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Improper resource allocation - Memory leak

Need​

Proper resource management and deallocation

Context​

  • Usage of PHP 7.0 for server-side scripting and web development
  • Usage of Illuminate/Http for HTTP request handling in Laravel
  • Usage of Illuminate/Support for providing foundational support classes and utilities in Laravel

Description​

Non compliant code​

public function processData(Request $request)
{
    $data = $request->all();

    $file = fopen('file.txt', 'w');

    foreach($data as $key => $value) {
        fwrite($file, $key . ' : ' . $value . "\\n");
    }

    // Missing fclose($file);
}

In the above code, we are opening a file called 'file.txt' in write mode. We then loop over the request data and write each key-value pair to the file. However, we are not properly closing the file after we are done with it using fclose($file);.

This can lead to a memory leak, as the system resources allocated for this file are not being properly released. Over time, as more and more resources are allocated without being released, the system may run out of memory and crash. This is a common issue known as a memory leak.

In PHP, all resources are usually closed at the end of the request, but for long-running scripts or if you are opening a lot of files, this can still cause issues. It is always a good practice to explicitly close any resources you open.

Steps​

  • Identify the resources that are being opened and not closed. In this case, it's a file resource.
  • After the resource is no longer needed, explicitly close it. In this case, you should close the file after writing to it.
  • Use the fclose() function to close the file resource. This function takes the file resource as an argument.
  • Place the fclose() function in a finally block to ensure it is executed even if an exception occurs.

Compliant code​

public function processData(Request $request)
{
    $data = $request->all();

    $file = fopen('file.txt', 'w');

    try {
        foreach($data as $key => $value) {
            fwrite($file, $key . ' : ' . $value . "\\n");
        }
    } finally {
        fclose($file);
    }
}

The updated code now includes a try-finally block. This block is used to ensure that the file resource is always closed, regardless of whether an exception occurs during the execution of the code within the try block.

The try block contains the code that may potentially throw an exception. In this case, it's the loop that writes data to the file. If an exception is thrown within this block, the execution of the code within the try block is immediately stopped, and the code within the finally block is executed.

The finally block contains the fclose($file); statement, which is used to close the file resource. This ensures that the file resource is always closed, even if an exception occurs. This prevents a memory leak, as the system resources used by the file are released when the file is closed.

This solution addresses the improper resource allocation vulnerability by ensuring that all opened resources are properly closed, even in the event of an exception.

References​

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