Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6.25
[linux-2.6] / net / netfilter / xt_tcpmss.c
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
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");
26
27 static bool
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)
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         }
73 out:
74         return info->invert;
75
76 dropit:
77         *hotdrop = true;
78         return false;
79 }
80
81 static 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
100 static int __init tcpmss_mt_init(void)
101 {
102         return xt_register_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
103 }
104
105 static void __exit tcpmss_mt_exit(void)
106 {
107         xt_unregister_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
108 }
109
110 module_init(tcpmss_mt_init);
111 module_exit(tcpmss_mt_exit);