2 * Transparent proxy support for Linux/iptables
4 * Copyright (c) 2006-2007 BalaBit IT Ltd.
5 * Author: Balazs Scheidler, Krisztian Kovacs
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
12 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
13 #include <linux/module.h>
14 #include <linux/skbuff.h>
16 #include <net/checksum.h>
18 #include <net/inet_sock.h>
20 #include <linux/netfilter/x_tables.h>
21 #include <linux/netfilter_ipv4/ip_tables.h>
22 #include <linux/netfilter/xt_TPROXY.h>
24 #include <net/netfilter/ipv4/nf_defrag_ipv4.h>
25 #include <net/netfilter/nf_tproxy_core.h>
28 * tproxy_handle_time_wait() - handle TCP TIME_WAIT reopen redirections
29 * @skb: The skb being processed.
30 * @par: Iptables target parameters.
31 * @sk: The TIME_WAIT TCP socket found by the lookup.
33 * We have to handle SYN packets arriving to TIME_WAIT sockets
34 * differently: instead of reopening the connection we should rather
35 * redirect the new connection to the proxy if there's a listener
38 * tproxy_handle_time_wait() consumes the socket reference passed in.
40 * Returns the listener socket if there's one, the TIME_WAIT socket if
41 * no such listener is found, or NULL if the TCP header is incomplete.
44 tproxy_handle_time_wait(struct sk_buff *skb, const struct xt_action_param *par, struct sock *sk)
46 const struct iphdr *iph = ip_hdr(skb);
47 const struct xt_tproxy_target_info *tgi = par->targinfo;
48 struct tcphdr _hdr, *hp;
50 hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
52 inet_twsk_put(inet_twsk(sk));
56 if (hp->syn && !hp->rst && !hp->ack && !hp->fin) {
57 /* SYN to a TIME_WAIT socket, we'd rather redirect it
58 * to a listener socket if there's one */
61 sk2 = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
62 iph->saddr, tgi->laddr ? tgi->laddr : iph->daddr,
63 hp->source, tgi->lport ? tgi->lport : hp->dest,
64 par->in, NFT_LOOKUP_LISTENER);
66 /* yeah, there's one, let's kill the TIME_WAIT
67 * socket and redirect to the listener
69 inet_twsk_deschedule(inet_twsk(sk), &tcp_death_row);
70 inet_twsk_put(inet_twsk(sk));
79 tproxy_tg(struct sk_buff *skb, const struct xt_action_param *par)
81 const struct iphdr *iph = ip_hdr(skb);
82 const struct xt_tproxy_target_info *tgi = par->targinfo;
83 struct udphdr _hdr, *hp;
86 hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
90 sk = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
91 iph->saddr, iph->daddr,
93 par->in, NFT_LOOKUP_ESTABLISHED);
95 /* UDP has no TCP_TIME_WAIT state, so we never enter here */
96 if (sk && sk->sk_state == TCP_TIME_WAIT)
97 sk = tproxy_handle_time_wait(skb, par, sk);
99 sk = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
100 iph->saddr, tgi->laddr ? tgi->laddr : iph->daddr,
101 hp->source, tgi->lport ? tgi->lport : hp->dest,
102 par->in, NFT_LOOKUP_LISTENER);
104 /* NOTE: assign_sock consumes our sk reference */
105 if (sk && nf_tproxy_assign_sock(skb, sk)) {
106 /* This should be in a separate target, but we don't do multiple
107 targets on the same rule yet */
108 skb->mark = (skb->mark & ~tgi->mark_mask) ^ tgi->mark_value;
110 pr_debug("redirecting: proto %u %08x:%u -> %08x:%u, mark: %x\n",
111 iph->protocol, ntohl(iph->daddr), ntohs(hp->dest),
112 ntohl(tgi->laddr), ntohs(tgi->lport), skb->mark);
116 pr_debug("no socket, dropping: proto %u %08x:%u -> %08x:%u, mark: %x\n",
117 iph->protocol, ntohl(iph->daddr), ntohs(hp->dest),
118 ntohl(tgi->laddr), ntohs(tgi->lport), skb->mark);
122 static int tproxy_tg_check(const struct xt_tgchk_param *par)
124 const struct ipt_ip *i = par->entryinfo;
126 if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP)
127 && !(i->invflags & IPT_INV_PROTO))
130 pr_info("Can be used only in combination with "
131 "either -p tcp or -p udp\n");
135 static struct xt_target tproxy_tg_reg __read_mostly = {
137 .family = NFPROTO_IPV4,
140 .targetsize = sizeof(struct xt_tproxy_target_info),
141 .checkentry = tproxy_tg_check,
142 .hooks = 1 << NF_INET_PRE_ROUTING,
146 static int __init tproxy_tg_init(void)
148 nf_defrag_ipv4_enable();
149 return xt_register_target(&tproxy_tg_reg);
152 static void __exit tproxy_tg_exit(void)
154 xt_unregister_target(&tproxy_tg_reg);
157 module_init(tproxy_tg_init);
158 module_exit(tproxy_tg_exit);
159 MODULE_LICENSE("GPL");
160 MODULE_AUTHOR("Krisztian Kovacs");
161 MODULE_DESCRIPTION("Netfilter transparent proxy (TPROXY) target module.");
162 MODULE_ALIAS("ipt_TPROXY");