linux-stable/lib/ts_bm.c
Colin Ian King 4a70ce5f93 lib/ts_bm.c: remove redundant store to variable consumed after addition
There is no need to store the result of the addition back to variable
consumed after the addition.  The store is redundant, replace += with just
+

Cleans up clang scan build warning: lib/ts_bm.c:83:11: warning: Although
the value stored to 'consumed' is used in the enclosing expression, the
value is never actually read from 'consumed' [deadcode.DeadStores]

Link: https://lkml.kernel.org/r/20220704215325.600993-1-colin.i.king@gmail.com
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-07-17 17:31:39 -07:00

203 lines
5.1 KiB
C

// 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 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;
}
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 = 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;
}
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);