--- /dev/null
+/*
+ * 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;
+}
+
+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);
Code Review / kvmfornfv.git / blobdiff