net/bridge/netfilter/ebt_arpreply.c

   1 /*
   2  *  ebt_arpreply
   3  *
   4  *      Authors:
   5  *      Grzegorz Borowiak <grzes@gnu.univ.gda.pl>
   6  *      Bart De Schuymer <bdschuym@pandora.be>
   7  *
   8  *  August, 2003
   9  *
  10  */
  11
  12 #include <linux/netfilter_bridge/ebtables.h>
  13 #include <linux/netfilter_bridge/ebt_arpreply.h>
  14 #include <linux/if_arp.h>
  15 #include <net/arp.h>
  16 #include <linux/module.h>
  17
  18 static int ebt_target_reply(struct sk_buff *skb, 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_arpreply_info *info = (void *)data;
  23         const __be32 *siptr, *diptr;
  24         __be32 _sip, _dip;
  25         const struct arphdr *ap;
  26         struct arphdr _ah;
  27         const unsigned char *shp;
  28         unsigned char _sha[ETH_ALEN];
  29
  30         ap = skb_header_pointer(skb, 0, sizeof(_ah), &_ah);
  31         if (ap == NULL)
  32                 return EBT_DROP;
  33
  34         if (ap->ar_op != htons(ARPOP_REQUEST) ||
  35             ap->ar_hln != ETH_ALEN ||
  36             ap->ar_pro != htons(ETH_P_IP) ||
  37             ap->ar_pln != 4)
  38                 return EBT_CONTINUE;
  39
  40         shp = skb_header_pointer(skb, sizeof(_ah), ETH_ALEN, &_sha);
  41         if (shp == NULL)
  42                 return EBT_DROP;
  43
  44         siptr = skb_header_pointer(skb, sizeof(_ah) + ETH_ALEN,
  45                                    sizeof(_sip), &_sip);
  46         if (siptr == NULL)
  47                 return EBT_DROP;
  48
  49         diptr = skb_header_pointer(skb,
  50                                    sizeof(_ah) + 2 * ETH_ALEN + sizeof(_sip),
  51                                    sizeof(_dip), &_dip);
  52         if (diptr == NULL)
  53                 return EBT_DROP;
  54
  55         arp_send(ARPOP_REPLY, ETH_P_ARP, *siptr, (struct net_device *)in,
  56                  *diptr, shp, info->mac, shp);
  57
  58         return info->target;
  59 }
  60
  61 static int ebt_target_reply_check(const char *tablename, unsigned int hookmask,
  62    const struct ebt_entry *e, void *data, unsigned int datalen)
  63 {
  64         const struct ebt_arpreply_info *info = data;
  65
  66         if (datalen != EBT_ALIGN(sizeof(struct ebt_arpreply_info)))
  67                 return -EINVAL;
  68         if (BASE_CHAIN && info->target == EBT_RETURN)
  69                 return -EINVAL;
  70         if (e->ethproto != htons(ETH_P_ARP) ||
  71             e->invflags & EBT_IPROTO)
  72                 return -EINVAL;
  73         CLEAR_BASE_CHAIN_BIT;
  74         if (strcmp(tablename, "nat") || hookmask & ~(1 << NF_BR_PRE_ROUTING))
  75                 return -EINVAL;
  76         return 0;
  77 }
  78
  79 static struct ebt_target reply_target __read_mostly = {
  80         .name           = EBT_ARPREPLY_TARGET,
  81         .target         = ebt_target_reply,
  82         .check          = ebt_target_reply_check,
  83         .me             = THIS_MODULE,
  84 };
  85
  86 static int __init ebt_arpreply_init(void)
  87 {
  88         return ebt_register_target(&reply_target);
  89 }
  90
  91 static void __exit ebt_arpreply_fini(void)
  92 {
  93         ebt_unregister_target(&reply_target);
  94 }
  95
  96 module_init(ebt_arpreply_init);
  97 module_exit(ebt_arpreply_fini);
  98 MODULE_DESCRIPTION("Ebtables: ARP reply target");
  99 MODULE_LICENSE("GPL");