// SPDX-License-Identifier: GPL-2.0-only
/*
 *  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, struct xt_action_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) &&
            NF_INVF(info, EBT_ARP_OPCODE, info->opcode != ah->ar_op))
                return false;
        if ((info->bitmask & EBT_ARP_HTYPE) &&
            NF_INVF(info, EBT_ARP_HTYPE, info->htype != ah->ar_hrd))
                return false;
        if ((info->bitmask & EBT_ARP_PTYPE) &&
            NF_INVF(info, EBT_ARP_PTYPE, info->ptype != ah->ar_pro))
                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) &&
                    NF_INVF(info, EBT_ARP_SRC_IP,
                            info->saddr != (*sap & info->smsk)))
                        return false;
                if ((info->bitmask & EBT_ARP_DST_IP) &&
                    NF_INVF(info, EBT_ARP_DST_IP,
                            info->daddr != (*dap & info->dmsk)))
                        return false;
                if ((info->bitmask & EBT_ARP_GRAT) &&
                    NF_INVF(info, EBT_ARP_GRAT, *dap != *sap))
                        return false;
        }

        if (info->bitmask & (EBT_ARP_SRC_MAC | EBT_ARP_DST_MAC)) {
                const unsigned char *mp;
                unsigned char _mac[ETH_ALEN];

                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;
                        if (NF_INVF(info, EBT_ARP_SRC_MAC,
                                    !ether_addr_equal_masked(mp, info->smaddr,
                                                             info->smmsk)))
                                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;
                        if (NF_INVF(info, EBT_ARP_DST_MAC,
                                    !ether_addr_equal_masked(mp, info->dmaddr,
                                                             info->dmmsk)))
                                return false;
                }
        }

        return true;
}

static int 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 -EINVAL;
        if (info->bitmask & ~EBT_ARP_MASK || info->invflags & ~EBT_ARP_MASK)
                return -EINVAL;
        return 0;
}

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      = 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");