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

/* (C) 1999-2000 Yon Uriarte <yon@astaro.de>
 */
#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 <yon@astaro.de>");
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);