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It is often insecure to synchronize a method that performs network transactions. Depending on the speed and reliability of the connection, synchronization can stall the program indefinitely causing a huge performance hit. At other times, it can result in temporary or permanent deadlock.

Noncompliant Code Example

This noncompliant code example shows the method sendPage() that sends a Page object from a server to a client. The method is synchronized so that the array pageBuff is accessed safely, when multiple threads request concurrent access.

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Calling writeObject() within the synchronized sendPage() method can result in delays and deadlock-like conditions in high latency networks or when network connections are inherently lossy.

Compliant Solution

This compliant solution entails separating the actions into a sequence of steps:

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public boolean sendReply(Socket socket, String pageName) { // No synchronization
  Page targetPage = getPage(pageName); 

  if(targetPage == null)
    return FAILURE;

  return sendPage(socket, targetPage);
}

private synchronized Page getPage(String pageName) { // Requires synchronization
  Page targetPage = null;

  for(Page p : pageBuff) {
    if(p.getName().equals(pageName)) {
      targetPage = p;
    }
  }
  return targetPage;
}

public boolean sendPage(Socket socket, Page page){
  try{
    // Get the output stream to write the Page to
    ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());

    // Send the Page to the client
    out.writeObject(page);

  } catch(IOException io){
    // If recovery is not possible return FAILURE
    return FAILURE;    
  } finally {
    out.flush();
    out.close();
  }  
  return SUCCESS;
}

Risk Assessment

If synchronized methods and statements contain network transactional logic, temporary or permanent deadlocks may result.

Related Vulnerabilities

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

References

\[[Grosso 01|AA. Java References#Grosso 01]\] [Chapter 10: Serialization|http://oreilly.com/catalog/javarmi/chapter/ch10.html]
\[[JLS 05|AA. Java References#JLS 05]\] [Chapter 17, Threads and Locks|http://java.sun.com/docs/books/jls/third_edition/html/memory.html]
\[[Rotem 08|AA. Java References#Rotem 08]\] [Falacies of Distributed Computing Explained|http://www.rgoarchitects.com/Files/fallacies.pdf]

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