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Linux/net/netfilter/xt_tcpudp.c

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  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 
 14 MODULE_DESCRIPTION("Xtables: TCP, UDP and UDP-Lite match");
 15 MODULE_LICENSE("GPL");
 16 MODULE_ALIAS("xt_tcp");
 17 MODULE_ALIAS("xt_udp");
 18 MODULE_ALIAS("ipt_udp");
 19 MODULE_ALIAS("ipt_tcp");
 20 MODULE_ALIAS("ip6t_udp");
 21 MODULE_ALIAS("ip6t_tcp");
 22 
 23 /* Returns 1 if the port is matched by the range, 0 otherwise */
 24 static inline bool
 25 port_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 
 30 static bool
 31 tcp_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 
 65 static 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 #define FWINVTCP(bool, invflg) ((bool) ^ !!(tcpinfo->invflags & (invflg)))
 87 
 88         th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
 89         if (th == NULL) {
 90                 /* We've been asked to examine this packet, and we
 91                    can't.  Hence, no choice but to drop. */
 92                 pr_debug("Dropping evil TCP offset=0 tinygram.\n");
 93                 par->hotdrop = true;
 94                 return false;
 95         }
 96 
 97         if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
 98                         ntohs(th->source),
 99                         !!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
100                 return false;
101         if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
102                         ntohs(th->dest),
103                         !!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
104                 return false;
105         if (!FWINVTCP((((unsigned char *)th)[13] & tcpinfo->flg_mask)
106                       == tcpinfo->flg_cmp,
107                       XT_TCP_INV_FLAGS))
108                 return false;
109         if (tcpinfo->option) {
110                 if (th->doff * 4 < sizeof(_tcph)) {
111                         par->hotdrop = true;
112                         return false;
113                 }
114                 if (!tcp_find_option(tcpinfo->option, skb, par->thoff,
115                                      th->doff*4 - sizeof(_tcph),
116                                      tcpinfo->invflags & XT_TCP_INV_OPTION,
117                                      &par->hotdrop))
118                         return false;
119         }
120         return true;
121 }
122 
123 static int tcp_mt_check(const struct xt_mtchk_param *par)
124 {
125         const struct xt_tcp *tcpinfo = par->matchinfo;
126 
127         /* Must specify no unknown invflags */
128         return (tcpinfo->invflags & ~XT_TCP_INV_MASK) ? -EINVAL : 0;
129 }
130 
131 static bool udp_mt(const struct sk_buff *skb, struct xt_action_param *par)
132 {
133         const struct udphdr *uh;
134         struct udphdr _udph;
135         const struct xt_udp *udpinfo = par->matchinfo;
136 
137         /* Must not be a fragment. */
138         if (par->fragoff != 0)
139                 return false;
140 
141         uh = skb_header_pointer(skb, par->thoff, sizeof(_udph), &_udph);
142         if (uh == NULL) {
143                 /* We've been asked to examine this packet, and we
144                    can't.  Hence, no choice but to drop. */
145                 pr_debug("Dropping evil UDP tinygram.\n");
146                 par->hotdrop = true;
147                 return false;
148         }
149 
150         return port_match(udpinfo->spts[0], udpinfo->spts[1],
151                           ntohs(uh->source),
152                           !!(udpinfo->invflags & XT_UDP_INV_SRCPT))
153                 && port_match(udpinfo->dpts[0], udpinfo->dpts[1],
154                               ntohs(uh->dest),
155                               !!(udpinfo->invflags & XT_UDP_INV_DSTPT));
156 }
157 
158 static int udp_mt_check(const struct xt_mtchk_param *par)
159 {
160         const struct xt_udp *udpinfo = par->matchinfo;
161 
162         /* Must specify no unknown invflags */
163         return (udpinfo->invflags & ~XT_UDP_INV_MASK) ? -EINVAL : 0;
164 }
165 
166 static struct xt_match tcpudp_mt_reg[] __read_mostly = {
167         {
168                 .name           = "tcp",
169                 .family         = NFPROTO_IPV4,
170                 .checkentry     = tcp_mt_check,
171                 .match          = tcp_mt,
172                 .matchsize      = sizeof(struct xt_tcp),
173                 .proto          = IPPROTO_TCP,
174                 .me             = THIS_MODULE,
175         },
176         {
177                 .name           = "tcp",
178                 .family         = NFPROTO_IPV6,
179                 .checkentry     = tcp_mt_check,
180                 .match          = tcp_mt,
181                 .matchsize      = sizeof(struct xt_tcp),
182                 .proto          = IPPROTO_TCP,
183                 .me             = THIS_MODULE,
184         },
185         {
186                 .name           = "udp",
187                 .family         = NFPROTO_IPV4,
188                 .checkentry     = udp_mt_check,
189                 .match          = udp_mt,
190                 .matchsize      = sizeof(struct xt_udp),
191                 .proto          = IPPROTO_UDP,
192                 .me             = THIS_MODULE,
193         },
194         {
195                 .name           = "udp",
196                 .family         = NFPROTO_IPV6,
197                 .checkentry     = udp_mt_check,
198                 .match          = udp_mt,
199                 .matchsize      = sizeof(struct xt_udp),
200                 .proto          = IPPROTO_UDP,
201                 .me             = THIS_MODULE,
202         },
203         {
204                 .name           = "udplite",
205                 .family         = NFPROTO_IPV4,
206                 .checkentry     = udp_mt_check,
207                 .match          = udp_mt,
208                 .matchsize      = sizeof(struct xt_udp),
209                 .proto          = IPPROTO_UDPLITE,
210                 .me             = THIS_MODULE,
211         },
212         {
213                 .name           = "udplite",
214                 .family         = NFPROTO_IPV6,
215                 .checkentry     = udp_mt_check,
216                 .match          = udp_mt,
217                 .matchsize      = sizeof(struct xt_udp),
218                 .proto          = IPPROTO_UDPLITE,
219                 .me             = THIS_MODULE,
220         },
221 };
222 
223 static int __init tcpudp_mt_init(void)
224 {
225         return xt_register_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
226 }
227 
228 static void __exit tcpudp_mt_exit(void)
229 {
230         xt_unregister_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
231 }
232 
233 module_init(tcpudp_mt_init);
234 module_exit(tcpudp_mt_exit);
235 

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