1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Transparent proxy support for Linux/iptables
4 *
5 * Copyright (c) 2006-2010 BalaBit IT Ltd.
6 * Author: Balazs Scheidler, Krisztian Kovacs
7 */
8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9#include <linux/module.h>
10#include <linux/skbuff.h>
11#include <linux/ip.h>
12#include <net/checksum.h>
13#include <net/udp.h>
14#include <net/tcp.h>
15#include <net/inet_sock.h>
16#include <net/inet_hashtables.h>
17#include <linux/inetdevice.h>
18#include <linux/netfilter/x_tables.h>
19#include <linux/netfilter_ipv4/ip_tables.h>
20
21#include <net/netfilter/ipv4/nf_defrag_ipv4.h>
22
23#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
24#define XT_TPROXY_HAVE_IPV6 1
25#include <net/if_inet6.h>
26#include <net/addrconf.h>
27#include <net/inet6_hashtables.h>
28#include <linux/netfilter_ipv6/ip6_tables.h>
29#include <net/netfilter/ipv6/nf_defrag_ipv6.h>
30#endif
31
32#include <net/netfilter/nf_tproxy.h>
33#include <linux/netfilter/xt_TPROXY.h>
34
35static unsigned int
36tproxy_tg4(struct net *net, struct sk_buff *skb, __be32 laddr, __be16 lport,
37	   u_int32_t mark_mask, u_int32_t mark_value)
38{
39	const struct iphdr *iph = ip_hdr(skb);
40	struct udphdr _hdr, *hp;
41	struct sock *sk;
42
43	hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
44	if (hp == NULL)
45		return NF_DROP;
46
47	/* check if there's an ongoing connection on the packet
48	 * addresses, this happens if the redirect already happened
49	 * and the current packet belongs to an already established
50	 * connection */
51	sk = nf_tproxy_get_sock_v4(net, skb, iph->protocol,
52				   iph->saddr, iph->daddr,
53				   hp->source, hp->dest,
54				   skb->dev, NF_TPROXY_LOOKUP_ESTABLISHED);
55
56	laddr = nf_tproxy_laddr4(skb, laddr, iph->daddr);
57	if (!lport)
58		lport = hp->dest;
59
60	/* UDP has no TCP_TIME_WAIT state, so we never enter here */
61	if (sk && sk->sk_state == TCP_TIME_WAIT)
62		/* reopening a TIME_WAIT connection needs special handling */
63		sk = nf_tproxy_handle_time_wait4(net, skb, laddr, lport, sk);
64	else if (!sk)
65		/* no, there's no established connection, check if
66		 * there's a listener on the redirected addr/port */
67		sk = nf_tproxy_get_sock_v4(net, skb, iph->protocol,
68					   iph->saddr, laddr,
69					   hp->source, lport,
70					   skb->dev, NF_TPROXY_LOOKUP_LISTENER);
71
72	/* NOTE: assign_sock consumes our sk reference */
73	if (sk && nf_tproxy_sk_is_transparent(sk)) {
74		/* This should be in a separate target, but we don't do multiple
75		   targets on the same rule yet */
76		skb->mark = (skb->mark & ~mark_mask) ^ mark_value;
77		nf_tproxy_assign_sock(skb, sk);
78		return NF_ACCEPT;
79	}
80
81	return NF_DROP;
82}
83
84static unsigned int
85tproxy_tg4_v0(struct sk_buff *skb, const struct xt_action_param *par)
86{
87	const struct xt_tproxy_target_info *tgi = par->targinfo;
88
89	return tproxy_tg4(xt_net(par), skb, tgi->laddr, tgi->lport,
90			  tgi->mark_mask, tgi->mark_value);
91}
92
93static unsigned int
94tproxy_tg4_v1(struct sk_buff *skb, const struct xt_action_param *par)
95{
96	const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
97
98	return tproxy_tg4(xt_net(par), skb, tgi->laddr.ip, tgi->lport,
99			  tgi->mark_mask, tgi->mark_value);
100}
101
102#ifdef XT_TPROXY_HAVE_IPV6
103
104static unsigned int
105tproxy_tg6_v1(struct sk_buff *skb, const struct xt_action_param *par)
106{
107	const struct ipv6hdr *iph = ipv6_hdr(skb);
108	const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
109	struct udphdr _hdr, *hp;
110	struct sock *sk;
111	const struct in6_addr *laddr;
112	__be16 lport;
113	int thoff = 0;
114	int tproto;
115
116	tproto = ipv6_find_hdr(skb, &thoff, -1, NULL, NULL);
117	if (tproto < 0)
118		return NF_DROP;
119
120	hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
121	if (!hp)
122		return NF_DROP;
123
124	/* check if there's an ongoing connection on the packet
125	 * addresses, this happens if the redirect already happened
126	 * and the current packet belongs to an already established
127	 * connection */
128	sk = nf_tproxy_get_sock_v6(xt_net(par), skb, thoff, tproto,
