1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
|
/*
* A module for stripping a specific TCP option from TCP packets.
*
* Copyright (C) 2007 Sven Schnelle <svens@bitebene.org>
* Copyright © CC Computer Consultants GmbH, 2007
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/tcp.h>
#include <net/ipv6.h>
#include <net/tcp.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_TCPOPTSTRIP.h>
static inline unsigned int optlen(const u_int8_t *opt, unsigned int offset)
{
/* Beware zero-length options: make finite progress */
if (opt[offset] <= TCPOPT_NOP || opt[offset+1] == 0)
return 1;
else
return opt[offset+1];
}
static unsigned int
tcpoptstrip_mangle_packet(struct sk_buff *skb,
const struct xt_action_param *par,
unsigned int tcphoff, unsigned int minlen)
{
const struct xt_tcpoptstrip_target_info *info = par->targinfo;
unsigned int optl, i, j;
struct tcphdr *tcph;
u_int16_t n, o;
u_int8_t *opt;
int len, tcp_hdrlen;
/* This is a fragment, no TCP header is available */
if (par->fragoff != 0)
return XT_CONTINUE;
if (!skb_make_writable(skb, skb->len))
return NF_DROP;
len = skb->len - tcphoff;
if (len < (int)sizeof(struct tcphdr))
return NF_DROP;
tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
tcp_hdrlen = tcph->doff * 4;
if (len < tcp_hdrlen)
return NF_DROP;
opt = (u_int8_t *)tcph;
/*
* Walk through all TCP options - if we find some option to remove,
* set all octets to %TCPOPT_NOP and adjust checksum.
*/
for (i = sizeof(struct tcphdr); i < tcp_hdrlen - 1; i += optl) {
optl = optlen(opt, i);
if (i + optl > tcp_hdrlen)
break;
if (!tcpoptstrip_test_bit(info->strip_bmap, opt[i]))
continue;
for (j = 0; j < optl; ++j) {
o = opt[i+j];
n = TCPOPT_NOP;
if ((i + j) % 2 == 0) {
o <<= 8;
n <<= 8;
}
inet_proto_csum_replace2(&tcph->check, skb, htons(o),
htons(n), 0);
}
memset(opt + i, TCPOPT_NOP, optl);
}
return XT_CONTINUE;
}
static unsigned int
tcpoptstrip_tg4(struct sk_buff *skb, const struct xt_action_param *par)
{
return tcpoptstrip_mangle_packet(skb, par, ip_hdrlen(skb),
sizeof(struct iphdr) + sizeof(struct tcphdr));
}
#if IS_ENABLED(CONFIG_IP6_NF_MANGLE)
static unsigned int
tcpoptstrip_tg6(struct sk_buff *skb, const struct xt_action_param *par)
{
struct ipv6hdr *ipv6h = ipv6_hdr(skb);
int tcphoff;
u_int8_t nexthdr;
__be16 frag_off;
nexthdr = ipv6h->nexthdr;
tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr, &frag_off);
if (tcphoff < 0)
return NF_DROP;
return tcpoptstrip_mangle_packet(skb, par, tcphoff,
sizeof(*ipv6h) + sizeof(struct tcphdr));
}
#endif
static struct xt_target tcpoptstrip_tg_reg[] __read_mostly = {
{
.name = "TCPOPTSTRIP",
.family = NFPROTO_IPV4,
.table = "mangle",
.proto = IPPROTO_TCP,
.target = tcpoptstrip_tg4,
.targetsize = sizeof(struct xt_tcpoptstrip_target_info),
.me = THIS_MODULE,
},
#if IS_ENABLED(CONFIG_IP6_NF_MANGLE)
{
.name = "TCPOPTSTRIP",
.family = NFPROTO_IPV6,
.table = "mangle",
.proto = IPPROTO_TCP,
.target = tcpoptstrip_tg6,
.targetsize = sizeof(struct xt_tcpoptstrip_target_info),
.me = THIS_MODULE,
},
#endif
};
static int __init tcpoptstrip_tg_init(void)
{
return xt_register_targets(tcpoptstrip_tg_reg,
ARRAY_SIZE(tcpoptstrip_tg_reg));
}
static void __exit tcpoptstrip_tg_exit(void)
{
xt_unregister_targets(tcpoptstrip_tg_reg,
ARRAY_SIZE(tcpoptstrip_tg_reg));
}
module_init(tcpoptstrip_tg_init);
module_exit(tcpoptstrip_tg_exit);
MODULE_AUTHOR("Sven Schnelle <svens@bitebene.org>, Jan Engelhardt <jengelh@medozas.de>");
MODULE_DESCRIPTION("Xtables: TCP option stripping");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_TCPOPTSTRIP");
MODULE_ALIAS("ip6t_TCPOPTSTRIP");
|
