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 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
 239 static int __init xt_tcpudp_init(void)
 240 {
 241         return xt_register_matches(xt_tcpudp_match,
 242                                    ARRAY_SIZE(xt_tcpudp_match));
 243 }
 244
 245 static void __exit xt_tcpudp_fini(void)
 246 {
 247         xt_unregister_matches(xt_tcpudp_match, ARRAY_SIZE(xt_tcpudp_match));
 248 }
 249
 250 module_init(xt_tcpudp_init);
 251 module_exit(xt_tcpudp_fini);