1/*
2 * This is the 1999 rewrite of IP Firewalling, aiming for kernel 2.3.x.
3 *
4 * Copyright (C) 1999 Paul `Rusty' Russell & Michael J. Neuling
5 * Copyright (C) 2000-2004 Netfilter Core Team <coreteam@netfilter.org>
6 *
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.
10 */
11#include <linux/module.h>
12#include <linux/netfilter_ipv4/ip_tables.h>
13#include <linux/netdevice.h>
14#include <linux/skbuff.h>
15#include <linux/slab.h>
16#include <net/sock.h>
17#include <net/route.h>
18#include <linux/ip.h>
19#include <net/ip.h>
20
21MODULE_LICENSE("GPL");
22MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
23MODULE_DESCRIPTION("iptables mangle table");
24
25#define MANGLE_VALID_HOOKS ((1 << NF_INET_PRE_ROUTING) | \
26			    (1 << NF_INET_LOCAL_IN) | \
27			    (1 << NF_INET_FORWARD) | \
28			    (1 << NF_INET_LOCAL_OUT) | \
29			    (1 << NF_INET_POST_ROUTING))
30
31static const struct xt_table packet_mangler = {
32	.name		= "mangle",
33	.valid_hooks	= MANGLE_VALID_HOOKS,
34	.me		= THIS_MODULE,
35	.af		= NFPROTO_IPV4,
36	.priority	= NF_IP_PRI_MANGLE,
37};
38
39static unsigned int
40ipt_mangle_out(struct sk_buff *skb, const struct nf_hook_state *state)
41{
42	unsigned int ret;
43	const struct iphdr *iph;
44	u_int8_t tos;
45	__be32 saddr, daddr;
46	u_int32_t mark;
47	int err;
48
49	/* root is playing with raw sockets. */
50	if (skb->len < sizeof(struct iphdr) ||
51	    ip_hdrlen(skb) < sizeof(struct iphdr))
52		return NF_ACCEPT;
53
54	/* Save things which could affect route */
55	mark = skb->mark;
56	iph = ip_hdr(skb);
57	saddr = iph->saddr;
58	daddr = iph->daddr;
59	tos = iph->tos;
60
61	ret = ipt_do_table(skb, state, state->net->ipv4.iptable_mangle);
62	/* Reroute for ANY change. */
63	if (ret != NF_DROP && ret != NF_STOLEN) {
64		iph = ip_hdr(skb);
65
66		if (iph->saddr != saddr ||
67		    iph->daddr != daddr ||
68		    skb->mark != mark ||
69		    iph->tos != tos) {
70			err = ip_route_me_harder(state->net, skb, RTN_UNSPEC);
71			if (err < 0)
72				ret = NF_DROP_ERR(err);
73		}
74	}
75
76	return ret;
77}
78
79/* The work comes in here from netfilter.c. */
80static unsigned int
81iptable_mangle_hook(void *priv,
82		     struct sk_buff *skb,
83		     const struct nf_hook_state *state)
84{
85	if (state->hook == NF_INET_LOCAL_OUT)
86		return ipt_mangle_out(skb, state);
87	if (state->hook == NF_INET_POST_ROUTING)
88		return ipt_do_table(skb, state,
89				    state->net->ipv4.iptable_mangle);
90	/* PREROUTING/INPUT/FORWARD: */
91	return ipt_do_table(skb, state, state->net->ipv4.iptable_mangle);
92}
93
94static struct nf_hook_ops *mangle_ops __read_mostly;
95
96static int __net_init iptable_mangle_net_init(struct net *net)
97{
98	struct ipt_replace *repl;
99
100	repl = ipt_alloc_initial_table(&packet_mangler);
101	if (repl == NULL)
102		return -ENOMEM;
103	net->ipv4.iptable_mangle =
104		ipt_register_table(net, &packet_mangler, repl);
105	kfree(repl);
106	return PTR_ERR_OR_ZERO(net->ipv4.iptable_mangle);
107}
108
109static void __net_exit iptable_mangle_net_exit(struct net *net)
110{
111	ipt_unregister_table(net, net->ipv4.iptable_mangle);
112}
113
114static struct pernet_operations iptable_mangle_net_ops = {
115	.init = iptable_mangle_net_init,
116	.exit = iptable_mangle_net_exit,
117};
118
119static int __init iptable_mangle_init(void)
120{
121	int ret;
122
123	ret = register_pernet_subsys(&iptable_mangle_net_ops);
124	if (ret < 0)
125		return ret;
126
127	/* Register hooks */
128	mangle_ops = xt_hook_link(&packet_mangler, iptable_mangle_hook);
129	if (IS_ERR(mangle_ops)) {
130		ret = PTR_ERR(mangle_ops);
131		unregister_pernet_subsys(&iptable_mangle_net_ops);
132	}
133
134	return ret;
135}
136
137static void __exit iptable_mangle_fini(void)
138{
139	xt_hook_unlink(&packet_mangler, mangle_ops);
140	unregister_pernet_subsys(&iptable_mangle_net_ops);
141}
142
143module_init(iptable_mangle_init);
144module_exit(iptable_mangle_fini);
145