helper: Make unhexify() robust on invalid data

The current implementation is not suitable for user provided data
because it does not detect invalid inputs in many cases. For example,
the string "aa0xbb" is successfully converted to the 3 bytes: 0xaa,
0x00 and 0xbb. An other example is "aabi" which is successfully
converted to the 2 bytes: 0xaa and 0x0b. Both are obviously incorrect.

Make unhexify() robust on invalid data and use more appropriate data
types for its parameters. Also, add a small documentation for the
function.

Change-Id: Idb799beb86fc608b066c8a76365021ed44c7f890
Signed-off-by: Marc Schink <openocd-dev@marcschink.de>
Reviewed-on: http://openocd.zylin.com/3792
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/helper/binarybuffer.c

@@ -369,17 +369,42 @@ void bit_copy_discard(struct bit_copy_queue *q)
 	}
 }
 
-int unhexify(char *bin, const char *hex, int count)
+/**
+ * Convert a string of hexadecimal pairs into its binary
+ * representation.
+ *
+ * @param[out] bin Buffer to store binary representation. The buffer size must
+ *                 be at least @p count.
+ * @param[in] hex String with hexadecimal pairs to convert into its binary
+ *                representation.
+ * @param[in] count Number of hexadecimal pairs to convert.
+ *
+ * @return The number of converted hexadecimal pairs.
+ */
+size_t unhexify(uint8_t *bin, const char *hex, size_t count)
 {
-	int i, tmp;
+	size_t i;
+	char tmp;
 
-	for (i = 0; i < count; i++) {
-		if (sscanf(hex + (2 * i), "%02x", &tmp) != 1)
-			return i;
-		bin[i] = tmp;
+	if (!bin || !hex)
+		return 0;
+
+	memset(bin, 0, count);
+
+	for (i = 0; i < 2 * count; i++) {
+		if (hex[i] >= 'a' && hex[i] <= 'f')
+			tmp = hex[i] - 'a' + 10;
+		else if (hex[i] >= 'A' && hex[i] <= 'F')
+			tmp = hex[i] - 'A' + 10;
+		else if (hex[i] >= '0' && hex[i] <= '9')
+			tmp = hex[i] - '0';
+		else
+			return i / 2;
+
+		bin[i / 2] |= tmp << (4 * ((i + 1) % 2));
 	}
 
-	return i;
+	return i / 2;
 }
 
 int hexify(char *hex, const char *bin, int count, int out_maxlen)

src/helper/binarybuffer.h

@@ -234,7 +234,7 @@ void bit_copy_discard(struct bit_copy_queue *q);
 
 /* functions to convert to/from hex encoded buffer
  * used in ti-icdi driver and gdb server */
-int unhexify(char *bin, const char *hex, int count);
+size_t unhexify(uint8_t *bin, const char *hex, size_t count);
 int hexify(char *hex, const char *bin, int count, int out_maxlen);
 void buffer_shr(void *_buf, unsigned buf_len, unsigned count);
 

src/jtag/drivers/ti_icdi_usb.c

@@ -266,7 +266,7 @@ static int icdi_get_cmd_result(void *handle)
 
 	if (h->read_buffer[offset] == 'E') {
 		/* get error code */
-		char result;
+		uint8_t result;
 		if (unhexify(&result, h->read_buffer + offset + 1, 1) != 1)
 			return ERROR_FAIL;
 		return result;
@@ -328,7 +328,7 @@ static int icdi_usb_version(void *handle)
 	}
 
 	/* convert reply */
-	if (unhexify(version, h->read_buffer + 2, 4) != 4) {
+	if (unhexify((uint8_t *)version, h->read_buffer + 2, 4) != 4) {
 		LOG_WARNING("unable to get ICDI version");
 		return ERROR_OK;
 	}
@@ -495,7 +495,7 @@ static int icdi_usb_read_reg(void *handle, int num, uint32_t *val)
 
 	/* convert result */
 	uint8_t buf[4];
-	if (unhexify((char *)buf, h->read_buffer + 2, 4) != 4) {
+	if (unhexify(buf, h->read_buffer + 2, 4) != 4) {
 		LOG_ERROR("failed to convert result");
 		return ERROR_FAIL;
 	}

src/rtos/rtos.c

@@ -213,7 +213,7 @@ int rtos_qsymbol(struct connection *connection, char const *packet, int packet_s
 		goto done;
 
 	/* Decode any symbol name in the packet*/
-	int len = unhexify(cur_sym, strchr(packet + 8, ':') + 1, strlen(strchr(packet + 8, ':') + 1));
+	size_t len = unhexify((uint8_t *)cur_sym, strchr(packet + 8, ':') + 1, strlen(strchr(packet + 8, ':') + 1));
 	cur_sym[len] = 0;
 
 	if ((strcmp(packet, "qSymbol::") != 0) &&               /* GDB is not offering symbol lookup for the first time */

src/server/gdb_server.c

@@ -1449,7 +1449,7 @@ static int gdb_write_memory_packet(struct connection *connection,
 
 	LOG_DEBUG("addr: 0x%8.8" PRIx32 ", len: 0x%8.8" PRIx32 "", addr, len);
 
-	if (unhexify((char *)buffer, separator, len) != (int)len)
+	if (unhexify(buffer, separator, len) != len)
 		LOG_ERROR("unable to decode memory packet");
 
 	retval = target_write_buffer(target, addr, len, buffer);
@@ -2277,7 +2277,7 @@ static int gdb_query_packet(struct connection *connection,
 		if (packet_size > 6) {
 			char *cmd;
 			cmd = malloc((packet_size - 6) / 2 + 1);
-			int len = unhexify(cmd, packet + 6, (packet_size - 6) / 2);
+			size_t len = unhexify((uint8_t *)cmd, packet + 6, (packet_size - 6) / 2);
 			cmd[len] = 0;
 
 			/* We want to print all debug output to GDB connection */