/* Kernel module to match ESP parameters. */
  
  /* (C) 1999-2000 Yon Uriarte <yon@astaro.de>
   *
   * 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 <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
  ",

  		 invert ? '!' : ' ', min, spi, max);

  	r = (spi >= min && spi <= max) ^ invert;

  	pr_debug(" result %s
  ", 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.
  ");

  		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
  ", 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);