net/netfilter/xt_tcpudp.c

   1 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   2 #include <linux/types.h>
   3 #include <linux/module.h>
   4 #include <net/ip.h>
   5 #include <linux/ipv6.h>
   6 #include <net/ipv6.h>
   7 #include <net/tcp.h>
   8 #include <net/udp.h>
   9 #include <linux/netfilter/x_tables.h>
  10 #include <linux/netfilter/xt_tcpudp.h>
  11 #include <linux/netfilter_ipv4/ip_tables.h>
  12 #include <linux/netfilter_ipv6/ip6_tables.h>
  13
  14 MODULE_DESCRIPTION("Xtables: TCP, UDP and UDP-Lite match");
  15 MODULE_LICENSE("GPL");
  16 MODULE_ALIAS("xt_tcp");
  17 MODULE_ALIAS("xt_udp");
  18 MODULE_ALIAS("ipt_udp");
  19 MODULE_ALIAS("ipt_tcp");
  20 MODULE_ALIAS("ip6t_udp");
  21 MODULE_ALIAS("ip6t_tcp");
  22
  23 /* Returns 1 if the port is matched by the range, 0 otherwise */
  24 static inline bool
  25 port_match(u_int16_t min, u_int16_t max, u_int16_t port, bool invert)
  26 {
  27         return (port >= min && port <= max) ^ invert;
  28 }
  29
  30 static bool
  31 tcp_find_option(u_int8_t option,
  32                 const struct sk_buff *skb,
  33                 unsigned int protoff,
  34                 unsigned int optlen,
  35                 bool invert,
  36                 bool *hotdrop)
  37 {
  38         /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
  39         const u_int8_t *op;
  40         u_int8_t _opt[60 - sizeof(struct tcphdr)];
  41         unsigned int i;
  42
  43         pr_debug("finding option\n");
  44
  45         if (!optlen)
  46                 return invert;
  47
  48         /* If we don't have the whole header, drop packet. */
  49         op = skb_header_pointer(skb, protoff + sizeof(struct tcphdr),
  50                                 optlen, _opt);
  51         if (op == NULL) {
  52                 *hotdrop = true;
  53                 return false;
  54         }
  55
  56         for (i = 0; i < optlen; ) {
  57                 if (op[i] == option) return !invert;
  58                 if (op[i] < 2) i++;
  59                 else i += op[i+1]?:1;
  60         }
  61
  62         return invert;
  63 }
  64
  65 static bool tcp_mt(const struct sk_buff *skb, struct xt_action_param *par)
  66 {
  67         const struct tcphdr *th;
  68         struct tcphdr _tcph;
  69         const struct xt_tcp *tcpinfo = par->matchinfo;
  70
  71         if (par->fragoff != 0) {
  72                 /* To quote Alan:
  73
  74                    Don't allow a fragment of TCP 8 bytes in. Nobody normal
  75                    causes this. Its a cracker trying to break in by doing a
  76                    flag overwrite to pass the direction checks.
  77                 */
  78                 if (par->fragoff == 1) {
  79                         pr_debug("Dropping evil TCP offset=1 frag.\n");
  80                         par->hotdrop = true;
  81                 }
  82                 /* Must not be a fragment. */
  83                 return false;
  84         }
  85
  86 #define FWINVTCP(bool, invflg) ((bool) ^ !!(tcpinfo->invflags & (invflg)))
  87
  88         th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
  89         if (th == NULL) {
  90                 /* We've been asked to examine this packet, and we
  91                    can't.  Hence, no choice but to drop. */
  92                 pr_debug("Dropping evil TCP offset=0 tinygram.\n");
  93                 par->hotdrop = true;
  94                 return false;
  95         }
  96
  97         if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
  98                         ntohs(th->source),
  99                         !!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
 100                 return false;
 101         if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
 102                         ntohs(th->dest),
 103                         !!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
 104                 return false;
 105         if (!FWINVTCP((((unsigned char *)th)[13] & tcpinfo->flg_mask)
 106                       == tcpinfo->flg_cmp,
 107                       XT_TCP_INV_FLAGS))
 108                 return false;
 109         if (tcpinfo->option) {
 110                 if (th->doff * 4 < sizeof(_tcph)) {
 111                         par->hotdrop = true;
 112                         return false;
 113                 }
 114                 if (!tcp_find_option(tcpinfo->option, skb, par->thoff,
 115                                      th->doff*4 - sizeof(_tcph),
 116                                      tcpinfo->invflags & XT_TCP_INV_OPTION,
 117                                      &par->hotdrop))
