summaryrefslogtreecommitdiff
path: root/net/netfilter/nfnetlink_cthelper.c
blob: be678a323598c3237a2cae09e4e3ed4bdea46614 (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
/*
 * (C) 2012 Pablo Neira Ayuso <pablo@netfilter.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation (or any later at your option).
 *
 * This software has been sponsored by Vyatta Inc. <http://www.vyatta.com>
 */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/netlink.h>
#include <linux/rculist.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/list.h>
#include <linux/errno.h>
#include <net/netlink.h>
#include <net/sock.h>

#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <net/netfilter/nf_conntrack_ecache.h>

#include <linux/netfilter/nfnetlink.h>
#include <linux/netfilter/nfnetlink_conntrack.h>
#include <linux/netfilter/nfnetlink_cthelper.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");
MODULE_DESCRIPTION("nfnl_cthelper: User-space connection tracking helpers");

struct nfnl_cthelper {
	struct list_head		list;
	struct nf_conntrack_helper	helper;
};

static LIST_HEAD(nfnl_cthelper_list);

static int
nfnl_userspace_cthelper(struct sk_buff *skb, unsigned int protoff,
			struct nf_conn *ct, enum ip_conntrack_info ctinfo)
{
	const struct nf_conn_help *help;
	struct nf_conntrack_helper *helper;

	help = nfct_help(ct);
	if (help == NULL)
		return NF_DROP;

	/* rcu_read_lock()ed by nf_hook_thresh */
	helper = rcu_dereference(help->helper);
	if (helper == NULL)
		return NF_DROP;

	/* This is a user-space helper not yet configured, skip. */
	if ((helper->flags &
	    (NF_CT_HELPER_F_USERSPACE | NF_CT_HELPER_F_CONFIGURED)) ==
	     NF_CT_HELPER_F_USERSPACE)
		return NF_ACCEPT;

	/* If the user-space helper is not available, don't block traffic. */
	return NF_QUEUE_NR(helper->queue_num) | NF_VERDICT_FLAG_QUEUE_BYPASS;
}

static const struct nla_policy nfnl_cthelper_tuple_pol[NFCTH_TUPLE_MAX+1] = {
	[NFCTH_TUPLE_L3PROTONUM] = { .type = NLA_U16, },
	[NFCTH_TUPLE_L4PROTONUM] = { .type = NLA_U8, },
};

static int
nfnl_cthelper_parse_tuple(struct nf_conntrack_tuple *tuple,
			  const struct nlattr *attr)
{
	int err;
	struct nlattr *tb[NFCTH_TUPLE_MAX+1];

	err = nla_parse_nested(tb, NFCTH_TUPLE_MAX, attr,
			       nfnl_cthelper_tuple_pol, NULL);
	if (err < 0)
		return err;

	if (!tb[NFCTH_TUPLE_L3PROTONUM] || !tb[NFCTH_TUPLE_L4PROTONUM])
		return -EINVAL;

	/* Not all fields are initialized so first zero the tuple */
	memset(tuple, 0, sizeof(struct nf_conntrack_tuple));

	tuple->src.l3num = ntohs(nla_get_be16(tb[NFCTH_TUPLE_L3PROTONUM]));
	tuple->dst.protonum = nla_get_u8(tb[NFCTH_TUPLE_L4PROTONUM]);

	return 0;
}

static int
nfnl_cthelper_from_nlattr(struct nlattr *attr, struct nf_conn *ct)
{
	struct nf_conn_help *help = nfct_help(ct);

	if (attr == NULL)
		return -EINVAL;

	if (help->helper->data_len == 0)
		return -EINVAL;

	nla_memcpy(help->data, nla_data(attr), sizeof(help->data));
	return 0;
}

static int
nfnl_cthelper_to_nlattr(struct sk_buff *skb, const struct nf_conn *ct)
{
	const struct nf_conn_help *help = nfct_help(ct);

