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   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 #include <linux/if_arp.h>
  12 #include <net/arp.h>
  13 #include <linux/module.h>
  14 #include <linux/netfilter/x_tables.h>
  15 #include <linux/netfilter_bridge/ebtables.h>
  16 #include <linux/netfilter_bridge/ebt_arpreply.h>
  17
  18 static unsigned int
  19 ebt_arpreply_tg(struct sk_buff *skb, const struct net_device *in,
  20                 const struct net_device *out, unsigned int hook_nr,
  21                 const struct xt_target *target, const void *data)
  22 {
  23         struct ebt_arpreply_info *info = (void *)data;
  24         const __be32 *siptr, *diptr;
  25         __be32 _sip, _dip;
  26         const struct arphdr *ap;
  27         struct arphdr _ah;
  28         const unsigned char *shp;
  29         unsigned char _sha[ETH_ALEN];
  30
  31         ap = skb_header_pointer(skb, 0, sizeof(_ah), &_ah);
  32         if (ap == NULL)
  33                 return EBT_DROP;
  34
  35         if (ap->ar_op != htons(ARPOP_REQUEST) ||
  36             ap->ar_hln != ETH_ALEN ||
  37             ap->ar_pro != htons(ETH_P_IP) ||
  38             ap->ar_pln != 4)
  39                 return EBT_CONTINUE;
  40
  41         shp = skb_header_pointer(skb, sizeof(_ah), ETH_ALEN, &_sha);
  42         if (shp == NULL)
  43                 return EBT_DROP;
  44
  45         siptr = skb_header_pointer(skb, sizeof(_ah) + ETH_ALEN,
  46                                    sizeof(_sip), &_sip);
  47         if (siptr == NULL)
  48                 return EBT_DROP;
  49
  50         diptr = skb_header_pointer(skb,
  51                                    sizeof(_ah) + 2 * ETH_ALEN + sizeof(_sip),
  52                                    sizeof(_dip), &_dip);
  53         if (diptr == NULL)
  54                 return EBT_DROP;
  55
  56         arp_send(ARPOP_REPLY, ETH_P_ARP, *siptr, (struct net_device *)in,
  57                  *diptr, shp, info->mac, shp);
  58
  59         return info->target;
  60 }
  61
  62 static bool
  63 ebt_arpreply_tg_check(const char *tablename, const void *entry,
  64                       const struct xt_target *target, void *data,
  65                       unsigned int hookmask)
  66 {
  67         const struct ebt_arpreply_info *info = data;
  68         const struct ebt_entry *e = entry;
  69
  70         if (BASE_CHAIN && info->target == EBT_RETURN)
  71                 return false;
  72         if (e->ethproto != htons(ETH_P_ARP) ||
  73             e->invflags & EBT_IPROTO)
  74                 return false;
  75         CLEAR_BASE_CHAIN_BIT;
  76         if (strcmp(tablename, "nat") || hookmask & ~(1 << NF_BR_PRE_ROUTING))
  77                 return false;
  78         return true;
  79 }
  80
  81 static struct ebt_target reply_target __read_mostly = {
  82         .name           = EBT_ARPREPLY_TARGET,
  83         .revision       = 0,
  84         .family         = NFPROTO_BRIDGE,
  85         .target         = ebt_arpreply_tg,
  86         .checkentry     = ebt_arpreply_tg_check,
  87         .targetsize     = XT_ALIGN(sizeof(struct ebt_arpreply_info)),
  88         .me             = THIS_MODULE,
  89 };
  90
  91 static int __init ebt_arpreply_init(void)
  92 {
  93         return ebt_register_target(&reply_target);
  94 }
  95
  96 static void __exit ebt_arpreply_fini(void)
  97 {
  98         ebt_unregister_target(&reply_target);
  99 }
 100
 101 module_init(ebt_arpreply_init);
 102 module_exit(ebt_arpreply_fini);
 103 MODULE_DESCRIPTION("Ebtables: ARP reply target");
 104 MODULE_LICENSE("GPL");