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[linux-2.6] / net / netfilter / xt_tcpudp.c
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("x_tables match for TCP and UDP(-Lite), supports IPv4 and IPv6");
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 int
31 port_match(u_int16_t min, u_int16_t max, u_int16_t port, int invert)
32 {
33         int ret;
34
35         ret = (port >= min && port <= max) ^ invert;
36         return ret;
37 }
38
39 static int
40 tcp_find_option(u_int8_t option,
41                 const struct sk_buff *skb,
42                 unsigned int protoff,
43                 unsigned int optlen,
44                 int invert,
45                 int *hotdrop)
46 {
47         /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
48         u_int8_t _opt[60 - sizeof(struct tcphdr)], *op;
49         unsigned int i;
50
51         duprintf("tcp_match: finding option\n");
52
53         if (!optlen)
54                 return invert;
55
56         /* If we don't have the whole header, drop packet. */
57         op = skb_header_pointer(skb, protoff + sizeof(struct tcphdr),
58                                 optlen, _opt);
59         if (op == NULL) {
60                 *hotdrop = 1;
61                 return 0;
62         }
63
64         for (i = 0; i < optlen; ) {
65                 if (op[i] == option) return !invert;
66                 if (op[i] < 2) i++;
67                 else i += op[i+1]?:1;
68         }
69
70         return invert;
71 }
72
73 static int
74 tcp_match(const struct sk_buff *skb,
75           const struct net_device *in,
76           const struct net_device *out,
77           const struct xt_match *match,
78           const void *matchinfo,
79           int offset,
80           unsigned int protoff,
81           int *hotdrop)
82 {
83         struct tcphdr _tcph, *th;
84         const struct xt_tcp *tcpinfo = matchinfo;
85
86         if (offset) {
87                 /* To quote Alan:
88
89                    Don't allow a fragment of TCP 8 bytes in. Nobody normal
90                    causes this. Its a cracker trying to break in by doing a
91                    flag overwrite to pass the direction checks.
92                 */
93                 if (offset == 1) {
94                         duprintf("Dropping evil TCP offset=1 frag.\n");
95                         *hotdrop = 1;
96                 }
97                 /* Must not be a fragment. */
98                 return 0;
99         }
100
101 #define FWINVTCP(bool,invflg) ((bool) ^ !!(tcpinfo->invflags & invflg))
102
103         th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
104         if (th == NULL) {
105                 /* We've been asked to examine this packet, and we
106                    can't.  Hence, no choice but to drop. */
107                 duprintf("Dropping evil TCP offset=0 tinygram.\n");
108                 *hotdrop = 1;
109                 return 0;
110         }
111
112         if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
113                         ntohs(th->source),
114                         !!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
115                 return 0;
116         if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
117                         ntohs(th->dest),
118                         !!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
119                 return 0;
120         if (!FWINVTCP((((unsigned char *)th)[13] & tcpinfo->flg_mask)
121                       == tcpinfo->flg_cmp,
122                       XT_TCP_INV_FLAGS))
123                 return 0;
124         if (tcpinfo->option) {
125                 if (th->doff * 4 < sizeof(_tcph)) {
126                         *hotdrop = 1;
127                         return 0;
128                 }
129                 if (!tcp_find_option(tcpinfo->option, skb, protoff,
130                                      th->doff*4 - sizeof(_tcph),
131                                      tcpinfo->invflags & XT_TCP_INV_OPTION,
132                                      hotdrop))
133                         return 0;
134         }
135         return 1;
136 }
137
138 /* Called when user tries to insert an entry of this type. */
139 static int
140 tcp_checkentry(const char *tablename,
141                const void *info,
142                const struct xt_match *match,
143                void *matchinfo,
144                unsigned int hook_mask)
145 {
146         const struct xt_tcp *tcpinfo = matchinfo;
147
148         /* Must specify no unknown invflags */
149         return !(tcpinfo->invflags & ~XT_TCP_INV_MASK);
