net/bridge/netfilter/ebt_arpreply.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  ebt_arpreply
   4  *
   5  *      Authors:
   6  *      Grzegorz Borowiak <grzes@gnu.univ.gda.pl>
   7  *      Bart De Schuymer <bdschuym@pandora.be>
   8  *
   9  *  August, 2003
  10  *
  11  */
  12 #include <linux/if_arp.h>
  13 #include <net/arp.h>
  14 #include <linux/module.h>
  15 #include <linux/netfilter/x_tables.h>
  16 #include <linux/netfilter_bridge/ebtables.h>
  17 #include <linux/netfilter_bridge/ebt_arpreply.h>
  18
  19 static unsigned int
  20 ebt_arpreply_tg(struct sk_buff *skb, const struct xt_action_param *par)
  21 {
  22         const struct ebt_arpreply_info *info = par->targinfo;
  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,
  56                  (struct net_device *)xt_in(par),
  57                  *diptr, shp, info->mac, shp);
  58
  59         return info->target;
  60 }
  61
  62 static int ebt_arpreply_tg_check(const struct xt_tgchk_param *par)
  63 {
  64         const struct ebt_arpreply_info *info = par->targinfo;
  65         const struct ebt_entry *e = par->entryinfo;
  66
  67         if (BASE_CHAIN && info->target == EBT_RETURN)
  68                 return -EINVAL;
  69         if (e->ethproto != htons(ETH_P_ARP) ||
  70             e->invflags & EBT_IPROTO)
  71                 return -EINVAL;
  72         if (ebt_invalid_target(info->target))
  73                 return -EINVAL;
  74
  75         return 0;
  76 }
  77
  78 static struct xt_target ebt_arpreply_tg_reg __read_mostly = {
  79         .name           = "arpreply",
  80         .revision       = 0,
  81         .family         = NFPROTO_BRIDGE,
  82         .table          = "nat",
  83         .hooks          = (1 << NF_BR_NUMHOOKS) | (1 << NF_BR_PRE_ROUTING),
  84         .target         = ebt_arpreply_tg,
  85         .checkentry     = ebt_arpreply_tg_check,
  86         .targetsize     = sizeof(struct ebt_arpreply_info),
  87         .me             = THIS_MODULE,
  88 };
  89
  90 static int __init ebt_arpreply_init(void)
  91 {
  92         return xt_register_target(&ebt_arpreply_tg_reg);
  93 }
  94
  95 static void __exit ebt_arpreply_fini(void)
  96 {
  97         xt_unregister_target(&ebt_arpreply_tg_reg);
  98 }
  99
 100 module_init(ebt_arpreply_init);
 101 module_exit(ebt_arpreply_fini);
 102 MODULE_DESCRIPTION("Ebtables: ARP reply target");
 103 MODULE_LICENSE("GPL");