util-spm-bs2bm.c

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/* Copyright (C) 2007-2010 Open Information Security Foundation
 *
 * You can copy, redistribute or modify this Program under the terms of
 * the GNU General Public License version 2 as published by the Free
 * Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */
 
/**
 * \file
 *
 * \author Pablo Rincon Crespo <pablo.rincon.crespo@gmail.com>
 *
 * Bs2Bm use a simple context array to determine the characters
 * that are not present on the pattern. This way on partial matches
 * broken by a char not present, we can skip to the next character
 * making less checks
 */
 
#include "suricata-common.h"
#include "suricata.h"
 
#include "util-spm-bs2bm.h"
 
/**
 * \brief Array setup function for Bs2Bm of bad characters index (not found at the needle)
 *
 * \param needle pointer to the pattern we ar searching for
 * \param needle_len length limit of the needle
 * \param badchars pointer to an empty array of bachars. The array prepared contains
 *                 characters that can't be inside the needle_len. So the skips can be
 *                 faster
 */
void Bs2BmBadchars(const uint8_t *needle, uint16_t needle_len, uint8_t *badchars)
{
    uint32_t i;
    for (i = 0; i < ALPHABET_SIZE; i++)
        badchars[i] = 1;
 
    /* set to 0 the values where index as ascii is present
     * because they are not badchars
     */
    for (i = 0; i < needle_len; i++)
        badchars[needle[i]] = 0;
}
 
/**
 * \brief Basic search with a bad characters array. The array badchars contains
 *        flags at character's ascii index that can't be inside the needle. So the skips can be
 *        faster
 *
 * \param haystack pointer to the buffer to search in
 * \param haystack_len length limit of the buffer
 * \param needle pointer to the pattern we ar searching for
 * \param needle_len length limit of the needle
 * \param badchars pointer to an array of bachars prepared by Bs2BmBadchars()
 *
 * \retval ptr to start of the match; NULL if no match
 */
uint8_t *Bs2Bm(const uint8_t *haystack, uint32_t haystack_len, const uint8_t *needle,
        uint16_t needle_len, const uint8_t badchars[])
{
    const uint8_t *h, *n;
    const uint8_t *hmax = haystack + haystack_len;
    const uint8_t *nmax = needle + needle_len;
 
    if (needle_len == 0 || needle_len > haystack_len)
        return NULL;
 
    for (n = needle; nmax - n <= hmax - haystack; haystack++) {
        if (*haystack != *n) {
            continue;
        }
        /* one byte needles */
        if (needle_len == 1)
            return (uint8_t *)haystack;
 
        for (h = haystack+1, n++; nmax - n <= hmax - haystack; h++, n++) {
            if (*h != *n) {
                if (badchars[*h] == 1) {
                    /* skip it! */
                    haystack = h;
                }
                break;
            }
            /* if we run out of needle we fully matched */
            if (n == nmax - 1 ) {
                return (uint8_t *)haystack;
            }
        }
        n = needle;
    }
 
    return NULL;
}
 
/**
 * \brief Basic search case less with a bad characters array. The array badchars contains
 *        flags at character's ascii index that can't be inside the needle. So the skips can be
 *        faster
 *
 * \param haystack pointer to the buffer to search in
 * \param haystack_len length limit of the buffer
 * \param needle pointer to the pattern we ar searching for
 * \param needle_len length limit of the needle
 * \param badchars pointer to an array of bachars prepared by Bs2BmBadchars()
 *
 * \retval ptr to start of the match; NULL if no match
 */
uint8_t *Bs2BmNocase(const uint8_t *haystack, uint32_t haystack_len, const uint8_t *needle,
        uint16_t needle_len, const uint8_t badchars[])
{
    const uint8_t *h, *n;
    const uint8_t *hmax = haystack + haystack_len;
    const uint8_t *nmax = needle + needle_len;
 
    if (needle_len == 0 || needle_len > haystack_len)
        return NULL;
 
    for (n = needle; nmax - n <= hmax - haystack; haystack++) {
        if (u8_tolower(*haystack) != u8_tolower(*n)) {
            continue;
        }
        /* one byte needles */
        if (needle_len == 1)
            return (uint8_t *)haystack;
 
        for (h = haystack+1, n++; nmax - n <= hmax - haystack; h++, n++) {
            if (u8_tolower(*h) != u8_tolower(*n)) {
                if (badchars[u8_tolower(*h)] == 1) {
                    /* skip it! */
                    haystack = h;
                }
                break;
            }
            /* if we run out of needle we fully matched */
            if (n == nmax - 1) {
                return (uint8_t *)haystack;
            }
        }
        n = needle;
    }
 
    return NULL;
}