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  *      (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
  92 u32_mt(const struct sk_buff *skb, const struct net_device *in,
  93        const struct net_device *out, const struct xt_match *match,
  94        const void *matchinfo, 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_mt_reg[] __read_mostly = {
 104         {
 105                 .name       = "u32",
 106                 .family     = AF_INET,
 107                 .match      = u32_mt,
 108                 .matchsize  = sizeof(struct xt_u32),
 109                 .me         = THIS_MODULE,
 110         },
 111         {
 112                 .name       = "u32",
 113                 .family     = AF_INET6,
 114                 .match      = u32_mt,
 115                 .matchsize  = sizeof(struct xt_u32),
 116                 .me         = THIS_MODULE,
 117         },
 118 };
 119
 120 static int __init u32_mt_init(void)
 121 {
 122         return xt_register_matches(u32_mt_reg, ARRAY_SIZE(u32_mt_reg));
 123 }
 124
 125 static void __exit u32_mt_exit(void)
 126 {
 127         xt_unregister_matches(u32_mt_reg, ARRAY_SIZE(u32_mt_reg));
 128 }
 129
 130 module_init(u32_mt_init);
 131 module_exit(u32_mt_exit);
 132 MODULE_AUTHOR("Jan Engelhardt <jengelh@computergmbh.de>");
 133 MODULE_DESCRIPTION("Xtables: arbitrary byte matching");
 134 MODULE_LICENSE("GPL");
 135 MODULE_ALIAS("ipt_u32");
 136 MODULE_ALIAS("ip6t_u32");