// SPDX-License-Identifier: GPL-2.0-only
/*
 * 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>
 */
#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_ratelimited("cannot match TCP bits 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_ratelimited("cannot match TCP bits 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);