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/* Copyright (C) 2020 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 <p.antoine@catenacyber.fr>
*
* Implements the url_decode transform keyword
*/
#include "suricata-common.h"
#include "detect.h"
#include "detect-engine.h"
#include "detect-engine-prefilter.h"
#include "detect-engine-build.h"
#include "detect-parse.h"
#include "detect-transform-urldecode.h"
#include "util-unittest.h"
#include "util-print.h"
static int DetectTransformUrlDecodeSetup (DetectEngineCtx *, Signature *, const char *);
#ifdef UNITTESTS
static void DetectTransformUrlDecodeRegisterTests(void);
#endif
static void TransformUrlDecode(InspectionBuffer *buffer, void *options);
void DetectTransformUrlDecodeRegister(void)
{
sigmatch_table[DETECT_TRANSFORM_URL_DECODE].name = "url_decode";
sigmatch_table[DETECT_TRANSFORM_URL_DECODE].desc =
"modify buffer to decode urlencoded data before inspection";
sigmatch_table[DETECT_TRANSFORM_URL_DECODE].url = "/rules/transforms.html#url-decode";
sigmatch_table[DETECT_TRANSFORM_URL_DECODE].Transform =
TransformUrlDecode;
sigmatch_table[DETECT_TRANSFORM_URL_DECODE].Setup =
DetectTransformUrlDecodeSetup;
#ifdef UNITTESTS
sigmatch_table[DETECT_TRANSFORM_URL_DECODE].RegisterTests =
DetectTransformUrlDecodeRegisterTests;
#endif
sigmatch_table[DETECT_TRANSFORM_URL_DECODE].flags |= SIGMATCH_NOOPT;
}
/**
* \internal
* \brief Apply the transform keyword to the last pattern match
* \param det_ctx detection engine ctx
* \param s signature
* \param nullstr should be null
* \retval 0 ok
* \retval -1 failure
*/
static int DetectTransformUrlDecodeSetup (DetectEngineCtx *de_ctx, Signature *s, const char *nullstr)
{
SCEnter();
int r = DetectSignatureAddTransform(s, DETECT_TRANSFORM_URL_DECODE, NULL);
SCReturnInt(r);
}
// util function so as to ease reuse sometimes
static bool BufferUrlDecode(const uint8_t *input, const uint32_t input_len, uint8_t *output, uint32_t *output_size)
{
bool changed = false;
uint8_t *oi = output;
//PrintRawDataFp(stdout, input, input_len);
for (uint32_t i = 0; i < input_len; i++) {
if (input[i] == '%') {
if (i + 2 < input_len) {
if ((isxdigit(input[i+1])) && (isxdigit(input[i+2]))) {
// Decode %HH encoding.
*oi = (uint8_t)((input[i + 1] >= 'A' ? ((input[i + 1] & 0xdf) - 'A') + 10
: (input[i + 1] - '0'))
<< 4);
*oi |= (input[i+2] >= 'A' ? ((input[i+2] & 0xdf) - 'A') + 10 : (input[i+2] - '0'));
oi++;
// one more increment before looping
i += 2;
changed = true;
} else {
// leaves incorrect percent
// does not handle unicode %u encoding
*oi++ = input[i];
}
} else {
// leaves trailing incomplete percent
*oi++ = input[i];
}
} else if (input[i] == '+') {
*oi++ = ' ';
changed = true;
} else {
*oi++ = input[i];
}
}
*output_size = oi - output;
return changed;
}
static void TransformUrlDecode(InspectionBuffer *buffer, void *options)
{
uint32_t output_size;
bool changed;
const uint8_t *input = buffer->inspect;
const uint32_t input_len = buffer->inspect_len;
if (input_len == 0) {
return;
}
uint8_t output[input_len]; // we can only shrink
changed = BufferUrlDecode(input, input_len, output, &output_size);
if (changed) {
InspectionBufferCopy(buffer, output, output_size);
}
}
#ifdef UNITTESTS
static int DetectTransformUrlDecodeTest01(void)
{
const uint8_t *input = (const uint8_t *)"Suricata%20is+%27%61wesome%21%27%25%30%30%ZZ%4";
uint32_t input_len = strlen((char *)input);
InspectionBuffer buffer;
InspectionBufferInit(&buffer, 8);
InspectionBufferSetup(NULL, -1, &buffer, input, input_len);
PrintRawDataFp(stdout, buffer.inspect, buffer.inspect_len);
TransformUrlDecode(&buffer, NULL);
PrintRawDataFp(stdout, buffer.inspect, buffer.inspect_len);
FAIL_IF (buffer.inspect_len != strlen("Suricata is 'awesome!'%00%ZZ%4"));
FAIL_IF (memcmp(buffer.inspect, "Suricata is 'awesome!'%00%ZZ%4", buffer.inspect_len) != 0);
InspectionBufferFree(&buffer);
PASS;
}
static int DetectTransformUrlDecodeTest02(void)
{
const char rule[] = "alert http any any -> any any (http.request_body; url_decode; content:\"mail=test@oisf.net\"; sid:1;)";
ThreadVars th_v;
DetectEngineThreadCtx *det_ctx = NULL;
memset(&th_v, 0, sizeof(th_v));
DetectEngineCtx *de_ctx = DetectEngineCtxInit();
FAIL_IF_NULL(de_ctx);
Signature *s = DetectEngineAppendSig(de_ctx, rule);
FAIL_IF_NULL(s);
SigGroupBuild(de_ctx);
DetectEngineThreadCtxInit(&th_v, (void *)de_ctx, (void *)&det_ctx);
DetectEngineThreadCtxDeinit(&th_v, (void *)det_ctx);
DetectEngineCtxFree(de_ctx);
PASS;
}
static void DetectTransformUrlDecodeRegisterTests(void)
{
UtRegisterTest("DetectTransformUrlDecodeTest01",
DetectTransformUrlDecodeTest01);
UtRegisterTest("DetectTransformUrlDecodeTest02",
DetectTransformUrlDecodeTest02);
}
#endif
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