Commit | Line | Data |
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338e8a79 SS |
1 | /* |
2 | * A module for stripping a specific TCP option from TCP packets. | |
3 | * | |
4 | * Copyright (C) 2007 Sven Schnelle <svens@bitebene.org> | |
5 | * Copyright © CC Computer Consultants GmbH, 2007 | |
6 | * Contact: Jan Engelhardt <jengelh@computergmbh.de> | |
7 | * | |
8 | * This program is free software; you can redistribute it and/or modify | |
9 | * it under the terms of the GNU General Public License version 2 as | |
10 | * published by the Free Software Foundation. | |
11 | */ | |
12 | ||
13 | #include <linux/module.h> | |
14 | #include <linux/skbuff.h> | |
15 | #include <linux/ip.h> | |
16 | #include <linux/ipv6.h> | |
17 | #include <linux/tcp.h> | |
18 | #include <net/ipv6.h> | |
19 | #include <net/tcp.h> | |
20 | #include <linux/netfilter/x_tables.h> | |
21 | #include <linux/netfilter/xt_TCPOPTSTRIP.h> | |
22 | ||
23 | static inline unsigned int optlen(const u_int8_t *opt, unsigned int offset) | |
24 | { | |
25 | /* Beware zero-length options: make finite progress */ | |
26 | if (opt[offset] <= TCPOPT_NOP || opt[offset+1] == 0) | |
27 | return 1; | |
28 | else | |
29 | return opt[offset+1]; | |
30 | } | |
31 | ||
32 | static unsigned int | |
33 | tcpoptstrip_mangle_packet(struct sk_buff *skb, | |
34 | const struct xt_tcpoptstrip_target_info *info, | |
35 | unsigned int tcphoff, unsigned int minlen) | |
36 | { | |
37 | unsigned int optl, i, j; | |
38 | struct tcphdr *tcph; | |
39 | u_int16_t n, o; | |
40 | u_int8_t *opt; | |
41 | ||
42 | if (!skb_make_writable(skb, skb->len)) | |
43 | return NF_DROP; | |
44 | ||
45 | tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff); | |
46 | opt = (u_int8_t *)tcph; | |
47 | ||
48 | /* | |
49 | * Walk through all TCP options - if we find some option to remove, | |
50 | * set all octets to %TCPOPT_NOP and adjust checksum. | |
51 | */ | |
52 | for (i = sizeof(struct tcphdr); i < tcp_hdrlen(skb); i += optl) { | |
53 | optl = optlen(opt, i); | |
54 | ||
55 | if (i + optl > tcp_hdrlen(skb)) | |
56 | break; | |
57 | ||
58 | if (!tcpoptstrip_test_bit(info->strip_bmap, opt[i])) | |
59 | continue; | |
60 | ||
61 | for (j = 0; j < optl; ++j) { | |
62 | o = opt[i+j]; | |
63 | n = TCPOPT_NOP; | |
64 | if ((i + j) % 2 == 0) { | |
65 | o <<= 8; | |
66 | n <<= 8; | |
67 | } | |
68 | inet_proto_csum_replace2(&tcph->check, skb, htons(o), | |
69 | htons(n), 0); | |
70 | } | |
71 | memset(opt + i, TCPOPT_NOP, optl); | |
72 | } | |
73 | ||
74 | return XT_CONTINUE; | |
75 | } | |
76 | ||
77 | static unsigned int | |
7eb35586 | 78 | tcpoptstrip_tg4(struct sk_buff *skb, const struct xt_target_param *par) |
338e8a79 | 79 | { |
7eb35586 | 80 | return tcpoptstrip_mangle_packet(skb, par->targinfo, ip_hdrlen(skb), |
338e8a79 SS |
81 | sizeof(struct iphdr) + sizeof(struct tcphdr)); |
82 | } | |
83 | ||
84 | #if defined(CONFIG_IP6_NF_MANGLE) || defined(CONFIG_IP6_NF_MANGLE_MODULE) | |
85 | static unsigned int | |
7eb35586 | 86 | tcpoptstrip_tg6(struct sk_buff *skb, const struct xt_target_param *par) |
338e8a79 SS |
87 | { |
88 | struct ipv6hdr *ipv6h = ipv6_hdr(skb); | |
be8d0d79 | 89 | int tcphoff; |
338e8a79 SS |
90 | u_int8_t nexthdr; |
91 | ||
92 | nexthdr = ipv6h->nexthdr; | |
93 | tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr); | |
94 | if (tcphoff < 0) | |
95 | return NF_DROP; | |
96 | ||
7eb35586 | 97 | return tcpoptstrip_mangle_packet(skb, par->targinfo, tcphoff, |
338e8a79 SS |
98 | sizeof(*ipv6h) + sizeof(struct tcphdr)); |
99 | } | |
100 | #endif | |
101 | ||
102 | static struct xt_target tcpoptstrip_tg_reg[] __read_mostly = { | |
103 | { | |
104 | .name = "TCPOPTSTRIP", | |
ee999d8b | 105 | .family = NFPROTO_IPV4, |
338e8a79 SS |
106 | .table = "mangle", |
107 | .proto = IPPROTO_TCP, | |
108 | .target = tcpoptstrip_tg4, | |
109 | .targetsize = sizeof(struct xt_tcpoptstrip_target_info), | |
110 | .me = THIS_MODULE, | |
111 | }, | |
112 | #if defined(CONFIG_IP6_NF_MANGLE) || defined(CONFIG_IP6_NF_MANGLE_MODULE) | |
113 | { | |
114 | .name = "TCPOPTSTRIP", | |
ee999d8b | 115 | .family = NFPROTO_IPV6, |
338e8a79 SS |
116 | .table = "mangle", |
117 | .proto = IPPROTO_TCP, | |
118 | .target = tcpoptstrip_tg6, | |
119 | .targetsize = sizeof(struct xt_tcpoptstrip_target_info), | |
120 | .me = THIS_MODULE, | |
121 | }, | |
122 | #endif | |
123 | }; | |
124 | ||
125 | static int __init tcpoptstrip_tg_init(void) | |
126 | { | |
127 | return xt_register_targets(tcpoptstrip_tg_reg, | |
128 | ARRAY_SIZE(tcpoptstrip_tg_reg)); | |
129 | } | |
130 | ||
131 | static void __exit tcpoptstrip_tg_exit(void) | |
132 | { | |
133 | xt_unregister_targets(tcpoptstrip_tg_reg, | |
134 | ARRAY_SIZE(tcpoptstrip_tg_reg)); | |
135 | } | |
136 | ||
137 | module_init(tcpoptstrip_tg_init); | |
138 | module_exit(tcpoptstrip_tg_exit); | |
139 | MODULE_AUTHOR("Sven Schnelle <svens@bitebene.org>, Jan Engelhardt <jengelh@computergmbh.de>"); | |
2ae15b64 | 140 | MODULE_DESCRIPTION("Xtables: TCP option stripping"); |
338e8a79 SS |
141 | MODULE_LICENSE("GPL"); |
142 | MODULE_ALIAS("ipt_TCPOPTSTRIP"); | |
143 | MODULE_ALIAS("ip6t_TCPOPTSTRIP"); |