tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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
23static 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
32static unsigned int
33tcpoptstrip_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
77static unsigned int
78tcpoptstrip_tg4(struct sk_buff *skb, const struct xt_target_param *par)
79{
80 return tcpoptstrip_mangle_packet(skb, par->targinfo, ip_hdrlen(skb),
81 sizeof(struct iphdr) + sizeof(struct tcphdr));
82}
83
84#if defined(CONFIG_IP6_NF_MANGLE) || defined(CONFIG_IP6_NF_MANGLE_MODULE)
85static unsigned int
86tcpoptstrip_tg6(struct sk_buff *skb, const struct xt_target_param *par)
87{
88 struct ipv6hdr *ipv6h = ipv6_hdr(skb);
89 int tcphoff;
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
97 return tcpoptstrip_mangle_packet(skb, par->targinfo, tcphoff,
98 sizeof(*ipv6h) + sizeof(struct tcphdr));
99}
100#endif
101
102static struct xt_target tcpoptstrip_tg_reg[] __read_mostly = {
103 {
104 .name = "TCPOPTSTRIP",
105 .family = NFPROTO_IPV4,
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",
115 .family = NFPROTO_IPV6,
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
125static int __init tcpoptstrip_tg_init(void)
126{
127 return xt_register_targets(tcpoptstrip_tg_reg,
128 ARRAY_SIZE(tcpoptstrip_tg_reg));
129}
130
131static void __exit tcpoptstrip_tg_exit(void)
132{
133 xt_unregister_targets(tcpoptstrip_tg_reg,
134 ARRAY_SIZE(tcpoptstrip_tg_reg));
135}
136
137module_init(tcpoptstrip_tg_init);
138module_exit(tcpoptstrip_tg_exit);
139MODULE_AUTHOR("Sven Schnelle <svens@bitebene.org>, Jan Engelhardt <jengelh@computergmbh.de>");
140MODULE_DESCRIPTION("Xtables: TCP option stripping");
141MODULE_LICENSE("GPL");
142MODULE_ALIAS("ipt_TCPOPTSTRIP");
143MODULE_ALIAS("ip6t_TCPOPTSTRIP");