129				   &iph->saddr, &iph->daddr,
130				   hp->source, hp->dest,
131				   xt_in(par), NF_TPROXY_LOOKUP_ESTABLISHED);
132
133	laddr = nf_tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr);
134	lport = tgi->lport ? tgi->lport : hp->dest;
135
136	/* UDP has no TCP_TIME_WAIT state, so we never enter here */
137	if (sk && sk->sk_state == TCP_TIME_WAIT) {
138		const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
139		/* reopening a TIME_WAIT connection needs special handling */
140		sk = nf_tproxy_handle_time_wait6(skb, tproto, thoff,
141					      xt_net(par),
142					      &tgi->laddr.in6,
143					      tgi->lport,
144					      sk);
145	}
146	else if (!sk)
147		/* no there's no established connection, check if
148		 * there's a listener on the redirected addr/port */
149		sk = nf_tproxy_get_sock_v6(xt_net(par), skb, thoff,
150					   tproto, &iph->saddr, laddr,
151					   hp->source, lport,
152					   xt_in(par), NF_TPROXY_LOOKUP_LISTENER);
153
154	/* NOTE: assign_sock consumes our sk reference */
155	if (sk && nf_tproxy_sk_is_transparent(sk)) {
156		/* This should be in a separate target, but we don't do multiple
157		   targets on the same rule yet */
158		skb->mark = (skb->mark & ~tgi->mark_mask) ^ tgi->mark_value;
159		nf_tproxy_assign_sock(skb, sk);
160		return NF_ACCEPT;
161	}
162
163	return NF_DROP;
164}
165
166static int tproxy_tg6_check(const struct xt_tgchk_param *par)
167{
168	const struct ip6t_ip6 *i = par->entryinfo;
169	int err;
170
171	err = nf_defrag_ipv6_enable(par->net);
172	if (err)
173		return err;
174
175	if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP) &&
176	    !(i->invflags & IP6T_INV_PROTO))
177		return 0;
178
179	pr_info_ratelimited("Can be used only with -p tcp or -p udp\n");
180	return -EINVAL;
181}
182
183static void tproxy_tg6_destroy(const struct xt_tgdtor_param *par)
184{
185	nf_defrag_ipv6_disable(par->net);
186}
187#endif
188
189static int tproxy_tg4_check(const struct xt_tgchk_param *par)
190{
191	const struct ipt_ip *i = par->entryinfo;
192	int err;
193
194	err = nf_defrag_ipv4_enable(par->net);
195	if (err)
196		return err;
197
198	if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP)
199	    && !(i->invflags & IPT_INV_PROTO))
200		return 0;
201
202	pr_info_ratelimited("Can be used only with -p tcp or -p udp\n");
203	return -EINVAL;
204}
205
206static void tproxy_tg4_destroy(const struct xt_tgdtor_param *par)
207{
208	nf_defrag_ipv4_disable(par->net);
209}
210
211static struct xt_target tproxy_tg_reg[] __read_mostly = {
212	{
213		.name		= "TPROXY",
214		.family		= NFPROTO_IPV4,
215		.table		= "mangle",
216		.target		= tproxy_tg4_v0,
217		.revision	= 0,
218		.targetsize	= sizeof(struct xt_tproxy_target_info),
219		.checkentry	= tproxy_tg4_check,
220		.destroy	= tproxy_tg4_destroy,
221		.hooks		= 1 << NF_INET_PRE_ROUTING,
222		.me		= THIS_MODULE,
223	},
224	{
225		.name		= "TPROXY",
226		.family		= NFPROTO_IPV4,
227		.table		= "mangle",
228		.target		= tproxy_tg4_v1,
229		.revision	= 1,
230		.targetsize	= sizeof(struct xt_tproxy_target_info_v1),
231		.checkentry	= tproxy_tg4_check,
232		.destroy	= tproxy_tg4_destroy,
233		.hooks		= 1 << NF_INET_PRE_ROUTING,
234		.me		= THIS_MODULE,
235	},
236#ifdef XT_TPROXY_HAVE_IPV6
237	{
238		.name		= "TPROXY",
239		.family		= NFPROTO_IPV6,
240		.table		= "mangle",
241		.target		= tproxy_tg6_v1,
242		.revision	= 1,
243		.targetsize	= sizeof(struct xt_tproxy_target_info_v1),
244		.checkentry	= tproxy_tg6_check,
245		.destroy	= tproxy_tg6_destroy,
246		.hooks		= 1 << NF_INET_PRE_ROUTING,
247		.me		= THIS_MODULE,
248	},
249#endif
250
251};
252
253static int __init tproxy_tg_init(void)
254{
255	return xt_register_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
256}
257
258static void __exit tproxy_tg_exit(void)
259{
260	xt_unregister_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
261}
262
263module_init(tproxy_tg_init);
264module_exit(tproxy_tg_exit);
265MODULE_LICENSE("GPL");
266MODULE_AUTHOR("Balazs Scheidler, Krisztian Kovacs");
267MODULE_DESCRIPTION("Netfilter transparent proxy (TPROXY) target module.");
268MODULE_ALIAS("ipt_TPROXY");
269MODULE_ALIAS("ip6t_TPROXY");
270