/* * 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){	int i, j, g; 	for (i = 0; i < ASIZE; i++)		bm->bad_shift[i] = bm->patlen;	for (i = 0; i < bm->patlen - 1; i++)		bm->bad_shift[bm->pattern[i]] = bm->patlen - 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;	memcpy(bm->pattern, pattern, len);	compute_prefix_tbl(bm); 	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);