EXP00-J. Do not ignore values returned by methods

Methods can return values to communicate failure or success or to update local objects or fields. Security risks can arise when method return values are ignored or when the invoking method fails to take suitable action. When getter methods are named after an action, a programmer might fail to realize that a return value is expected. For example, the only purpose of the ProcessBuilder.redirectErrorStream() method is to report via return value whether the process builder successfully merges standard error and standard output. The method that actually performs redirection of the error stream is the overloaded single-argument version.

Noncompliant Code Example (File Deletion)

This noncompliant code example attempts to delete a file, but fails to check whether the operation has succeeded.

  File someFile = new File("someFileName.txt");
  // do something with someFile
  someFile.delete();

Compliant Solution

This compliant solution checks the (boolean) value returned by the delete() method and handles any resulting errors.

  File someFile = new File("someFileName.txt");
  // do something with someFile
  if (!someFile.delete()) {
    // handle failure to delete the file
  }

Noncompliant Code Example (String Replacement)

This noncompliant code example ignores the return value of the String.replace() method, failing to update the original string. The String.replace() method cannot modify the state of the String (because String objects are immutable); rather, it returns a reference to a new String object containing the desired result.

public class Ignore {
  public static void main(String[] args) {
    String original = "insecure";
    original.replace( 'i', '9' );
    System.out.println(original);
  }
}

Compliant Solution

This compliant solution correctly updates the String reference original with the return value from the String.replace() method.

public class DoNotIgnore {
  public static void main(String[] args) {
    String original = "insecure";
    original = original.replace( 'i', '9' );
    System.out.println(original);
  }
}

Risk Assessment

Ignoring method return values can lead to unexpected program behavior.

Automated Detection

The Coverity Prevent Version 5.0 CHECKED_RETURN checker can detect the instance where Value returned from a function is not checked for errors before being used.

Related Vulnerabilities

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

Related Guidelines

C Secure Coding Standard: [seccode:EXP12-C. Do not ignore values returned by functions]

C++ Secure Coding Standard: [cplusplus:EXP12-CPP. Do not ignore values returned by functions or methods]

Related Guidelines

MITRE CWE: CWE-252 "Unchecked Return Value"

Bibliography

[[API 2006]] method delete() and method replace()
[[Green 2008]] "String.replace"
[[Pugh 2009]] misusing putIfAbsent

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