150 }
151
152 static int
153 udp_match(const struct sk_buff *skb,
154           const struct net_device *in,
155           const struct net_device *out,
156           const struct xt_match *match,
157           const void *matchinfo,
158           int offset,
159           unsigned int protoff,
160           int *hotdrop)
161 {
162         struct udphdr _udph, *uh;
163         const struct xt_udp *udpinfo = matchinfo;
164
165         /* Must not be a fragment. */
166         if (offset)
167                 return 0;
168
169         uh = skb_header_pointer(skb, protoff, sizeof(_udph), &_udph);
170         if (uh == NULL) {
171                 /* We've been asked to examine this packet, and we
172                    can't.  Hence, no choice but to drop. */
173                 duprintf("Dropping evil UDP tinygram.\n");
174                 *hotdrop = 1;
175                 return 0;
176         }
177
178         return port_match(udpinfo->spts[0], udpinfo->spts[1],
179                           ntohs(uh->source),
180                           !!(udpinfo->invflags & XT_UDP_INV_SRCPT))
181                 && port_match(udpinfo->dpts[0], udpinfo->dpts[1],
182                               ntohs(uh->dest),
183                               !!(udpinfo->invflags & XT_UDP_INV_DSTPT));
184 }
185
186 /* Called when user tries to insert an entry of this type. */
187 static int
188 udp_checkentry(const char *tablename,
189                const void *info,
190                const struct xt_match *match,
191                void *matchinfo,
192                unsigned int hook_mask)
193 {
194         const struct xt_tcp *udpinfo = matchinfo;
195
196         /* Must specify no unknown invflags */
197         return !(udpinfo->invflags & ~XT_UDP_INV_MASK);
198 }
199
200 static struct xt_match xt_tcpudp_match[] = {
201         {
202                 .name           = "tcp",
203                 .family         = AF_INET,
204                 .checkentry     = tcp_checkentry,
205                 .match          = tcp_match,
206                 .matchsize      = sizeof(struct xt_tcp),
207                 .proto          = IPPROTO_TCP,
208                 .me             = THIS_MODULE,
209         },
210         {
211                 .name           = "tcp",
212                 .family         = AF_INET6,
213                 .checkentry     = tcp_checkentry,
214                 .match          = tcp_match,
215                 .matchsize      = sizeof(struct xt_tcp),
216                 .proto          = IPPROTO_TCP,
217                 .me             = THIS_MODULE,
218         },
219         {
220                 .name           = "udp",
221                 .family         = AF_INET,
222                 .checkentry     = udp_checkentry,
223                 .match          = udp_match,
224                 .matchsize      = sizeof(struct xt_udp),
225                 .proto          = IPPROTO_UDP,
226                 .me             = THIS_MODULE,
227         },
228         {
229                 .name           = "udp",
230                 .family         = AF_INET6,
231                 .checkentry     = udp_checkentry,
232                 .match          = udp_match,
233                 .matchsize      = sizeof(struct xt_udp),
234                 .proto          = IPPROTO_UDP,
235                 .me             = THIS_MODULE,
236         },
237         {
238                 .name           = "udplite",
239                 .family         = AF_INET,
240                 .checkentry     = udp_checkentry,
241                 .match          = udp_match,
242                 .matchsize      = sizeof(struct xt_udp),
243                 .proto          = IPPROTO_UDPLITE,
244                 .me             = THIS_MODULE,
245         },
246         {
247                 .name           = "udplite",
248                 .family         = AF_INET6,
249                 .checkentry     = udp_checkentry,
250                 .match          = udp_match,
251                 .matchsize      = sizeof(struct xt_udp),
252                 .proto          = IPPROTO_UDPLITE,
253                 .me             = THIS_MODULE,
254         },
255 };
256
257 static int __init xt_tcpudp_init(void)
258 {
259         return xt_register_matches(xt_tcpudp_match,
260                                    ARRAY_SIZE(xt_tcpudp_match));
261 }
262
263 static void __exit xt_tcpudp_fini(void)
264 {
265         xt_unregister_matches(xt_tcpudp_match, ARRAY_SIZE(xt_tcpudp_match));
266 }
267
268 module_init(xt_tcpudp_init);
269 module_exit(xt_tcpudp_fini);