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   1 /*
   2  *  ebt_arp
   3  *
   4  *      Authors:
   5  *      Bart De Schuymer <bdschuym@pandora.be>
   6  *      Tim Gardner <timg@tpi.com>
   7  *
   8  *  April, 2002
   9  *
  10  */
  11 #include <linux/if_arp.h>
  12 #include <linux/if_ether.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_arp.h>
  17
  18 static bool
  19 ebt_arp_mt(const struct sk_buff *skb, const struct net_device *in,
  20            const struct net_device *out, const struct xt_match *match,
  21            const void *data, int offset, unsigned int protoff, bool *hotdrop)
  22 {
  23         const struct ebt_arp_info *info = data;
  24         const struct arphdr *ah;
  25         struct arphdr _arph;
  26
  27         ah = skb_header_pointer(skb, 0, sizeof(_arph), &_arph);
  28         if (ah == NULL)
  29                 return false;
  30         if (info->bitmask & EBT_ARP_OPCODE && FWINV(info->opcode !=
  31            ah->ar_op, EBT_ARP_OPCODE))
  32                 return false;
  33         if (info->bitmask & EBT_ARP_HTYPE && FWINV(info->htype !=
  34            ah->ar_hrd, EBT_ARP_HTYPE))
  35                 return false;
  36         if (info->bitmask & EBT_ARP_PTYPE && FWINV(info->ptype !=
  37            ah->ar_pro, EBT_ARP_PTYPE))
  38                 return false;
  39
  40         if (info->bitmask & (EBT_ARP_SRC_IP | EBT_ARP_DST_IP | EBT_ARP_GRAT)) {
  41                 const __be32 *sap, *dap;
  42                 __be32 saddr, daddr;
  43
  44                 if (ah->ar_pln != sizeof(__be32) || ah->ar_pro != htons(ETH_P_IP))
  45                         return false;
  46                 sap = skb_header_pointer(skb, sizeof(struct arphdr) +
  47                                         ah->ar_hln, sizeof(saddr),
  48                                         &saddr);
  49                 if (sap == NULL)
  50                         return false;
  51                 dap = skb_header_pointer(skb, sizeof(struct arphdr) +
  52                                         2*ah->ar_hln+sizeof(saddr),
  53                                         sizeof(daddr), &daddr);
  54                 if (dap == NULL)
  55                         return false;
  56                 if (info->bitmask & EBT_ARP_SRC_IP &&
  57                     FWINV(info->saddr != (*sap & info->smsk), EBT_ARP_SRC_IP))
  58                         return false;
  59                 if (info->bitmask & EBT_ARP_DST_IP &&
  60                     FWINV(info->daddr != (*dap & info->dmsk), EBT_ARP_DST_IP))
  61                         return false;
  62                 if (info->bitmask & EBT_ARP_GRAT &&
  63                     FWINV(*dap != *sap, EBT_ARP_GRAT))
  64                         return false;
  65         }
  66
  67         if (info->bitmask & (EBT_ARP_SRC_MAC | EBT_ARP_DST_MAC)) {
  68                 const unsigned char *mp;
  69                 unsigned char _mac[ETH_ALEN];
  70                 uint8_t verdict, i;
  71
  72                 if (ah->ar_hln != ETH_ALEN || ah->ar_hrd != htons(ARPHRD_ETHER))
  73                         return false;
  74                 if (info->bitmask & EBT_ARP_SRC_MAC) {
  75                         mp = skb_header_pointer(skb, sizeof(struct arphdr),
  76                                                 sizeof(_mac), &_mac);
  77                         if (mp == NULL)
  78                                 return false;
  79                         verdict = 0;
  80                         for (i = 0; i < 6; i++)
  81                                 verdict |= (mp[i] ^ info->smaddr[i]) &
  82                                        info->smmsk[i];
  83                         if (FWINV(verdict != 0, EBT_ARP_SRC_MAC))
  84                                 return false;
  85                 }
  86
  87                 if (info->bitmask & EBT_ARP_DST_MAC) {
  88                         mp = skb_header_pointer(skb, sizeof(struct arphdr) +
  89                                                 ah->ar_hln + ah->ar_pln,
  90                                                 sizeof(_mac), &_mac);
  91                         if (mp == NULL)
  92                                 return false;
  93                         verdict = 0;
  94                         for (i = 0; i < 6; i++)
  95                                 verdict |= (mp[i] ^ info->dmaddr[i]) &
  96                                         info->dmmsk[i];
  97                         if (FWINV(verdict != 0, EBT_ARP_DST_MAC))
  98                                 return false;
  99                 }
 100         }
 101
 102         return true;
 103 }
 104
 105 static bool
 106 ebt_arp_mt_check(const char *table, const void *entry,
 107                  const struct xt_match *match, void *data,
 108                  unsigned int hook_mask)
 109 {
 110         const struct ebt_arp_info *info = data;
 111         const struct ebt_entry *e = entry;
 112
 113         if ((e->ethproto != htons(ETH_P_ARP) &&
 114            e->ethproto != htons(ETH_P_RARP)) ||
 115            e->invflags & EBT_IPROTO)
 116                 return false;
 117         if (info->bitmask & ~EBT_ARP_MASK || info->invflags & ~EBT_ARP_MASK)
 118                 return false;
 119         return true;
 120 }
 121
 122 static struct ebt_match filter_arp __read_mostly = {
 123         .name           = EBT_ARP_MATCH,
 124         .revision       = 0,
 125         .family         = NFPROTO_BRIDGE,
 126         .match          = ebt_arp_mt,
 127         .checkentry     = ebt_arp_mt_check,
 128         .matchsize      = XT_ALIGN(sizeof(struct ebt_arp_info)),
 129         .me             = THIS_MODULE,
 130 };
 131
 132 static int __init ebt_arp_init(void)
 133 {
 134         return ebt_register_match(&filter_arp);
 135 }
 136
 137 static void __exit ebt_arp_fini(void)
 138 {
 139         ebt_unregister_match(&filter_arp);
 140 }
 141
 142 module_init(ebt_arp_init);
 143 module_exit(ebt_arp_fini);
 144 MODULE_DESCRIPTION("Ebtables: ARP protocol packet match");
 145 MODULE_LICENSE("GPL");