Something went wrong. Try again.
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Something went wrong. Try again.
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238// SPDX-License-Identifier: GPL-2.0-or-later/* * lib/ts_bm.c Boyer-Moore text search implementation * * 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. * 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 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[];};
static unsigned int matchpat(const u8 *pattern, unsigned int patlen, const u8 *text, bool icase){ unsigned int i;
for (i = 0; i < patlen; i++) { u8 t = *(text-i);
if (icase) t = toupper(t);
if (t != *(pattern-i)) break; }
return i;}
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 bs; const u8 icase = conf->flags & TS_IGNORECASE;
for (;;) { int shift = bm->patlen - 1;
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]);
i = matchpat(&bm->pattern[bm->patlen-1], bm->patlen, &text[shift], icase); if (i == bm->patlen) { /* London calling... */ DEBUGP("found!\n"); return consumed + (shift-(bm->patlen-1)); }
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 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; } }}
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; size_t priv_size;
/* Zero-length patterns would underflow bm_find()'s initial shift. */ if (unlikely(!len)) return ERR_PTR(-EINVAL);
/* * bm->pattern is stored immediately after the good_shift[] table. * Reject lengths that would wrap while sizing either region. */ if (unlikely(check_mul_overflow(len, sizeof(*bm->good_shift), &prefix_tbl_len) || check_add_overflow(sizeof(*bm), (size_t)len, &priv_size) || check_add_overflow(priv_size, prefix_tbl_len, &priv_size))) return ERR_PTR(-EINVAL);
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;}
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_DESCRIPTION("Boyer-Moore text search implementation");MODULE_LICENSE("GPL");
module_init(init_bm);module_exit(exit_bm);