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Commit | Line | Data |
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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"); |
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 |
62fc8051 | 28 | tcpmss_mt(const struct sk_buff *skb, struct xt_action_param *par) |
1da177e4 | 29 | { |
f7108a20 | 30 | const struct xt_tcpmss_match_info *info = par->matchinfo; |
3cf93c96 JE |
31 | const struct tcphdr *th; |
32 | struct tcphdr _tcph; | |
1da177e4 | 33 | /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */ |
3cf93c96 JE |
34 | const u_int8_t *op; |
35 | u8 _opt[15 * 4 - sizeof(_tcph)]; | |
1da177e4 LT |
36 | unsigned int i, optlen; |
37 | ||
38 | /* If we don't have the whole header, drop packet. */ | |
f7108a20 | 39 | th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph); |
1da177e4 LT |
40 | if (th == NULL) |
41 | goto dropit; | |
42 | ||
43 | /* Malformed. */ | |
44 | if (th->doff*4 < sizeof(*th)) | |
45 | goto dropit; | |
46 | ||
47 | optlen = th->doff*4 - sizeof(*th); | |
48 | if (!optlen) | |
49 | goto out; | |
50 | ||
51 | /* Truncated options. */ | |
f7108a20 | 52 | op = skb_header_pointer(skb, par->thoff + sizeof(*th), optlen, _opt); |
1da177e4 LT |
53 | if (op == NULL) |
54 | goto dropit; | |
55 | ||
56 | for (i = 0; i < optlen; ) { | |
57 | if (op[i] == TCPOPT_MSS | |
58 | && (optlen - i) >= TCPOLEN_MSS | |
59 | && op[i+1] == TCPOLEN_MSS) { | |
60 | u_int16_t mssval; | |
61 | ||
62 | mssval = (op[i+2] << 8) | op[i+3]; | |
601e68e1 | 63 | |
ce556b3a | 64 | return (mssval >= info->mss_min && |
601e68e1 | 65 | mssval <= info->mss_max) ^ info->invert; |
1da177e4 | 66 | } |
ce556b3a PM |
67 | if (op[i] < 2) |
68 | i++; | |
69 | else | |
70 | i += op[i+1] ? : 1; | |
1da177e4 LT |
71 | } |
72 | out: | |
ce556b3a | 73 | return info->invert; |
1da177e4 | 74 | |
ce556b3a | 75 | dropit: |
b4ba2611 | 76 | par->hotdrop = true; |
1d93a9cb | 77 | return false; |
1da177e4 LT |
78 | } |
79 | ||
d3c5ee6d | 80 | static struct xt_match tcpmss_mt_reg[] __read_mostly = { |
4470bbc7 PM |
81 | { |
82 | .name = "tcpmss", | |
ee999d8b | 83 | .family = NFPROTO_IPV4, |
d3c5ee6d | 84 | .match = tcpmss_mt, |
4470bbc7 PM |
85 | .matchsize = sizeof(struct xt_tcpmss_match_info), |
86 | .proto = IPPROTO_TCP, | |
87 | .me = THIS_MODULE, | |
88 | }, | |
89 | { | |
90 | .name = "tcpmss", | |
ee999d8b | 91 | .family = NFPROTO_IPV6, |
d3c5ee6d | 92 | .match = tcpmss_mt, |
4470bbc7 PM |
93 | .matchsize = sizeof(struct xt_tcpmss_match_info), |
94 | .proto = IPPROTO_TCP, | |
95 | .me = THIS_MODULE, | |
96 | }, | |
1da177e4 LT |
97 | }; |
98 | ||
d3c5ee6d | 99 | static int __init tcpmss_mt_init(void) |
1da177e4 | 100 | { |
d3c5ee6d | 101 | return xt_register_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg)); |
1da177e4 LT |
102 | } |
103 | ||
d3c5ee6d | 104 | static void __exit tcpmss_mt_exit(void) |
1da177e4 | 105 | { |
d3c5ee6d | 106 | xt_unregister_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg)); |
1da177e4 LT |
107 | } |
108 | ||
d3c5ee6d JE |
109 | module_init(tcpmss_mt_init); |
110 | module_exit(tcpmss_mt_exit); |