1. 根目录:
2. net
3. netfilter
4. xt_state.c

/* Kernel module to match connection tracking information. */

/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2005 Netfilter Core Team <coreteam@netfilter.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/module.h>
#include <linux/skbuff.h>
#include <net/netfilter/nf_conntrack.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_state.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
MODULE_DESCRIPTION("ip[6]_tables connection tracking state match module");
MODULE_ALIAS("ipt_state");
MODULE_ALIAS("ip6t_state");

static bool
state_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
	const struct xt_state_info *sinfo = par->matchinfo;
	enum ip_conntrack_info ctinfo;
	unsigned int statebit;
	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

	if (!ct)
		statebit = XT_STATE_INVALID;
	else {
		if (nf_ct_is_untracked(ct))
			statebit = XT_STATE_UNTRACKED;
		else
			statebit = XT_STATE_BIT(ctinfo);
	}
	return (sinfo->statemask & statebit);
}

static int state_mt_check(const struct xt_mtchk_param *par)
{
	int ret;

	ret = nf_ct_l3proto_try_module_get(par->family);
	if (ret < 0)
		pr_info("cannot load conntrack support for proto=%u\n",
			par->family);
	return ret;
}

static void state_mt_destroy(const struct xt_mtdtor_param *par)
{
	nf_ct_l3proto_module_put(par->family);
}

static struct xt_match state_mt_reg __read_mostly = {
	.name       = "state",
	.family     = NFPROTO_UNSPEC,
	.checkentry = state_mt_check,
	.match      = state_mt,
	.destroy    = state_mt_destroy,
	.matchsize  = sizeof(struct xt_state_info),
	.me         = THIS_MODULE,
};

static int __init state_mt_init(void)
{
	return xt_register_match(&state_mt_reg);
}

static void __exit state_mt_exit(void)
{
	xt_unregister_match(&state_mt_reg);
}

module_init(state_mt_init);
module_exit(state_mt_exit);