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![Joonwoo Park](/assets/img/avatar_default.png)
Add support for case insensitive search to Boyer-Moore algorithm. Signed-off-by: Joonwoo Park <joonwpark81@gmail.com> Signed-off-by: Patrick McHardy <kaber@trash.net> Signed-off-by: David S. Miller <davem@davemloft.net>
207 lines
5.3 KiB
C
207 lines
5.3 KiB
C
/*
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* lib/ts_bm.c Boyer-Moore text search implementation
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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* Authors: Pablo Neira Ayuso <pablo@eurodev.net>
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*
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* ==========================================================================
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*
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* Implements Boyer-Moore string matching algorithm:
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*
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* [1] A Fast String Searching Algorithm, R.S. Boyer and Moore.
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* Communications of the Association for Computing Machinery,
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* 20(10), 1977, pp. 762-772.
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* http://www.cs.utexas.edu/users/moore/publications/fstrpos.pdf
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*
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* [2] Handbook of Exact String Matching Algorithms, Thierry Lecroq, 2004
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* http://www-igm.univ-mlv.fr/~lecroq/string/string.pdf
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*
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* Note: Since Boyer-Moore (BM) performs searches for matchings from right
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* to left, it's still possible that a matching could be spread over
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* multiple blocks, in that case this algorithm won't find any coincidence.
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*
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* If you're willing to ensure that such thing won't ever happen, use the
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* Knuth-Pratt-Morris (KMP) implementation instead. In conclusion, choose
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* the proper string search algorithm depending on your setting.
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*
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* Say you're using the textsearch infrastructure for filtering, NIDS or
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* any similar security focused purpose, then go KMP. Otherwise, if you
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* really care about performance, say you're classifying packets to apply
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* Quality of Service (QoS) policies, and you don't mind about possible
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* matchings spread over multiple fragments, then go BM.
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/types.h>
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#include <linux/string.h>
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#include <linux/ctype.h>
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#include <linux/textsearch.h>
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/* Alphabet size, use ASCII */
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#define ASIZE 256
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#if 0
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#define DEBUGP printk
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#else
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#define DEBUGP(args, format...)
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#endif
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struct ts_bm
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{
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u8 * pattern;
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unsigned int patlen;
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unsigned int bad_shift[ASIZE];
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unsigned int good_shift[0];
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};
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static unsigned int bm_find(struct ts_config *conf, struct ts_state *state)
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{
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struct ts_bm *bm = ts_config_priv(conf);
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unsigned int i, text_len, consumed = state->offset;
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const u8 *text;
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int shift = bm->patlen - 1, bs;
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const u8 icase = conf->flags & TS_IGNORECASE;
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for (;;) {
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text_len = conf->get_next_block(consumed, &text, conf, state);
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if (unlikely(text_len == 0))
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break;
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while (shift < text_len) {
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DEBUGP("Searching in position %d (%c)\n",
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shift, text[shift]);
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for (i = 0; i < bm->patlen; i++)
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if ((icase ? toupper(text[shift-i])
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: text[shift-i])
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!= bm->pattern[bm->patlen-1-i])
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goto next;
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/* London calling... */
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DEBUGP("found!\n");
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return consumed += (shift-(bm->patlen-1));
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next: bs = bm->bad_shift[text[shift-i]];
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/* Now jumping to... */
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shift = max_t(int, shift-i+bs, shift+bm->good_shift[i]);
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}
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consumed += text_len;
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}
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return UINT_MAX;
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}
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static int subpattern(u8 *pattern, int i, int j, int g)
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{
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int x = i+g-1, y = j+g-1, ret = 0;
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while(pattern[x--] == pattern[y--]) {
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if (y < 0) {
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ret = 1;
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break;
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}
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if (--g == 0) {
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ret = pattern[i-1] != pattern[j-1];
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break;
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}
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}
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return ret;
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}
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static void compute_prefix_tbl(struct ts_bm *bm, int flags)
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{
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int i, j, g;
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for (i = 0; i < ASIZE; i++)
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bm->bad_shift[i] = bm->patlen;
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for (i = 0; i < bm->patlen - 1; i++) {
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bm->bad_shift[bm->pattern[i]] = bm->patlen - 1 - i;
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if (flags & TS_IGNORECASE)
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bm->bad_shift[tolower(bm->pattern[i])]
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= bm->patlen - 1 - i;
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}
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/* Compute the good shift array, used to match reocurrences
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* of a subpattern */
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bm->good_shift[0] = 1;
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for (i = 1; i < bm->patlen; i++)
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bm->good_shift[i] = bm->patlen;
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for (i = bm->patlen-1, g = 1; i > 0; g++, i--) {
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for (j = i-1; j >= 1-g ; j--)
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if (subpattern(bm->pattern, i, j, g)) {
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bm->good_shift[g] = bm->patlen-j-g;
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break;
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}
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}
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}
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static struct ts_config *bm_init(const void *pattern, unsigned int len,
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gfp_t gfp_mask, int flags)
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{
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struct ts_config *conf;
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struct ts_bm *bm;
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int i;
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unsigned int prefix_tbl_len = len * sizeof(unsigned int);
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size_t priv_size = sizeof(*bm) + len + prefix_tbl_len;
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conf = alloc_ts_config(priv_size, gfp_mask);
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if (IS_ERR(conf))
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return conf;
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conf->flags = flags;
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bm = ts_config_priv(conf);
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bm->patlen = len;
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bm->pattern = (u8 *) bm->good_shift + prefix_tbl_len;
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if (flags & TS_IGNORECASE)
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for (i = 0; i < len; i++)
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bm->pattern[i] = toupper(((u8 *)pattern)[i]);
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else
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memcpy(bm->pattern, pattern, len);
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compute_prefix_tbl(bm, flags);
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return conf;
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}
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static void *bm_get_pattern(struct ts_config *conf)
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{
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struct ts_bm *bm = ts_config_priv(conf);
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return bm->pattern;
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}
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static unsigned int bm_get_pattern_len(struct ts_config *conf)
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{
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struct ts_bm *bm = ts_config_priv(conf);
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return bm->patlen;
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}
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static struct ts_ops bm_ops = {
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.name = "bm",
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.find = bm_find,
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.init = bm_init,
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.get_pattern = bm_get_pattern,
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.get_pattern_len = bm_get_pattern_len,
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.owner = THIS_MODULE,
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.list = LIST_HEAD_INIT(bm_ops.list)
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};
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static int __init init_bm(void)
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{
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return textsearch_register(&bm_ops);
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}
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static void __exit exit_bm(void)
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{
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textsearch_unregister(&bm_ops);
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}
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MODULE_LICENSE("GPL");
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module_init(init_bm);
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module_exit(exit_bm);
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