text: /*
   *  ebt_arp
   *
   *	Authors:
   *	Bart De Schuymer <bdschuym@pandora.be>
   *	Tim Gardner <timg@tpi.com>
   *
   *  April, 2002
   *
   */
  #include <linux/if_arp.h>
  #include <linux/if_ether.h>
  #include <linux/module.h>
  #include <linux/netfilter/x_tables.h>
  #include <linux/netfilter_bridge/ebtables.h>
  #include <linux/netfilter_bridge/ebt_arp.h>
  
  static bool
  ebt_arp_mt(const struct sk_buff *skb, const struct xt_match_param *par)
  {
  	const struct ebt_arp_info *info = par->matchinfo;
  	const struct arphdr *ah;
  	struct arphdr _arph;
  
  	ah = skb_header_pointer(skb, 0, sizeof(_arph), &_arph);
  	if (ah == NULL)
  		return false;
  	if (info->bitmask & EBT_ARP_OPCODE && FWINV(info->opcode !=
  	   ah->ar_op, EBT_ARP_OPCODE))
  		return false;
  	if (info->bitmask & EBT_ARP_HTYPE && FWINV(info->htype !=
  	   ah->ar_hrd, EBT_ARP_HTYPE))
  		return false;
  	if (info->bitmask & EBT_ARP_PTYPE && FWINV(info->ptype !=
  	   ah->ar_pro, EBT_ARP_PTYPE))
  		return false;
  
  	if (info->bitmask & (EBT_ARP_SRC_IP | EBT_ARP_DST_IP | EBT_ARP_GRAT)) {
  		const __be32 *sap, *dap;
  		__be32 saddr, daddr;
  
  		if (ah->ar_pln != sizeof(__be32) || ah->ar_pro != htons(ETH_P_IP))
  			return false;
  		sap = skb_header_pointer(skb, sizeof(struct arphdr) +
  					ah->ar_hln, sizeof(saddr),
  					&saddr);
  		if (sap == NULL)
  			return false;
  		dap = skb_header_pointer(skb, sizeof(struct arphdr) +
  					2*ah->ar_hln+sizeof(saddr),
  					sizeof(daddr), &daddr);
  		if (dap == NULL)
  			return false;
  		if (info->bitmask & EBT_ARP_SRC_IP &&
  		    FWINV(info->saddr != (*sap & info->smsk), EBT_ARP_SRC_IP))
  			return false;
  		if (info->bitmask & EBT_ARP_DST_IP &&
  		    FWINV(info->daddr != (*dap & info->dmsk), EBT_ARP_DST_IP))
  			return false;
  		if (info->bitmask & EBT_ARP_GRAT &&
  		    FWINV(*dap != *sap, EBT_ARP_GRAT))
  			return false;
  	}
  
  	if (info->bitmask & (EBT_ARP_SRC_MAC | EBT_ARP_DST_MAC)) {
  		const unsigned char *mp;
  		unsigned char _mac[ETH_ALEN];
  		uint8_t verdict, i;
  
  		if (ah->ar_hln != ETH_ALEN || ah->ar_hrd != htons(ARPHRD_ETHER))
  			return false;
  		if (info->bitmask & EBT_ARP_SRC_MAC) {
  			mp = skb_header_pointer(skb, sizeof(struct arphdr),
  						sizeof(_mac), &_mac);
  			if (mp == NULL)
  				return false;
  			verdict = 0;
  			for (i = 0; i < 6; i++)
  				verdict |= (mp[i] ^ info->smaddr[i]) &
  				       info->smmsk[i];
  			if (FWINV(verdict != 0, EBT_ARP_SRC_MAC))
  				return false;
  		}
  
  		if (info->bitmask & EBT_ARP_DST_MAC) {
  			mp = skb_header_pointer(skb, sizeof(struct arphdr) +
  						ah->ar_hln + ah->ar_pln,
  						sizeof(_mac), &_mac);
  			if (mp == NULL)
  				return false;
  			verdict = 0;
  			for (i = 0; i < 6; i++)
  				verdict |= (mp[i] ^ info->dmaddr[i]) &
  					info->dmmsk[i];
  			if (FWINV(verdict != 0, EBT_ARP_DST_MAC))
  				return false;
  		}
  	}
  
  	return true;
  }
  
  static bool ebt_arp_mt_check(const struct xt_mtchk_param *par)
  {
  	const struct ebt_arp_info *info = par->matchinfo;
  	const struct ebt_entry *e = par->entryinfo;
  
  	if ((e->ethproto != htons(ETH_P_ARP) &&
  	   e->ethproto != htons(ETH_P_RARP)) ||
  	   e->invflags & EBT_IPROTO)
  		return false;
  	if (info->bitmask & ~EBT_ARP_MASK || info->invflags & ~EBT_ARP_MASK)
  		return false;
  	return true;
  }
  
  static struct xt_match ebt_arp_mt_reg __read_mostly = {
  	.name		= "arp",
  	.revision	= 0,
  	.family		= NFPROTO_BRIDGE,
  	.match		= ebt_arp_mt,
  	.checkentry	= ebt_arp_mt_check,
  	.matchsize	= XT_ALIGN(sizeof(struct ebt_arp_info)),
  	.me		= THIS_MODULE,
  };
  
  static int __init ebt_arp_init(void)
  {
  	return xt_register_match(&ebt_arp_mt_reg);
  }
  
  static void __exit ebt_arp_fini(void)
  {
  	xt_unregister_match(&ebt_arp_mt_reg);
  }
  
  module_init(ebt_arp_init);
  module_exit(ebt_arp_fini);
  MODULE_DESCRIPTION("Ebtables: ARP protocol packet match");
  MODULE_LICENSE("GPL");
  