[LIB]: Boyer-Moore extension for textsearch infrastructure strike #2

config TEXTSEARCH_KMP

	tristate

config TEXTSEARCH_BM

        depends on TEXTSEARCH

        tristate "Boyer-Moore"

        help

          Say Y here if you want to be able to search text using the

          Boyer-Moore textsearch algorithm.

          To compile this code as a module, choose M here: the

          module will be called ts_bm.

config TEXTSEARCH_FSM

	tristate

obj-$(CONFIG_TEXTSEARCH) += textsearch.o

obj-$(CONFIG_TEXTSEARCH_KMP) += ts_kmp.o

obj-$(CONFIG_TEXTSEARCH_BM) += ts_bm.o

obj-$(CONFIG_TEXTSEARCH_FSM) += ts_fsm.o

hostprogs-y	:= gen_crc32table

/*

 * 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/config.h>

#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 void compute_prefix_tbl(struct ts_bm *bm, const u8 *pattern,

			       unsigned int len)

{

	int i, j, ended, l[ASIZE];

	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 */

	for (i = 1; i < bm->patlen; i++) {

		for (j = 0; j < bm->patlen && bm->pattern[bm->patlen - 1 - j]

				== bm->pattern[bm->patlen - 1 - i - j]; j++);

		l[i] = j;

	}  

	bm->good_shift[0] = 1;

	for (i = 1; i < bm->patlen; i++)

		bm->good_shift[i] = bm->patlen;

	for (i = bm->patlen - 1; i > 0; i--)

		bm->good_shift[l[i]] = i;

	ended = 0;

	for (i = 0; i < bm->patlen; i++) {

		if (l[i] == bm->patlen - 1 - i)

			ended = i;

		if (ended)

			bm->good_shift[i] = ended;

	}

}

static struct ts_config *bm_init(const void *pattern, unsigned int len,

				 int 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);