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
  11 #include <linux/netfilter_bridge/ebtables.h>
  12 #include <linux/netfilter_bridge/ebt_nat.h>
  13 #include <linux/module.h>
  14 #include <net/sock.h>
  15 #include <linux/if_arp.h>
  16 #include <net/arp.h>
  17
  18 static int ebt_target_snat(struct sk_buff **pskb, unsigned int hooknr,
  19    const struct net_device *in, const struct net_device *out,
  20    const void *data, unsigned int datalen)
  21 {
  22         struct ebt_nat_info *info = (struct ebt_nat_info *) data;
  23
  24         if (skb_shared(*pskb) || skb_cloned(*pskb)) {
  25                 struct sk_buff *nskb;
  26
  27                 nskb = skb_copy(*pskb, GFP_ATOMIC);
  28                 if (!nskb)
  29                         return NF_DROP;
  30                 if ((*pskb)->sk)
  31                         skb_set_owner_w(nskb, (*pskb)->sk);
  32                 kfree_skb(*pskb);
  33                 *pskb = nskb;
  34         }
  35         memcpy(eth_hdr(*pskb)->h_source, info->mac, ETH_ALEN);
  36         if (!(info->target & NAT_ARP_BIT) &&
  37             eth_hdr(*pskb)->h_proto == htons(ETH_P_ARP)) {
  38                 struct arphdr _ah, *ap;
  39
  40                 ap = skb_header_pointer(*pskb, 0, sizeof(_ah), &_ah);
  41                 if (ap == NULL)
  42                         return EBT_DROP;
  43                 if (ap->ar_hln != ETH_ALEN)
  44                         goto out;
  45                 if (skb_store_bits(*pskb, sizeof(_ah), info->mac,ETH_ALEN))
  46                         return EBT_DROP;
  47         }
  48 out:
  49         return info->target | ~EBT_VERDICT_BITS;
  50 }
  51
  52 static int ebt_target_snat_check(const char *tablename, unsigned int hookmask,
  53    const struct ebt_entry *e, void *data, unsigned int datalen)
  54 {
  55         struct ebt_nat_info *info = (struct ebt_nat_info *) data;
  56         int tmp;
  57
  58         if (datalen != EBT_ALIGN(sizeof(struct ebt_nat_info)))
  59                 return -EINVAL;
  60         tmp = info->target | ~EBT_VERDICT_BITS;
  61         if (BASE_CHAIN && tmp == EBT_RETURN)
  62                 return -EINVAL;
  63         CLEAR_BASE_CHAIN_BIT;
  64         if (strcmp(tablename, "nat"))
  65                 return -EINVAL;
  66         if (hookmask & ~(1 << NF_BR_POST_ROUTING))
  67                 return -EINVAL;
  68
  69         if (tmp < -NUM_STANDARD_TARGETS || tmp >= 0)
  70                 return -EINVAL;
  71         tmp = info->target | EBT_VERDICT_BITS;
  72         if ((tmp & ~NAT_ARP_BIT) != ~NAT_ARP_BIT)
  73                 return -EINVAL;
  74         return 0;
  75 }
  76
  77 static struct ebt_target snat =
  78 {
  79         .name           = EBT_SNAT_TARGET,
  80         .target         = ebt_target_snat,
  81         .check          = ebt_target_snat_check,
  82         .me             = THIS_MODULE,
  83 };
  84
  85 static int __init ebt_snat_init(void)
  86 {
  87         return ebt_register_target(&snat);
  88 }
  89
  90 static void __exit ebt_snat_fini(void)
  91 {
  92         ebt_unregister_target(&snat);
  93 }
  94
  95 module_init(ebt_snat_init);
  96 module_exit(ebt_snat_fini);
  97 MODULE_LICENSE("GPL");