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