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   1 /*
   2  *  ebt_snat
   3  *
   4  *      Authors:
   5  *      Bart De Schuymer <bdschuym@pandora.be>
   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>
  17 #include <linux/netfilter_bridge/ebt_nat.h>
  18
  19 static unsigned int
  20 ebt_snat_tg(struct sk_buff *skb, const struct net_device *in,
  21             const struct net_device *out, unsigned int hook_nr,
  22             const struct xt_target *target, const void *data)
  23 {
  24         const struct ebt_nat_info *info = data;
  25
  26         if (!skb_make_writable(skb, 0))
  27                 return EBT_DROP;
  28
  29         memcpy(eth_hdr(skb)->h_source, info->mac, ETH_ALEN);
  30         if (!(info->target & NAT_ARP_BIT) &&
  31             eth_hdr(skb)->h_proto == htons(ETH_P_ARP)) {
  32                 const struct arphdr *ap;
  33                 struct arphdr _ah;
  34
  35                 ap = skb_header_pointer(skb, 0, sizeof(_ah), &_ah);
  36                 if (ap == NULL)
  37                         return EBT_DROP;
  38                 if (ap->ar_hln != ETH_ALEN)
  39                         goto out;
  40                 if (skb_store_bits(skb, sizeof(_ah), info->mac,ETH_ALEN))
  41                         return EBT_DROP;
  42         }
  43 out:
  44         return info->target | ~EBT_VERDICT_BITS;
  45 }
  46
  47 static bool
  48 ebt_snat_tg_check(const char *tablename, const void *e,
  49                   const struct xt_target *target, void *data,
  50                   unsigned int hookmask)
  51 {
  52         const struct ebt_nat_info *info = data;
  53         int tmp;
  54
  55         tmp = info->target | ~EBT_VERDICT_BITS;
  56         if (BASE_CHAIN && tmp == EBT_RETURN)
  57                 return false;
  58         CLEAR_BASE_CHAIN_BIT;
  59
  60         if (tmp < -NUM_STANDARD_TARGETS || tmp >= 0)
  61                 return false;
  62         tmp = info->target | EBT_VERDICT_BITS;
  63         if ((tmp & ~NAT_ARP_BIT) != ~NAT_ARP_BIT)
  64                 return false;
  65         return true;
  66 }
  67
  68 static struct xt_target ebt_snat_tg_reg __read_mostly = {
  69         .name           = "snat",
  70         .revision       = 0,
  71         .family         = NFPROTO_BRIDGE,
  72         .table          = "nat",
  73         .hooks          = (1 << NF_BR_NUMHOOKS) | (1 << NF_BR_POST_ROUTING),
  74         .target         = ebt_snat_tg,
  75         .checkentry     = ebt_snat_tg_check,
  76         .targetsize     = XT_ALIGN(sizeof(struct ebt_nat_info)),
  77         .me             = THIS_MODULE,
  78 };
  79
  80 static int __init ebt_snat_init(void)
  81 {
  82         return xt_register_target(&ebt_snat_tg_reg);
  83 }
  84
  85 static void __exit ebt_snat_fini(void)
  86 {
  87         xt_unregister_target(&ebt_snat_tg_reg);
  88 }
  89
  90 module_init(ebt_snat_init);
  91 module_exit(ebt_snat_fini);
  92 MODULE_DESCRIPTION("Ebtables: Source MAC address translation");
  93 MODULE_LICENSE("GPL");