Linux Kernel  3.7.1
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ebt_snat.c
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1 /*
2  * ebt_snat
3  *
4  * Authors:
5  * Bart De Schuymer <[email protected]>
6  *
7  * June, 2002
8  *
9  */
10 #include <linux/module.h>
11 #include <net/sock.h>
12 #include <linux/if_arp.h>
13 #include <net/arp.h>
14 #include <linux/netfilter.h>
15 #include <linux/netfilter/x_tables.h>
16 #include <linux/netfilter_bridge/ebtables.h>
18 
19 static unsigned int
20 ebt_snat_tg(struct sk_buff *skb, const struct xt_action_param *par)
21 {
22  const struct ebt_nat_info *info = par->targinfo;
23 
24  if (!skb_make_writable(skb, 0))
25  return EBT_DROP;
26 
27  memcpy(eth_hdr(skb)->h_source, info->mac, ETH_ALEN);
28  if (!(info->target & NAT_ARP_BIT) &&
29  eth_hdr(skb)->h_proto == htons(ETH_P_ARP)) {
30  const struct arphdr *ap;
31  struct arphdr _ah;
32 
33  ap = skb_header_pointer(skb, 0, sizeof(_ah), &_ah);
34  if (ap == NULL)
35  return EBT_DROP;
36  if (ap->ar_hln != ETH_ALEN)
37  goto out;
38  if (skb_store_bits(skb, sizeof(_ah), info->mac,ETH_ALEN))
39  return EBT_DROP;
40  }
41 out:
42  return info->target | ~EBT_VERDICT_BITS;
43 }
44 
45 static int ebt_snat_tg_check(const struct xt_tgchk_param *par)
46 {
47  const struct ebt_nat_info *info = par->targinfo;
48  int tmp;
49 
50  tmp = info->target | ~EBT_VERDICT_BITS;
51  if (BASE_CHAIN && tmp == EBT_RETURN)
52  return -EINVAL;
53 
54  if (tmp < -NUM_STANDARD_TARGETS || tmp >= 0)
55  return -EINVAL;
56  tmp = info->target | EBT_VERDICT_BITS;
57  if ((tmp & ~NAT_ARP_BIT) != ~NAT_ARP_BIT)
58  return -EINVAL;
59  return 0;
60 }
61 
62 static struct xt_target ebt_snat_tg_reg __read_mostly = {
63  .name = "snat",
64  .revision = 0,
65  .family = NFPROTO_BRIDGE,
66  .table = "nat",
67  .hooks = (1 << NF_BR_NUMHOOKS) | (1 << NF_BR_POST_ROUTING),
68  .target = ebt_snat_tg,
69  .checkentry = ebt_snat_tg_check,
70  .targetsize = sizeof(struct ebt_nat_info),
71  .me = THIS_MODULE,
72 };
73 
74 static int __init ebt_snat_init(void)
75 {
76  return xt_register_target(&ebt_snat_tg_reg);
77 }
78 
79 static void __exit ebt_snat_fini(void)
80 {
81  xt_unregister_target(&ebt_snat_tg_reg);
82 }
83 
84 module_init(ebt_snat_init);
85 module_exit(ebt_snat_fini);
86 MODULE_DESCRIPTION("Ebtables: Source MAC address translation");
87 MODULE_LICENSE("GPL");