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 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 matchsize,
 145                unsigned int hook_mask)
 146 {
 147         const struct xt_tcp *tcpinfo = matchinfo;
 148
 149         /* Must specify no unknown invflags */
 150         return !(tcpinfo->invflags & ~XT_TCP_INV_MASK);
 151 }
 152
 153 static int
 154 udp_match(const struct sk_buff *skb,
 155           const struct net_device *in,
 156           const struct net_device *out,
 157           const struct xt_match *match,
 158           const void *matchinfo,
 159           int offset,
 160           unsigned int protoff,
 161           int *hotdrop)
 162 {
 163         struct udphdr _udph, *uh;
 164         const struct xt_udp *udpinfo = matchinfo;
 165
 166         /* Must not be a fragment. */
 167         if (offset)
 168                 return 0;
 169
 170         uh = skb_header_pointer(skb, protoff, sizeof(_udph), &_udph);
 171         if (uh == NULL) {
 172                 /* We've been asked to examine this packet, and we
 173                    can't.  Hence, no choice but to drop. */
 174                 duprintf("Dropping evil UDP tinygram.\n");
 175                 *hotdrop = 1;
 176                 return 0;
 177         }
 178
 179         return port_match(udpinfo->spts[0], udpinfo->spts[1],
 180                           ntohs(uh->source),
 181                           !!(udpinfo->invflags & XT_UDP_INV_SRCPT))
 182                 && port_match(udpinfo->dpts[0], udpinfo->dpts[1],
 183                               ntohs(uh->dest),
 184                               !!(udpinfo->invflags & XT_UDP_INV_DSTPT));
 185 }
 186
 187 /* Called when user tries to insert an entry of this type. */
 188 static int
 189 udp_checkentry(const char *tablename,
 190                const void *info,
 191                const struct xt_match *match,
 192                void *matchinfo,
 193                unsigned int matchsize,
 194                unsigned int hook_mask)
 195 {
 196         const struct xt_tcp *udpinfo = matchinfo;
 197
 198         /* Must specify no unknown invflags */
 199         return !(udpinfo->invflags & ~XT_UDP_INV_MASK);
 200 }
 201
 202 static struct xt_match tcp_matchstruct = {
 203         .name           = "tcp",
 204         .match          = tcp_match,
 205         .matchsize      = sizeof(struct xt_tcp),
 206         .proto          = IPPROTO_TCP,
 207         .family         = AF_INET,
 208         .checkentry     = tcp_checkentry,
 209         .me             = THIS_MODULE,
 210 };
 211
 212 static struct xt_match tcp6_matchstruct = {
 213         .name           = "tcp",
 214         .match          = tcp_match,
 215         .matchsize      = sizeof(struct xt_tcp),
 216         .proto          = IPPROTO_TCP,
 217         .family         = AF_INET6,
 218         .checkentry     = tcp_checkentry,
 219         .me             = THIS_MODULE,
 220 };
 221
 222 static struct xt_match udp_matchstruct = {
 223         .name           = "udp",
 224         .match          = udp_match,
 225         .matchsize      = sizeof(struct xt_udp),
 226         .proto          = IPPROTO_UDP,
 227         .family         = AF_INET,
 228         .checkentry     = udp_checkentry,
 229         .me             = THIS_MODULE,
 230 };
 231 static struct xt_match udp6_matchstruct = {
 232         .name           = "udp",
 233         .match          = udp_match,
 234         .matchsize      = sizeof(struct xt_udp),
 235         .proto          = IPPROTO_UDP,
 236         .family         = AF_INET6,
 237         .checkentry     = udp_checkentry,
 238         .me             = THIS_MODULE,
 239 };
 240
 241 static int __init xt_tcpudp_init(void)
 242 {
 243         int ret;
 244         ret = xt_register_match(&tcp_matchstruct);
 245         if (ret)
 246                 return ret;
 247
 248         ret = xt_register_match(&tcp6_matchstruct);
 249         if (ret)
 250                 goto out_unreg_tcp;
 251
 252         ret = xt_register_match(&udp_matchstruct);
 253         if (ret)
 254                 goto out_unreg_tcp6;
 255
 256         ret = xt_register_match(&udp6_matchstruct);
 257         if (ret)
 258                 goto out_unreg_udp;
 259
 260         return ret;
 261
 262 out_unreg_udp:
 263         xt_unregister_match(&tcp_matchstruct);
 264 out_unreg_tcp6:
 265         xt_unregister_match(&tcp6_matchstruct);
 266 out_unreg_tcp:
 267         xt_unregister_match(&tcp_matchstruct);
 268         return ret;
 269 }
 270
 271 static void __exit xt_tcpudp_fini(void)
 272 {
 273         xt_unregister_match(&udp6_matchstruct);
 274         xt_unregister_match(&udp_matchstruct);
 275         xt_unregister_match(&tcp6_matchstruct);
 276         xt_unregister_match(&tcp_matchstruct);
 277 }
 278
 279 module_init(xt_tcpudp_init);
 280 module_exit(xt_tcpudp_fini);