xt_ecn.c

Go to the documentation of this file.

/*
 * Xtables module for matching the value of the IPv4/IPv6 and TCP ECN bits
 *
 * (C) 2002 by Harald Welte <[email protected]>
 * (C) 2011 Patrick McHardy <[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/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 <[email protected]>");
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);