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/* 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);
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