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
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
|
// SPDX-License-Identifier: GPL-2.0-only
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/types.h>
#include <linux/module.h>
#include <net/ip.h>
#include <linux/ipv6.h>
#include <net/ipv6.h>
#include <net/tcp.h>
#include <net/udp.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_tcpudp.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
MODULE_DESCRIPTION("Xtables: TCP, UDP and UDP-Lite match");
MODULE_LICENSE("GPL");
MODULE_ALIAS("xt_tcp");
MODULE_ALIAS("xt_udp");
MODULE_ALIAS("ipt_udp");
MODULE_ALIAS("ipt_tcp");
MODULE_ALIAS("ip6t_udp");
MODULE_ALIAS("ip6t_tcp");
/* Returns 1 if the port is matched by the range, 0 otherwise */
static inline bool
port_match(u_int16_t min, u_int16_t max, u_int16_t port, bool invert)
{
return (port >= min && port <= max) ^ invert;
}
static bool
tcp_find_option(u_int8_t option,
const struct sk_buff *skb,
unsigned int protoff,
unsigned int optlen,
bool invert,
bool *hotdrop)
{
/* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
const u_int8_t *op;
u_int8_t _opt[60 - sizeof(struct tcphdr)];
unsigned int i;
pr_debug("finding option\n");
if (!optlen)
return invert;
/* If we don't have the whole header, drop packet. */
op = skb_header_pointer(skb, protoff + sizeof(struct tcphdr),
optlen, _opt);
if (op == NULL) {
*hotdrop = true;
return false;
}
for (i = 0; i < optlen; ) {
if (op[i] == option) return !invert;
if (op[i] < 2) i++;
else i += op[i+1]?:1;
}
return invert;
}
static bool tcp_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
const struct tcphdr *th;
struct tcphdr _tcph;
const struct xt_tcp *tcpinfo = par->matchinfo;
if (par->fragoff != 0) {
/* To quote Alan:
Don't allow a fragment of TCP 8 bytes in. Nobody normal
causes this. Its a cracker trying to break in by doing a
flag overwrite to pass the direction checks.
*/
if (par->fragoff == 1) {
pr_debug("Dropping evil TCP offset=1 frag.\n");
par->hotdrop = true;
}
/* Must not be a fragment. */
return false;
}
th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
if (th == NULL) {
/* We've been asked to examine this packet, and we
can't. Hence, no choice but to drop. */
pr_debug("Dropping evil TCP offset=0 tinygram.\n");
par->hotdrop = true;
return false;
}
if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
ntohs(th->source),
!!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
return false;
if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
ntohs(th->dest),
!!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
return false;
if (!NF_INVF(tcpinfo, XT_TCP_INV_FLAGS,
(((unsigned char *)th)[13] & tcpinfo->flg_mask) == tcpinfo->flg_cmp))
return false;
if (tcpinfo->option) {
if (th->doff * 4 < sizeof(_tcph)) {
par->hotdrop = true;
return false;
}
if (!tcp_find_option(tcpinfo->option, skb, par->thoff,
th->doff*4 - sizeof(_tcph),
tcpinfo->invflags & XT_TCP_INV_OPTION,
&par->hotdrop))
return false;
}
return true;
}
static int tcp_mt_check(const struct xt_mtchk_param *par)
{
const struct xt_tcp *tcpinfo = par->matchinfo;
/* Must specify no unknown invflags */
return (tcpinfo->invflags & ~XT_TCP_INV_MASK) ? -EINVAL : 0;
}
static bool udp_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
const struct udphdr *uh;
struct udphdr _udph;
const struct xt_udp *udpinfo = par->matchinfo;
/* Must not be a fragment. */
if (par->fragoff != 0)
return false;
uh = skb_header_pointer(skb, par->thoff, sizeof(_udph), &_udph);
if (uh == NULL) {
/* We've been asked to examine this packet, and we
can't. Hence, no choice but to drop. */
pr_debug("Dropping evil UDP tinygram.\n");
par->hotdrop = true;
return false;
}
return port_match(udpinfo->spts[0], udpinfo->spts[1],
ntohs(uh->source),
!!(udpinfo->invflags & XT_UDP_INV_SRCPT))
&& port_match(udpinfo->dpts[0], udpinfo->dpts[1],
ntohs(uh->dest),
!!(udpinfo->invflags & XT_UDP_INV_DSTPT));
}
static int udp_mt_check(const struct xt_mtchk_param *par)
{
const struct xt_udp *udpinfo = par->matchinfo;
/* Must specify no unknown invflags */
return (udpinfo->invflags & ~XT_UDP_INV_MASK) ? -EINVAL : 0;
}
static struct xt_match tcpudp_mt_reg[] __read_mostly = {
{
.name = "tcp",
.family = NFPROTO_IPV4,
.checkentry = tcp_mt_check,
.match = tcp_mt,
.matchsize = sizeof(struct xt_tcp),
.proto = IPPROTO_TCP,
.me = THIS_MODULE,
},
{
.name = "tcp",
.family = NFPROTO_IPV6,
.checkentry = tcp_mt_check,
.match = tcp_mt,
.matchsize = sizeof(struct xt_tcp),
.proto = IPPROTO_TCP,
.me = THIS_MODULE,
},
{
.name = "udp",
.family = NFPROTO_IPV4,
.checkentry = udp_mt_check,
.match = udp_mt,
.matchsize = sizeof(struct xt_udp),
.proto = IPPROTO_UDP,
.me = THIS_MODULE,
},
{
.name = "udp",
.family = NFPROTO_IPV6,
.checkentry = udp_mt_check,
.match = udp_mt,
.matchsize = sizeof(struct xt_udp),
.proto = IPPROTO_UDP,
.me = THIS_MODULE,
},
{
.name = "udplite",
.family = NFPROTO_IPV4,
.checkentry = udp_mt_check,
.match = udp_mt,
.matchsize = sizeof(struct xt_udp),
.proto = IPPROTO_UDPLITE,
.me = THIS_MODULE,
},
{
.name = "udplite",
.family = NFPROTO_IPV6,
.checkentry = udp_mt_check,
.match = udp_mt,
.matchsize = sizeof(struct xt_udp),
.proto = IPPROTO_UDPLITE,
.me = THIS_MODULE,
},
};
static int __init tcpudp_mt_init(void)
{
return xt_register_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
}
static void __exit tcpudp_mt_exit(void)
{
xt_unregister_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
}
module_init(tcpudp_mt_init);
module_exit(tcpudp_mt_exit);
|
