1 /* NETMAP - static NAT mapping of IP network addresses (1:1).
2 * The mapping can be applied to source (POSTROUTING),
3 * destination (PREROUTING), or both (with separate rules).
4 */
5
6 /* (C) 2000-2001 Svenning Soerensen <svenning@post5.tele.dk>
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License version 2 as
10 * published by the Free Software Foundation.
11 */
12
13 #include <linux/ip.h>
14 #include <linux/module.h>
15 #include <linux/netdevice.h>
16 #include <linux/netfilter.h>
17 #include <linux/netfilter_ipv4.h>
18 #include <linux/netfilter/x_tables.h>
19 #include <net/netfilter/nf_nat_rule.h>
20
21 MODULE_LICENSE("GPL");
22 MODULE_AUTHOR("Svenning Soerensen <svenning@post5.tele.dk>");
23 MODULE_DESCRIPTION("Xtables: 1:1 NAT mapping of IPv4 subnets");
24
25 static bool
26 netmap_tg_check(const char *tablename, const void *e,
27 const struct xt_target *target, void *targinfo,
28 unsigned int hook_mask)
29 {
30 const struct nf_nat_multi_range_compat *mr = targinfo;
31
32 if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
33 pr_debug("NETMAP:check: bad MAP_IPS.\n");
34 return false;
35 }
36 if (mr->rangesize != 1) {
37 pr_debug("NETMAP:check: bad rangesize %u.\n", mr->rangesize);
38 return false;
39 }
40 return true;
41 }
42
43 static unsigned int
44 netmap_tg(struct sk_buff *skb, const struct net_device *in,
45 const struct net_device *out, unsigned int hooknum,
46 const struct xt_target *target, const void *targinfo)
47 {
48 struct nf_conn *ct;
49 enum ip_conntrack_info ctinfo;
50 __be32 new_ip, netmask;
51 const struct nf_nat_multi_range_compat *mr = targinfo;
52 struct nf_nat_range newrange;
53
54 NF_CT_ASSERT(hooknum == NF_INET_PRE_ROUTING
55 || hooknum == NF_INET_POST_ROUTING
56 || hooknum == NF_INET_LOCAL_OUT);
57 ct = nf_ct_get(skb, &ctinfo);
58
59 netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
60
61 if (hooknum == NF_INET_PRE_ROUTING || hooknum == NF_INET_LOCAL_OUT)
62 new_ip = ip_hdr(skb)->daddr & ~netmask;
63 else
64 new_ip = ip_hdr(skb)->saddr & ~netmask;
65 new_ip |= mr->range[0].min_ip & netmask;
66
67 newrange = ((struct nf_nat_range)
68 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
69 new_ip, new_ip,
70 mr->range[0].min, mr->range[0].max });
71
72 /* Hand modified range to generic setup. */
73 return nf_nat_setup_info(ct, &newrange, HOOK2MANIP(hooknum));
74 }
75
76 static struct xt_target netmap_tg_reg __read_mostly = {
77 .name = "NETMAP",
78 .family = AF_INET,
79 .target = netmap_tg,
80 .targetsize = sizeof(struct nf_nat_multi_range_compat),
81 .table = "nat",
82 .hooks = (1 << NF_INET_PRE_ROUTING) |
83 (1 << NF_INET_POST_ROUTING) |
84 (1 << NF_INET_LOCAL_OUT),
85 .checkentry = netmap_tg_check,
86 .me = THIS_MODULE
87 };
88
89 static int __init netmap_tg_init(void)
90 {
91 return xt_register_target(&netmap_tg_reg);
92 }
93
94 static void __exit netmap_tg_exit(void)
95 {
96 xt_unregister_target(&netmap_tg_reg);
97 }
98
99 module_init(netmap_tg_init);
100 module_exit(netmap_tg_exit);
101
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