xt_conntrack.c

/* Kernel module to match connection tracking information.
 * Superset of Rusty's minimalistic state match.
 *
 * (C) 2001  Marc Boucher (marc@mbsi.ca).
 *
 * 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 <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_conntrack.h>
#include <net/netfilter/nf_conntrack.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
MODULE_DESCRIPTION("iptables connection tracking match module");
MODULE_ALIAS("ipt_conntrack");

static bool
match(const struct sk_buff *skb,
      const struct net_device *in,
      const struct net_device *out,
      const struct xt_match *match,
      const void *matchinfo,
      int offset,
      unsigned int protoff,
      bool *hotdrop)
{
	const struct xt_conntrack_info *sinfo = matchinfo;
	const struct nf_conn *ct;
	enum ip_conntrack_info ctinfo;
	unsigned int statebit;

	ct = nf_ct_get(skb, &ctinfo);

#define FWINV(bool,invflg) ((bool) ^ !!(sinfo->invflags & invflg))

	if (ct == &nf_conntrack_untracked)
		statebit = XT_CONNTRACK_STATE_UNTRACKED;
	else if (ct)
		statebit = XT_CONNTRACK_STATE_BIT(ctinfo);
	else
		statebit = XT_CONNTRACK_STATE_INVALID;

	if (sinfo->flags & XT_CONNTRACK_STATE) {
		if (ct) {
			if (test_bit(IPS_SRC_NAT_BIT, &ct->status))
				statebit |= XT_CONNTRACK_STATE_SNAT;
			if (test_bit(IPS_DST_NAT_BIT, &ct->status))
				statebit |= XT_CONNTRACK_STATE_DNAT;
		}
		if (FWINV((statebit & sinfo->statemask) == 0,
			  XT_CONNTRACK_STATE))
			return false;
	}

	if (ct == NULL) {
		if (sinfo->flags & ~XT_CONNTRACK_STATE)
			return false;
		return true;
	}

	if (sinfo->flags & XT_CONNTRACK_PROTO &&
	    FWINV(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.protonum !=
		  sinfo->tuple[IP_CT_DIR_ORIGINAL].dst.protonum,
		  XT_CONNTRACK_PROTO))
		return false;

	if (sinfo->flags & XT_CONNTRACK_ORIGSRC &&
	    FWINV((ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip &
		   sinfo->sipmsk[IP_CT_DIR_ORIGINAL].s_addr) !=
		  sinfo->tuple[IP_CT_DIR_ORIGINAL].src.ip,
		  XT_CONNTRACK_ORIGSRC))
		return false;

	if (sinfo->flags & XT_CONNTRACK_ORIGDST &&
	    FWINV((ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.u3.ip &
		   sinfo->dipmsk[IP_CT_DIR_ORIGINAL].s_addr) !=
		  sinfo->tuple[IP_CT_DIR_ORIGINAL].dst.ip,
		  XT_CONNTRACK_ORIGDST))
		return false;

	if (sinfo->flags & XT_CONNTRACK_REPLSRC &&
	    FWINV((ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u3.ip &
		   sinfo->sipmsk[IP_CT_DIR_REPLY].s_addr) !=
		  sinfo->tuple[IP_CT_DIR_REPLY].src.ip,
		  XT_CONNTRACK_REPLSRC))
		return false;

	if (sinfo->flags & XT_CONNTRACK_REPLDST &&
	    FWINV((ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3.ip &
		   sinfo->dipmsk[IP_CT_DIR_REPLY].s_addr) !=
		  sinfo->tuple[IP_CT_DIR_REPLY].dst.ip,
		  XT_CONNTRACK_REPLDST))
		return false;

	if (sinfo->flags & XT_CONNTRACK_STATUS &&
	    FWINV((ct->status & sinfo->statusmask) == 0,
		  XT_CONNTRACK_STATUS))
		return false;

	if(sinfo->flags & XT_CONNTRACK_EXPIRES) {
		unsigned long expires = timer_pending(&ct->timeout) ?
					(ct->timeout.expires - jiffies)/HZ : 0;

		if (FWINV(!(expires >= sinfo->expires_min &&
			    expires <= sinfo->expires_max),
			  XT_CONNTRACK_EXPIRES))
			return false;
	}
	return true;
}

static bool
checkentry(const char *tablename,
	   const void *ip,
	   const struct xt_match *match,
	   void *matchinfo,
	   unsigned int hook_mask)
{
	if (nf_ct_l3proto_try_module_get(match->family) < 0) {
		printk(KERN_WARNING "can't load conntrack support for "
				    "proto=%d\n", match->family);
		return false;
	}
	return true;
}

static void destroy(const struct xt_match *match, void *matchinfo)
{
	nf_ct_l3proto_module_put(match->family);
}

#ifdef CONFIG_COMPAT
struct compat_xt_conntrack_info
{
	compat_uint_t			statemask;
	compat_uint_t			statusmask;
	struct ip_conntrack_old_tuple	tuple[IP_CT_DIR_MAX];
	struct in_addr			sipmsk[IP_CT_DIR_MAX];
	struct in_addr			dipmsk[IP_CT_DIR_MAX];
	compat_ulong_t			expires_min;
	compat_ulong_t			expires_max;
	u_int8_t			flags;
	u_int8_t			invflags;
};

static void compat_from_user(void *dst, void *src)
{
	const struct compat_xt_conntrack_info *cm = src;
	struct xt_conntrack_info m = {
		.statemask	= cm->statemask,
		.statusmask	= cm->statusmask,
		.expires_min	= cm->expires_min,
		.expires_max	= cm->expires_max,
		.flags		= cm->flags,
		.invflags	= cm->invflags,
	};
	memcpy(m.tuple, cm->tuple, sizeof(m.tuple));
	memcpy(m.sipmsk, cm->sipmsk, sizeof(m.sipmsk));
	memcpy(m.dipmsk, cm->dipmsk, sizeof(m.dipmsk));
	memcpy(dst, &m, sizeof(m));
}

static int compat_to_user(void __user *dst, void *src)
{
	const struct xt_conntrack_info *m = src;
	struct compat_xt_conntrack_info cm = {
		.statemask	= m->statemask,
		.statusmask	= m->statusmask,
		.expires_min	= m->expires_min,
		.expires_max	= m->expires_max,
		.flags		= m->flags,
		.invflags	= m->invflags,
	};
	memcpy(cm.tuple, m->tuple, sizeof(cm.tuple));
	memcpy(cm.sipmsk, m->sipmsk, sizeof(cm.sipmsk));
	memcpy(cm.dipmsk, m->dipmsk, sizeof(cm.dipmsk));
	return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
}
#endif

static struct xt_match conntrack_match __read_mostly = {
	.name		= "conntrack",
	.match		= match,
	.checkentry	= checkentry,
	.destroy	= destroy,
	.matchsize	= sizeof(struct xt_conntrack_info),
#ifdef CONFIG_COMPAT
	.compatsize	= sizeof(struct compat_xt_conntrack_info),
	.compat_from_user = compat_from_user,
	.compat_to_user	= compat_to_user,
#endif
	.family		= AF_INET,
	.me		= THIS_MODULE,
};

static int __init xt_conntrack_init(void)
{
	return xt_register_match(&conntrack_match);
}

static void __exit xt_conntrack_fini(void)
{
	xt_unregister_match(&conntrack_match);
}

module_init(xt_conntrack_init);
module_exit(xt_conntrack_fini);