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"); 139