tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
2#include <linux/types.h>
3#include <linux/module.h>
4#include <net/ip.h>
5#include <linux/ipv6.h>
6#include <net/ipv6.h>
7#include <net/tcp.h>
8#include <net/udp.h>
9#include <linux/netfilter/x_tables.h>
10#include <linux/netfilter/xt_tcpudp.h>
11#include <linux/netfilter_ipv4/ip_tables.h>
12#include <linux/netfilter_ipv6/ip6_tables.h>
13
14MODULE_DESCRIPTION("Xtables: TCP, UDP and UDP-Lite match");
15MODULE_LICENSE("GPL");
16MODULE_ALIAS("xt_tcp");
17MODULE_ALIAS("xt_udp");
18MODULE_ALIAS("ipt_udp");
19MODULE_ALIAS("ipt_tcp");
20MODULE_ALIAS("ip6t_udp");
21MODULE_ALIAS("ip6t_tcp");
22
23/* Returns 1 if the port is matched by the range, 0 otherwise */
24static inline bool
25port_match(u_int16_t min, u_int16_t max, u_int16_t port, bool invert)
26{
27 return (port >= min && port <= max) ^ invert;
28}
29
30static bool
31tcp_find_option(u_int8_t option,
32 const struct sk_buff *skb,
33 unsigned int protoff,
34 unsigned int optlen,
35 bool invert,
36 bool *hotdrop)
37{
38 /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
39 const u_int8_t *op;
40 u_int8_t _opt[60 - sizeof(struct tcphdr)];
41 unsigned int i;
42
43 pr_debug("finding option\n");
44
45 if (!optlen)
46 return invert;
47
48 /* If we don't have the whole header, drop packet. */
49 op = skb_header_pointer(skb, protoff + sizeof(struct tcphdr),
50 optlen, _opt);
51 if (op == NULL) {
52 *hotdrop = true;
53 return false;
54 }
55
56 for (i = 0; i < optlen; ) {
57 if (op[i] == option) return !invert;
58 if (op[i] < 2) i++;
59 else i += op[i+1]?:1;
60 }
61
62 return invert;
63}
64
65static bool tcp_mt(const struct sk_buff *skb, struct xt_action_param *par)
66{
67 const struct tcphdr *th;
68 struct tcphdr _tcph;
69 const struct xt_tcp *tcpinfo = par->matchinfo;
70
71 if (par->fragoff != 0) {
72 /* To quote Alan:
73
74 Don't allow a fragment of TCP 8 bytes in. Nobody normal
75 causes this. Its a cracker trying to break in by doing a
76 flag overwrite to pass the direction checks.
77 */
78 if (par->fragoff == 1) {
79 pr_debug("Dropping evil TCP offset=1 frag.\n");
80 par->hotdrop = true;
81 }
82 /* Must not be a fragment. */
83 return false;
84 }
85
86 th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
87 if (th == NULL) {
88 /* We've been asked to examine this packet, and we
89 can't. Hence, no choice but to drop. */
90 pr_debug("Dropping evil TCP offset=0 tinygram.\n");
91 par->hotdrop = true;
92 return false;
93 }
94
95 if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
96 ntohs(th->source),
97 !!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
98 return false;
99 if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
100 ntohs(th->dest),
101 !!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
102 return false;
103 if (!NF_INVF(tcpinfo, XT_TCP_INV_FLAGS,
104 (((unsigned char *)th)[13] & tcpinfo->flg_mask) == tcpinfo->flg_cmp))
105 return false;
106 if (tcpinfo->option) {
107 if (th->doff * 4 < sizeof(_tcph)) {
108 par->hotdrop = true;
109 return false;
110 }
111 if (!tcp_find_option(tcpinfo->option, skb, par->thoff,