	if (help->helper->data_len &&
	    nla_put(skb, CTA_HELP_INFO, help->helper->data_len, &help->data))
		goto nla_put_failure;

	return 0;

nla_put_failure:
	return -ENOSPC;
}

static const struct nla_policy nfnl_cthelper_expect_pol[NFCTH_POLICY_MAX+1] = {
	[NFCTH_POLICY_NAME] = { .type = NLA_NUL_STRING,
				.len = NF_CT_HELPER_NAME_LEN-1 },
	[NFCTH_POLICY_EXPECT_MAX] = { .type = NLA_U32, },
	[NFCTH_POLICY_EXPECT_TIMEOUT] = { .type = NLA_U32, },
};

static int
nfnl_cthelper_expect_policy(struct nf_conntrack_expect_policy *expect_policy,
			    const struct nlattr *attr)
{
	int err;
	struct nlattr *tb[NFCTH_POLICY_MAX+1];

	err = nla_parse_nested(tb, NFCTH_POLICY_MAX, attr,
			       nfnl_cthelper_expect_pol, NULL);
	if (err < 0)
		return err;

	if (!tb[NFCTH_POLICY_NAME] ||
	    !tb[NFCTH_POLICY_EXPECT_MAX] ||
	    !tb[NFCTH_POLICY_EXPECT_TIMEOUT])
		return -EINVAL;

	strncpy(expect_policy->name,
		nla_data(tb[NFCTH_POLICY_NAME]), NF_CT_HELPER_NAME_LEN);
	expect_policy->max_expected =
		ntohl(nla_get_be32(tb[NFCTH_POLICY_EXPECT_MAX]));
	if (expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
		return -EINVAL;

	expect_policy->timeout =
		ntohl(nla_get_be32(tb[NFCTH_POLICY_EXPECT_TIMEOUT]));

	return 0;
}

static const struct nla_policy
nfnl_cthelper_expect_policy_set[NFCTH_POLICY_SET_MAX+1] = {
	[NFCTH_POLICY_SET_NUM] = { .type = NLA_U32, },
};

static int
nfnl_cthelper_parse_expect_policy(struct nf_conntrack_helper *helper,
				  const struct nlattr *attr)
{
	int i, ret;
	struct nf_conntrack_expect_policy *expect_policy;
	struct nlattr *tb[NFCTH_POLICY_SET_MAX+1];
	unsigned int class_max;

	ret = nla_parse_nested(tb, NFCTH_POLICY_SET_MAX, attr,
			       nfnl_cthelper_expect_policy_set, NULL);
	if (ret < 0)
		return ret;

	if (!tb[NFCTH_POLICY_SET_NUM])
		return -EINVAL;

	class_max = ntohl(nla_get_be32(tb[NFCTH_POLICY_SET_NUM]));
	if (class_max == 0)
		return -EINVAL;
	if (class_max > NF_CT_MAX_EXPECT_CLASSES)
		return -EOVERFLOW;

	expect_policy = kzalloc(sizeof(struct nf_conntrack_expect_policy) *
				class_max, GFP_KERNEL);
	if (expect_policy == NULL)
		return -ENOMEM;

	for (i = 0; i < class_max; i++) {
		if (!tb[NFCTH_POLICY_SET+i])
			goto err;

		ret = nfnl_cthelper_expect_policy(&expect_policy[i],
						  tb[NFCTH_POLICY_SET+i]);
		if (ret < 0)
			goto err;
	}

	helper->expect_class_max = class_max - 1;
	helper->expect_policy = expect_policy;
	return 0;
err:
	kfree(expect_policy);
	return -EINVAL;
}

static int
nfnl_cthelper_create(const struct nlattr * const tb[],
		     struct nf_conntrack_tuple *tuple)
{
	struct nf_conntrack_helper *helper;
	struct nfnl_cthelper *nfcth;
	unsigned int size;
	int ret;

