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 int __net_init iptable_mangle_table_init(struct net *net);
29 
30 static const struct xt_table packet_mangler = {
31 	.name		= "mangle",
32 	.valid_hooks	= MANGLE_VALID_HOOKS,
33 	.me		= THIS_MODULE,
34 	.af		= NFPROTO_IPV4,
35 	.priority	= NF_IP_PRI_MANGLE,
36 	.table_init	= iptable_mangle_table_init,
37 };
38 
39 static unsigned int
40 ipt_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 	/* Save things which could affect route */
50 	mark = skb->mark;
51 	iph = ip_hdr(skb);
52 	saddr = iph->saddr;
53 	daddr = iph->daddr;
54 	tos = iph->tos;
55 
56 	ret = ipt_do_table(skb, state, state->net->ipv4.iptable_mangle);
57 	/* Reroute for ANY change. */
58 	if (ret != NF_DROP && ret != NF_STOLEN) {
59 		iph = ip_hdr(skb);
60 
61 		if (iph->saddr != saddr ||
62 		    iph->daddr != daddr ||
63 		    skb->mark != mark ||
64 		    iph->tos != tos) {
65 			err = ip_route_me_harder(state->net, state->sk, skb, RTN_UNSPEC);
66 			if (err < 0)
67 				ret = NF_DROP_ERR(err);
68 		}
69 	}
70 
71 	return ret;
72 }
73 
74 /* The work comes in here from netfilter.c. */
75 static unsigned int
76 iptable_mangle_hook(void *priv,
77 		     struct sk_buff *skb,
78 		     const struct nf_hook_state *state)
79 {
80 	if (state->hook == NF_INET_LOCAL_OUT)
81 		return ipt_mangle_out(skb, state);
82 	return ipt_do_table(skb, state, state->net->ipv4.iptable_mangle);
83 }
84 
85 static struct nf_hook_ops *mangle_ops __read_mostly;
86 static int __net_init iptable_mangle_table_init(struct net *net)
87 {
88 	struct ipt_replace *repl;
89 	int ret;
90 
91 	if (net->ipv4.iptable_mangle)
92 		return 0;
93 
94 	repl = ipt_alloc_initial_table(&packet_mangler);
95 	if (repl == NULL)
96 		return -ENOMEM;
97 	ret = ipt_register_table(net, &packet_mangler, repl, mangle_ops,
98 				 &net->ipv4.iptable_mangle);
99 	kfree(repl);
100 	return ret;
101 }
102 
103 static void __net_exit iptable_mangle_net_pre_exit(struct net *net)
104 {
105 	if (net->ipv4.iptable_mangle)
106 		ipt_unregister_table_pre_exit(net, net->ipv4.iptable_mangle,
107 					      mangle_ops);
108 }
109 
110 static void __net_exit iptable_mangle_net_exit(struct net *net)
111 {
112 	if (!net->ipv4.iptable_mangle)
113 		return;
114 	ipt_unregister_table_exit(net, net->ipv4.iptable_mangle);
115 	net->ipv4.iptable_mangle = NULL;
116 }
117 
118 static struct pernet_operations iptable_mangle_net_ops = {
119 	.pre_exit = iptable_mangle_net_pre_exit,
120 	.exit = iptable_mangle_net_exit,
121 };
122 
123 static int __init iptable_mangle_init(void)
124 {
125 	int ret;
126 
127 	mangle_ops = xt_hook_ops_alloc(&packet_mangler, iptable_mangle_hook);
128 	if (IS_ERR(mangle_ops)) {
129 		ret = PTR_ERR(mangle_ops);
130 		return ret;
131 	}
132 
133 	ret = register_pernet_subsys(&iptable_mangle_net_ops);
134 	if (ret < 0) {
135 		kfree(mangle_ops);
136 		return ret;
137 	}
138 
139 	ret = iptable_mangle_table_init(&init_net);
140 	if (ret) {
141 		unregister_pernet_subsys(&iptable_mangle_net_ops);
142 		kfree(mangle_ops);
143 	}
144 
145 	return ret;
146 }
147 
148 static void __exit iptable_mangle_fini(void)
149 {
150 	unregister_pernet_subsys(&iptable_mangle_net_ops);
151 	kfree(mangle_ops);
152 }
153 
154 module_init(iptable_mangle_init);
155 module_exit(iptable_mangle_fini);
156