// SPDX-License-Identifier: GPL-2.0-only
/*
 * IPv6 packet mangling table, a port of the IPv4 mangle table to IPv6
 *
 * Copyright (C) 2000-2001 by Harald Welte <laforge@gnumonks.org>
 * Copyright (C) 2000-2004 Netfilter Core Team <coreteam@netfilter.org>
 */
#include <linux/module.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/slab.h>
#include <net/ipv6.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
MODULE_DESCRIPTION("ip6tables 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_IPV6,
        .priority       = NF_IP6_PRI_MANGLE,
};

static unsigned int
ip6t_mangle_out(void *priv, struct sk_buff *skb, const struct nf_hook_state *state)
{
        struct in6_addr saddr, daddr;
        unsigned int ret, verdict;
        u32 flowlabel, mark;
        u8 hop_limit;
        int err;

        /* save source/dest address, mark, hoplimit, flowlabel, priority,  */
        memcpy(&saddr, &ipv6_hdr(skb)->saddr, sizeof(saddr));
        memcpy(&daddr, &ipv6_hdr(skb)->daddr, sizeof(daddr));
        mark = skb->mark;
        hop_limit = ipv6_hdr(skb)->hop_limit;

        /* flowlabel and prio (includes version, which shouldn't change either */
        flowlabel = *((u_int32_t *)ipv6_hdr(skb));

        ret = ip6t_do_table(priv, skb, state);
        verdict = ret & NF_VERDICT_MASK;

        if (verdict != NF_DROP && verdict != NF_STOLEN &&
            (!ipv6_addr_equal(&ipv6_hdr(skb)->saddr, &saddr) ||
             !ipv6_addr_equal(&ipv6_hdr(skb)->daddr, &daddr) ||
             skb->mark != mark ||
             ipv6_hdr(skb)->hop_limit != hop_limit ||
             flowlabel != *((u_int32_t *)ipv6_hdr(skb)))) {
                err = ip6_route_me_harder(state->net, state->sk, skb);
                if (err < 0)
                        ret = NF_DROP_ERR(err);
        }

        return ret;
}

/* The work comes in here from netfilter.c. */
static unsigned int
ip6table_mangle_hook(void *priv, struct sk_buff *skb,
                     const struct nf_hook_state *state)
{
        if (state->hook == NF_INET_LOCAL_OUT)
                return ip6t_mangle_out(priv, skb, state);
        return ip6t_do_table(priv, skb, state);
}

static struct nf_hook_ops *mangle_ops __read_mostly;
static int ip6table_mangle_table_init(struct net *net)
{
        struct ip6t_replace *repl;
        int ret;

        repl = ip6t_alloc_initial_table(&packet_mangler);
        if (repl == NULL)
                return -ENOMEM;
        ret = ip6t_register_table(net, &packet_mangler, repl, mangle_ops);
        kfree(repl);
        return ret;
}

static void __net_exit ip6table_mangle_net_pre_exit(struct net *net)
{
        ip6t_unregister_table_pre_exit(net, "mangle");
}

static void __net_exit ip6table_mangle_net_exit(struct net *net)
{
        ip6t_unregister_table_exit(net, "mangle");
}

static struct pernet_operations ip6table_mangle_net_ops = {
        .pre_exit = ip6table_mangle_net_pre_exit,
        .exit = ip6table_mangle_net_exit,
};

static int __init ip6table_mangle_init(void)
{
        int ret = xt_register_template(&packet_mangler,
                                       ip6table_mangle_table_init);

        if (ret < 0)
                return ret;

        mangle_ops = xt_hook_ops_alloc(&packet_mangler, ip6table_mangle_hook);
        if (IS_ERR(mangle_ops)) {
                xt_unregister_template(&packet_mangler);
                return PTR_ERR(mangle_ops);
        }

        ret = register_pernet_subsys(&ip6table_mangle_net_ops);
        if (ret < 0) {
                xt_unregister_template(&packet_mangler);
                kfree(mangle_ops);
                return ret;
        }

        return ret;
}

static void __exit ip6table_mangle_fini(void)
{
        unregister_pernet_subsys(&ip6table_mangle_net_ops);
        xt_unregister_template(&packet_mangler);
        kfree(mangle_ops);
}

module_init(ip6table_mangle_init);
module_exit(ip6table_mangle_fini);