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 
21 MODULE_LICENSE("GPL");
22 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
23 MODULE_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 
31 static int __net_init iptable_mangle_table_init(struct net *net);
32 
33 static const struct xt_table packet_mangler = {
34 	.name		= "mangle",
35 	.valid_hooks	= MANGLE_VALID_HOOKS,
36 	.me		= THIS_MODULE,
37 	.af		= NFPROTO_IPV4,
38 	.priority	= NF_IP_PRI_MANGLE,
39 	.table_init	= iptable_mangle_table_init,
40 };
41 
42 static unsigned int
43 ipt_mangle_out(struct sk_buff *skb, const struct nf_hook_state *state)
44 {
45 	unsigned int ret;
46 	const struct iphdr *iph;
47 	u_int8_t tos;
48 	__be32 saddr, daddr;
49 	u_int32_t mark;
50 	int err;
51 
52 	/* root is playing with raw sockets. */
53 	if (skb->len < sizeof(struct iphdr) ||
54 	    ip_hdrlen(skb) < sizeof(struct iphdr))
55 		return NF_ACCEPT;
56 
57 	/* Save things which could affect route */
58 	mark = skb->mark;
59 	iph = ip_hdr(skb);
60 	saddr = iph->saddr;
61 	daddr = iph->daddr;
62 	tos = iph->tos;
63 
64 	ret = ipt_do_table(skb, state, state->net->ipv4.iptable_mangle);
65 	/* Reroute for ANY change. */
66 	if (ret != NF_DROP && ret != NF_STOLEN) {
67 		iph = ip_hdr(skb);
68 
69 		if (iph->saddr != saddr ||
70 		    iph->daddr != daddr ||
71 		    skb->mark != mark ||
72 		    iph->tos != tos) {
73 			err = ip_route_me_harder(state->net, skb, RTN_UNSPEC);
74 			if (err < 0)
75 				ret = NF_DROP_ERR(err);
76 		}
77 	}
78 
79 	return ret;
80 }
81 
82 /* The work comes in here from netfilter.c. */
83 static unsigned int
84 iptable_mangle_hook(void *priv,
85 		     struct sk_buff *skb,
86 		     const struct nf_hook_state *state)
87 {
88 	if (state->hook == NF_INET_LOCAL_OUT)
89 		return ipt_mangle_out(skb, state);
90 	if (state->hook == NF_INET_POST_ROUTING)
91 		return ipt_do_table(skb, state,
92 				    state->net->ipv4.iptable_mangle);
93 	/* PREROUTING/INPUT/FORWARD: */
94 	return ipt_do_table(skb, state, state->net->ipv4.iptable_mangle);
95 }
96 
97 static struct nf_hook_ops *mangle_ops __read_mostly;
98 static int __net_init iptable_mangle_table_init(struct net *net)
99 {
100 	struct ipt_replace *repl;
101 	int ret;
102 
103 	if (net->ipv4.iptable_mangle)
104 		return 0;
105 
106 	repl = ipt_alloc_initial_table(&packet_mangler);
107 	if (repl == NULL)
108 		return -ENOMEM;
109 	ret = ipt_register_table(net, &packet_mangler, repl, mangle_ops,
110 				 &net->ipv4.iptable_mangle);
111 	kfree(repl);
112 	return ret;
113 }
114 
115 static void __net_exit iptable_mangle_net_exit(struct net *net)
116 {
117 	if (!net->ipv4.iptable_mangle)
118 		return;
119 	ipt_unregister_table(net, net->ipv4.iptable_mangle, mangle_ops);
120 	net->ipv4.iptable_mangle = NULL;
121 }
122 
123 static struct pernet_operations iptable_mangle_net_ops = {
124 	.exit = iptable_mangle_net_exit,
125 };
126 
127 static int __init iptable_mangle_init(void)
128 {
129 	int ret;
130 
131 	mangle_ops = xt_hook_ops_alloc(&packet_mangler, iptable_mangle_hook);
132 	if (IS_ERR(mangle_ops)) {
133 		ret = PTR_ERR(mangle_ops);
134 		return ret;
135 	}
136 
137 	ret = register_pernet_subsys(&iptable_mangle_net_ops);
138 	if (ret < 0) {
139 		kfree(mangle_ops);
140 		return ret;
141 	}
142 
143 	ret = iptable_mangle_table_init(&init_net);
144 	if (ret) {
145 		unregister_pernet_subsys(&iptable_mangle_net_ops);
146 		kfree(mangle_ops);
147 	}
148 
149 	return ret;
150 }
151 
152 static void __exit iptable_mangle_fini(void)
153 {
154 	unregister_pernet_subsys(&iptable_mangle_net_ops);
155 	kfree(mangle_ops);
156 }
157 
158 module_init(iptable_mangle_init);
159 module_exit(iptable_mangle_fini);
160