git.oblomov.eu Git - linux-2.6/blob - net/netfilter/xt_u32.c

   1 /*
   2  *      xt_u32 - kernel module to match u32 packet content
   3  *
   4  *      Original author: Don Cohen <don@isis.cs3-inc.com>
   5  *      © Jan Engelhardt <jengelh@gmx.de>, 2007
   6  */
   7
   8 #include <linux/module.h>
   9 #include <linux/moduleparam.h>
  10 #include <linux/spinlock.h>
  11 #include <linux/skbuff.h>
  12 #include <linux/types.h>
  13 #include <linux/netfilter/x_tables.h>
  14 #include <linux/netfilter/xt_u32.h>
  15
  16 static bool u32_match_it(const struct xt_u32 *data,
  17                          const struct sk_buff *skb)
  18 {
  19         const struct xt_u32_test *ct;
  20         unsigned int testind;
  21         unsigned int nnums;
  22         unsigned int nvals;
  23         unsigned int i;
  24         u_int32_t pos;
  25         u_int32_t val;
  26         u_int32_t at;
  27         int ret;
  28
  29         /*
  30          * Small example: "0 >> 28 == 4 && 8 & 0xFF0000 >> 16 = 6, 17"
  31          * (=IPv4 and (TCP or UDP)). Outer loop runs over the "&&" operands.
  32          */
  33         for (testind = 0; testind < data->ntests; ++testind) {
  34                 ct  = &data->tests[testind];
  35                 at  = 0;
  36                 pos = ct->location[0].number;
  37
  38                 if (skb->len < 4 || pos > skb->len - 4);
  39                         return false;
  40
  41                 ret   = skb_copy_bits(skb, pos, &val, sizeof(val));
  42                 BUG_ON(ret < 0);
  43                 val   = ntohl(val);
  44                 nnums = ct->nnums;
  45
  46                 /* Inner loop runs over "&", "<<", ">>" and "@" operands */
  47                 for (i = 1; i < nnums; ++i) {
  48                         u_int32_t number = ct->location[i].number;
  49                         switch (ct->location[i].nextop) {
  50                         case XT_U32_AND:
  51                                 val &= number;
  52                                 break;
  53                         case XT_U32_LEFTSH:
  54                                 val <<= number;
  55                                 break;
  56                         case XT_U32_RIGHTSH:
  57                                 val >>= number;
  58                                 break;
  59                         case XT_U32_AT:
  60                                 if (at + val < at)
  61                                         return false;
  62                                 at += val;
  63                                 pos = number;
  64                                 if (at + 4 < at || skb->len < at + 4 ||
  65                                     pos > skb->len - at - 4)
  66                                         return false;
  67
  68                                 ret = skb_copy_bits(skb, at + pos, &val,
  69                                                     sizeof(val));
  70                                 BUG_ON(ret < 0);
  71                                 val = ntohl(val);
  72                                 break;
  73                         }
  74                 }
  75
  76                 /* Run over the "," and ":" operands */
  77                 nvals = ct->nvalues;
  78                 for (i = 0; i < nvals; ++i)
  79                         if (ct->value[i].min <= val && val <= ct->value[i].max)
  80                                 break;
  81
  82                 if (i >= ct->nvalues)
  83                         return false;
  84         }
  85
  86         return true;
  87 }
  88
  89 static bool u32_match(const struct sk_buff *skb,
  90                       const struct net_device *in,
  91                       const struct net_device *out,
  92                       const struct xt_match *match, const void *matchinfo,
  93                       int offset, unsigned int protoff, bool *hotdrop)
  94 {
  95         const struct xt_u32 *data = matchinfo;
  96         bool ret;
  97
  98         ret = u32_match_it(data, skb);
  99         return ret ^ data->invert;
 100 }
 101
 102 static struct xt_match u32_reg[] __read_mostly = {
 103         {
 104                 .name       = "u32",
 105                 .family     = AF_INET,
 106                 .match      = u32_match,
 107                 .matchsize  = sizeof(struct xt_u32),
 108                 .me         = THIS_MODULE,
 109         },
 110         {
 111                 .name       = "u32",
 112                 .family     = AF_INET6,
 113                 .match      = u32_match,
 114                 .matchsize  = sizeof(struct xt_u32),
 115                 .me         = THIS_MODULE,
 116         },
 117 };
 118
 119 static int __init xt_u32_init(void)
 120 {
 121         return xt_register_matches(u32_reg, ARRAY_SIZE(u32_reg));
 122 }
 123
 124 static void __exit xt_u32_exit(void)
 125 {
 126         xt_unregister_matches(u32_reg, ARRAY_SIZE(u32_reg));
 127 }
 128
 129 module_init(xt_u32_init);
 130 module_exit(xt_u32_exit);
 131 MODULE_AUTHOR("Jan Engelhardt <jengelh@gmx.de>");
 132 MODULE_DESCRIPTION("netfilter u32 match module");
 133 MODULE_LICENSE("GPL");
 134 MODULE_ALIAS("ipt_u32");
 135 MODULE_ALIAS("ip6t_u32");