195 строки
4.9 KiB
C
195 строки
4.9 KiB
C
/*
|
|
* lib/ts_bm.c Boyer-Moore text search implementation
|
|
*
|
|
* This program is free software; you can redistribute it and/or
|
|
* modify it under the terms of the GNU General Public License
|
|
* as published by the Free Software Foundation; either version
|
|
* 2 of the License, or (at your option) any later version.
|
|
*
|
|
* Authors: Pablo Neira Ayuso <pablo@eurodev.net>
|
|
*
|
|
* ==========================================================================
|
|
*
|
|
* Implements Boyer-Moore string matching algorithm:
|
|
*
|
|
* [1] A Fast String Searching Algorithm, R.S. Boyer and Moore.
|
|
* Communications of the Association for Computing Machinery,
|
|
* 20(10), 1977, pp. 762-772.
|
|
* http://www.cs.utexas.edu/users/moore/publications/fstrpos.pdf
|
|
*
|
|
* [2] Handbook of Exact String Matching Algorithms, Thierry Lecroq, 2004
|
|
* http://www-igm.univ-mlv.fr/~lecroq/string/string.pdf
|
|
*
|
|
* Note: Since Boyer-Moore (BM) performs searches for matchings from right
|
|
* to left, it's still possible that a matching could be spread over
|
|
* multiple blocks, in that case this algorithm won't find any coincidence.
|
|
*
|
|
* If you're willing to ensure that such thing won't ever happen, use the
|
|
* Knuth-Pratt-Morris (KMP) implementation instead. In conclusion, choose
|
|
* the proper string search algorithm depending on your setting.
|
|
*
|
|
* Say you're using the textsearch infrastructure for filtering, NIDS or
|
|
* any similar security focused purpose, then go KMP. Otherwise, if you
|
|
* really care about performance, say you're classifying packets to apply
|
|
* Quality of Service (QoS) policies, and you don't mind about possible
|
|
* matchings spread over multiple fragments, then go BM.
|
|
*/
|
|
|
|
#include <linux/kernel.h>
|
|
#include <linux/module.h>
|
|
#include <linux/types.h>
|
|
#include <linux/string.h>
|
|
#include <linux/textsearch.h>
|
|
|
|
/* Alphabet size, use ASCII */
|
|
#define ASIZE 256
|
|
|
|
#if 0
|
|
#define DEBUGP printk
|
|
#else
|
|
#define DEBUGP(args, format...)
|
|
#endif
|
|
|
|
struct ts_bm
|
|
{
|
|
u8 * pattern;
|
|
unsigned int patlen;
|
|
unsigned int bad_shift[ASIZE];
|
|
unsigned int good_shift[0];
|
|
};
|
|
|
|
static unsigned int bm_find(struct ts_config *conf, struct ts_state *state)
|
|
{
|
|
struct ts_bm *bm = ts_config_priv(conf);
|
|
unsigned int i, text_len, consumed = state->offset;
|
|
const u8 *text;
|
|
int shift = bm->patlen, bs;
|
|
|
|
for (;;) {
|
|
text_len = conf->get_next_block(consumed, &text, conf, state);
|
|
|
|
if (unlikely(text_len == 0))
|
|
break;
|
|
|
|
while (shift < text_len) {
|
|
DEBUGP("Searching in position %d (%c)\n",
|
|
shift, text[shift]);
|
|
for (i = 0; i < bm->patlen; i++)
|
|
if (text[shift-i] != bm->pattern[bm->patlen-1-i])
|
|
goto next;
|
|
|
|
/* London calling... */
|
|
DEBUGP("found!\n");
|
|
return consumed += (shift-(bm->patlen-1));
|
|
|
|
next: bs = bm->bad_shift[text[shift-i]];
|
|
|
|
/* Now jumping to... */
|
|
shift = max_t(int, shift-i+bs, shift+bm->good_shift[i]);
|
|
}
|
|
consumed += text_len;
|
|
}
|
|
|
|
return UINT_MAX;
|
|
}
|
|
|
|
static int subpattern(u8 *pattern, int i, int j, int g)
|
|
{
|
|
int x = i+g-1, y = j+g-1, ret = 0;
|
|
|
|
while(pattern[x--] == pattern[y--]) {
|
|
if (y < 0) {
|
|
ret = 1;
|
|
break;
|
|
}
|
|
if (--g == 0) {
|
|
ret = pattern[i-1] != pattern[j-1];
|
|
break;
|
|
}
|
|
}
|
|
|
|
return ret;
|
|
}
|
|
|
|
static void compute_prefix_tbl(struct ts_bm *bm, const u8 *pattern,
|
|
unsigned int len)
|
|
{
|
|
int i, j, g;
|
|
|
|
for (i = 0; i < ASIZE; i++)
|
|
bm->bad_shift[i] = len;
|
|
for (i = 0; i < len - 1; i++)
|
|
bm->bad_shift[pattern[i]] = len - 1 - i;
|
|
|
|
/* Compute the good shift array, used to match reocurrences
|
|
* of a subpattern */
|
|
bm->good_shift[0] = 1;
|
|
for (i = 1; i < bm->patlen; i++)
|
|
bm->good_shift[i] = bm->patlen;
|
|
for (i = bm->patlen-1, g = 1; i > 0; g++, i--) {
|
|
for (j = i-1; j >= 1-g ; j--)
|
|
if (subpattern(bm->pattern, i, j, g)) {
|
|
bm->good_shift[g] = bm->patlen-j-g;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
static struct ts_config *bm_init(const void *pattern, unsigned int len,
|
|
gfp_t gfp_mask)
|
|
{
|
|
struct ts_config *conf;
|
|
struct ts_bm *bm;
|
|
unsigned int prefix_tbl_len = len * sizeof(unsigned int);
|
|
size_t priv_size = sizeof(*bm) + len + prefix_tbl_len;
|
|
|
|
conf = alloc_ts_config(priv_size, gfp_mask);
|
|
if (IS_ERR(conf))
|
|
return conf;
|
|
|
|
bm = ts_config_priv(conf);
|
|
bm->patlen = len;
|
|
bm->pattern = (u8 *) bm->good_shift + prefix_tbl_len;
|
|
compute_prefix_tbl(bm, pattern, len);
|
|
memcpy(bm->pattern, pattern, len);
|
|
|
|
return conf;
|
|
}
|
|
|
|
static void *bm_get_pattern(struct ts_config *conf)
|
|
{
|
|
struct ts_bm *bm = ts_config_priv(conf);
|
|
return bm->pattern;
|
|
}
|
|
|
|
static unsigned int bm_get_pattern_len(struct ts_config *conf)
|
|
{
|
|
struct ts_bm *bm = ts_config_priv(conf);
|
|
return bm->patlen;
|
|
}
|
|
|
|
static struct ts_ops bm_ops = {
|
|
.name = "bm",
|
|
.find = bm_find,
|
|
.init = bm_init,
|
|
.get_pattern = bm_get_pattern,
|
|
.get_pattern_len = bm_get_pattern_len,
|
|
.owner = THIS_MODULE,
|
|
.list = LIST_HEAD_INIT(bm_ops.list)
|
|
};
|
|
|
|
static int __init init_bm(void)
|
|
{
|
|
return textsearch_register(&bm_ops);
|
|
}
|
|
|
|
static void __exit exit_bm(void)
|
|
{
|
|
textsearch_unregister(&bm_ops);
|
|
}
|
|
|
|
MODULE_LICENSE("GPL");
|
|
|
|
module_init(init_bm);
|
|
module_exit(exit_bm);
|