// SPDX-License-Identifier: GPL-2.0-only
/* Kernel module to match AH parameters. */

/* (C) 2001-2002 Andras Kis-Szabo <kisza@sch.bme.hu>
 */
#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 <kisza@sch.bme.hu>");

/* 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 = ipv6_authlen(ah);

        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 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);