/*
 *      NetBIOS name service broadcast connection tracking helper
 *
 *      (c) 2005 Patrick McHardy <kaber@trash.net>
 *
 *      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/skbuff.h>
#include <linux/netdevice.h>
#include <linux/inetdevice.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <net/route.h>

#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netfilter_ipv4/ip_conntrack.h>
#include <linux/netfilter_ipv4/ip_conntrack_helper.h>

#define NMBD_PORT	137

MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
MODULE_DESCRIPTION("NetBIOS name service broadcast connection tracking helper");
MODULE_LICENSE("GPL");

static unsigned int timeout = 3;
module_param(timeout, int, 0600);
MODULE_PARM_DESC(timeout, "timeout for master connection/replies in seconds");

static int help(struct sk_buff **pskb,
                struct ip_conntrack *ct, enum ip_conntrack_info ctinfo)
{
	struct ip_conntrack_expect *exp;
	struct iphdr *iph = (*pskb)->nh.iph;
	struct rtable *rt = (struct rtable *)(*pskb)->dst;
	struct in_device *in_dev;
	u_int32_t mask = 0;

	/* we're only interested in locally generated packets */
	if ((*pskb)->sk == NULL)
		goto out;
	if (rt == NULL || !(rt->rt_flags & RTCF_BROADCAST))
		goto out;
	if (CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
		goto out;

	rcu_read_lock();
	in_dev = __in_dev_get_rcu(rt->u.dst.dev);
	if (in_dev != NULL) {
		for_primary_ifa(in_dev) {
			if (ifa->ifa_broadcast == iph->daddr) {
				mask = ifa->ifa_mask;
				break;
			}
		} endfor_ifa(in_dev);
	}
	rcu_read_unlock();

	if (mask == 0)
		goto out;

	exp = ip_conntrack_expect_alloc(ct);
	if (exp == NULL)
		goto out;

	exp->tuple                = ct->tuplehash[IP_CT_DIR_REPLY].tuple;
	exp->tuple.src.u.udp.port = ntohs(NMBD_PORT);

	exp->mask.src.ip          = mask;
	exp->mask.src.u.udp.port  = 0xFFFF;
	exp->mask.dst.ip          = 0xFFFFFFFF;
	exp->mask.dst.u.udp.port  = 0xFFFF;
	exp->mask.dst.protonum    = 0xFF;

	exp->expectfn             = NULL;
	exp->flags                = IP_CT_EXPECT_PERMANENT;

	ip_conntrack_expect_related(exp);
	ip_conntrack_expect_put(exp);

	ip_ct_refresh(ct, *pskb, timeout * HZ);
out:
	return NF_ACCEPT;
}

static struct ip_conntrack_helper helper = {
	.name			= "netbios-ns",
	.tuple = {
		.src = {
			.u = {
				.udp = {
					.port	= __constant_htons(NMBD_PORT),
				}
			}
		},
		.dst = {
			.protonum	= IPPROTO_UDP,
		},
	},
	.mask = {
		.src = {
			.u = {
				.udp = {
					.port	= 0xFFFF,
				}
			}
		},
		.dst = {
			.protonum	= 0xFF,
		},
	},
	.max_expected		= 1,
	.me			= THIS_MODULE,
	.help			= help,
};

static int __init init(void)
{
	helper.timeout = timeout;
	return ip_conntrack_helper_register(&helper);
}

static void __exit fini(void)
{
	ip_conntrack_helper_unregister(&helper);
}

module_init(init);
module_exit(fini);