1// SPDX-License-Identifier: GPL-2.0-only
2/* iptables module to match on related connections */
3/*
4 * (C) 2001 Martin Josefsson <gandalf@wlug.westbo.se>
5 */
6#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
7#include <linux/module.h>
8#include <linux/skbuff.h>
9#include <linux/netfilter.h>
10#include <net/netfilter/nf_conntrack.h>
11#include <net/netfilter/nf_conntrack_core.h>
12#include <net/netfilter/nf_conntrack_helper.h>
13#include <linux/netfilter/x_tables.h>
14#include <linux/netfilter/xt_helper.h>
15
16MODULE_LICENSE("GPL");
17MODULE_AUTHOR("Martin Josefsson <gandalf@netfilter.org>");
18MODULE_DESCRIPTION("Xtables: Related connection matching");
19MODULE_ALIAS("ipt_helper");
20MODULE_ALIAS("ip6t_helper");
21
22
23static bool
24helper_mt(const struct sk_buff *skb, struct xt_action_param *par)
25{
26	const struct xt_helper_info *info = par->matchinfo;
27	const struct nf_conn *ct;
28	const struct nf_conn_help *master_help;
29	const struct nf_conntrack_helper *helper;
30	enum ip_conntrack_info ctinfo;
31	bool ret = info->invert;
32
33	ct = nf_ct_get(skb, &ctinfo);
34	if (!ct || !ct->master)
35		return ret;
36
37	master_help = nfct_help(ct->master);
38	if (!master_help)
39		return ret;
40
41	/* rcu_read_lock()ed by nf_hook_thresh */
42	helper = rcu_dereference(master_help->helper);
43	if (!helper)
44		return ret;
45
46	if (info->name[0] == '\0')
47		ret = !ret;
48	else
49		ret ^= !strncmp(helper->name, info->name,
50				strlen(helper->name));
51	return ret;
52}
53
54static int helper_mt_check(const struct xt_mtchk_param *par)
55{
56	struct xt_helper_info *info = par->matchinfo;
57	int ret;
58
59	ret = nf_ct_netns_get(par->net, par->family);
60	if (ret < 0) {
61		pr_info_ratelimited("cannot load conntrack support for proto=%u\n",
62				    par->family);
63		return ret;
64	}
65	info->name[sizeof(info->name) - 1] = '\0';
66	return 0;
67}
68
69static void helper_mt_destroy(const struct xt_mtdtor_param *par)
70{
71	nf_ct_netns_put(par->net, par->family);
72}
73
74static struct xt_match helper_mt_reg __read_mostly = {
75	.name       = "helper",
76	.revision   = 0,
77	.family     = NFPROTO_UNSPEC,
78	.checkentry = helper_mt_check,
79	.match      = helper_mt,
80	.destroy    = helper_mt_destroy,
81	.matchsize  = sizeof(struct xt_helper_info),
82	.me         = THIS_MODULE,
83};
84
85static int __init helper_mt_init(void)
86{
87	return xt_register_match(&helper_mt_reg);
88}
89
90static void __exit helper_mt_exit(void)
91{
92	xt_unregister_match(&helper_mt_reg);
93}
94
95module_init(helper_mt_init);
96module_exit(helper_mt_exit);
97