	if (!tb[NFCTH_TUPLE] || !tb[NFCTH_POLICY] || !tb[NFCTH_PRIV_DATA_LEN])
		return -EINVAL;

	nfcth = kzalloc(sizeof(*nfcth), GFP_KERNEL);
	if (nfcth == NULL)
		return -ENOMEM;
	helper = &nfcth->helper;

	ret = nfnl_cthelper_parse_expect_policy(helper, tb[NFCTH_POLICY]);
	if (ret < 0)
		goto err1;

	strncpy(helper->name, nla_data(tb[NFCTH_NAME]), NF_CT_HELPER_NAME_LEN);
	size = ntohl(nla_get_be32(tb[NFCTH_PRIV_DATA_LEN]));
	if (size > FIELD_SIZEOF(struct nf_conn_help, data)) {
		ret = -ENOMEM;
		goto err2;
	}

	helper->flags |= NF_CT_HELPER_F_USERSPACE;
	memcpy(&helper->tuple, tuple, sizeof(struct nf_conntrack_tuple));

	helper->me = THIS_MODULE;
	helper->help = nfnl_userspace_cthelper;
	helper->from_nlattr = nfnl_cthelper_from_nlattr;
	helper->to_nlattr = nfnl_cthelper_to_nlattr;

	/* Default to queue number zero, this can be updated at any time. */
	if (tb[NFCTH_QUEUE_NUM])
		helper->queue_num = ntohl(nla_get_be32(tb[NFCTH_QUEUE_NUM]));

	if (tb[NFCTH_STATUS]) {
		int status = ntohl(nla_get_be32(tb[NFCTH_STATUS]));

		switch(status) {
		case NFCT_HELPER_STATUS_ENABLED:
			helper->flags |= NF_CT_HELPER_F_CONFIGURED;
			break;
		case NFCT_HELPER_STATUS_DISABLED:
			helper->flags &= ~NF_CT_HELPER_F_CONFIGURED;
			break;
		}
	}

	ret = nf_conntrack_helper_register(helper);
	if (ret < 0)
		goto err2;

	list_add_tail(&nfcth->list, &nfnl_cthelper_list);
	return 0;
err2:
	kfree(helper->expect_policy);
err1:
	kfree(nfcth);
	return ret;
}

static int
nfnl_cthelper_update_policy_one(const struct nf_conntrack_expect_policy *policy,
				struct nf_conntrack_expect_policy *new_policy,
				const struct nlattr *attr)
{
	struct nlattr *tb[NFCTH_POLICY_MAX + 1];
	int err;

	err = nla_parse_nested(tb, NFCTH_POLICY_MAX, attr,
			       nfnl_cthelper_expect_pol, NULL);
	if (err < 0)
		return err;

	if (!tb[NFCTH_POLICY_NAME] ||
	    !tb[NFCTH_POLICY_EXPECT_MAX] ||
	    !tb[NFCTH_POLICY_EXPECT_TIMEOUT])
		return -EINVAL;

	if (nla_strcmp(tb[NFCTH_POLICY_NAME], policy->name))
		return -EBUSY;

	new_policy->max_expected =
		ntohl(nla_get_be32(tb[NFCTH_POLICY_EXPECT_MAX]));
	if (new_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
		return -EINVAL;

	new_policy->timeout =
		ntohl(nla_get_be32(tb[NFCTH_POLICY_EXPECT_TIMEOUT]));

	return 0;
}

static int nfnl_cthelper_update_policy_all(struct nlattr *tb[],
					   struct nf_conntrack_helper *helper)
{
	struct nf_conntrack_expect_policy new_policy[helper->expect_class_max + 1];
	struct nf_conntrack_expect_policy *policy;
	int i, err;

