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         const u_int8_t *op;
  46         u_int8_t _opt[60 - sizeof(struct tcphdr)];
  47         unsigned int i;
  48
  49         duprintf("tcp_match: finding option\n");
  50
  51         if (!optlen)
  52                 return invert;
  53
  54         /* If we don't have the whole header, drop packet. */
  55         op = skb_header_pointer(skb, protoff + sizeof(struct tcphdr),
  56                                 optlen, _opt);
  57         if (op == NULL) {
  58                 *hotdrop = true;
  59                 return false;
  60         }
  61
  62         for (i = 0; i < optlen; ) {
  63                 if (op[i] == option) return !invert;
  64                 if (op[i] < 2) i++;
  65                 else i += op[i+1]?:1;
  66         }
  67
  68         return invert;
  69 }
  70
  71 static bool tcp_mt(const struct sk_buff *skb, const struct xt_match_param *par)
  72 {
  73         const struct tcphdr *th;
  74         struct tcphdr _tcph;
  75         const struct xt_tcp *tcpinfo = par->matchinfo;
  76
  77         if (par->fragoff != 0) {
  78                 /* To quote Alan:
  79
  80                    Don't allow a fragment of TCP 8 bytes in. Nobody normal
  81                    causes this. Its a cracker trying to break in by doing a
  82                    flag overwrite to pass the direction checks.
  83                 */
  84                 if (par->fragoff == 1) {
  85                         duprintf("Dropping evil TCP offset=1 frag.\n");
  86                         *par->hotdrop = true;
  87                 }
  88                 /* Must not be a fragment. */
  89                 return false;
  90         }
  91
  92 #define FWINVTCP(bool, invflg) ((bool) ^ !!(tcpinfo->invflags & (invflg)))
  93
  94         th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
  95         if (th == NULL) {
  96                 /* We've been asked to examine this packet, and we
  97                    can't.  Hence, no choice but to drop. */
  98                 duprintf("Dropping evil TCP offset=0 tinygram.\n");
  99                 *par->hotdrop = true;
 100                 return false;
 101         }
 102
 103         if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
 104                         ntohs(th->source),
 105                         !!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
 106                 return false;
 107         if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
 108                         ntohs(th->dest),
 109                         !!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
 110                 return false;
 111         if (!FWINVTCP((((unsigned char *)th)[13] & tcpinfo->flg_mask)
 112                       == tcpinfo->flg_cmp,
 113                       XT_TCP_INV_FLAGS))
 114                 return false;
 115         if (tcpinfo->option) {
 116                 if (th->doff * 4 < sizeof(_tcph)) {
 117                         *par->hotdrop = true;
 118                         return false;
 119                 }
 120                 if (!tcp_find_option(tcpinfo->option, skb, par->thoff,
 121                                      th->doff*4 - sizeof(_tcph),
 122                                      tcpinfo->invflags & XT_TCP_INV_OPTION,
 123                                      par->hotdrop))
 124                         return false;
 125         }
 126         return true;
 127 }
 128
 129 static bool tcp_mt_check(const struct xt_mtchk_param *par)
 130 {
 131         const struct xt_tcp *tcpinfo = par->matchinfo;
 132
 133         /* Must specify no unknown invflags */
 134         return !(tcpinfo->invflags & ~XT_TCP_INV_MASK);
 135 }
 136
 137 static bool udp_mt(const struct sk_buff *skb, const struct xt_match_param *par)
 138 {
 139         const struct udphdr *uh;
 140         struct udphdr _udph;
 141         const struct xt_udp *udpinfo = par->matchinfo;
 142
 143         /* Must not be a fragment. */
 144         if (par->fragoff != 0)
 145                 return false;
 146
 147         uh = skb_header_pointer(skb, par->thoff, sizeof(_udph), &_udph);
 148         if (uh == NULL) {
 149                 /* We've been asked to examine this packet, and we
 150                    can't.  Hence, no choice but to drop. */
 151                 duprintf("Dropping evil UDP tinygram.\n");
 152                 *par->hotdrop = true;
 153                 return false;
 154         }
 155
 156         return port_match(udpinfo->spts[0], udpinfo->spts[1],
 157                           ntohs(uh->source),
 158                           !!(udpinfo->invflags & XT_UDP_INV_SRCPT))
 159                 && port_match(udpinfo->dpts[0], udpinfo->dpts[1],
 160                               ntohs(uh->dest),
 161                               !!(udpinfo->invflags & XT_UDP_INV_DSTPT));
 162 }
 163
 164 static bool udp_mt_check(const struct xt_mtchk_param *par)
 165 {
 166         const struct xt_udp *udpinfo = par->matchinfo;
 167
 168         /* Must specify no unknown invflags */
 169         return !(udpinfo->invflags & ~XT_UDP_INV_MASK);
 170 }
 171
 172 static struct xt_match tcpudp_mt_reg[] __read_mostly = {
 173         {
 174                 .name           = "tcp",
 175                 .family         = NFPROTO_IPV4,
 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           = "tcp",
 184                 .family         = NFPROTO_IPV6,
 185                 .checkentry     = tcp_mt_check,
 186                 .match          = tcp_mt,
 187                 .matchsize      = sizeof(struct xt_tcp),
 188                 .proto          = IPPROTO_TCP,
 189                 .me             = THIS_MODULE,
 190         },
 191         {
 192                 .name           = "udp",
 193                 .family         = NFPROTO_IPV4,
 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           = "udp",
 202                 .family         = NFPROTO_IPV6,
 203                 .checkentry     = udp_mt_check,
 204                 .match          = udp_mt,
 205                 .matchsize      = sizeof(struct xt_udp),
 206                 .proto          = IPPROTO_UDP,
 207                 .me             = THIS_MODULE,
 208         },
 209         {
 210                 .name           = "udplite",
 211                 .family         = NFPROTO_IPV4,
 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                 .name           = "udplite",
 220                 .family         = NFPROTO_IPV6,
 221                 .checkentry     = udp_mt_check,
 222                 .match          = udp_mt,
 223                 .matchsize      = sizeof(struct xt_udp),
 224                 .proto          = IPPROTO_UDPLITE,
 225                 .me             = THIS_MODULE,
 226         },
 227 };
 228
 229 static int __init tcpudp_mt_init(void)
 230 {
 231         return xt_register_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
 232 }
 233
 234 static void __exit tcpudp_mt_exit(void)
 235 {
 236         xt_unregister_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
 237 }
 238
 239 module_init(tcpudp_mt_init);
 240 module_exit(tcpudp_mt_exit);