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         th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
  87         if (th == NULL) {
  88                 /* We've been asked to examine this packet, and we
  89                    can't.  Hence, no choice but to drop. */
  90                 pr_debug("Dropping evil TCP offset=0 tinygram.\n");
  91                 par->hotdrop = true;
  92                 return false;
  93         }
  94
  95         if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
  96                         ntohs(th->source),
  97                         !!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
  98                 return false;
  99         if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
 100                         ntohs(th->dest),
 101                         !!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
 102                 return false;
 103         if (!NF_INVF(tcpinfo, XT_TCP_INV_FLAGS,
 104                      (((unsigned char *)th)[13] & tcpinfo->flg_mask) == tcpinfo->flg_cmp))
 105                 return false;
 106         if (tcpinfo->option) {
 107                 if (th->doff * 4 < sizeof(_tcph)) {
 108                         par->hotdrop = true;
 109                         return false;
 110                 }
 111                 if (!tcp_find_option(tcpinfo->option, skb, par->thoff,
 112                                      th->doff*4 - sizeof(_tcph),
 113                                      tcpinfo->invflags & XT_TCP_INV_OPTION,
 114                                      &par->hotdrop))
 115                         return false;
 116         }
 117         return true;
 118 }
 119
 120 static int tcp_mt_check(const struct xt_mtchk_param *par)
 121 {
 122         const struct xt_tcp *tcpinfo = par->matchinfo;
 123
 124         /* Must specify no unknown invflags */
 125         return (tcpinfo->invflags & ~XT_TCP_INV_MASK) ? -EINVAL : 0;
 126 }
 127
 128 static bool udp_mt(const struct sk_buff *skb, struct xt_action_param *par)
 129 {
 130         const struct udphdr *uh;
 131         struct udphdr _udph;
 132         const struct xt_udp *udpinfo = par->matchinfo;
 133
 134         /* Must not be a fragment. */
 135         if (par->fragoff != 0)
 136                 return false;
 137
 138         uh = skb_header_pointer(skb, par->thoff, sizeof(_udph), &_udph);
 139         if (uh == NULL) {
 140                 /* We've been asked to examine this packet, and we
 141                    can't.  Hence, no choice but to drop. */
 142                 pr_debug("Dropping evil UDP tinygram.\n");
 143                 par->hotdrop = true;
 144                 return false;
 145         }
 146
 147         return port_match(udpinfo->spts[0], udpinfo->spts[1],
 148                           ntohs(uh->source),
 149                           !!(udpinfo->invflags & XT_UDP_INV_SRCPT))
 150                 && port_match(udpinfo->dpts[0], udpinfo->dpts[1],
 151                               ntohs(uh->dest),
 152                               !!(udpinfo->invflags & XT_UDP_INV_DSTPT));
 153 }
 154
 155 static int udp_mt_check(const struct xt_mtchk_param *par)
 156 {
 157         const struct xt_udp *udpinfo = par->matchinfo;
 158
 159         /* Must specify no unknown invflags */
 160         return (udpinfo->invflags & ~XT_UDP_INV_MASK) ? -EINVAL : 0;
 161 }
 162
 163 static struct xt_match tcpudp_mt_reg[] __read_mostly = {
 164         {
 165                 .name           = "tcp",
 166                 .family         = NFPROTO_IPV4,
 167                 .checkentry     = tcp_mt_check,
 168                 .match          = tcp_mt,
 169                 .matchsize      = sizeof(struct xt_tcp),
 170                 .proto          = IPPROTO_TCP,
 171                 .me             = THIS_MODULE,
 172         },
 173         {
 174                 .name           = "tcp",
 175                 .family         = NFPROTO_IPV6,
 176                 .checkentry     = tcp_mt_check,
 177                 .match          = tcp_mt,
 178                 .matchsize      = sizeof(struct xt_tcp),
 179                 .proto          = IPPROTO_TCP,
 180                 .me             = THIS_MODULE,
 181         },
 182         {
 183                 .name           = "udp",
 184                 .family         = NFPROTO_IPV4,
 185                 .checkentry     = udp_mt_check,
 186                 .match          = udp_mt,
 187                 .matchsize      = sizeof(struct xt_udp),
 188                 .proto          = IPPROTO_UDP,
 189                 .me             = THIS_MODULE,
 190         },
 191         {
 192                 .name           = "udp",
 193                 .family         = NFPROTO_IPV6,
 194                 .checkentry     = udp_mt_check,
 195                 .match          = udp_mt,
 196                 .matchsize      = sizeof(struct xt_udp),
 197                 .proto          = IPPROTO_UDP,
 198                 .me             = THIS_MODULE,
 199         },
 200         {
 201                 .name           = "udplite",
 202                 .family         = NFPROTO_IPV4,
 203                 .checkentry     = udp_mt_check,
 204                 .match          = udp_mt,
 205                 .matchsize      = sizeof(struct xt_udp),
 206                 .proto          = IPPROTO_UDPLITE,
 207                 .me             = THIS_MODULE,
 208         },
 209         {
 210                 .name           = "udplite",
 211                 .family         = NFPROTO_IPV6,
 212                 .checkentry     = udp_mt_check,
 213                 .match          = udp_mt,
 214                 .matchsize      = sizeof(struct xt_udp),
 215                 .proto          = IPPROTO_UDPLITE,
 216                 .me             = THIS_MODULE,
 217         },
 218 };
 219
 220 static int __init tcpudp_mt_init(void)
 221 {
 222         return xt_register_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
 223 }
 224
 225 static void __exit tcpudp_mt_exit(void)
 226 {
 227         xt_unregister_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
 228 }
 229
 230 module_init(tcpudp_mt_init);
 231 module_exit(tcpudp_mt_exit);