ip6t_ah.c

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/* Kernel module to match AH parameters. */

/* (C) 2001-2002 Andras Kis-Szabo <[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/ip.h>
#include <linux/ipv6.h>
#include <linux/types.h>
#include <net/checksum.h>
#include <net/ipv6.h>

#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/netfilter_ipv6/ip6t_ah.h>

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Xtables: IPv6 IPsec-AH match");
MODULE_AUTHOR("Andras Kis-Szabo <[email protected]>");

/* 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_mt6(const struct sk_buff *skb, struct xt_action_param *par)
{
    struct ip_auth_hdr _ah;
    const struct ip_auth_hdr *ah;
    const struct ip6t_ah *ahinfo = par->matchinfo;
    unsigned int ptr = 0;
    unsigned int hdrlen = 0;
    int err;

    err = ipv6_find_hdr(skb, &ptr, NEXTHDR_AUTH, NULL, NULL);
    if (err < 0) {
        if (err != -ENOENT)
            par->hotdrop = true;
        return false;
    }

    ah = skb_header_pointer(skb, ptr, sizeof(_ah), &_ah);
    if (ah == NULL) {
        par->hotdrop = true;
        return false;
    }

    hdrlen = (ah->hdrlen + 2) << 2;

    pr_debug("IPv6 AH LEN %u %u ", hdrlen, ah->hdrlen);
    pr_debug("RES %04X ", ah->reserved);
    pr_debug("SPI %u %08X\n", ntohl(ah->spi), ntohl(ah->spi));

    pr_debug("IPv6 AH spi %02X ",
         spi_match(ahinfo->spis[0], ahinfo->spis[1],
               ntohl(ah->spi),
               !!(ahinfo->invflags & IP6T_AH_INV_SPI)));
    pr_debug("len %02X %04X %02X ",
         ahinfo->hdrlen, hdrlen,
         (!ahinfo->hdrlen ||
          (ahinfo->hdrlen == hdrlen) ^
          !!(ahinfo->invflags & IP6T_AH_INV_LEN)));
    pr_debug("res %02X %04X %02X\n",
         ahinfo->hdrres, ah->reserved,
         !(ahinfo->hdrres && ah->reserved));

    return (ah != NULL) &&
        spi_match(ahinfo->spis[0], ahinfo->spis[1],
              ntohl(ah->spi),
              !!(ahinfo->invflags & IP6T_AH_INV_SPI)) &&
        (!ahinfo->hdrlen ||
         (ahinfo->hdrlen == hdrlen) ^
         !!(ahinfo->invflags & IP6T_AH_INV_LEN)) &&
        !(ahinfo->hdrres && ah->reserved);
}

static int ah_mt6_check(const struct xt_mtchk_param *par)
{
    const struct ip6t_ah *ahinfo = par->matchinfo;

    if (ahinfo->invflags & ~IP6T_AH_INV_MASK) {
        pr_debug("unknown flags %X\n", ahinfo->invflags);
        return -EINVAL;
    }
    return 0;
}

static struct xt_match ah_mt6_reg __read_mostly = {
    .name       = "ah",
    .family     = NFPROTO_IPV6,
    .match      = ah_mt6,
    .matchsize  = sizeof(struct ip6t_ah),
    .checkentry = ah_mt6_check,
    .me     = THIS_MODULE,
};

static int __init ah_mt6_init(void)
{
    return xt_register_match(&ah_mt6_reg);
}

static void __exit ah_mt6_exit(void)
{
    xt_unregister_match(&ah_mt6_reg);
}

module_init(ah_mt6_init);
module_exit(ah_mt6_exit);