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
  16static 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
  89static 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
  98static 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
 107static int __init u32_mt_init(void)
 108{
 109        return xt_register_match(&xt_u32_mt_reg);
 110}
 111
 112static void __exit u32_mt_exit(void)
 113{
 114        xt_unregister_match(&xt_u32_mt_reg);
 115}
 116
 117module_init(u32_mt_init);
 118module_exit(u32_mt_exit);
 119MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 120MODULE_DESCRIPTION("Xtables: arbitrary byte matching");
 121MODULE_LICENSE("GPL");
 122MODULE_ALIAS("ipt_u32");
 123MODULE_ALIAS("ip6t_u32");
 124
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