	/* Check first that all policy attributes are well-formed, so we don't
	 * leave things in inconsistent state on errors.
	 */
	for (i = 0; i < helper->expect_class_max + 1; i++) {

		if (!tb[NFCTH_POLICY_SET + i])
			return -EINVAL;

		err = nfnl_cthelper_update_policy_one(&helper->expect_policy[i],
						      &new_policy[i],
						      tb[NFCTH_POLICY_SET + i]);
		if (err < 0)
			return err;
	}
	/* Now we can safely update them. */
	for (i = 0; i < helper->expect_class_max + 1; i++) {
		policy = (struct nf_conntrack_expect_policy *)
				&helper->expect_policy[i];
		policy->max_expected = new_policy->max_expected;
		policy->timeout	= new_policy->timeout;
	}

	return 0;
}

static int nfnl_cthelper_update_policy(struct nf_conntrack_helper *helper,
				       const struct nlattr *attr)
{
	struct nlattr *tb[NFCTH_POLICY_SET_MAX + 1];
	unsigned int class_max;
	int err;

	err = nla_parse_nested(tb, NFCTH_POLICY_SET_MAX, attr,
			       nfnl_cthelper_expect_policy_set, NULL);
	if (err < 0)
		return err;

	if (!tb[NFCTH_POLICY_SET_NUM])
		return -EINVAL;

	class_max = ntohl(nla_get_be32(tb[NFCTH_POLICY_SET_NUM]));
	if (helper->expect_class_max + 1 != class_max)
		return -EBUSY;

	return nfnl_cthelper_update_policy_all(tb, helper);
}

static int
nfnl_cthelper_update(const struct nlattr * const tb[],
		     struct nf_conntrack_helper *helper)
{
	int ret;

	if (tb[NFCTH_PRIV_DATA_LEN])
		return -EBUSY;

	if (tb[NFCTH_POLICY]) {
		ret = nfnl_cthelper_update_policy(helper, tb[NFCTH_POLICY]);
		if (ret < 0)
			return ret;
	}
	if (tb[NFCTH_QUEUE_NUM])
		helper->queue_num = ntohl(nla_get_be32(tb[NFCTH_QUEUE_NUM]));

	if (tb[NFCTH_STATUS]) {
		int status = ntohl(nla_get_be32(tb[NFCTH_STATUS]));

		switch(status) {
		case NFCT_HELPER_STATUS_ENABLED:
			helper->flags |= NF_CT_HELPER_F_CONFIGURED;
			break;
		case NFCT_HELPER_STATUS_DISABLED:
			helper->flags &= ~NF_CT_HELPER_F_CONFIGURED;
			break;
		}
	}
	return 0;
}

static int nfnl_cthelper_new(struct net *net, struct sock *nfnl,
			     struct sk_buff *skb, const struct nlmsghdr *nlh,
			     const struct nlattr * const tb[])
{
	const char *helper_name;
	struct nf_conntrack_helper *cur, *helper = NULL;
	struct nf_conntrack_tuple tuple;
	struct nfnl_cthelper *nlcth;
	int ret = 0;

	if (!tb[NFCTH_NAME] || !tb[NFCTH_TUPLE])
		return -EINVAL;

	helper_name = nla_data(tb[NFCTH_NAME]);

	ret = nfnl_cthelper_parse_tuple(&tuple, tb[NFCTH_TUPLE]);
	if (ret < 0)
		return ret;

	list_for_each_entry(nlcth, &nfnl_cthelper_list, list) {
		cur = &nlcth->helper;

		if (strncmp(cur->name, helper_name, NF_CT_HELPER_NAME_LEN))
			continue;

		if ((tuple.src.l3num != cur->tuple.src.l3num ||
		     tuple.dst.protonum != cur->tuple.dst.protonum))
			continue;

		if (nlh->nlmsg_flags & NLM_F_EXCL)
			return -EEXIST;

		helper = cur;
		break;
	}

	if (helper == NULL)
		ret = nfnl_cthelper_create(tb, &tuple);
	else
		ret = nfnl_cthelper_update(tb, helper);

