ebt_among.c

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/*
 *  ebt_among
 *
 *  Authors:
 *  Grzegorz Borowiak <[email protected]>
 *
 *  August, 2003
 *
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/ip.h>
#include <linux/if_arp.h>
#include <linux/module.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_bridge/ebtables.h>
#include <linux/netfilter_bridge/ebt_among.h>

static bool ebt_mac_wormhash_contains(const struct ebt_mac_wormhash *wh,
                      const char *mac, __be32 ip)
{
    /* You may be puzzled as to how this code works.
     * Some tricks were used, refer to
     *  include/linux/netfilter_bridge/ebt_among.h
     * as there you can find a solution of this mystery.
     */
    const struct ebt_mac_wormhash_tuple *p;
    int start, limit, i;
    uint32_t cmp[2] = { 0, 0 };
    int key = ((const unsigned char *)mac)[5];

    memcpy(((char *) cmp) + 2, mac, 6);
    start = wh->table[key];
    limit = wh->table[key + 1];
    if (ip) {
        for (i = start; i < limit; i++) {
            p = &wh->pool[i];
            if (cmp[1] == p->cmp[1] && cmp[0] == p->cmp[0])
                if (p->ip == 0 || p->ip == ip)
                    return true;
        }
    } else {
        for (i = start; i < limit; i++) {
            p = &wh->pool[i];
            if (cmp[1] == p->cmp[1] && cmp[0] == p->cmp[0])
                if (p->ip == 0)
                    return true;
        }
    }
    return false;
}

static int ebt_mac_wormhash_check_integrity(const struct ebt_mac_wormhash
                        *wh)
{
    int i;

    for (i = 0; i < 256; i++) {
        if (wh->table[i] > wh->table[i + 1])
            return -0x100 - i;
        if (wh->table[i] < 0)
            return -0x200 - i;
        if (wh->table[i] > wh->poolsize)
            return -0x300 - i;
    }
    if (wh->table[256] > wh->poolsize)
        return -0xc00;
    return 0;
}

static int get_ip_dst(const struct sk_buff *skb, __be32 *addr)
{
    if (eth_hdr(skb)->h_proto == htons(ETH_P_IP)) {
        const struct iphdr *ih;
        struct iphdr _iph;

        ih = skb_header_pointer(skb, 0, sizeof(_iph), &_iph);
        if (ih == NULL)
            return -1;
        *addr = ih->daddr;
    } else if (eth_hdr(skb)->h_proto == htons(ETH_P_ARP)) {
        const struct arphdr *ah;
        struct arphdr _arph;
        const __be32 *bp;
        __be32 buf;

        ah = skb_header_pointer(skb, 0, sizeof(_arph), &_arph);
        if (ah == NULL ||
            ah->ar_pln != sizeof(__be32) ||
            ah->ar_hln != ETH_ALEN)
            return -1;
        bp = skb_header_pointer(skb, sizeof(struct arphdr) +
                    2 * ETH_ALEN + sizeof(__be32),
                    sizeof(__be32), &buf);
        if (bp == NULL)
            return -1;
        *addr = *bp;
    }
    return 0;
}

static int get_ip_src(const struct sk_buff *skb, __be32 *addr)
{
    if (eth_hdr(skb)->h_proto == htons(ETH_P_IP)) {
        const struct iphdr *ih;
        struct iphdr _iph;

        ih = skb_header_pointer(skb, 0, sizeof(_iph), &_iph);
        if (ih == NULL)
            return -1;
        *addr = ih->saddr;
    } else if (eth_hdr(skb)->h_proto == htons(ETH_P_ARP)) {
        const struct arphdr *ah;
        struct arphdr _arph;
        const __be32 *bp;
        __be32 buf;

        ah = skb_header_pointer(skb, 0, sizeof(_arph), &_arph);
        if (ah == NULL ||
            ah->ar_pln != sizeof(__be32) ||
            ah->ar_hln != ETH_ALEN)
            return -1;
        bp = skb_header_pointer(skb, sizeof(struct arphdr) +
                    ETH_ALEN, sizeof(__be32), &buf);
        if (bp == NULL)
            return -1;
        *addr = *bp;
    }
    return 0;
}

static bool
ebt_among_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
    const struct ebt_among_info *info = par->matchinfo;
    const char *dmac, *smac;
    const struct ebt_mac_wormhash *wh_dst, *wh_src;
    __be32 dip = 0, sip = 0;

    wh_dst = ebt_among_wh_dst(info);
    wh_src = ebt_among_wh_src(info);

    if (wh_src) {
        smac = eth_hdr(skb)->h_source;
        if (get_ip_src(skb, &sip))
            return false;
        if (!(info->bitmask & EBT_AMONG_SRC_NEG)) {
            /* we match only if it contains */
            if (!ebt_mac_wormhash_contains(wh_src, smac, sip))
                return false;
        } else {
            /* we match only if it DOES NOT contain */
            if (ebt_mac_wormhash_contains(wh_src, smac, sip))
                return false;
        }
    }

    if (wh_dst) {
        dmac = eth_hdr(skb)->h_dest;
        if (get_ip_dst(skb, &dip))
            return false;
        if (!(info->bitmask & EBT_AMONG_DST_NEG)) {
            /* we match only if it contains */
            if (!ebt_mac_wormhash_contains(wh_dst, dmac, dip))
                return false;
        } else {
            /* we match only if it DOES NOT contain */
            if (ebt_mac_wormhash_contains(wh_dst, dmac, dip))
                return false;
        }
    }

    return true;
}

static int ebt_among_mt_check(const struct xt_mtchk_param *par)
{
    const struct ebt_among_info *info = par->matchinfo;
    const struct ebt_entry_match *em =
        container_of(par->matchinfo, const struct ebt_entry_match, data);
    int expected_length = sizeof(struct ebt_among_info);
    const struct ebt_mac_wormhash *wh_dst, *wh_src;
    int err;

    wh_dst = ebt_among_wh_dst(info);
    wh_src = ebt_among_wh_src(info);
    expected_length += ebt_mac_wormhash_size(wh_dst);
    expected_length += ebt_mac_wormhash_size(wh_src);

    if (em->match_size != EBT_ALIGN(expected_length)) {
        pr_info("wrong size: %d against expected %d, rounded to %Zd\n",
            em->match_size, expected_length,
            EBT_ALIGN(expected_length));
        return -EINVAL;
    }
    if (wh_dst && (err = ebt_mac_wormhash_check_integrity(wh_dst))) {
        pr_info("dst integrity fail: %x\n", -err);
        return -EINVAL;
    }
    if (wh_src && (err = ebt_mac_wormhash_check_integrity(wh_src))) {
        pr_info("src integrity fail: %x\n", -err);
        return -EINVAL;
    }
    return 0;
}

static struct xt_match ebt_among_mt_reg __read_mostly = {
    .name       = "among",
    .revision   = 0,
    .family     = NFPROTO_BRIDGE,
    .match      = ebt_among_mt,
    .checkentry = ebt_among_mt_check,
    .matchsize  = -1, /* special case */
    .me     = THIS_MODULE,
};

static int __init ebt_among_init(void)
{
    return xt_register_match(&ebt_among_mt_reg);
}

static void __exit ebt_among_fini(void)
{
    xt_unregister_match(&ebt_among_mt_reg);
}

module_init(ebt_among_init);
module_exit(ebt_among_fini);
MODULE_DESCRIPTION("Ebtables: Combined MAC/IP address list matching");
MODULE_LICENSE("GPL");