[deliverable/linux.git] / net / netfilter / xt_tcpmss.c

/* Kernel module to match TCP MSS values. */

/* Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
 * Portions (C) 2005 by Harald Welte <laforge@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/tcp.h>

#include <linux/netfilter/xt_tcpmss.h>
#include <linux/netfilter/x_tables.h>

#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
MODULE_DESCRIPTION("Xtables: TCP MSS match");
MODULE_ALIAS("ipt_tcpmss");
MODULE_ALIAS("ip6t_tcpmss");

static bool
tcpmss_mt(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_tcpmss_match_info *info = matchinfo;
	const struct tcphdr *th;
	struct tcphdr _tcph;
	/* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
	const u_int8_t *op;
	u8 _opt[15 * 4 - sizeof(_tcph)];
	unsigned int i, optlen;

	/* If we don't have the whole header, drop packet. */
	th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
	if (th == NULL)
		goto dropit;

	/* Malformed. */
	if (th->doff*4 < sizeof(*th))
		goto dropit;

	optlen = th->doff*4 - sizeof(*th);
	if (!optlen)
		goto out;

	/* Truncated options. */
	op = skb_header_pointer(skb, protoff + sizeof(*th), optlen, _opt);
	if (op == NULL)
		goto dropit;

	for (i = 0; i < optlen; ) {
		if (op[i] == TCPOPT_MSS
		    && (optlen - i) >= TCPOLEN_MSS
		    && op[i+1] == TCPOLEN_MSS) {
			u_int16_t mssval;

			mssval = (op[i+2] << 8) | op[i+3];

			return (mssval >= info->mss_min &&
				mssval <= info->mss_max) ^ info->invert;
		}
		if (op[i] < 2)
			i++;
		else
			i += op[i+1] ? : 1;
	}
out:
	return info->invert;

dropit:
	*hotdrop = true;
	return false;
}

static struct xt_match tcpmss_mt_reg[] __read_mostly = {
	{
		.name		= "tcpmss",
		.family		= AF_INET,
		.match		= tcpmss_mt,
		.matchsize	= sizeof(struct xt_tcpmss_match_info),
		.proto		= IPPROTO_TCP,
		.me		= THIS_MODULE,
	},
	{
		.name		= "tcpmss",
		.family		= AF_INET6,
		.match		= tcpmss_mt,
		.matchsize	= sizeof(struct xt_tcpmss_match_info),
		.proto		= IPPROTO_TCP,
		.me		= THIS_MODULE,
	},
};

static int __init tcpmss_mt_init(void)
{
	return xt_register_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
}

static void __exit tcpmss_mt_exit(void)
{
	xt_unregister_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
}

