// SPDX-License-Identifier: GPL-2.0-only
/*
 * This is the 1999 rewrite of IP Firewalling, aiming for kernel 2.3.x.
 *
 * Copyright (C) 1999 Paul `Rusty' Russell & Michael J. Neuling
 * Copyright (C) 2000-2004 Netfilter Core Team <coreteam@netfilter.org>
 */
#include <linux/module.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <net/route.h>
#include <linux/ip.h>
#include <net/ip.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
MODULE_DESCRIPTION("iptables mangle table");

#define MANGLE_VALID_HOOKS ((1 << NF_INET_PRE_ROUTING) | \
                            (1 << NF_INET_LOCAL_IN) | \
                            (1 << NF_INET_FORWARD) | \
                            (1 << NF_INET_LOCAL_OUT) | \
                            (1 << NF_INET_POST_ROUTING))

static const struct xt_table packet_mangler = {
        .name           = "mangle",
        .valid_hooks    = MANGLE_VALID_HOOKS,
        .me             = THIS_MODULE,
        .af             = NFPROTO_IPV4,
        .priority       = NF_IP_PRI_MANGLE,
};

static unsigned int
ipt_mangle_out(void *priv, struct sk_buff *skb, const struct nf_hook_state *state)
{
        unsigned int ret, verdict;
        const struct iphdr *iph;
        __be32 saddr, daddr;
        u32 mark;
        int err;
        u8 tos;

        /* Save things which could affect route */
        mark = skb->mark;
        iph = ip_hdr(skb);
        saddr = iph->saddr;
        daddr = iph->daddr;
        tos = iph->tos;

        ret = ipt_do_table(priv, skb, state);
        verdict = ret & NF_VERDICT_MASK;
        /* Reroute for ANY change. */
        if (verdict != NF_DROP && verdict != NF_STOLEN) {
                iph = ip_hdr(skb);

                if (iph->saddr != saddr ||
                    iph->daddr != daddr ||
                    skb->mark != mark ||
                    iph->tos != tos) {
                        err = ip_route_me_harder(state->net, state->sk, skb, RTN_UNSPEC);
                        if (err < 0)
                                ret = NF_DROP_ERR(err);
                }
        }

        return ret;
}

/* The work comes in here from netfilter.c. */
static unsigned int
iptable_mangle_hook(void *priv,
                     struct sk_buff *skb,
                     const struct nf_hook_state *state)
{
        if (state->hook == NF_INET_LOCAL_OUT)
                return ipt_mangle_out(priv, skb, state);
        return ipt_do_table(priv, skb, state);
}

static struct nf_hook_ops *mangle_ops __read_mostly;
static int iptable_mangle_table_init(struct net *net)
{
        struct ipt_replace *repl;
        int ret;

        repl = ipt_alloc_initial_table(&packet_mangler);
        if (repl == NULL)
                return -ENOMEM;
        ret = ipt_register_table(net, &packet_mangler, repl, mangle_ops);
        kfree(repl);
        return ret;
}

static void __net_exit iptable_mangle_net_pre_exit(struct net *net)
{
        ipt_unregister_table_pre_exit(net, "mangle");
}

static void __net_exit iptable_mangle_net_exit(struct net *net)
{
        ipt_unregister_table_exit(net, "mangle");
}

static struct pernet_operations iptable_mangle_net_ops = {
        .pre_exit = iptable_mangle_net_pre_exit,
        .exit = iptable_mangle_net_exit,
};

static int __init iptable_mangle_init(void)
{
        int ret = xt_register_template(&packet_mangler,
                                       iptable_mangle_table_init);
        if (ret < 0)
                return ret;

        mangle_ops = xt_hook_ops_alloc(&packet_mangler, iptable_mangle_hook);
        if (IS_ERR(mangle_ops)) {
                xt_unregister_template(&packet_mangler);
                ret = PTR_ERR(mangle_ops);
                return ret;
        }

        ret = register_pernet_subsys(&iptable_mangle_net_ops);
        if (ret < 0) {
                xt_unregister_template(&packet_mangler);
                kfree(mangle_ops);
                return ret;
        }

        return ret;
}

static void __exit iptable_mangle_fini(void)
{
        unregister_pernet_subsys(&iptable_mangle_net_ops);
        xt_unregister_template(&packet_mangler);
        kfree(mangle_ops);
}

module_init(iptable_mangle_init);
module_exit(iptable_mangle_fini);