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/* Kernel module to match a string into a packet.
*
* Copyright (C) 2000 Emmanuel Roger <winfield@freegates.be>
*
* ChangeLog
* 19.02.2002: Gianni Tedesco <gianni@ecsc.co.uk>
* Fixed SMP re-entrancy problem using per-cpu data areas
* for the skip/shift tables.
* 02.05.2001: Gianni Tedesco <gianni@ecsc.co.uk>
* Fixed kernel panic, due to overrunning boyer moore string
* tables. Also slightly tweaked heuristic for deciding what
* search algo to use.
* 27.01.2001: Gianni Tedesco <gianni@ecsc.co.uk>
* Implemented Boyer Moore Sublinear search algorithm
* alongside the existing linear search based on memcmp().
* Also a quick check to decide which method to use on a per
* packet basis.
*/
#include <linux/smp.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/file.h>
#include <net/sock.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv4/ipt_string.h>
MODULE_LICENSE("GPL");
struct string_per_cpu {
int *skip;
int *shift;
int *len;
};
struct string_per_cpu *bm_string_data=NULL;
/* Boyer Moore Sublinear string search - VERY FAST */
char *search_sublinear (char *needle, char *haystack, int needle_len, int haystack_len)
{
int M1, right_end, sk, sh;
int ended, j, i;
int *skip, *shift, *len;
/* use data suitable for this CPU */
shift=bm_string_data[smp_processor_id()].shift;
skip=bm_string_data[smp_processor_id()].skip;
len=bm_string_data[smp_processor_id()].len;
/* Setup skip/shift tables */
M1 = right_end = needle_len-1;
for (i = 0; i < BM_MAX_HLEN; i++) skip[i] = needle_len;
for (i = 0; needle[i]; i++) skip[needle[i]] = M1 - i;
for (i = 1; i < needle_len; i++) {
for (j = 0; j < needle_len && needle[M1 - j] == needle[M1 - i - j]; j++);
len[i] = j;
}
shift[0] = 1;
for (i = 1; i < needle_len; i++) shift[i] = needle_len;
for (i = M1; i > 0; i--) shift[len[i]] = i;
ended = 0;
for (i = 0; i < needle_len; i++) {
if (len[i] == M1 - i) ended = i;
if (ended) shift[i] = ended;
}
/* Do the search*/
while (right_end < haystack_len)
{
for (i = 0; i < needle_len && haystack[right_end - i] == needle[M1 - i]; i++);
if (i == needle_len) {
return haystack+(right_end - M1);
}
sk = skip[haystack[right_end - i]];
sh = shift[i];
right_end = max(right_end - i + sk, right_end + sh);
}
return NULL;
}
/* Linear string search based on memcmp() */
char *search_linear (char *needle, char *haystack, int needle_len, int haystack_len)
{
char *k = haystack + (haystack_len-needle_len);
char *t = haystack;
while ( t <= k ) {
if (memcmp(t, needle, needle_len) == 0)
return t;
t++;
}
return NULL;
}
static int
match(const struct sk_buff *skb,
const struct net_device *in,
const struct net_device *out,
const void *matchinfo,
int offset,
const void *hdr,
u_int16_t datalen,
int *hotdrop)
{
const struct ipt_string_info *info = matchinfo;
struct iphdr *ip = skb->nh.iph;
int hlen, nlen;
char *needle, *haystack;
proc_ipt_search search=search_linear;
if ( !ip ) return 0;
/* get lenghts, and validate them */
nlen=info->len;
hlen=ntohs(ip->tot_len)-(ip->ihl*4);
if ( nlen > hlen ) return 0;
needle=(char *)&info->string;
haystack=(char *)ip+(ip->ihl*4);
/* The sublinear search comes in to its own
* on the larger packets */
if ( (hlen>IPT_STRING_HAYSTACK_THRESH) &&
(nlen>IPT_STRING_NEEDLE_THRESH) ) {
if ( hlen < BM_MAX_HLEN ) {
search=search_sublinear;
}else{
if (net_ratelimit())
printk(KERN_INFO "ipt_string: Packet too big "
"to attempt sublinear string search "
"(%d bytes)\n", hlen );
}
}
return ((search(needle, haystack, nlen, hlen)!=NULL) ^ info->invert);
}
static int
checkentry(const char *tablename,
const struct ipt_ip *ip,
void *matchinfo,
unsigned int matchsize,
unsigned int hook_mask)
{
if (matchsize != IPT_ALIGN(sizeof(struct ipt_string_info)))
return 0;
return 1;
}
void string_freeup_data(void)
{
int c;
if ( bm_string_data ) {
for(c=0; c<smp_num_cpus; c++) {
if ( bm_string_data[c].shift ) kfree(bm_string_data[c].shift);
if ( bm_string_data[c].skip ) kfree(bm_string_data[c].skip);
if ( bm_string_data[c].len ) kfree(bm_string_data[c].len);
}
kfree(bm_string_data);
}
}
static struct ipt_match string_match
= { { NULL, NULL }, "string", &match, &checkentry, NULL, THIS_MODULE };
static int __init init(void)
{
int c;
size_t tlen;
size_t alen;
tlen=sizeof(struct string_per_cpu)*smp_num_cpus;
alen=sizeof(int)*BM_MAX_HLEN;
/* allocate array of structures */
if ( !(bm_string_data=kmalloc(tlen,GFP_KERNEL)) ) {
return 0;
}
memset(bm_string_data, 0, tlen);
/* allocate our skip/shift tables */
for(c=0; c<smp_num_cpus; c++) {
if ( !(bm_string_data[c].shift=kmalloc(alen, GFP_KERNEL)) )
goto alloc_fail;
if ( !(bm_string_data[c].skip=kmalloc(alen, GFP_KERNEL)) )
goto alloc_fail;
if ( !(bm_string_data[c].len=kmalloc(alen, GFP_KERNEL)) )
goto alloc_fail;
}
return ipt_register_match(&string_match);
alloc_fail:
string_freeup_data();
return 0;
}
static void __exit fini(void)
{
ipt_unregister_match(&string_match);
string_freeup_data();
}
module_init(init);
module_exit(fini);
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