1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
|
/*
* 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/config.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/string.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, bs;
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 (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 void compute_prefix_tbl(struct ts_bm *bm, const u8 *pattern,
unsigned int len)
{
int i, j, ended, l[ASIZE];
for (i = 0; i < ASIZE; i++)
bm->bad_shift[i] = len;
for (i = 0; i < len - 1; i++)
bm->bad_shift[pattern[i]] = len - 1 - i;
/* Compute the good shift array, used to match reocurrences
* of a subpattern */
for (i = 1; i < bm->patlen; i++) {
for (j = 0; j < bm->patlen && bm->pattern[bm->patlen - 1 - j]
== bm->pattern[bm->patlen - 1 - i - j]; j++);
l[i] = j;
}
bm->good_shift[0] = 1;
for (i = 1; i < bm->patlen; i++)
bm->good_shift[i] = bm->patlen;
for (i = bm->patlen - 1; i > 0; i--)
bm->good_shift[l[i]] = i;
ended = 0;
for (i = 0; i < bm->patlen; i++) {
if (l[i] == bm->patlen - 1 - i)
ended = i;
if (ended)
bm->good_shift[i] = ended;
}
}
static struct ts_config *bm_init(const void *pattern, unsigned int len,
gfp_t gfp_mask)
{
struct ts_config *conf;
struct ts_bm *bm;
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;
bm = ts_config_priv(conf);
bm->patlen = len;
bm->pattern = (u8 *) bm->good_shift + prefix_tbl_len;
compute_prefix_tbl(bm, pattern, len);
memcpy(bm->pattern, pattern, len);
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);
|