	return ret;
}

static int
nfnl_cthelper_dump_tuple(struct sk_buff *skb,
			 struct nf_conntrack_helper *helper)
{
	struct nlattr *nest_parms;

	nest_parms = nla_nest_start(skb, NFCTH_TUPLE | NLA_F_NESTED);
	if (nest_parms == NULL)
		goto nla_put_failure;

	if (nla_put_be16(skb, NFCTH_TUPLE_L3PROTONUM,
			 htons(helper->tuple.src.l3num)))
		goto nla_put_failure;

	if (nla_put_u8(skb, NFCTH_TUPLE_L4PROTONUM, helper->tuple.dst.protonum))
		goto nla_put_failure;

	nla_nest_end(skb, nest_parms);
	return 0;

nla_put_failure:
	return -1;
}

static int
nfnl_cthelper_dump_policy(struct sk_buff *skb,
			struct nf_conntrack_helper *helper)
{
	int i;
	struct nlattr *nest_parms1, *nest_parms2;

	nest_parms1 = nla_nest_start(skb, NFCTH_POLICY | NLA_F_NESTED);
	if (nest_parms1 == NULL)
		goto nla_put_failure;

	if (nla_put_be32(skb, NFCTH_POLICY_SET_NUM,
			 htonl(helper->expect_class_max + 1)))
		goto nla_put_failure;

	for (i = 0; i < helper->expect_class_max + 1; i++) {
		nest_parms2 = nla_nest_start(skb,
				(NFCTH_POLICY_SET+i) | NLA_F_NESTED);
		if (nest_parms2 == NULL)
			goto nla_put_failure;

		if (nla_put_string(skb, NFCTH_POLICY_NAME,
				   helper->expect_policy[i].name))
			goto nla_put_failure;

		if (nla_put_be32(skb, NFCTH_POLICY_EXPECT_MAX,
				 htonl(helper->expect_policy[i].max_expected)))
			goto nla_put_failure;

		if (nla_put_be32(skb, NFCTH_POLICY_EXPECT_TIMEOUT,
				 htonl(helper->expect_policy[i].timeout)))
			goto nla_put_failure;

		nla_nest_end(skb, nest_parms2);
	}
	nla_nest_end(skb, nest_parms1);
	return 0;

nla_put_failure:
	return -1;
}

static int
nfnl_cthelper_fill_info(struct sk_buff *skb, u32 portid, u32 seq, u32 type,
			int event, struct nf_conntrack_helper *helper)
{
	struct nlmsghdr *nlh;
	struct nfgenmsg *nfmsg;
	unsigned int flags = portid ? NLM_F_MULTI : 0;
	int status;

	event = nfnl_msg_type(NFNL_SUBSYS_CTHELPER, event);
	nlh = nlmsg_put(skb, portid, seq, event, sizeof(*nfmsg), flags);
	if (nlh == NULL)
		goto nlmsg_failure;

	nfmsg = nlmsg_data(nlh);
	nfmsg->nfgen_family = AF_UNSPEC;
	nfmsg->version = NFNETLINK_V0;
	nfmsg->res_id = 0;

	if (nla_put_string(skb, NFCTH_NAME, helper->name))
		goto nla_put_failure;

	if (nla_put_be32(skb, NFCTH_QUEUE_NUM, htonl(helper->queue_num)))
		goto nla_put_failure;

	if (nfnl_cthelper_dump_tuple(skb, helper) < 0)
		goto nla_put_failure;

	if (nfnl_cthelper_dump_policy(skb, helper) < 0)
		goto nla_put_failure;

	if (nla_put_be32(skb, NFCTH_PRIV_DATA_LEN, htonl(helper->data_len)))
		goto nla_put_failure;

	if (helper->flags & NF_CT_HELPER_F_CONFIGURED)
		status = NFCT_HELPER_STATUS_ENABLED;
	else
		status = NFCT_HELPER_STATUS_DISABLED;

