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         __be32 n;
  25         u_int32_t pos;
  26         u_int32_t val;
  27         u_int32_t at;
  28         int ret;
  29
  30         /*
  31          * Small example: "0 >> 28 == 4 && 8 & 0xFF0000 >> 16 = 6, 17"
  32          * (=IPv4 and (TCP or UDP)). Outer loop runs over the "&&" operands.
  33          */
  34         for (testind = 0; testind < data->ntests; ++testind) {
  35                 ct  = &data->tests[testind];
  36                 at  = 0;
  37                 pos = ct->location[0].number;
  38
  39                 if (skb->len < 4 || pos > skb->len - 4)
  40                         return false;
  41
  42                 ret   = skb_copy_bits(skb, pos, &n, sizeof(n));
  43                 BUG_ON(ret < 0);
  44                 val   = ntohl(n);
  45                 nnums = ct->nnums;
  46
  47                 /* Inner loop runs over "&", "<<", ">>" and "@" operands */
  48                 for (i = 1; i < nnums; ++i) {
  49                         u_int32_t number = ct->location[i].number;
  50                         switch (ct->location[i].nextop) {
  51                         case XT_U32_AND:
  52                                 val &= number;
  53                                 break;
  54                         case XT_U32_LEFTSH:
  55                                 val <<= number;
  56                                 break;
  57                         case XT_U32_RIGHTSH:
  58                                 val >>= number;
  59                                 break;
  60                         case XT_U32_AT:
  61                                 if (at + val < at)
  62                                         return false;
  63                                 at += val;
  64                                 pos = number;
  65                                 if (at + 4 < at || skb->len < at + 4 ||
  66                                     pos > skb->len - at - 4)
  67                                         return false;
  68
  69                                 ret = skb_copy_bits(skb, at + pos, &n,
  70                                                     sizeof(n));
  71                                 BUG_ON(ret < 0);
  72                                 val = ntohl(n);
  73                                 break;
  74                         }
  75                 }
  76
  77                 /* Run over the "," and ":" operands */
  78                 nvals = ct->nvalues;
  79                 for (i = 0; i < nvals; ++i)
  80                         if (ct->value[i].min <= val && val <= ct->value[i].max)
  81                                 break;
  82
  83                 if (i >= ct->nvalues)
  84                         return false;
  85         }
  86
  87         return true;
  88 }
  89
  90 static bool u32_match(const struct sk_buff *skb,
  91                       const struct net_device *in,
  92                       const struct net_device *out,
  93                       const struct xt_match *match, const void *matchinfo,
  94                       int offset, unsigned int protoff, bool *hotdrop)
  95 {
  96         const struct xt_u32 *data = matchinfo;
  97         bool ret;
  98
  99         ret = u32_match_it(data, skb);
 100         return ret ^ data->invert;
 101 }
 102
 103 static struct xt_match u32_reg[] __read_mostly = {
 104         {
 105                 .name       = "u32",
 106                 .family     = AF_INET,
 107                 .match      = u32_match,
 108                 .matchsize  = sizeof(struct xt_u32),
 109                 .me         = THIS_MODULE,
 110         },
 111         {
 112                 .name       = "u32",
 113                 .family     = AF_INET6,
 114                 .match      = u32_match,
 115                 .matchsize  = sizeof(struct xt_u32),
 116                 .me         = THIS_MODULE,
 117         },
 118 };
 119
 120 static int __init xt_u32_init(void)
 121 {
 122         return xt_register_matches(u32_reg, ARRAY_SIZE(u32_reg));
 123 }
 124
 125 static void __exit xt_u32_exit(void)
 126 {
 127         xt_unregister_matches(u32_reg, ARRAY_SIZE(u32_reg));
 128 }
 129
 130 module_init(xt_u32_init);
 131 module_exit(xt_u32_exit);
 132 MODULE_AUTHOR("Jan Engelhardt <jengelh@gmx.de>");
 133 MODULE_DESCRIPTION("netfilter u32 match module");
 134 MODULE_LICENSE("GPL");
 135 MODULE_ALIAS("ipt_u32");
 136 MODULE_ALIAS("ip6t_u32");