xt_ecn.c

/*
 * Xtables module for matching the value of the IPv4/IPv6 and TCP ECN bits
 *
 * (C) 2002 by Harald Welte <laforge@gnumonks.org>
 * (C) 2011 Patrick McHardy <kaber@trash.net>
 *
 * 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/in.h>
#include <linux/ip.h>
#include <net/ip.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/tcp.h>

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

MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag match");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_ecn");
MODULE_ALIAS("ip6t_ecn");

static bool match_tcp(const struct sk_buff *skb, struct xt_action_param *par)
{
	const struct xt_ecn_info *einfo = par->matchinfo;
	struct tcphdr _tcph;
	const struct tcphdr *th;

	/* In practice, TCP match does this, so can't fail.  But let's
	 * be good citizens.
	 */
	th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
	if (th == NULL)
		return false;

	if (einfo->operation & XT_ECN_OP_MATCH_ECE) {
		if (einfo->invert & XT_ECN_OP_MATCH_ECE) {
			if (th->ece == 1)
				return false;
		} else {
			if (th->ece == 0)
				return false;
		}
	}

	if (einfo->operation & XT_ECN_OP_MATCH_CWR) {
		if (einfo->invert & XT_ECN_OP_MATCH_CWR) {
			if (th->cwr == 1)
				return false;
		} else {
			if (th->cwr == 0)
				return false;
		}
	}

	return true;
}

static inline bool match_ip(const struct sk_buff *skb,
			    const struct xt_ecn_info *einfo)
{
	return ((ip_hdr(skb)->tos & XT_ECN_IP_MASK) == einfo->ip_ect) ^
	       !!(einfo->invert & XT_ECN_OP_MATCH_IP);
}

static bool ecn_mt4(const struct sk_buff *skb, struct xt_action_param *par)
{
	const struct xt_ecn_info *info = par->matchinfo;

	if (info->operation & XT_ECN_OP_MATCH_IP && !match_ip(skb, info))
		return false;

	if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
	    !match_tcp(skb, par))
		return false;

	return true;
}

static int ecn_mt_check4(const struct xt_mtchk_param *par)
{
	const struct xt_ecn_info *info = par->matchinfo;
	const struct ipt_ip *ip = par->entryinfo;

	if (info->operation & XT_ECN_OP_MATCH_MASK)
		return -EINVAL;

	if (info->invert & XT_ECN_OP_MATCH_MASK)
		return -EINVAL;

	if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
	    (ip->proto != IPPROTO_TCP || ip->invflags & IPT_INV_PROTO)) {
		pr_info("cannot match TCP bits in rule for non-tcp packets\n");
		return -EINVAL;
	}

	return 0;
}

static inline bool match_ipv6(const struct sk_buff *skb,
			      const struct xt_ecn_info *einfo)
{
	return (((ipv6_hdr(skb)->flow_lbl[0] >> 4) & XT_ECN_IP_MASK) ==
	        einfo->ip_ect) ^
	       !!(einfo->invert & XT_ECN_OP_MATCH_IP);
}

static bool ecn_mt6(const struct sk_buff *skb, struct xt_action_param *par)
{
	const struct xt_ecn_info *info = par->matchinfo;

	if (info->operation & XT_ECN_OP_MATCH_IP && !match_ipv6(skb, info))
		return false;

	if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
	    !match_tcp(skb, par))
		return false;

	return true;
}

static int ecn_mt_check6(const struct xt_mtchk_param *par)
{
	const struct xt_ecn_info *info = par->matchinfo;
	const struct ip6t_ip6 *ip = par->entryinfo;

	if (info->operation & XT_ECN_OP_MATCH_MASK)
		return -EINVAL;

	if (info->invert & XT_ECN_OP_MATCH_MASK)
		return -EINVAL;

	if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
	    (ip->proto != IPPROTO_TCP || ip->invflags & IP6T_INV_PROTO)) {
		pr_info("cannot match TCP bits in rule for non-tcp packets\n");
		return -EINVAL;
	}

	return 0;
}

static struct xt_match ecn_mt_reg[] __read_mostly = {
	{
		.name		= "ecn",
		.family		= NFPROTO_IPV4,
		.match		= ecn_mt4,
		.matchsize	= sizeof(struct xt_ecn_info),
		.checkentry	= ecn_mt_check4,
		.me		= THIS_MODULE,
	},
	{
		.name		= "ecn",
		.family		= NFPROTO_IPV6,
		.match		= ecn_mt6,
		.matchsize	= sizeof(struct xt_ecn_info),
		.checkentry	= ecn_mt_check6,
		.me		= THIS_MODULE,
	},
};

static int __init ecn_mt_init(void)
{
	return xt_register_matches(ecn_mt_reg, ARRAY_SIZE(ecn_mt_reg));
}

static void __exit ecn_mt_exit(void)
{
	xt_unregister_matches(ecn_mt_reg, ARRAY_SIZE(ecn_mt_reg));
}

module_init(ecn_mt_init);
module_exit(ecn_mt_exit);