Need

Proper resource management and deallocation

Context

• Usage of Scala for building scalable and functional applications
• Usage of java.io.File for file input/output operations in Java
• Usage of java.io.FileInputStream for reading data from a file
• Usage of BufferedInputStream for efficient reading of data from an input stream in Java
• Handling of IOException in Java Input/Output operations

Description

Non compliant code

        import java.io._

class ResourceHandler {

  def handleResource(): Unit = {
    val file = new File("test.txt")
    val fis = new FileInputStream(file)
    val bis = new BufferedInputStream(fis)
    try {
      bis.read()
      // Processing the file
    } catch {
      case e: IOException => e.printStackTrace()
    }
    // Missing finally block to close the resources
  }
}
        
        

In the above Scala code, we are creating a ResourceHandler class with a method handleResource(). This method is responsible for reading a file named "test.txt". We are using FileInputStream and BufferedInputStream for reading the file.

The vulnerability in this code is that we are not properly releasing the resources after we are done with them. After the try block where we read the file, we are not closing the FileInputStream ( fis) and BufferedInputStream ( bis). This could potentially lead to a memory leak as these resources stay open and continue to consume memory, even though they are not needed anymore.

This is a common problem known as Improper Resource Allocation or Memory Leak. It happens when the system is unable to release resources that have been opened because they are not explicitly closed within the source code. In this case, the resources are the file input streams that we opened to read the file.

To fix this vulnerability, we need to close these resources explicitly in a finally block after the try-catch block. The finally block ensures that the resources are closed regardless of whether an exception occurs or not.

Steps

• Add a finally block after the catch block.
• Inside the finally block, close the resources (file, fis, bis) using the close() method.
• Handle any exceptions that may occur while closing the resources.

Compliant code

        import java.io._

class ResourceHandler {

  def handleResource(): Unit = {
    var fis: FileInputStream = null
    var bis: BufferedInputStream = null
    try {
      val file = new File("test.txt")
      fis = new FileInputStream(file)
      bis = new BufferedInputStream(fis)
      bis.read()
      // Processing the file
    } catch {
      case e: IOException => e.printStackTrace()
    } finally {
      if (bis != null) {
        try {
          bis.close()
        } catch {
          case e: IOException => e.printStackTrace()
        }
      }
      if (fis != null) {
        try {
          fis.close()
        } catch {
          case e: IOException => e.printStackTrace()
        }
      }
    }
  }
}
        
        

The above code fixes the memory leak vulnerability by ensuring that the resources are properly closed after they have been used.

In the original code, the FileInputStream and BufferedInputStream were not being closed, which could lead to a memory leak as the system may not be able to release these resources.

In the fixed code, a finally block has been added after the catch block. The finally block is a block of code that will be executed after a try/catch block has completed regardless of whether an exception was thrown. This makes it the perfect place to close our resources.

Inside the finally block, the FileInputStream and BufferedInputStream are closed using the close() method. This method releases the resources that these streams are holding onto.

However, the close() method itself can throw an IOException, so we need to handle this potential exception. This is done by wrapping each close() call in a separate try/catch block. If an IOException is thrown during the closing of the resources, it will be caught and the stack trace will be printed. This ensures that the program can continue running even if an error occurs while closing the resources.

References

• 317. Improper resource allocation - Memory leak