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	struct net_device *out = state->out;
43	unsigned int ret;
44	const struct iphdr *iph;
45	u_int8_t tos;
46	__be32 saddr, daddr;
47	u_int32_t mark;
48	int err;
49
50	/* root is playing with raw sockets. */
51	if (skb->len < sizeof(struct iphdr) ||
52	    ip_hdrlen(skb) < sizeof(struct iphdr))
53		return NF_ACCEPT;
54
55	/* Save things which could affect route */
56	mark = skb->mark;
57	iph = ip_hdr(skb);
58	saddr = iph->saddr;
59	daddr = iph->daddr;
60	tos = iph->tos;
61
62	ret = ipt_do_table(skb, NF_INET_LOCAL_OUT, state,
63			   dev_net(out)->ipv4.iptable_mangle);
64	/* Reroute for ANY change. */
65	if (ret != NF_DROP && ret != NF_STOLEN) {
66		iph = ip_hdr(skb);
67
68		if (iph->saddr != saddr ||
69		    iph->daddr != daddr ||
70		    skb->mark != mark ||
71		    iph->tos != tos) {
72			err = ip_route_me_harder(skb, RTN_UNSPEC);
73			if (err < 0)
74				ret = NF_DROP_ERR(err);
75		}
76	}
77
78	return ret;
79}
80
81/* The work comes in here from netfilter.c. */
82static unsigned int
83iptable_mangle_hook(const struct nf_hook_ops *ops,
84		     struct sk_buff *skb,
85		     const struct nf_hook_state *state)
86{
87	if (ops->hooknum == NF_INET_LOCAL_OUT)
88		return ipt_mangle_out(skb, state);
89	if (ops->hooknum == NF_INET_POST_ROUTING)
90		return ipt_do_table(skb, ops->hooknum, state,
91				    dev_net(state->out)->ipv4.iptable_mangle);
92	/* PREROUTING/INPUT/FORWARD: */
93	return ipt_do_table(skb, ops->hooknum, state,
94			    dev_net(state->in)->ipv4.iptable_mangle);
95}
96
97static struct nf_hook_ops *mangle_ops __read_mostly;
98
99static int __net_init iptable_mangle_net_init(struct net *net)
100{
101	struct ipt_replace *repl;
102
103	repl = ipt_alloc_initial_table(&packet_mangler);
104	if (repl == NULL)
105		return -ENOMEM;
106	net->ipv4.iptable_mangle =
107		ipt_register_table(net, &packet_mangler, repl);
108	kfree(repl);
109	return PTR_ERR_OR_ZERO(net->ipv4.iptable_mangle);
110}
111
112static void __net_exit iptable_mangle_net_exit(struct net *net)
113{
114	ipt_unregister_table(net, net->ipv4.iptable_mangle);
115}
116
117static struct pernet_operations iptable_mangle_net_ops = {
118	.init = iptable_mangle_net_init,
119	.exit = iptable_mangle_net_exit,
120};
121
122static int __init iptable_mangle_init(void)
123{
124	int ret;
125
126	ret = register_pernet_subsys(&iptable_mangle_net_ops);
127	if (ret < 0)
128		return ret;
129
130	/* Register hooks */
131	mangle_ops = xt_hook_link(&packet_mangler, iptable_mangle_hook);
132	if (IS_ERR(mangle_ops)) {
133		ret = PTR_ERR(mangle_ops);
134		unregister_pernet_subsys(&iptable_mangle_net_ops);
135	}
136
137	return ret;
138}
139
140static void __exit iptable_mangle_fini(void)
141{
142	xt_hook_unlink(&packet_mangler, mangle_ops);
143	unregister_pernet_subsys(&iptable_mangle_net_ops);
144}
145
146module_init(iptable_mangle_init);
147module_exit(iptable_mangle_fini);
148