	if (nla_put_be32(skb, NFCTH_STATUS, htonl(status)))
		goto nla_put_failure;

	nlmsg_end(skb, nlh);
	return skb->len;

nlmsg_failure:
nla_put_failure:
	nlmsg_cancel(skb, nlh);
	return -1;
}

static int
nfnl_cthelper_dump_table(struct sk_buff *skb, struct netlink_callback *cb)
{
	struct nf_conntrack_helper *cur, *last;

	rcu_read_lock();
	last = (struct nf_conntrack_helper *)cb->args[1];
	for (; cb->args[0] < nf_ct_helper_hsize; cb->args[0]++) {
restart:
		hlist_for_each_entry_rcu(cur,
				&nf_ct_helper_hash[cb->args[0]], hnode) {

			/* skip non-userspace conntrack helpers. */
			if (!(cur->flags & NF_CT_HELPER_F_USERSPACE))
				continue;

			if (cb->args[1]) {
				if (cur != last)
					continue;
				cb->args[1] = 0;
			}
			if (nfnl_cthelper_fill_info(skb,
					    NETLINK_CB(cb->skb).portid,
					    cb->nlh->nlmsg_seq,
					    NFNL_MSG_TYPE(cb->nlh->nlmsg_type),
					    NFNL_MSG_CTHELPER_NEW, cur) < 0) {
				cb->args[1] = (unsigned long)cur;
				goto out;
			}
		}
	}
	if (cb->args[1]) {
		cb->args[1] = 0;
		goto restart;
	}
out:
	rcu_read_unlock();
	return skb->len;
}

static int nfnl_cthelper_get(struct net *net, struct sock *nfnl,
			     struct sk_buff *skb, const struct nlmsghdr *nlh,
			     const struct nlattr * const tb[])
{
	int ret = -ENOENT;
	struct nf_conntrack_helper *cur;
	struct sk_buff *skb2;
	char *helper_name = NULL;
	struct nf_conntrack_tuple tuple;
	struct nfnl_cthelper *nlcth;
	bool tuple_set = false;

	if (nlh->nlmsg_flags & NLM_F_DUMP) {
		struct netlink_dump_control c = {
			.dump = nfnl_cthelper_dump_table,
		};
		return netlink_dump_start(nfnl, skb, nlh, &c);
	}

	if (tb[NFCTH_NAME])
		helper_name = nla_data(tb[NFCTH_NAME]);

	if (tb[NFCTH_TUPLE]) {
		ret = nfnl_cthelper_parse_tuple(&tuple, tb[NFCTH_TUPLE]);
		if (ret < 0)
			return ret;

		tuple_set = true;
	}

	list_for_each_entry(nlcth, &nfnl_cthelper_list, list) {
		cur = &nlcth->helper;
		if (helper_name &&
		    strncmp(cur->name, helper_name, NF_CT_HELPER_NAME_LEN))
			continue;

		if (tuple_set &&
		    (tuple.src.l3num != cur->tuple.src.l3num ||
		     tuple.dst.protonum != cur->tuple.dst.protonum))
			continue;

		skb2 = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
		if (skb2 == NULL) {
			ret = -ENOMEM;
			break;
		}

		ret = nfnl_cthelper_fill_info(skb2, NETLINK_CB(skb).portid,
					      nlh->nlmsg_seq,
					      NFNL_MSG_TYPE(nlh->nlmsg_type),
					      NFNL_MSG_CTHELPER_NEW, cur);
		if (ret <= 0) {
			kfree_skb(skb2);
			break;
		}

		ret = netlink_unicast(nfnl, skb2, NETLINK_CB(skb).portid,
				      MSG_DONTWAIT);
		if (ret > 0)
			ret = 0;

