linux/lib/ts_bm.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * lib/ts_bm.c		Boyer-Moore text search implementation
 *
 * Authors:	Pablo Neira Ayuso <[email protected]>
 *
 * ==========================================================================
 * 
 *   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.
 *       https://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/ctype.h>
#include <linux/textsearch.h>

/* Alphabet size, use ASCII */
#define ASIZE …

#if 0
#define DEBUGP …
#else
#define DEBUGP(args, format...) …
#endif

struct ts_bm
{ … };

static unsigned int matchpat(const u8 *pattern, unsigned int patlen,
			     const u8 *text, bool icase)
{ … }

static unsigned int bm_find(struct ts_config *conf, struct ts_state *state)
{ … }

static int subpattern(u8 *pattern, int i, int j, int g)
{ … }

static void compute_prefix_tbl(struct ts_bm *bm, int flags)
{ … }

static struct ts_config *bm_init(const void *pattern, unsigned int len,
				 gfp_t gfp_mask, int flags)
{ … }

static void *bm_get_pattern(struct ts_config *conf)
{ … }

static unsigned int bm_get_pattern_len(struct ts_config *conf)
{ … }

static struct ts_ops bm_ops = …;

static int __init init_bm(void)
{ … }

static void __exit exit_bm(void)
{ … }

MODULE_DESCRIPTION(…) …;
MODULE_LICENSE(…) …;

module_init(…) …;
module_exit(exit_bm);