module_init(tcpmss_mt_init);
module_exit(tcpmss_mt_exit);
Commit	Line	Data
1da177e4 LT	1	/* Kernel module to match TCP MSS values. */
	2
	3	/* Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
2e4e6a17	4	* Portions (C) 2005 by Harald Welte <laforge@netfilter.org>
1da177e4 LT	5	*
	6	* This program is free software; you can redistribute it and/or modify
	7	* it under the terms of the GNU General Public License version 2 as
	8	* published by the Free Software Foundation.
	9	*/
	10
	11	#include <linux/module.h>
	12	#include <linux/skbuff.h>
	13	#include <net/tcp.h>
	14
2e4e6a17 HW	15	#include <linux/netfilter/xt_tcpmss.h>
	16	#include <linux/netfilter/x_tables.h>
	17
1da177e4	18	#include <linux/netfilter_ipv4/ip_tables.h>
2e4e6a17	19	#include <linux/netfilter_ipv6/ip6_tables.h>
1da177e4	20
1da177e4 LT	21	MODULE_LICENSE("GPL");
1da177e4 LT	22	MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
2ae15b64	23	MODULE_DESCRIPTION("Xtables: TCP MSS match");
2e4e6a17	24	MODULE_ALIAS("ipt_tcpmss");
73aaf935	25	MODULE_ALIAS("ip6t_tcpmss");
1da177e4	26
1d93a9cb	27	static bool
d3c5ee6d JE	28	tcpmss_mt(const struct sk_buff skb, const struct net_device in,
	29	const struct net_device out, const struct xt_match match,
	30	const void *matchinfo, int offset, unsigned int protoff,
	31	bool *hotdrop)
1da177e4	32	{
ce556b3a	33	const struct xt_tcpmss_match_info *info = matchinfo;
3cf93c96 JE	34	const struct tcphdr *th;
3cf93c96 JE	35	struct tcphdr _tcph;
1da177e4	36	/* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
3cf93c96 JE	37	const u_int8_t *op;
3cf93c96 JE	38	u8 _opt[15 * 4 - sizeof(_tcph)];
1da177e4 LT	39	unsigned int i, optlen;
	40
	41	/* If we don't have the whole header, drop packet. */
2e4e6a17	42	th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
1da177e4 LT	43	if (th == NULL)
	44	goto dropit;
	45
	46	/* Malformed. */
	47	if (th->doff4 < sizeof(th))
	48	goto dropit;
	49
	50	optlen = th->doff4 - sizeof(th);
	51	if (!optlen)
	52	goto out;
	53
	54	/* Truncated options. */
2e4e6a17	55	op = skb_header_pointer(skb, protoff + sizeof(*th), optlen, _opt);
1da177e4 LT	56	if (op == NULL)
	57	goto dropit;
	58
	59	for (i = 0; i < optlen; ) {
	60	if (op[i] == TCPOPT_MSS
	61	&& (optlen - i) >= TCPOLEN_MSS
	62	&& op[i+1] == TCPOLEN_MSS) {
	63	u_int16_t mssval;
	64
	65	mssval = (op[i+2] << 8) \| op[i+3];
601e68e1	66
ce556b3a	67	return (mssval >= info->mss_min &&
601e68e1	68	mssval <= info->mss_max) ^ info->invert;
1da177e4	69	}
ce556b3a PM	70	if (op[i] < 2)
	71	i++;
	72	else
	73	i += op[i+1] ? : 1;
1da177e4 LT	74	}
1da177e4 LT	75	out:
ce556b3a	76	return info->invert;
1da177e4	77
ce556b3a	78	dropit:
cff533ac	79	*hotdrop = true;
1d93a9cb	80	return false;
1da177e4 LT	81	}
1da177e4 LT	82
d3c5ee6d	83	static struct xt_match tcpmss_mt_reg[] __read_mostly = {
4470bbc7 PM	84	{
	85	.name = "tcpmss",
	86	.family = AF_INET,
d3c5ee6d	87	.match = tcpmss_mt,
4470bbc7 PM	88	.matchsize = sizeof(struct xt_tcpmss_match_info),
	89	.proto = IPPROTO_TCP,
	90	.me = THIS_MODULE,
	91	},
	92	{
	93	.name = "tcpmss",
	94	.family = AF_INET6,
d3c5ee6d	95	.match = tcpmss_mt,
4470bbc7 PM	96	.matchsize = sizeof(struct xt_tcpmss_match_info),
	97	.proto = IPPROTO_TCP,
	98	.me = THIS_MODULE,
	99	},
1da177e4 LT	100	};
1da177e4 LT	101
d3c5ee6d	102	static int __init tcpmss_mt_init(void)
1da177e4	103	{
d3c5ee6d	104	return xt_register_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
1da177e4 LT	105	}
1da177e4 LT	106
d3c5ee6d	107	static void __exit tcpmss_mt_exit(void)
1da177e4	108	{
d3c5ee6d	109	xt_unregister_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
1da177e4 LT	110	}
1da177e4 LT	111
d3c5ee6d JE	112	module_init(tcpmss_mt_init);
d3c5ee6d JE	113	module_exit(tcpmss_mt_exit);