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 *      NetBIOS name service broadcast connection tracking helper
 *      (c) 2005 Patrick McHardy <>
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 *      This helper tracks locally originating NetBIOS name service
 *      requests by issuing permanent expectations (valid until
 *      timing out) matching all reply connections from the
 *      destination network. The only NetBIOS specific thing is
 *      actually the port number.
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/in.h>

#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_expect.h>

#define NMBD_PORT	137

MODULE_AUTHOR("Patrick McHardy <>");
MODULE_DESCRIPTION("NetBIOS name service broadcast connection tracking helper");

static unsigned int timeout __read_mostly = 3;
module_param(timeout, uint, S_IRUSR);
MODULE_PARM_DESC(timeout, "timeout for master connection/replies in seconds");

static struct nf_conntrack_expect_policy exp_policy = {
	.max_expected	= 1,

static int netbios_ns_help(struct sk_buff *skb, unsigned int protoff,
		   struct nf_conn *ct, enum ip_conntrack_info ctinfo)
	return nf_conntrack_broadcast_help(skb, protoff, ct, ctinfo, timeout);

static struct nf_conntrack_helper helper __read_mostly = {
	.name			= "netbios-ns",
	.tuple.src.l3num	= NFPROTO_IPV4,
	.tuple.src.u.udp.port	= cpu_to_be16(NMBD_PORT),
	.tuple.dst.protonum	= IPPROTO_UDP,
	.me			= THIS_MODULE,
	.help			= netbios_ns_help,
	.expect_policy		= &exp_policy,

static int __init nf_conntrack_netbios_ns_init(void)
	exp_policy.timeout = timeout;
	return nf_conntrack_helper_register(&helper);

static void __exit nf_conntrack_netbios_ns_fini(void)