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/*
* xt_u32 - kernel module to match u32 packet content
*
* Original author: Don Cohen <don@isis.cs3-inc.com>
* (C) CC Computer Consultants GmbH, 2007
* Contact: <jengelh@computergmbh.de>
*/
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/spinlock.h>
#include <linux/skbuff.h>
#include <linux/types.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_u32.h>
static bool u32_match_it(const struct xt_u32 *data,
const struct sk_buff *skb)
{
const struct xt_u32_test *ct;
unsigned int testind;
unsigned int nnums;
unsigned int nvals;
unsigned int i;
__be32 n;
u_int32_t pos;
u_int32_t val;
u_int32_t at;
/*
* Small example: "0 >> 28 == 4 && 8 & 0xFF0000 >> 16 = 6, 17"
* (=IPv4 and (TCP or UDP)). Outer loop runs over the "&&" operands.
*/
for (testind = 0; testind < data->ntests; ++testind) {
ct = &data->tests[testind];
at = 0;
pos = ct->location[0].number;
if (skb->len < 4 || pos > skb->len - 4)
return false;
if (skb_copy_bits(skb, pos, &n, sizeof(n)) < 0)
BUG();
val = ntohl(n);
nnums = ct->nnums;
/* Inner loop runs over "&", "<<", ">>" and "@" operands */
for (i = 1; i < nnums; ++i) {
u_int32_t number = ct->location[i].number;
switch (ct->location[i].nextop) {
case XT_U32_AND:
val &= number;
break;
case XT_U32_LEFTSH:
val <<= number;
break;
case XT_U32_RIGHTSH:
val >>= number;
break;
case XT_U32_AT:
if (at + val < at)
return false;
at += val;
pos = number;
if (at + 4 < at || skb->len < at + 4 ||
pos > skb->len - at - 4)
return false;
if (skb_copy_bits(skb, at + pos, &n,
sizeof(n)) < 0)
BUG();
val = ntohl(n);
break;
}
}
/* Run over the "," and ":" operands */
nvals = ct->nvalues;
for (i = 0; i < nvals; ++i)
if (ct->value[i].min <= val && val <= ct->value[i].max)
break;
if (i >= ct->nvalues)
return false;
}
return true;
}
static bool u32_mt(const struct sk_buff *skb, const struct xt_match_param *par)
{
const struct xt_u32 *data = par->matchinfo;
bool ret;
ret = u32_match_it(data, skb);
return ret ^ data->invert;
}
static struct xt_match xt_u32_mt_reg __read_mostly = {
.name = "u32",
.revision = 0,
.family = NFPROTO_UNSPEC,
.match = u32_mt,
.matchsize = sizeof(struct xt_u32),
.me = THIS_MODULE,
};
static int __init u32_mt_init(void)
{
return xt_register_match(&xt_u32_mt_reg);
}
static void __exit u32_mt_exit(void)
{
xt_unregister_match(&xt_u32_mt_reg);
}
module_init(u32_mt_init);
module_exit(u32_mt_exit);
MODULE_AUTHOR("Jan Engelhardt <jengelh@computergmbh.de>");
MODULE_DESCRIPTION("Xtables: arbitrary byte matching");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_u32");
MODULE_ALIAS("ip6t_u32");
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