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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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