drivers: sensor: fcx_mldx5: Fix potential buffer overflow in UART frame

Fix Coverity issue CID 363738 (CWE-120): A potential buffer overflow could
occur in fcx_mldx5_uart_send() due to unchecked memcpy() when copying
command data into a fixed-size frame buffer.

This patch ensures that the length of the data being copied validated
against the remaining buffer size to prevent overruns. Also replaces a
redundant strlen() call with the precomputed cmd_data_len.

Fixes: #92634

Signed-off-by: sudarsan N <[email protected]>

Author: sudarsan-22

drivers/sensor/fcx_mldx5/fcx_mldx5.c

@@ -235,8 +235,14 @@ static void fcx_mldx5_uart_send(const struct device *dev, enum fcx_mldx5_cmd cmd
 
 	buf[FCX_MLDX5_STX_INDEX] = FCX_MLDX5_STX;
 	memcpy(&buf[FCX_MLDX5_CMD_INDEX], fcx_mldx5_cmds[cmd], FCX_MLDX5_CMD_LEN);
-	if (cmd_data_len != 0 && cmd_data_len == fcx_mldx5_cmds_data_len[cmd]) {
-		memcpy(&buf[FCX_MLDX5_DATA_INDEX], cmd_data, strlen(cmd_data));
+
+	if (cmd_data_len != 0) {
+		if ((FCX_MLDX5_DATA_INDEX + cmd_data_len) <= FCX_MLDX5_MAX_FRAME_LEN) {
+			memcpy(&buf[FCX_MLDX5_DATA_INDEX], cmd_data, cmd_data_len);
+		} else {
+			LOG_ERR("%s: cmd_data too large for buffer", __func__);
+			return;
+		}
 	}
 
 	checksum = fcx_mldx5_calculate_checksum(&buf[FCX_MLDX5_CMD_INDEX],