// SPDX-License-Identifier: GPL-2.0-or-later
/* IRC extension for TCP NAT alteration.
 *
 * (C) 2000-2001 by Harald Welte <laforge@gnumonks.org>
 * (C) 2004 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
 * based on a copy of RR's ip_nat_ftp.c
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/tcp.h>
#include <linux/kernel.h>

#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_helper.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <linux/netfilter/nf_conntrack_irc.h>

#define NAT_HELPER_NAME "irc"

MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
MODULE_DESCRIPTION("IRC (DCC) NAT helper");
MODULE_LICENSE("GPL");
MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);

static struct nf_conntrack_nat_helper nat_helper_irc =
        NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);

static unsigned int help(struct sk_buff *skb,
                         enum ip_conntrack_info ctinfo,
                         unsigned int protoff,
                         unsigned int matchoff,
                         unsigned int matchlen,
                         struct nf_conntrack_expect *exp)
{
        char buffer[sizeof("4294967296 65635")];
        struct nf_conn *ct = exp->master;
        union nf_inet_addr newaddr;
        u_int16_t port;

        /* Reply comes from server. */
        newaddr = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3;

        exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
        exp->dir = IP_CT_DIR_REPLY;
        exp->expectfn = nf_nat_follow_master;

        port = nf_nat_exp_find_port(exp,
                                    ntohs(exp->saved_proto.tcp.port));
        if (port == 0) {
                nf_ct_helper_log(skb, ct, "all ports in use");
                return NF_DROP;
        }

        /* strlen("\1DCC CHAT chat AAAAAAAA P\1\n")=27
         * strlen("\1DCC SCHAT chat AAAAAAAA P\1\n")=28
         * strlen("\1DCC SEND F AAAAAAAA P S\1\n")=26
         * strlen("\1DCC MOVE F AAAAAAAA P S\1\n")=26
         * strlen("\1DCC TSEND F AAAAAAAA P S\1\n")=27
         *
         * AAAAAAAAA: bound addr (1.0.0.0==16777216, min 8 digits,
         *                        255.255.255.255==4294967296, 10 digits)
         * P:         bound port (min 1 d, max 5d (65635))
         * F:         filename   (min 1 d )
         * S:         size       (min 1 d )
         * 0x01, \n:  terminators
         */
        /* AAA = "us", ie. where server normally talks to. */
        snprintf(buffer, sizeof(buffer), "%u %u", ntohl(newaddr.ip), port);
        pr_debug("inserting '%s' == %pI4, port %u\n",
                 buffer, &newaddr.ip, port);

        if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
                                      matchlen, buffer, strlen(buffer))) {
                nf_ct_helper_log(skb, ct, "cannot mangle packet");
                nf_ct_unexpect_related(exp);
                return NF_DROP;
        }

        return NF_ACCEPT;
}

static void __exit nf_nat_irc_fini(void)
{
        nf_nat_helper_unregister(&nat_helper_irc);
        RCU_INIT_POINTER(nf_nat_irc_hook, NULL);
        synchronize_rcu();
}

static int __init nf_nat_irc_init(void)
{
        BUG_ON(nf_nat_irc_hook != NULL);
        nf_nat_helper_register(&nat_helper_irc);
        RCU_INIT_POINTER(nf_nat_irc_hook, help);
        return 0;
}

/* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
static int warn_set(const char *val, const struct kernel_param *kp)
{
        pr_info("kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
        return 0;
}
module_param_call(ports, warn_set, NULL, NULL, 0);

module_init(nf_nat_irc_init);
module_exit(nf_nat_irc_fini);