1 #include <linux/types.h>
2 #include <linux/module.h>
3 #include <net/ip.h>
4 #include <linux/ipv6.h>
5 #include <net/ipv6.h>
6 #include <net/tcp.h>
7 #include <net/udp.h>
8 #include <linux/netfilter/x_tables.h>
9 #include <linux/netfilter/xt_tcpudp.h>
10 #include <linux/netfilter_ipv4/ip_tables.h>
11 #include <linux/netfilter_ipv6/ip6_tables.h>
12
13 MODULE_DESCRIPTION("Xtables: TCP, UDP and UDP-Lite match");
14 MODULE_LICENSE("GPL");
15 MODULE_ALIAS("xt_tcp");
16 MODULE_ALIAS("xt_udp");
17 MODULE_ALIAS("ipt_udp");
18 MODULE_ALIAS("ipt_tcp");
19 MODULE_ALIAS("ip6t_udp");
20 MODULE_ALIAS("ip6t_tcp");
21
22 #ifdef DEBUG_IP_FIREWALL_USER
23 #define duprintf(format, args...) printk(format , ## args)
24 #else
25 #define duprintf(format, args...)
26 #endif
27
28
29 /* Returns 1 if the port is matched by the range, 0 otherwise */
30 static inline bool
31 port_match(u_int16_t min, u_int16_t max, u_int16_t port, bool invert)
32 {
33 return (port >= min && port <= max) ^ invert;
34 }
35
36 static bool
37 tcp_find_option(u_int8_t option,
38 const struct sk_buff *skb,
39 unsigned int protoff,
40 unsigned int optlen,
41 bool invert,
42 bool *hotdrop)
43 {
44 /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
45 const u_int8_t *op;
46 u_int8_t _opt[60 - sizeof(struct tcphdr)];
47 unsigned int i;
48
49 duprintf("tcp_match: finding option\n");
50
51 if (!optlen)
52 return invert;
53
54 /* If we don't have the whole header, drop packet. */
55 op = skb_header_pointer(skb, protoff + sizeof(struct tcphdr),
56 optlen, _opt);
57 if (op == NULL) {
58 *hotdrop = true;
59 return false;
60 }
61
62 for (i = 0; i < optlen; ) {
63 if (op[i] == option) return !invert;
64 if (op[i] < 2) i++;
65 else i += op[i+1]?:1;
66 }
67
68 return invert;
69 }
70
71 static bool tcp_mt(const struct sk_buff *skb, const struct xt_match_param *par)
72 {
73 const struct tcphdr *th;
74 struct tcphdr _tcph;
75 const struct xt_tcp *tcpinfo = par->matchinfo;
76
77 if (par->fragoff != 0) {
78 /* To quote Alan:
79
80 Don't allow a fragment of TCP 8 bytes in. Nobody normal
81 causes this. Its a cracker trying to break in by doing a
82 flag overwrite to pass the direction checks.
83 */
84 if (par->fragoff == 1) {
85 duprintf("Dropping evil TCP offset=1 frag.\n");
86 *par->hotdrop = true;
87 }
88 /* Must not be a fragment. */
89 return false;
90 }
91
92 #define FWINVTCP(bool, invflg) ((bool) ^ !!(tcpinfo->invflags & (invflg)))
93
94 th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
95 if (th == NULL) {
96 /* We've been asked to examine this packet, and we
97 can't. Hence, no choice but to drop. */
98 duprintf("Dropping evil TCP offset=0 tinygram.\n");
99 *par->hotdrop = true;
100 return false;
101 }
102
103 if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
104 ntohs(th->source),
105 !!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
106 return false;
107 if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
108 ntohs(th->dest),
109 !!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
110 return false;
111 if (!FWINVTCP((((unsigned char *)th)[13] & tcpinfo->flg_mask)
112 == tcpinfo->flg_cmp,
113 XT_TCP_INV_FLAGS))
114 return false;
115 if (tcpinfo->option) {
116 if (th->doff * 4 < sizeof(_tcph)) {
117 *par->hotdrop = true;
118 return false;
119 }
120 if (!tcp_find_option(tcpinfo->option, skb, par->thoff,
121 th->doff*4 - sizeof(_tcph),
122 tcpinfo->invflags & XT_TCP_INV_OPTION,
123 par->hotdrop))
124 return false;
125 }
126 return true;
127 }
128
129 static bool tcp_mt_check(const struct xt_mtchk_param *par)
130 {
131 const struct xt_tcp *tcpinfo = par->matchinfo;
132
133 /* Must specify no unknown invflags */
134 return !(tcpinfo->invflags & ~XT_TCP_INV_MASK);
135 }
136
137 static bool udp_mt(const struct sk_buff *skb, const struct xt_match_param *par)
138 {
139 const struct udphdr *uh;
140 struct udphdr _udph;
141 const struct xt_udp *udpinfo = par->matchinfo;
142
143 /* Must not be a fragment. */
144 if (par->fragoff != 0)
145 return false;
146
147 uh = skb_header_pointer(skb, par->thoff, sizeof(_udph), &_udph);
148 if (uh == NULL) {
149 /* We've been asked to examine this packet, and we
150 can't. Hence, no choice but to drop. */
151 duprintf("Dropping evil UDP tinygram.\n");
152 *par->hotdrop = true;
153 return false;
154 }
155
156 return port_match(udpinfo->spts[0], udpinfo->spts[1],
157 ntohs(uh->source),
158 !!(udpinfo->invflags & XT_UDP_INV_SRCPT))
159 && port_match(udpinfo->dpts[0], udpinfo->dpts[1],
160 ntohs(uh->dest),
161 !!(udpinfo->invflags & XT_UDP_INV_DSTPT));
162 }
163
164 static bool udp_mt_check(const struct xt_mtchk_param *par)
165 {
166 const struct xt_udp *udpinfo = par->matchinfo;
167
168 /* Must specify no unknown invflags */
169 return !(udpinfo->invflags & ~XT_UDP_INV_MASK);
170 }
171
172 static struct xt_match tcpudp_mt_reg[] __read_mostly = {
173 {
174 .name = "tcp",
175 .family = NFPROTO_IPV4,
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 = "tcp",
184 .family = NFPROTO_IPV6,
185 .checkentry = tcp_mt_check,
186 .match = tcp_mt,
187 .matchsize = sizeof(struct xt_tcp),
188 .proto = IPPROTO_TCP,
189 .me = THIS_MODULE,
190 },
191 {
192 .name = "udp",
193 .family = NFPROTO_IPV4,
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 = "udp",
202 .family = NFPROTO_IPV6,
203 .checkentry = udp_mt_check,
204 .match = udp_mt,
205 .matchsize = sizeof(struct xt_udp),
206 .proto = IPPROTO_UDP,
207 .me = THIS_MODULE,
208 },
209 {
210 .name = "udplite",
211 .family = NFPROTO_IPV4,
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 .name = "udplite",
220 .family = NFPROTO_IPV6,
221 .checkentry = udp_mt_check,
222 .match = udp_mt,
223 .matchsize = sizeof(struct xt_udp),
224 .proto = IPPROTO_UDPLITE,
225 .me = THIS_MODULE,
226 },
227 };
228
229 static int __init tcpudp_mt_init(void)
230 {
231 return xt_register_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
232 }
233
234 static void __exit tcpudp_mt_exit(void)
235 {
236 xt_unregister_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
237 }
238
239 module_init(tcpudp_mt_init);
240 module_exit(tcpudp_mt_exit);
241
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