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/* 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[input_len];
for (uint32_t i = 0; i < input_len; i++) {
output[i] = input[i] ^ pxd->key[i % pxd->length];
}
InspectionBufferCopy(buffer, output, input_len);
}
#ifdef UNITTESTS
#include "tests/detect-transform-xor.c"
#endif
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