112 th->doff*4 - sizeof(_tcph),
113 tcpinfo->invflags & XT_TCP_INV_OPTION,
114 &par->hotdrop))
115 return false;
116 }
117 return true;
118}
119
120static int tcp_mt_check(const struct xt_mtchk_param *par)
121{
122 const struct xt_tcp *tcpinfo = par->matchinfo;
123
124 /* Must specify no unknown invflags */
125 return (tcpinfo->invflags & ~XT_TCP_INV_MASK) ? -EINVAL : 0;
126}
127
128static bool udp_mt(const struct sk_buff *skb, struct xt_action_param *par)
129{
130 const struct udphdr *uh;
131 struct udphdr _udph;
132 const struct xt_udp *udpinfo = par->matchinfo;
133
134 /* Must not be a fragment. */
135 if (par->fragoff != 0)
136 return false;
137
138 uh = skb_header_pointer(skb, par->thoff, sizeof(_udph), &_udph);
139 if (uh == NULL) {
140 /* We've been asked to examine this packet, and we
141 can't. Hence, no choice but to drop. */
142 pr_debug("Dropping evil UDP tinygram.\n");
143 par->hotdrop = true;
144 return false;
145 }
146
147 return port_match(udpinfo->spts[0], udpinfo->spts[1],
148 ntohs(uh->source),
149 !!(udpinfo->invflags & XT_UDP_INV_SRCPT))
150 && port_match(udpinfo->dpts[0], udpinfo->dpts[1],
151 ntohs(uh->dest),
152 !!(udpinfo->invflags & XT_UDP_INV_DSTPT));
153}
154
155static int udp_mt_check(const struct xt_mtchk_param *par)
156{
157 const struct xt_udp *udpinfo = par->matchinfo;
158
159 /* Must specify no unknown invflags */
160 return (udpinfo->invflags & ~XT_UDP_INV_MASK) ? -EINVAL : 0;
161}
162
163static struct xt_match tcpudp_mt_reg[] __read_mostly = {
164 {
165 .name = "tcp",
166 .family = NFPROTO_IPV4,
167 .checkentry = tcp_mt_check,
168 .match = tcp_mt,
169 .matchsize = sizeof(struct xt_tcp),
170 .proto = IPPROTO_TCP,
171 .me = THIS_MODULE,
172 },
173 {
174 .name = "tcp",
175 .family = NFPROTO_IPV6,
176 .checkentry = tcp_mt_check,
177 .match = tcp_mt,
178 .matchsize = sizeof(struct xt_tcp),
179 .proto = IPPROTO_TCP,
180 .me = THIS_MODULE,
181 },
182 {
183 .name = "udp",
184 .family = NFPROTO_IPV4,
185 .checkentry = udp_mt_check,
186 .match = udp_mt,
187 .matchsize = sizeof(struct xt_udp),
188 .proto = IPPROTO_UDP,
189 .me = THIS_MODULE,
190 },
191 {
192 .name = "udp",
193 .family = NFPROTO_IPV6,
194 .checkentry = udp_mt_check,
195 .match = udp_mt,
196 .matchsize = sizeof(struct xt_udp),
197 .proto = IPPROTO_UDP,
198 .me = THIS_MODULE,
199 },
200 {
201 .name = "udplite",
202 .family = NFPROTO_IPV4,
203 .checkentry = udp_mt_check,
204 .match = udp_mt,
205 .matchsize = sizeof(struct xt_udp),
206 .proto = IPPROTO_UDPLITE,
207 .me = THIS_MODULE,
208 },
209 {
210 .name = "udplite",
211 .family = NFPROTO_IPV6,
212 .checkentry = udp_mt_check,
213 .match = udp_mt,
214 .matchsize = sizeof(struct xt_udp),
215 .proto = IPPROTO_UDPLITE,
216 .me = THIS_MODULE,
217 },
218};
219
220static int __init tcpudp_mt_init(void)
221{
222 return xt_register_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
223}
224
225static void __exit tcpudp_mt_exit(void)
226{
227 xt_unregister_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
228}
229
230module_init(tcpudp_mt_init);
231module_exit(tcpudp_mt_exit);