/* Copyright (C) 2021 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 Philippe Antoine <contact@catenacyber.fr>

 *

 * Implements the xor transform keyword with option support

 */

#include "suricata-common.h"

#include "detect.h"

#include "detect-engine.h"

#include "detect-parse.h"

#include "detect-transform-xor.h"

typedef struct DetectTransformXorData {

    uint8_t *key;

    // limit the key length

    uint8_t length;

} DetectTransformXorData;

static int DetectTransformXorSetup(DetectEngineCtx *, Signature *, const char *);

static void DetectTransformXorFree(DetectEngineCtx *, void *);

static void DetectTransformXor(InspectionBuffer *buffer, void *options);

#ifdef UNITTESTS

void DetectTransformXorRegisterTests(void);

#endif

void DetectTransformXorRegister(void)

{

    sigmatch_table[DETECT_TRANSFORM_XOR].name = "xor";

    sigmatch_table[DETECT_TRANSFORM_XOR].desc = "modify buffer via XOR decoding before inspection";

    sigmatch_table[DETECT_TRANSFORM_XOR].url = "/rules/transforms.html#xor";

    sigmatch_table[DETECT_TRANSFORM_XOR].Transform = DetectTransformXor;

    sigmatch_table[DETECT_TRANSFORM_XOR].Free = DetectTransformXorFree;

    sigmatch_table[DETECT_TRANSFORM_XOR].Setup = DetectTransformXorSetup;

#ifdef UNITTESTS

    sigmatch_table[DETECT_TRANSFORM_XOR].RegisterTests = DetectTransformXorRegisterTests;

#endif

    sigmatch_table[DETECT_TRANSFORM_XOR].flags |= SIGMATCH_QUOTES_MANDATORY;

}

static void DetectTransformXorFree(DetectEngineCtx *de_ctx, void *ptr)

{

    if (ptr != NULL) {

        DetectTransformXorData *pxd = (DetectTransformXorData *)ptr;

        SCFree(pxd->key);

        SCFree(pxd);

    }

}

/**

 *  \internal

 *  \brief Apply the xor keyword to the last pattern match

 *  \param det_ctx detection engine ctx

 *  \param s signature

 *  \param optstr options string

 *  \retval 0 ok

 *  \retval -1 failure

 */

static int DetectTransformXorSetup(DetectEngineCtx *de_ctx, Signature *s, const char *optstr)

{

    SCEnter();

    // Create pxd from optstr

    DetectTransformXorData *pxd = SCCalloc(1, sizeof(*pxd));

    if (pxd == NULL) {

        SCLogError("memory allocation failed");

        SCReturnInt(-1);

    }

    size_t keylen = strlen(optstr);

    if (keylen % 2 == 1) {

        SCLogError("XOR transform key's length must be an even number");

        DetectTransformXorFree(de_ctx, pxd);

        SCReturnInt(-1);

    }

    if (keylen / 2 > UINT8_MAX) {

        SCLogError("Key length too big for XOR transform");

        DetectTransformXorFree(de_ctx, pxd);

        SCReturnInt(-1);

    }

    pxd->length = (uint8_t)(keylen / 2);

    pxd->key = SCMalloc(keylen / 2);

    if (pxd->key == NULL) {

        SCLogError("memory allocation failed");

        DetectTransformXorFree(de_ctx, pxd);

        SCReturnInt(-1);

    }

    for (size_t i = 0; i < keylen / 2; i++) {

        if ((isxdigit(optstr[2 * i])) && (isxdigit(optstr[2 * i + 1]))) {

            pxd->key[i] = (uint8_t)((optstr[2 * i] >= 'A' ? ((optstr[2 * i] & 0xdf) - 'A') + 10

                                                          : (optstr[2 * i] - '0'))

                                    << 4);

            pxd->key[i] |= (optstr[2 * i + 1] >= 'A' ? ((optstr[2 * i + 1] & 0xdf) - 'A') + 10

                                                     : (optstr[2 * i + 1] - '0'));

        } else {

            SCLogError("XOR transform key must be hexadecimal characters only");

            DetectTransformXorFree(de_ctx, pxd);

            SCReturnInt(-1);

        }

    }

    int r = DetectSignatureAddTransform(s, DETECT_TRANSFORM_XOR, pxd);

    if (r != 0) {

        DetectTransformXorFree(de_ctx, pxd);

    }

    SCReturnInt(r);

}

static void DetectTransformXor(InspectionBuffer *buffer, void *options)

{

    const uint8_t *input = buffer->inspect;

    const uint32_t input_len = buffer->inspect_len;

    DetectTransformXorData *pxd = options;

    if (input_len == 0) {

        return;

    }

    uint8_t *output = InspectionBufferCheckAndExpand(buffer, input_len);

    if (output == NULL) {

        return;

    }

    for (uint32_t i = 0; i < input_len; i++) {

        output[i] = input[i] ^ pxd->key[i % pxd->length];

    }

    InspectionBufferTruncate(buffer, input_len);

}

#ifdef UNITTESTS

#include "tests/detect-transform-xor.c"

#endif