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   1 /*
   2  *      xt_u32 - kernel module to match u32 packet content
   3  *
   4  *      Original author: Don Cohen <don@isis.cs3-inc.com>
   5  *      (C) CC Computer Consultants GmbH, 2007
   6  *      Contact: <jengelh@computergmbh.de>
   7  */
   8
   9 #include <linux/module.h>
  10 #include <linux/moduleparam.h>
  11 #include <linux/spinlock.h>
  12 #include <linux/skbuff.h>
  13 #include <linux/types.h>
  14 #include <linux/netfilter/x_tables.h>
  15 #include <linux/netfilter/xt_u32.h>
  16
  17 static bool u32_match_it(const struct xt_u32 *data,
  18                          const struct sk_buff *skb)
  19 {
  20         const struct xt_u32_test *ct;
  21         unsigned int testind;
  22         unsigned int nnums;
  23         unsigned int nvals;
  24         unsigned int i;
  25         __be32 n;
  26         u_int32_t pos;
  27         u_int32_t val;
  28         u_int32_t at;
  29         int ret;
  30
  31         /*
  32          * Small example: "0 >> 28 == 4 && 8 & 0xFF0000 >> 16 = 6, 17"
  33          * (=IPv4 and (TCP or UDP)). Outer loop runs over the "&&" operands.
  34          */
  35         for (testind = 0; testind < data->ntests; ++testind) {
  36                 ct  = &data->tests[testind];
  37                 at  = 0;
  38                 pos = ct->location[0].number;
  39
  40                 if (skb->len < 4 || pos > skb->len - 4)
  41                         return false;
  42
  43                 ret   = skb_copy_bits(skb, pos, &n, sizeof(n));
  44                 BUG_ON(ret < 0);
  45                 val   = ntohl(n);
  46                 nnums = ct->nnums;
  47
  48                 /* Inner loop runs over "&", "<<", ">>" and "@" operands */
  49                 for (i = 1; i < nnums; ++i) {
  50                         u_int32_t number = ct->location[i].number;
  51                         switch (ct->location[i].nextop) {
  52                         case XT_U32_AND:
  53                                 val &= number;
  54                                 break;
  55                         case XT_U32_LEFTSH:
  56                                 val <<= number;
  57                                 break;
  58                         case XT_U32_RIGHTSH:
  59                                 val >>= number;
  60                                 break;
  61                         case XT_U32_AT:
  62                                 if (at + val < at)
  63                                         return false;
  64                                 at += val;
  65                                 pos = number;
  66                                 if (at + 4 < at || skb->len < at + 4 ||
  67                                     pos > skb->len - at - 4)
  68                                         return false;
  69
  70                                 ret = skb_copy_bits(skb, at + pos, &n,
  71                                                     sizeof(n));
  72                                 BUG_ON(ret < 0);
  73                                 val = ntohl(n);
  74                                 break;
  75                         }
  76                 }
  77
  78                 /* Run over the "," and ":" operands */
  79                 nvals = ct->nvalues;
  80                 for (i = 0; i < nvals; ++i)
  81                         if (ct->value[i].min <= val && val <= ct->value[i].max)
  82                                 break;
  83
  84                 if (i >= ct->nvalues)
  85                         return false;
  86         }
  87
  88         return true;
  89 }
  90
  91 static bool u32_match(const struct sk_buff *skb,
  92                       const struct net_device *in,
  93                       const struct net_device *out,
  94                       const struct xt_match *match, const void *matchinfo,
  95                       int offset, unsigned int protoff, bool *hotdrop)
  96 {
  97         const struct xt_u32 *data = matchinfo;
  98         bool ret;
  99
 100         ret = u32_match_it(data, skb);
 101         return ret ^ data->invert;
 102 }
 103
 104 static struct xt_match u32_reg[] __read_mostly = {
 105         {
 106                 .name       = "u32",
 107                 .family     = AF_INET,
 108                 .match      = u32_match,
 109                 .matchsize  = sizeof(struct xt_u32),
 110                 .me         = THIS_MODULE,
 111         },
 112         {
 113                 .name       = "u32",
 114                 .family     = AF_INET6,
 115                 .match      = u32_match,
 116                 .matchsize  = sizeof(struct xt_u32),
 117                 .me         = THIS_MODULE,
 118         },
 119 };
 120
 121 static int __init xt_u32_init(void)
 122 {
 123         return xt_register_matches(u32_reg, ARRAY_SIZE(u32_reg));
 124 }
 125
 126 static void __exit xt_u32_exit(void)
 127 {
 128         xt_unregister_matches(u32_reg, ARRAY_SIZE(u32_reg));
 129 }
 130
 131 module_init(xt_u32_init);
 132 module_exit(xt_u32_exit);
 133 MODULE_AUTHOR("Jan Engelhardt <jengelh@computergmbh.de>");
 134 MODULE_DESCRIPTION("netfilter u32 match module");
 135 MODULE_LICENSE("GPL");
 136 MODULE_ALIAS("ipt_u32");
 137 MODULE_ALIAS("ip6t_u32");