Skip to main content

Improper resource allocation - Memory leak

Need​

Proper management of resource allocation and deallocation

Context​

  • Usage of C# for building robust and scalable applications
  • Usage of System for managing and interacting with the operating system
  • Usage of System.IO for input and output operations in .NET development

Description​

Non compliant code​

using System;
using System.IO;

public class ResourceAllocation
{
    public void ProcessFile(string filePath)
    {
        StreamReader fileStream = null;
        try
        {
            fileStream = new StreamReader(filePath);
            string line;
            while ((line = fileStream.ReadLine()) != null)
            {
                Console.WriteLine(line);
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }
    }
}

The above C# code demonstrates a scenario where a StreamReader object is created to read a file. The ProcessFile method opens a file stream and reads the file line by line, outputting the content to the console.

However, the code has a critical vulnerability related to improper resource allocation. Specifically, there is a memory leak issue as the StreamReader object is not being properly disposed of after use.

In .NET, many types encapsulate unmanaged resources, such as file streams, network connections, bitmap handles, etc. These types implement the IDisposable interface, which contains a single parameterless method, Dispose(), for releasing unmanaged resources. If Dispose() is not called, the unmanaged resources that the object holds onto are not released until the garbage collector finalizes the object. This can lead to a significant delay in reclaiming resources, which can be problematic in scenarios where resources are scarce or expensive.

In the above code, the StreamReader object is not being closed or disposed of, leading to a memory leak. This can cause the system to run out of resources and slow down or even crash if the method is called frequently enough.

Steps​

  • Use the 'using' statement to ensure proper resource allocation and disposal.
  • Wrap the StreamReader object in a 'using' statement to automatically close the file stream when it is no longer needed.
  • Remove the try-catch block and let any exceptions propagate to the calling code for proper handling.

Compliant code​

using System;
using System.IO;

public class ResourceAllocation
{
    public void ProcessFile(string filePath)
    {
        using (StreamReader fileStream = new StreamReader(filePath))
        {
            string line;
            while ((line = fileStream.ReadLine()) != null)
            {
                Console.WriteLine(line);
            }
        }
    }
}

The updated code now uses the using statement to handle the StreamReader object. The using statement in C# is a convenient syntax that ensures the correct use of IDisposable objects. Once the StreamReader object is no longer in use, it will automatically be disposed of, ensuring that all resources are correctly released and preventing memory leaks.

The try-catch block has been removed. This is because it's generally a good practice to let exceptions propagate up to a level where they can be handled appropriately, rather than suppressing them at the point where they occur. In this case, any exceptions that occur during the reading of the file will now be thrown to the calling code, which can then decide how to handle the exception. This provides more flexibility and control over error handling.

References​

Last updated on