1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * This is the 1999 rewrite of IP Firewalling, aiming for kernel 2.3.x.
4  *
5  * Copyright (C) 1999 Paul `Rusty' Russell & Michael J. Neuling
6  * Copyright (C) 2000-2004 Netfilter Core Team <coreteam@netfilter.org>
7  */
8 #include <linux/module.h>
9 #include <linux/netfilter_ipv4/ip_tables.h>
10 #include <linux/netdevice.h>
11 #include <linux/skbuff.h>
12 #include <linux/slab.h>
13 #include <net/sock.h>
14 #include <net/route.h>
15 #include <linux/ip.h>
16 #include <net/ip.h>
17 
18 MODULE_LICENSE("GPL");
19 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
20 MODULE_DESCRIPTION("iptables mangle table");
21 
22 #define MANGLE_VALID_HOOKS ((1 << NF_INET_PRE_ROUTING) | \
23 			    (1 << NF_INET_LOCAL_IN) | \
24 			    (1 << NF_INET_FORWARD) | \
25 			    (1 << NF_INET_LOCAL_OUT) | \
26 			    (1 << NF_INET_POST_ROUTING))
27 
28 static const struct xt_table packet_mangler = {
29 	.name		= "mangle",
30 	.valid_hooks	= MANGLE_VALID_HOOKS,
31 	.me		= THIS_MODULE,
32 	.af		= NFPROTO_IPV4,
33 	.priority	= NF_IP_PRI_MANGLE,
34 };
35 
36 static unsigned int
37 ipt_mangle_out(void *priv, struct sk_buff *skb, const struct nf_hook_state *state)
38 {
39 	unsigned int ret, verdict;
40 	const struct iphdr *iph;
41 	__be32 saddr, daddr;
42 	u32 mark;
43 	int err;
44 	u8 tos;
45 
46 	/* Save things which could affect route */
47 	mark = skb->mark;
48 	iph = ip_hdr(skb);
49 	saddr = iph->saddr;
50 	daddr = iph->daddr;
51 	tos = iph->tos;
52 
53 	ret = ipt_do_table(priv, skb, state);
54 	verdict = ret & NF_VERDICT_MASK;
55 	/* Reroute for ANY change. */
56 	if (verdict != NF_DROP && verdict != NF_STOLEN) {
57 		iph = ip_hdr(skb);
58 
59 		if (iph->saddr != saddr ||
60 		    iph->daddr != daddr ||
61 		    skb->mark != mark ||
62 		    iph->tos != tos) {
63 			err = ip_route_me_harder(state->net, state->sk, skb, RTN_UNSPEC);
64 			if (err < 0)
65 				ret = NF_DROP_ERR(err);
66 		}
67 	}
68 
69 	return ret;
70 }
71 
72 /* The work comes in here from netfilter.c. */
73 static unsigned int
74 iptable_mangle_hook(void *priv,
75 		     struct sk_buff *skb,
76 		     const struct nf_hook_state *state)
77 {
78 	if (state->hook == NF_INET_LOCAL_OUT)
79 		return ipt_mangle_out(priv, skb, state);
80 	return ipt_do_table(priv, skb, state);
81 }
82 
83 static struct nf_hook_ops *mangle_ops __read_mostly;
84 static int iptable_mangle_table_init(struct net *net)
85 {
86 	struct ipt_replace *repl;
87 	int ret;
88 
89 	repl = ipt_alloc_initial_table(&packet_mangler);
90 	if (repl == NULL)
91 		return -ENOMEM;
92 	ret = ipt_register_table(net, &packet_mangler, repl, mangle_ops);
93 	kfree(repl);
94 	return ret;
95 }
96 
97 static void __net_exit iptable_mangle_net_pre_exit(struct net *net)
98 {
99 	ipt_unregister_table_pre_exit(net, "mangle");
100 }
101 
102 static void __net_exit iptable_mangle_net_exit(struct net *net)
103 {
104 	ipt_unregister_table_exit(net, "mangle");
105 }
106 
107 static struct pernet_operations iptable_mangle_net_ops = {
108 	.pre_exit = iptable_mangle_net_pre_exit,
109 	.exit = iptable_mangle_net_exit,
110 };
111 
112 static int __init iptable_mangle_init(void)
113 {
114 	int ret = xt_register_template(&packet_mangler,
115 				       iptable_mangle_table_init);
116 	if (ret < 0)
117 		return ret;
118 
119 	mangle_ops = xt_hook_ops_alloc(&packet_mangler, iptable_mangle_hook);
120 	if (IS_ERR(mangle_ops)) {
121 		xt_unregister_template(&packet_mangler);
122 		ret = PTR_ERR(mangle_ops);
123 		return ret;
124 	}
125 
126 	ret = register_pernet_subsys(&iptable_mangle_net_ops);
127 	if (ret < 0) {
128 		xt_unregister_template(&packet_mangler);
129 		kfree(mangle_ops);
130 		return ret;
131 	}
132 
133 	return ret;
134 }
135 
136 static void __exit iptable_mangle_fini(void)
137 {
138 	unregister_pernet_subsys(&iptable_mangle_net_ops);
139 	xt_unregister_template(&packet_mangler);
140 	kfree(mangle_ops);
141 }
142 
143 module_init(iptable_mangle_init);
144 module_exit(iptable_mangle_fini);
145