tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1/* Kernel module to match TCP MSS values. */
2
3/* Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
4 * Portions (C) 2005 by Harald Welte <laforge@netfilter.org>
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
15#include <linux/netfilter/xt_tcpmss.h>
16#include <linux/netfilter/x_tables.h>
17
18#include <linux/netfilter_ipv4/ip_tables.h>
19#include <linux/netfilter_ipv6/ip6_tables.h>
20
21MODULE_LICENSE("GPL");
22MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
23MODULE_DESCRIPTION("Xtables: TCP MSS match");
24MODULE_ALIAS("ipt_tcpmss");
25MODULE_ALIAS("ip6t_tcpmss");
26
27static bool
28tcpmss_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)
32{
33 const struct xt_tcpmss_match_info *info = matchinfo;
34 struct tcphdr _tcph, *th;
35 /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
36 u8 _opt[15 * 4 - sizeof(_tcph)], *op;
37 unsigned int i, optlen;
38
39 /* If we don't have the whole header, drop packet. */
40 th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
41 if (th == NULL)
42 goto dropit;
43
44 /* Malformed. */
45 if (th->doff*4 < sizeof(*th))
46 goto dropit;
47
48 optlen = th->doff*4 - sizeof(*th);
49 if (!optlen)
50 goto out;
51
52 /* Truncated options. */
53 op = skb_header_pointer(skb, protoff + sizeof(*th), optlen, _opt);
54 if (op == NULL)
55 goto dropit;
56
57 for (i = 0; i < optlen; ) {
58 if (op[i] == TCPOPT_MSS
59 && (optlen - i) >= TCPOLEN_MSS
60 && op[i+1] == TCPOLEN_MSS) {
61 u_int16_t mssval;
62
63 mssval = (op[i+2] << 8) | op[i+3];
64
65 return (mssval >= info->mss_min &&
66 mssval <= info->mss_max) ^ info->invert;
67 }
68 if (op[i] < 2)
69 i++;
70 else
71 i += op[i+1] ? : 1;
72 }
73out:
74 return info->invert;
75
76dropit:
77 *hotdrop = true;
78 return false;
79}
80
81static struct xt_match tcpmss_mt_reg[] __read_mostly = {
82 {
83 .name = "tcpmss",
84 .family = AF_INET,
85 .match = tcpmss_mt,
86 .matchsize = sizeof(struct xt_tcpmss_match_info),
87 .proto = IPPROTO_TCP,
88 .me = THIS_MODULE,
89 },
90 {
91 .name = "tcpmss",
92 .family = AF_INET6,
93 .match = tcpmss_mt,
94 .matchsize = sizeof(struct xt_tcpmss_match_info),
95 .proto = IPPROTO_TCP,
96 .me = THIS_MODULE,
97 },
98};
99
100static int __init tcpmss_mt_init(void)
101{
102 return xt_register_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
103}
104
105static void __exit tcpmss_mt_exit(void)
106{
107 xt_unregister_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
108}
109
110module_init(tcpmss_mt_init);
111module_exit(tcpmss_mt_exit);