MSC09-J. Do not assume infinite heap space

A Java OutofMemoryError occurs if infinite heap space is assumed. This error can result from:

• A memory leak
• An infinite loop
• The program requires more memory than what is available by default on the heap
• Incorrect implementation of common data structures (hash tables, vectors and so on)
• Unbound deserialization
• Upon writing a large number of objects to an ObjectOutputStream

Noncompliant Code Example (1)

This noncompliant code example places no upper bounds on the memory space required to execute the program. Consequently, the program can easily exhaust the heap.

public class ShowHeapError {

  Vector<String> names = new Vector<String>();
  String newName=null;
  InputStreamReader input = new InputStreamReader(System.in);
  BufferedReader reader = new BufferedReader(input);

  public void addNames(){
    do {
      // Adding unknown number of records to a list
      // the user can enter as much data as he wants and exhaust the heap
      System.out.print(" To quit, enter \"quit\"\nEnter record: ");
      try {
        newName = reader.readLine();
        if(!newName.equalsIgnoreCase("quit")){
          // names are continued to be added without 
          // bothering about the size on the heap
          names.addElement(newName);
        }
      } catch (IOException e) {
        // forward to handler 
      }
    
      System.out.println(newName);
    }while (!newName.equalsIgnoreCase("quit"));
  }

  public static void main(String[] args) {
    ShowHeapError demo = new ShowHeapError();
    demo.addNames();
  }
}

Compliant Solution (1)

If the objects or data structures are large enough to potentially cause heap exhaustion, the programmer must consider using databases instead.

To remedy the noncompliant code example, the user can reuse a single long variable to store the input and write that value into a database containing a table User, with a field userID along with any other required fields. This prevents the heap from getting exhausted.

Noncompliant Code Example (2)

In this example, the program needs more memory on the heap than is available by default. In a server-class machine running either VM (client or server) with a parallel garbage collector, the default initial and maximum heap sizes are as follows for J2SE 6.0 [[Sun 06]]:

• initial heap size: larger of 1/64th of the machine's physical memory on the machine or some reasonable minimum

• maximum heap size: smaller of 1/4th of the physical memory or 1GB

public class ShowHeapError {

  /* Assuming the heap size as 512 MB (calculated as 1/4th of 2 GB RAM = 512 MB)
   * Considering long values being entered (64 bits each, the max number of elements
   * would be 5122 MB/64bits = 67108864)
   */
   Vector<Long> names = new Vector<Long>(67108865);
   long newID=0L;
   int count = 67108865;
   int i = 0;
   InputStreamReader input = new InputStreamReader(System.in);
   Scanner reader = new Scanner(input);

   public void addNames(){
     do{
       /* Adding unknown number of records to a list
        * the user can enter more number of IDs than what the heap can support and 
        * exhaust the heap. Assume that the record ID is a 64 bit long value
       */
       System.out.print(" To quit, enter -1\nEnter recordID: ");
       newID = reader.nextLong();
       //names are continued to be added without bothering about the size on the heap
       names.addElement(newID);
       System.out.println(newID);
       i++;

     }while (i<count || newID!=-1);
   }

   public static void main(String[] args) {
     ShowHeapError demo = new ShowHeapError();
     demo.addNames();
   }
}

Compliant Solution (2)

The OutOfMemoryError can be avoided by making sure that there are no infinite loops, memory leaks or unnecessary object retention. If memory requirements are known ahead of time, the heap size in Java can be tailored to fit the requirements using the following runtime parameters [[Java 06]]:

java -Xms<initial heap size> -Xmx<maximum heap size>

For example:

java -Xms128m -Xmx512m ShowHeapError

Here the initial heap size is set to 128 MB and the maximum heap size to 512 MB.

This setting can be changed either in the Java Control Panel or on the command line. It cannot be adjusted through the application itself.

Noncompliant Code Example (2)

According to [[API 06]], Class ObjectInputStream documentation:

ObjectOutputStream and ObjectInputStream can provide an application with persistent storage for graphs of objects when used with a FileOutputStream and FileInputStream respectively. ObjectInputStream is used to recover the objects previously serialized. Other uses include passing objects between hosts using a socket stream or for marshaling and unmarshaling arguments and parameters in a remote communication system.

By design, only the first time an object is written, does it get reflected in the stream. Subsequent writes write a handle to the object into the stream. A table mapping the objects written to the stream to the corresponding handle is also maintained. Because of this handle, references that may not persist during normal runs of the program are also retained. This can cause an OutOfMemoryError when streams remain open for extended durations.

FileOutputStream fos = new FileOutputStream("data.txt");
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(new Date());
// ... 

Compliant Solution (3)

If heap related issues arise, it is recommended that the ObjectOutputStream.reset() method be called so that references to previously written objects may be garbage collected.

FileOutputStream fos = new FileOutputStream("data.txt");
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(new Date());
oos.reset();  // Reset the Object-Handle table to its initial state
// ... 

Risk Assessment

Assuming that infinite heap space is available can result in denial of service.

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website

Other Languages

This rule appears in the C Secure Coding Standard as MEM11-C. Do not assume infinite heap space.

This rule appears in the C++ Secure Coding Standard as MEM12-CPP. Do not assume infinite heap space.

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

[[Sun 06]] Garbage Collection Ergonomics, "Default values for the Initial and Maximum heap size"
[[Java 06]] java - the Java application launcher, "Syntax for increasing the heap size"
[[Sun 03]] Chapter 5: Tuning the Java Runtime System, Tuning the Java Heap
[[API 06]] Class ObjectInputStream and ObjectOutputStream
[[SDN 08]] Serialization FAQ
[[MITRE 09]] CWE ID 400 "Uncontrolled Resource Consumption (aka 'Resource Exhaustion')"

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