 118                         return false;
 119         }
 120         return true;
 121 }
 122
 123 static int tcp_mt_check(const struct xt_mtchk_param *par)
 124 {
 125         const struct xt_tcp *tcpinfo = par->matchinfo;
 126
 127         /* Must specify no unknown invflags */
 128         return (tcpinfo->invflags & ~XT_TCP_INV_MASK) ? -EINVAL : 0;
 129 }
 130
 131 static bool udp_mt(const struct sk_buff *skb, struct xt_action_param *par)
 132 {
 133         const struct udphdr *uh;
 134         struct udphdr _udph;
 135         const struct xt_udp *udpinfo = par->matchinfo;
 136
 137         /* Must not be a fragment. */
 138         if (par->fragoff != 0)
 139                 return false;
 140
 141         uh = skb_header_pointer(skb, par->thoff, sizeof(_udph), &_udph);
 142         if (uh == NULL) {
 143                 /* We've been asked to examine this packet, and we
 144                    can't.  Hence, no choice but to drop. */
 145                 pr_debug("Dropping evil UDP tinygram.\n");
 146                 par->hotdrop = true;
 147                 return false;
 148         }
 149
 150         return port_match(udpinfo->spts[0], udpinfo->spts[1],
 151                           ntohs(uh->source),
 152                           !!(udpinfo->invflags & XT_UDP_INV_SRCPT))
 153                 && port_match(udpinfo->dpts[0], udpinfo->dpts[1],
 154                               ntohs(uh->dest),
 155                               !!(udpinfo->invflags & XT_UDP_INV_DSTPT));
 156 }
 157
 158 static int udp_mt_check(const struct xt_mtchk_param *par)
 159 {
 160         const struct xt_udp *udpinfo = par->matchinfo;
 161
 162         /* Must specify no unknown invflags */
 163         return (udpinfo->invflags & ~XT_UDP_INV_MASK) ? -EINVAL : 0;
 164 }
 165
 166 static struct xt_match tcpudp_mt_reg[] __read_mostly = {
 167         {
 168                 .name           = "tcp",
 169                 .family         = NFPROTO_IPV4,
 170                 .checkentry     = tcp_mt_check,
 171                 .match          = tcp_mt,
 172                 .matchsize      = sizeof(struct xt_tcp),
 173                 .proto          = IPPROTO_TCP,
 174                 .me             = THIS_MODULE,
 175         },
 176         {
 177                 .name           = "tcp",
 178                 .family         = NFPROTO_IPV6,
 179                 .checkentry     = tcp_mt_check,
 180                 .match          = tcp_mt,
 181                 .matchsize      = sizeof(struct xt_tcp),
 182                 .proto          = IPPROTO_TCP,
 183                 .me             = THIS_MODULE,
 184         },
 185         {
 186                 .name           = "udp",
 187                 .family         = NFPROTO_IPV4,
 188                 .checkentry     = udp_mt_check,
 189                 .match          = udp_mt,
 190                 .matchsize      = sizeof(struct xt_udp),
 191                 .proto          = IPPROTO_UDP,
 192                 .me             = THIS_MODULE,
 193         },
 194         {
 195                 .name           = "udp",
 196                 .family         = NFPROTO_IPV6,
 197                 .checkentry     = udp_mt_check,
 198                 .match          = udp_mt,
 199                 .matchsize      = sizeof(struct xt_udp),
 200                 .proto          = IPPROTO_UDP,
 201                 .me             = THIS_MODULE,
 202         },
 203         {
 204                 .name           = "udplite",
 205                 .family         = NFPROTO_IPV4,
 206                 .checkentry     = udp_mt_check,
 207                 .match          = udp_mt,
 208                 .matchsize      = sizeof(struct xt_udp),
 209                 .proto          = IPPROTO_UDPLITE,
 210                 .me             = THIS_MODULE,
 211         },
 212         {
 213                 .name           = "udplite",
 214                 .family         = NFPROTO_IPV6,
 215                 .checkentry     = udp_mt_check,
 216                 .match          = udp_mt,
 217                 .matchsize      = sizeof(struct xt_udp),
 218                 .proto          = IPPROTO_UDPLITE,
 219                 .me             = THIS_MODULE,
 220         },
 221 };
 222
 223 static int __init tcpudp_mt_init(void)
 224 {
 225         return xt_register_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
 226 }
 227
 228 static void __exit tcpudp_mt_exit(void)
 229 {
 230         xt_unregister_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
 231 }
 232
 233 module_init(tcpudp_mt_init);
 234 module_exit(tcpudp_mt_exit);