cregit-Linux how code gets into the kernel

Release 4.14 lib/ts_bm.c

Directory: lib
/*
 * 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/ctype.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 - 1, bs; const u8 icase = conf->flags & TS_IGNORECASE; 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 ((icase ? toupper(text[shift-i]) : 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; }

Contributors

PersonTokensPropCommitsCommitProp
Pablo Neira Ayuso21389.12%133.33%
Joonwoo Park2610.88%266.67%
Total239100.00%3100.00%


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; }

Contributors

PersonTokensPropCommitsCommitProp
Pablo Neira Ayuso98100.00%1100.00%
Total98100.00%1100.00%


static void compute_prefix_tbl(struct ts_bm *bm, int flags) { 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; if (flags & TS_IGNORECASE) bm->bad_shift[tolower(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; } } }

Contributors

PersonTokensPropCommitsCommitProp
Pablo Neira Ayuso18080.00%250.00%
Joonwoo Park3415.11%125.00%
Michael Rash114.89%125.00%
Total225100.00%4100.00%


static struct ts_config *bm_init(const void *pattern, unsigned int len, gfp_t gfp_mask, int flags) { struct ts_config *conf; struct ts_bm *bm; int i; 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; conf->flags = flags; bm = ts_config_priv(conf); bm->patlen = len; bm->pattern = (u8 *) bm->good_shift + prefix_tbl_len; if (flags & TS_IGNORECASE) for (i = 0; i < len; i++) bm->pattern[i] = toupper(((u8 *)pattern)[i]); else memcpy(bm->pattern, pattern, len); compute_prefix_tbl(bm, flags); return conf; }

Contributors

PersonTokensPropCommitsCommitProp
Pablo Neira Ayuso11565.71%125.00%
Joonwoo Park5531.43%125.00%
Michael Rash42.29%125.00%
Al Viro10.57%125.00%
Total175100.00%4100.00%


static void *bm_get_pattern(struct ts_config *conf) { struct ts_bm *bm = ts_config_priv(conf); return bm->pattern; }

Contributors

PersonTokensPropCommitsCommitProp
Pablo Neira Ayuso27100.00%1100.00%
Total27100.00%1100.00%


static unsigned int bm_get_pattern_len(struct ts_config *conf) { struct ts_bm *bm = ts_config_priv(conf); return bm->patlen; }

Contributors

PersonTokensPropCommitsCommitProp
Pablo Neira Ayuso27100.00%1100.00%
Total27100.00%1100.00%

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); }

Contributors

PersonTokensPropCommitsCommitProp
Pablo Neira Ayuso16100.00%1100.00%
Total16100.00%1100.00%


static void __exit exit_bm(void) { textsearch_unregister(&bm_ops); }

Contributors

PersonTokensPropCommitsCommitProp
Pablo Neira Ayuso15100.00%1100.00%
Total15100.00%1100.00%

MODULE_LICENSE("GPL"); module_init(init_bm); module_exit(exit_bm);

Overall Contributors

PersonTokensPropCommitsCommitProp
Pablo Neira Ayuso81985.94%233.33%
Joonwoo Park11812.38%233.33%
Michael Rash151.57%116.67%
Al Viro10.10%116.67%
Total953100.00%6100.00%
Directory: lib
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