net/bridge/netfilter/ebt_arp.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  ebt_arp
   4  *
   5  *      Authors:
   6  *      Bart De Schuymer <bdschuym@pandora.be>
   7  *      Tim Gardner <timg@tpi.com>
   8  *
   9  *  April, 2002
  10  *
  11  */
  12 #include <linux/if_arp.h>
  13 #include <linux/if_ether.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_arp.h>
  18
  19 static bool
  20 ebt_arp_mt(const struct sk_buff *skb, struct xt_action_param *par)
  21 {
  22         const struct ebt_arp_info *info = par->matchinfo;
  23         const struct arphdr *ah;
  24         struct arphdr _arph;
  25
  26         ah = skb_header_pointer(skb, 0, sizeof(_arph), &_arph);
  27         if (ah == NULL)
  28                 return false;
  29         if ((info->bitmask & EBT_ARP_OPCODE) &&
  30             NF_INVF(info, EBT_ARP_OPCODE, info->opcode != ah->ar_op))
  31                 return false;
  32         if ((info->bitmask & EBT_ARP_HTYPE) &&
  33             NF_INVF(info, EBT_ARP_HTYPE, info->htype != ah->ar_hrd))
  34                 return false;
  35         if ((info->bitmask & EBT_ARP_PTYPE) &&
  36             NF_INVF(info, EBT_ARP_PTYPE, info->ptype != ah->ar_pro))
  37                 return false;
  38
  39         if (info->bitmask & (EBT_ARP_SRC_IP | EBT_ARP_DST_IP | EBT_ARP_GRAT)) {
  40                 const __be32 *sap, *dap;
  41                 __be32 saddr, daddr;
  42
  43                 if (ah->ar_pln != sizeof(__be32) || ah->ar_pro != htons(ETH_P_IP))
  44                         return false;
  45                 sap = skb_header_pointer(skb, sizeof(struct arphdr) +
  46                                         ah->ar_hln, sizeof(saddr),
  47                                         &saddr);
  48                 if (sap == NULL)
  49                         return false;
  50                 dap = skb_header_pointer(skb, sizeof(struct arphdr) +
  51                                         2*ah->ar_hln+sizeof(saddr),
  52                                         sizeof(daddr), &daddr);
  53                 if (dap == NULL)
  54                         return false;
  55                 if ((info->bitmask & EBT_ARP_SRC_IP) &&
  56                     NF_INVF(info, EBT_ARP_SRC_IP,
  57                             info->saddr != (*sap & info->smsk)))
  58                         return false;
  59                 if ((info->bitmask & EBT_ARP_DST_IP) &&
  60                     NF_INVF(info, EBT_ARP_DST_IP,
  61                             info->daddr != (*dap & info->dmsk)))
  62                         return false;
  63                 if ((info->bitmask & EBT_ARP_GRAT) &&
  64                     NF_INVF(info, EBT_ARP_GRAT, *dap != *sap))
  65                         return false;
  66         }
  67
  68         if (info->bitmask & (EBT_ARP_SRC_MAC | EBT_ARP_DST_MAC)) {
  69                 const unsigned char *mp;
  70                 unsigned char _mac[ETH_ALEN];
  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                         if (NF_INVF(info, EBT_ARP_SRC_MAC,
  80                                     !ether_addr_equal_masked(mp, info->smaddr,
  81                                                              info->smmsk)))
  82                                 return false;
  83                 }
  84
  85                 if (info->bitmask & EBT_ARP_DST_MAC) {
  86                         mp = skb_header_pointer(skb, sizeof(struct arphdr) +
  87                                                 ah->ar_hln + ah->ar_pln,
  88                                                 sizeof(_mac), &_mac);
  89                         if (mp == NULL)
  90                                 return false;
  91                         if (NF_INVF(info, EBT_ARP_DST_MAC,
  92                                     !ether_addr_equal_masked(mp, info->dmaddr,
  93                                                              info->dmmsk)))
  94                                 return false;
  95                 }
  96         }
  97
  98         return true;
  99 }
 100
 101 static int ebt_arp_mt_check(const struct xt_mtchk_param *par)
 102 {
 103         const struct ebt_arp_info *info = par->matchinfo;
 104         const struct ebt_entry *e = par->entryinfo;
 105
 106         if ((e->ethproto != htons(ETH_P_ARP) &&
 107            e->ethproto != htons(ETH_P_RARP)) ||
 108            e->invflags & EBT_IPROTO)
 109                 return -EINVAL;
 110         if (info->bitmask & ~EBT_ARP_MASK || info->invflags & ~EBT_ARP_MASK)
 111                 return -EINVAL;
 112         return 0;
 113 }
 114
 115 static struct xt_match ebt_arp_mt_reg __read_mostly = {
 116         .name           = "arp",
 117         .revision       = 0,
 118         .family         = NFPROTO_BRIDGE,
 119         .match          = ebt_arp_mt,
 120         .checkentry     = ebt_arp_mt_check,
 121         .matchsize      = sizeof(struct ebt_arp_info),
 122         .me             = THIS_MODULE,
 123 };
 124
 125 static int __init ebt_arp_init(void)
 126 {
 127         return xt_register_match(&ebt_arp_mt_reg);
 128 }
 129
 130 static void __exit ebt_arp_fini(void)
 131 {
 132         xt_unregister_match(&ebt_arp_mt_reg);
 133 }
 134
 135 module_init(ebt_arp_init);
 136 module_exit(ebt_arp_fini);
 137 MODULE_DESCRIPTION("Ebtables: ARP protocol packet match");
 138 MODULE_LICENSE("GPL");