1 /* Kernel module to match TCP MSS values. */
3 /* Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
4 * Portions (C) 2005 by Harald Welte <laforge@netfilter.org>
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.
11 #include <linux/module.h>
12 #include <linux/skbuff.h>
15 #include <linux/netfilter/xt_tcpmss.h>
16 #include <linux/netfilter/x_tables.h>
18 #include <linux/netfilter_ipv4/ip_tables.h>
19 #include <linux/netfilter_ipv6/ip6_tables.h>
21 MODULE_LICENSE("GPL");
22 MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
23 MODULE_DESCRIPTION("Xtables: TCP MSS match");
24 MODULE_ALIAS("ipt_tcpmss");
25 MODULE_ALIAS("ip6t_tcpmss");
28 tcpmss_mt(const struct sk_buff *skb, const struct xt_match_param *par)
30 const struct xt_tcpmss_match_info *info = par->matchinfo;
31 const struct tcphdr *th;
33 /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
35 u8 _opt[15 * 4 - sizeof(_tcph)];
36 unsigned int i, optlen;
38 /* If we don't have the whole header, drop packet. */
39 th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
44 if (th->doff*4 < sizeof(*th))
47 optlen = th->doff*4 - sizeof(*th);
51 /* Truncated options. */
52 op = skb_header_pointer(skb, par->thoff + sizeof(*th), optlen, _opt);
56 for (i = 0; i < optlen; ) {
57 if (op[i] == TCPOPT_MSS
58 && (optlen - i) >= TCPOLEN_MSS
59 && op[i+1] == TCPOLEN_MSS) {
62 mssval = (op[i+2] << 8) | op[i+3];
64 return (mssval >= info->mss_min &&
65 mssval <= info->mss_max) ^ info->invert;
80 static struct xt_match tcpmss_mt_reg[] __read_mostly = {
83 .family = NFPROTO_IPV4,
85 .matchsize = sizeof(struct xt_tcpmss_match_info),
91 .family = NFPROTO_IPV6,
93 .matchsize = sizeof(struct xt_tcpmss_match_info),
99 static int __init tcpmss_mt_init(void)
101 return xt_register_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
104 static void __exit tcpmss_mt_exit(void)
106 xt_unregister_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
109 module_init(tcpmss_mt_init);
110 module_exit(tcpmss_mt_exit);