linux/net/netfilter/xt_tcpudp.c
<<
>>
Prefs
   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
  14MODULE_DESCRIPTION("Xtables: TCP, UDP and UDP-Lite match");
  15MODULE_LICENSE("GPL");
  16MODULE_ALIAS("xt_tcp");
  17MODULE_ALIAS("xt_udp");
  18MODULE_ALIAS("ipt_udp");
  19MODULE_ALIAS("ipt_tcp");
  20MODULE_ALIAS("ip6t_udp");
  21MODULE_ALIAS("ip6t_tcp");
  22
  23/* Returns 1 if the port is matched by the range, 0 otherwise */
  24static inline bool
  25port_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
  30static bool
  31tcp_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
  65static 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
 123static 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
 131static 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
 158static 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
 166static 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
 223static int __init tcpudp_mt_init(void)
 224{
 225        return xt_register_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
 226}
 227
 228static void __exit tcpudp_mt_exit(void)
 229{
 230        xt_unregister_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
 231}
 232
 233module_init(tcpudp_mt_init);
 234module_exit(tcpudp_mt_exit);
 235
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.