		/* this avoids a loop in nfnetlink. */
		return ret == -EAGAIN ? -ENOBUFS : ret;
	}
	return ret;
}

static int nfnl_cthelper_del(struct net *net, struct sock *nfnl,
			     struct sk_buff *skb, const struct nlmsghdr *nlh,
			     const struct nlattr * const tb[])
{
	char *helper_name = NULL;
	struct nf_conntrack_helper *cur;
	struct nf_conntrack_tuple tuple;
	bool tuple_set = false, found = false;
	struct nfnl_cthelper *nlcth, *n;
	int j = 0, ret;

	if (tb[NFCTH_NAME])
		helper_name = nla_data(tb[NFCTH_NAME]);

	if (tb[NFCTH_TUPLE]) {
		ret = nfnl_cthelper_parse_tuple(&tuple, tb[NFCTH_TUPLE]);
		if (ret < 0)
			return ret;

		tuple_set = true;
	}

	ret = -ENOENT;
	list_for_each_entry_safe(nlcth, n, &nfnl_cthelper_list, list) {
		cur = &nlcth->helper;
		j++;

		if (helper_name &&
		    strncmp(cur->name, helper_name, NF_CT_HELPER_NAME_LEN))
			continue;

		if (tuple_set &&
		    (tuple.src.l3num != cur->tuple.src.l3num ||
		     tuple.dst.protonum != cur->tuple.dst.protonum))
			continue;

		if (refcount_dec_if_one(&cur->refcnt)) {
			found = true;
			nf_conntrack_helper_unregister(cur);
			kfree(cur->expect_policy);

			list_del(&nlcth->list);
			kfree(nlcth);
		} else {
			ret = -EBUSY;
		}
	}

	/* Make sure we return success if we flush and there is no helpers */
	return (found || j == 0) ? 0 : ret;
}

static const struct nla_policy nfnl_cthelper_policy[NFCTH_MAX+1] = {
	[NFCTH_NAME] = { .type = NLA_NUL_STRING,
			 .len = NF_CT_HELPER_NAME_LEN-1 },
	[NFCTH_QUEUE_NUM] = { .type = NLA_U32, },
};

static const struct nfnl_callback nfnl_cthelper_cb[NFNL_MSG_CTHELPER_MAX] = {
	[NFNL_MSG_CTHELPER_NEW]		= { .call = nfnl_cthelper_new,
					    .attr_count = NFCTH_MAX,
					    .policy = nfnl_cthelper_policy },
	[NFNL_MSG_CTHELPER_GET]		= { .call = nfnl_cthelper_get,
					    .attr_count = NFCTH_MAX,
					    .policy = nfnl_cthelper_policy },
	[NFNL_MSG_CTHELPER_DEL]		= { .call = nfnl_cthelper_del,
					    .attr_count = NFCTH_MAX,
					    .policy = nfnl_cthelper_policy },
};

static const struct nfnetlink_subsystem nfnl_cthelper_subsys = {
	.name				= "cthelper",
	.subsys_id			= NFNL_SUBSYS_CTHELPER,
	.cb_count			= NFNL_MSG_CTHELPER_MAX,
	.cb				= nfnl_cthelper_cb,
};

MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_CTHELPER);

static int __init nfnl_cthelper_init(void)
{
	int ret;

	ret = nfnetlink_subsys_register(&nfnl_cthelper_subsys);
	if (ret < 0) {
		pr_err("nfnl_cthelper: cannot register with nfnetlink.\n");
		goto err_out;
	}
	return 0;
err_out:
	return ret;
}

static void __exit nfnl_cthelper_exit(void)
{
	struct nf_conntrack_helper *cur;
	struct nfnl_cthelper *nlcth, *n;

	nfnetlink_subsys_unregister(&nfnl_cthelper_subsys);

	list_for_each_entry_safe(nlcth, n, &nfnl_cthelper_list, list) {
		cur = &nlcth->helper;

		nf_conntrack_helper_unregister(cur);
		kfree(cur->expect_policy);
		kfree(nlcth);
	}
}

module_init(nfnl_cthelper_init);
module_exit(nfnl_cthelper_exit);