xt_esp.c

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/* Kernel module to match ESP 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/module.h>
#include <linux/skbuff.h>
#include <linux/in.h>
#include <linux/ip.h>

#include <linux/netfilter/xt_esp.h>
#include <linux/netfilter/x_tables.h>

#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Yon Uriarte <[email protected]>");
MODULE_DESCRIPTION("Xtables: IPsec-ESP packet match");
MODULE_ALIAS("ipt_esp");
MODULE_ALIAS("ip6t_esp");

/* 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 esp_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
    const struct ip_esp_hdr *eh;
    struct ip_esp_hdr _esp;
    const struct xt_esp *espinfo = par->matchinfo;

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

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

    return spi_match(espinfo->spis[0], espinfo->spis[1], ntohl(eh->spi),
             !!(espinfo->invflags & XT_ESP_INV_SPI));
}

static int esp_mt_check(const struct xt_mtchk_param *par)
{
    const struct xt_esp *espinfo = par->matchinfo;

    if (espinfo->invflags & ~XT_ESP_INV_MASK) {
        pr_debug("unknown flags %X\n", espinfo->invflags);
        return -EINVAL;
    }

    return 0;
}

static struct xt_match esp_mt_reg[] __read_mostly = {
    {
        .name       = "esp",
        .family     = NFPROTO_IPV4,
        .checkentry = esp_mt_check,
        .match      = esp_mt,
        .matchsize  = sizeof(struct xt_esp),
        .proto      = IPPROTO_ESP,
        .me     = THIS_MODULE,
    },
    {
        .name       = "esp",
        .family     = NFPROTO_IPV6,
        .checkentry = esp_mt_check,
        .match      = esp_mt,
        .matchsize  = sizeof(struct xt_esp),
        .proto      = IPPROTO_ESP,
        .me     = THIS_MODULE,
    },
};

static int __init esp_mt_init(void)
{
    return xt_register_matches(esp_mt_reg, ARRAY_SIZE(esp_mt_reg));
}

static void __exit esp_mt_exit(void)
{
    xt_unregister_matches(esp_mt_reg, ARRAY_SIZE(esp_mt_reg));
}

module_init(esp_mt_init);
module_exit(esp_mt_exit);