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