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Linux/net/netfilter/xt_u32.c

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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  */
  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 
 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                 if (skb_copy_bits(skb, pos, &n, sizeof(n)) < 0)
 42                         BUG();
 43                 val   = ntohl(n);
 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                                 if (skb_copy_bits(skb, at + pos, &n,
 69                                                     sizeof(n)) < 0)
 70                                         BUG();
 71                                 val = ntohl(n);
 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_mt(const struct sk_buff *skb, struct xt_action_param *par)
 90 {
 91         const struct xt_u32 *data = par->matchinfo;
 92         bool ret;
 93 
 94         ret = u32_match_it(data, skb);
 95         return ret ^ data->invert;
 96 }
 97 
 98 static struct xt_match xt_u32_mt_reg __read_mostly = {
 99         .name       = "u32",
100         .revision   = 0,
101         .family     = NFPROTO_UNSPEC,
102         .match      = u32_mt,
103         .matchsize  = sizeof(struct xt_u32),
104         .me         = THIS_MODULE,
105 };
106 
107 static int __init u32_mt_init(void)
108 {
109         return xt_register_match(&xt_u32_mt_reg);
110 }
111 
112 static void __exit u32_mt_exit(void)
113 {
114         xt_unregister_match(&xt_u32_mt_reg);
115 }
116 
117 module_init(u32_mt_init);
118 module_exit(u32_mt_exit);
119 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
120 MODULE_DESCRIPTION("Xtables: arbitrary byte matching");
121 MODULE_LICENSE("GPL");
122 MODULE_ALIAS("ipt_u32");
123 MODULE_ALIAS("ip6t_u32");
124 

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