && type == FEAT_UNKNOWN)
			return DCCP_RESET_CODE_MANDATORY_ERROR;

		if (!local && type == FEAT_NN)		/* 6.3.2 */
			goto confirmation_failed;
		return 0;
	}

	if (entry->state != FEAT_CHANGING)		/* 6.6.2 */
		return 0;

	if (len == 0) {
		if (dccp_feat_must_be_understood(feat))	/* 6.6.7 */
			goto confirmation_failed;
		/*
		 * Empty Confirm during connection setup: this means reverting
		 * to the `old' value, which in this case is the default. Since
		 * we handle default values automatically when no other values
		 * have been set, we revert to the old value by removing this
		 * entry from the list.
		 */
		dccp_feat_list_pop(entry);
		return 0;
	}

	if (type == FEAT_NN) {
		if (len > sizeof(entry->val.nn))
			goto confirmation_failed;

		if (entry->val.nn == dccp_decode_value_var(val, len))
			goto confirmation_succeeded;

		DCCP_WARN("Bogus Confirm for non-existing value\n");
		goto confirmation_failed;
	}

	/*
	 * Parsing SP Confirms: the first element of @val is the preferred
	 * SP value which the peer confirms, the remainder depends on @len.
	 * Note that only the confirmed value need to be a valid SP value.
	 */
	if (!dccp_feat_is_valid_sp_val(feat, *val))
		goto confirmation_failed;

	if (len == 1) {		/* peer didn't supply a preference list */
		plist = val;
		plen  = len;
	} else {		/* preferred value + preference list */
		plist = val + 1;
		plen  = len - 1;
	}

	/* Check whether the peer got the reconciliation right (6.6.8) */
	if (dccp_feat_reconcile(&entry->val, plist, plen, server, 0) != *val) {
		DCCP_WARN("Confirm selected the wrong value %u\n", *val);
		return DCCP_RESET_CODE_OPTION_ERROR;
	}
	entry->val.sp.vec[0] = *val;

confirmation_succeeded:
	entry->state = FEAT_STABLE;
	return 0;

confirmation_failed:
	DCCP_WARN("Confirmation failed\n");
	return is_mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
			    : DCCP_RESET_CODE_OPTION_ERROR;
}

/**
 * dccp_feat_parse_options  -  Process Feature-Negotiation Options
 * @sk: for general use and used by the client during connection setup
 * @dreq: used by the server during connection setup
 * @mandatory: whether @opt was preceded by a Mandatory option
 * @opt: %DCCPO_CHANGE_L | %DCCPO_CHANGE_R | %DCCPO_CONFIRM_L | %DCCPO_CONFIRM_R
 * @feat: one of %dccp_feature_numbers
 * @val: value contents of @opt
 * @len: length of @val in bytes
 * Returns 0 on success, a Reset code for ending the connection otherwise.
 */
int dccp_feat_parse_options(struct sock *sk, struct dccp_request_sock *dreq,
			    u8 mandatory, u8 opt, u8 feat, u8 *val, u8 len)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct list_head *fn = dreq ? &dreq->dreq_featneg : &dp->dccps_featneg;
	bool server = false;

	switch (sk->sk_state) {
	/*
	 *	Negotiation during connection setup
	 */
	case DCCP_LISTEN:
		server = true;			/* fall through */
	case DCCP_REQUESTING:
		switch (opt) {
		case DCCPO_CHANGE_L:
		case DCCPO_CHANGE_R:
			return dccp_feat_change_recv(fn, mandatory, opt, feat,
						     val, len, server);
		case DCCPO_CONFIRM_R:
		case DCCPO_CONFIRM_L:
			return dccp_feat_confirm_recv(fn, mandatory, opt, feat,
						      val, len, server);
		}
	}
	return 0;	/* ignore FN options in all other states */
}

int dccp_feat_init(struct sock *sk)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct dccp_minisock *dmsk = dccp_msk(sk);
	int rc;

	INIT_LIST_HEAD(&dmsk->dccpms_pending);	/* XXX no longer used */
	INIT_LIST_HEAD(&dmsk->dccpms_conf);	/* XXX no longer used */

	/* CCID L */
	rc = __feat_register_sp(&dp->dccps_featneg, DCCPF_CCID, 1, 0,
				&dmsk->dccpms_tx_ccid, 1);
	if (rc)
		goto out;

	/* CCID R */
	rc = __feat_register_sp(&dp->dccps_featneg, DCCPF_CCID, 0, 0,
				&dmsk->dccpms_rx_ccid, 1);
	if (rc)
		goto out;

	/* Ack ratio */
	rc = __feat_register_nn(&dp->dccps_featneg, DCCPF_ACK_RATIO, 0,
				dp->dccps_l_ack_ratio);
out:
	return rc;
}

