net/bridge/netfilter/ebt_snat.c

   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 xt_target_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 false;
  53
  54         if (tmp < -NUM_STANDARD_TARGETS || tmp >= 0)
  55                 return false;
  56         tmp = info->target | EBT_VERDICT_BITS;
  57         if ((tmp & ~NAT_ARP_BIT) != ~NAT_ARP_BIT)
  58                 return false;
  59         return true;
  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");