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, 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 void *matchinfo,
  78           int offset,
  79           unsigned int protoff,
  80           int *hotdrop)
  81 {
  82         struct tcphdr _tcph, *th;
  83         const struct xt_tcp *tcpinfo = matchinfo;
  84
  85         if (offset) {
  86                 /* To quote Alan:
  87
  88                    Don't allow a fragment of TCP 8 bytes in. Nobody normal
  89                    causes this. Its a cracker trying to break in by doing a
  90                    flag overwrite to pass the direction checks.
  91                 */
  92                 if (offset == 1) {
  93                         duprintf("Dropping evil TCP offset=1 frag.\n");
  94                         *hotdrop = 1;
  95                 }
  96                 /* Must not be a fragment. */
  97                 return 0;
  98         }
  99
 100 #define FWINVTCP(bool,invflg) ((bool) ^ !!(tcpinfo->invflags & invflg))
 101
 102         th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
 103         if (th == NULL) {
 104                 /* We've been asked to examine this packet, and we
 105                    can't.  Hence, no choice but to drop. */
 106                 duprintf("Dropping evil TCP offset=0 tinygram.\n");
 107                 *hotdrop = 1;
 108                 return 0;
 109         }
 110
 111         if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
 112                         ntohs(th->source),
 113                         !!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
 114                 return 0;
 115         if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
 116                         ntohs(th->dest),
 117                         !!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
 118                 return 0;
 119         if (!FWINVTCP((((unsigned char *)th)[13] & tcpinfo->flg_mask)
 120                       == tcpinfo->flg_cmp,
 121                       XT_TCP_INV_FLAGS))
 122                 return 0;
 123         if (tcpinfo->option) {
 124                 if (th->doff * 4 < sizeof(_tcph)) {
 125                         *hotdrop = 1;
 126                         return 0;
 127                 }
 128                 if (!tcp_find_option(tcpinfo->option, skb, protoff,
 129                                      th->doff*4 - sizeof(_tcph),
 130                                      tcpinfo->invflags & XT_TCP_INV_OPTION,
 131                                      hotdrop))
 132                         return 0;
 133         }
 134         return 1;
 135 }
 136
 137 /* Called when user tries to insert an entry of this type. */
 138 static int
 139 tcp_checkentry(const char *tablename,
 140                const void *info,
 141                void *matchinfo,
 142                unsigned int matchsize,
 143                unsigned int hook_mask)
 144 {
 145         const struct ipt_ip *ip = info;
 146         const struct xt_tcp *tcpinfo = matchinfo;
 147
 148         /* Must specify proto == TCP, and no unknown invflags */
 149         return ip->proto == IPPROTO_TCP
 150                 && !(ip->invflags & XT_INV_PROTO)
 151                 && matchsize == XT_ALIGN(sizeof(struct xt_tcp))
 152                 && !(tcpinfo->invflags & ~XT_TCP_INV_MASK);
 153 }
 154
 155 /* Called when user tries to insert an entry of this type. */
 156 static int
 157 tcp6_checkentry(const char *tablename,
 158                const void *entry,
 159                void *matchinfo,
 160                unsigned int matchsize,
 161                unsigned int hook_mask)
 162 {
 163         const struct ip6t_ip6 *ipv6 = entry;
 164         const struct xt_tcp *tcpinfo = matchinfo;
 165
 166         /* Must specify proto == TCP, and no unknown invflags */
 167         return ipv6->proto == IPPROTO_TCP
 168                 && !(ipv6->invflags & XT_INV_PROTO)
 169                 && matchsize == XT_ALIGN(sizeof(struct xt_tcp))
 170                 && !(tcpinfo->invflags & ~XT_TCP_INV_MASK);
 171 }
 172
 173
 174 static int
 175 udp_match(const struct sk_buff *skb,
 176           const struct net_device *in,
 177           const struct net_device *out,
 178           const void *matchinfo,
 179           int offset,
 180           unsigned int protoff,
 181           int *hotdrop)
 182 {
 183         struct udphdr _udph, *uh;
 184         const struct xt_udp *udpinfo = matchinfo;
 185
 186         /* Must not be a fragment. */
 187         if (offset)
 188                 return 0;
 189
 190         uh = skb_header_pointer(skb, protoff, sizeof(_udph), &_udph);
 191         if (uh == NULL) {
 192                 /* We've been asked to examine this packet, and we
 193                    can't.  Hence, no choice but to drop. */
 194                 duprintf("Dropping evil UDP tinygram.\n");
 195                 *hotdrop = 1;
 196                 return 0;
 197         }
 198
 199         return port_match(udpinfo->spts[0], udpinfo->spts[1],