EXPORT_SYMBOL_GPL(dccp_feat_init);

int dccp_feat_activate_values(struct sock *sk, struct list_head *fn_list)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct dccp_feat_entry *cur, *next;
	int idx;
	dccp_feat_val *fvals[DCCP_FEAT_SUPPORTED_MAX][2] = {
		 [0 ... DCCP_FEAT_SUPPORTED_MAX-1] = { NULL, NULL }
	};

	list_for_each_entry(cur, fn_list, node) {
		/*
		 * An empty Confirm means that either an unknown feature type
		 * or an invalid value was present. In the first case there is
		 * nothing to activate, in the other the default value is used.
		 */
		if (cur->empty_confirm)
			continue;

		idx = dccp_feat_index(cur->feat_num);
		if (idx < 0) {
			DCCP_BUG("Unknown feature %u", cur->feat_num);
			goto activation_failed;
		}
		if (cur->state != FEAT_STABLE) {
			DCCP_CRIT("Negotiation of %s %u failed in state %u",
				  cur->is_local ? "local" : "remote",
				  cur->feat_num, cur->state);
			goto activation_failed;
		}
		fvals[idx][cur->is_local] = &cur->val;
	}

	/*
	 * Activate in decreasing order of index, so that the CCIDs are always
	 * activated as the last feature. This avoids the case where a CCID
	 * relies on the initialisation of one or more features that it depends
	 * on (e.g. Send NDP Count, Send Ack Vector, and Ack Ratio features).
	 */
	for (idx = DCCP_FEAT_SUPPORTED_MAX; --idx >= 0;)
		if (__dccp_feat_activate(sk, idx, 0, fvals[idx][0]) ||
		    __dccp_feat_activate(sk, idx, 1, fvals[idx][1])) {
			DCCP_CRIT("Could not activate %d", idx);
			goto activation_failed;
		}

	/* Clean up Change options which have been confirmed already */
	list_for_each_entry_safe(cur, next, fn_list, node)
		if (!cur->needs_confirm)
			dccp_feat_list_pop(cur);

	dccp_pr_debug("Activation OK\n");
	return 0;

activation_failed:
	/*
	 * We clean up everything that may have been allocated, since
	 * it is difficult to track at which stage negotiation failed.
	 * This is ok, since all allocation functions below are robust
	 * against NULL arguments.
	 */
	ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
	ccid_hc_tx_delete(dp->dccps_hc_tx_ccid, sk);
	dp->dccps_hc_rx_ccid = dp->dccps_hc_tx_ccid = NULL;
	dccp_ackvec_free(dp->dccps_hc_rx_ackvec);
	dp->dccps_hc_rx_ackvec = NULL;
	return -1;
}

#ifdef CONFIG_IP_DCCP_DEBUG
const char *dccp_feat_typename(const u8 type)
{
	switch(type) {
	case DCCPO_CHANGE_L:  return("ChangeL");
	case DCCPO_CONFIRM_L: return("ConfirmL");
	case DCCPO_CHANGE_R:  return("ChangeR");
	case DCCPO_CONFIRM_R: return("ConfirmR");
	/* the following case must not appear in feature negotation  */
	default:	      dccp_pr_debug("unknown type %d [BUG!]\n", type);
	}
	return NULL;
}

EXPORT_SYMBOL_GPL(dccp_feat_typename);

const char *dccp_feat_name(const u8 feat)
{
	static const char *feature_names[] = {
		[DCCPF_RESERVED]	= "Reserved",
		[DCCPF_CCID]		= "CCID",
		[DCCPF_SHORT_SEQNOS]	= "Allow Short Seqnos",
		[DCCPF_SEQUENCE_WINDOW]	= "Sequence Window",
		[DCCPF_ECN_INCAPABLE]	= "ECN Incapable",
		[DCCPF_ACK_RATIO]	= "Ack Ratio",
		[DCCPF_SEND_ACK_VECTOR]	= "Send ACK Vector",
		[DCCPF_SEND_NDP_COUNT]	= "Send NDP Count",
		[DCCPF_MIN_CSUM_COVER]	= "Min. Csum Coverage",
		[DCCPF_DATA_CHECKSUM]	= "Send Data Checksum",
	};
	if (feat > DCCPF_DATA_CHECKSUM && feat < DCCPF_MIN_CCID_SPECIFIC)
		return feature_names[DCCPF_RESERVED];

	if (feat ==  DCCPF_SEND_LEV_RATE)
		return "Send Loss Event Rate";
	if (feat >= DCCPF_MIN_CCID_SPECIFIC)
		return "CCID-specific";

	return feature_names[feat];
}

EXPORT_SYMBOL_GPL(dccp_feat_name);
#endif /* CONFIG_IP_DCCP_DEBUG */