ipt_ah.c

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/* Kernel module to match AH parameters. */
/* (C) 1999-2000 Yon Uriarte <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/in.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>

#include <linux/netfilter_ipv4/ipt_ah.h>
#include <linux/netfilter/x_tables.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Yon Uriarte <[email protected]>");
MODULE_DESCRIPTION("Xtables: IPv4 IPsec-AH SPI match");

/* Returns 1 if the spi is matched by the range, 0 otherwise */
static inline bool
spi_match(u_int32_t min, u_int32_t max, u_int32_t spi, bool invert)
{
    bool r;
    pr_debug("spi_match:%c 0x%x <= 0x%x <= 0x%x\n",
         invert ? '!' : ' ', min, spi, max);
    r=(spi >= min && spi <= max) ^ invert;
    pr_debug(" result %s\n", r ? "PASS" : "FAILED");
    return r;
}

static bool ah_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
    struct ip_auth_hdr _ahdr;
    const struct ip_auth_hdr *ah;
    const struct ipt_ah *ahinfo = par->matchinfo;

    /* Must not be a fragment. */
    if (par->fragoff != 0)
        return false;

    ah = skb_header_pointer(skb, par->thoff, sizeof(_ahdr), &_ahdr);
    if (ah == NULL) {
        /* We've been asked to examine this packet, and we
         * can't.  Hence, no choice but to drop.
         */
        pr_debug("Dropping evil AH tinygram.\n");
        par->hotdrop = true;
        return 0;
    }

    return spi_match(ahinfo->spis[0], ahinfo->spis[1],
             ntohl(ah->spi),
             !!(ahinfo->invflags & IPT_AH_INV_SPI));
}

static int ah_mt_check(const struct xt_mtchk_param *par)
{
    const struct ipt_ah *ahinfo = par->matchinfo;

    /* Must specify no unknown invflags */
    if (ahinfo->invflags & ~IPT_AH_INV_MASK) {
        pr_debug("unknown flags %X\n", ahinfo->invflags);
        return -EINVAL;
    }
    return 0;
}

static struct xt_match ah_mt_reg __read_mostly = {
    .name       = "ah",
    .family     = NFPROTO_IPV4,
    .match      = ah_mt,
    .matchsize  = sizeof(struct ipt_ah),
    .proto      = IPPROTO_AH,
    .checkentry = ah_mt_check,
    .me     = THIS_MODULE,
};

static int __init ah_mt_init(void)
{
    return xt_register_match(&ah_mt_reg);
}

static void __exit ah_mt_exit(void)
{
    xt_unregister_match(&ah_mt_reg);
}

module_init(ah_mt_init);
module_exit(ah_mt_exit);