 200                           ntohs(uh->source),
 201                           !!(udpinfo->invflags & XT_UDP_INV_SRCPT))
 202                 && port_match(udpinfo->dpts[0], udpinfo->dpts[1],
 203                               ntohs(uh->dest),
 204                               !!(udpinfo->invflags & XT_UDP_INV_DSTPT));
 205 }
 206
 207 /* Called when user tries to insert an entry of this type. */
 208 static int
 209 udp_checkentry(const char *tablename,
 210                const void *info,
 211                void *matchinfo,
 212                unsigned int matchinfosize,
 213                unsigned int hook_mask)
 214 {
 215         const struct ipt_ip *ip = info;
 216         const struct xt_udp *udpinfo = matchinfo;
 217
 218         /* Must specify proto == UDP, and no unknown invflags */
 219         if (ip->proto != IPPROTO_UDP || (ip->invflags & XT_INV_PROTO)) {
 220                 duprintf("ipt_udp: Protocol %u != %u\n", ip->proto,
 221                          IPPROTO_UDP);
 222                 return 0;
 223         }
 224         if (matchinfosize != XT_ALIGN(sizeof(struct xt_udp))) {
 225                 duprintf("ipt_udp: matchsize %u != %u\n",
 226                          matchinfosize, XT_ALIGN(sizeof(struct xt_udp)));
 227                 return 0;
 228         }
 229         if (udpinfo->invflags & ~XT_UDP_INV_MASK) {
 230                 duprintf("ipt_udp: unknown flags %X\n",
 231                          udpinfo->invflags);
 232                 return 0;
 233         }
 234
 235         return 1;
 236 }
 237
 238 /* Called when user tries to insert an entry of this type. */
 239 static int
 240 udp6_checkentry(const char *tablename,
 241                const void *entry,
 242                void *matchinfo,
 243                unsigned int matchinfosize,
 244                unsigned int hook_mask)
 245 {
 246         const struct ip6t_ip6 *ipv6 = entry;
 247         const struct xt_udp *udpinfo = matchinfo;
 248
 249         /* Must specify proto == UDP, and no unknown invflags */
 250         if (ipv6->proto != IPPROTO_UDP || (ipv6->invflags & XT_INV_PROTO)) {
 251                 duprintf("ip6t_udp: Protocol %u != %u\n", ipv6->proto,
 252                          IPPROTO_UDP);
 253                 return 0;
 254         }
 255         if (matchinfosize != XT_ALIGN(sizeof(struct xt_udp))) {
 256                 duprintf("ip6t_udp: matchsize %u != %u\n",
 257                          matchinfosize, XT_ALIGN(sizeof(struct xt_udp)));
 258                 return 0;
 259         }
 260         if (udpinfo->invflags & ~XT_UDP_INV_MASK) {
 261                 duprintf("ip6t_udp: unknown flags %X\n",
 262                          udpinfo->invflags);
 263                 return 0;
 264         }
 265
 266         return 1;
 267 }
 268
 269 static struct xt_match tcp_matchstruct = {
 270         .name           = "tcp",
 271         .match          = &tcp_match,
 272         .checkentry     = &tcp_checkentry,
 273         .me             = THIS_MODULE,
 274 };
 275 static struct xt_match tcp6_matchstruct = {
 276         .name           = "tcp",
 277         .match          = &tcp_match,
 278         .checkentry     = &tcp6_checkentry,
 279         .me             = THIS_MODULE,
 280 };
 281
 282 static struct xt_match udp_matchstruct = {
 283         .name           = "udp",
 284         .match          = &udp_match,
 285         .checkentry     = &udp_checkentry,
 286         .me             = THIS_MODULE,
 287 };
 288 static struct xt_match udp6_matchstruct = {
 289         .name           = "udp",
 290         .match          = &udp_match,
 291         .checkentry     = &udp6_checkentry,
 292         .me             = THIS_MODULE,
 293 };
 294
 295 static int __init init(void)
 296 {
 297         int ret;
 298         ret = xt_register_match(AF_INET, &tcp_matchstruct);
 299         if (ret)
 300                 return ret;
 301
 302         ret = xt_register_match(AF_INET6, &tcp6_matchstruct);
 303         if (ret)
 304                 goto out_unreg_tcp;
 305
 306         ret = xt_register_match(AF_INET, &udp_matchstruct);
 307         if (ret)
 308                 goto out_unreg_tcp6;
 309
 310         ret = xt_register_match(AF_INET6, &udp6_matchstruct);
 311         if (ret)
 312                 goto out_unreg_udp;
 313
 314         return ret;
 315
 316 out_unreg_udp:
 317         xt_unregister_match(AF_INET, &tcp_matchstruct);
 318 out_unreg_tcp6:
 319         xt_unregister_match(AF_INET6, &tcp6_matchstruct);
 320 out_unreg_tcp:
 321         xt_unregister_match(AF_INET, &tcp_matchstruct);
 322         return ret;
 323 }
 324
 325 static void __exit fini(void)
 326 {
 327         xt_unregister_match(AF_INET6, &udp6_matchstruct);
 328         xt_unregister_match(AF_INET, &udp_matchstruct);
 329         xt_unregister_match(AF_INET6, &tcp6_matchstruct);
 330         xt_unregister_match(AF_INET, &tcp_matchstruct);
 331 }
 332
 333 module_init(init);
 334 module_exit(fini);