Double-Checked Locking

Opis

The product uses double-checked locking to access a resource without the overhead of explicit synchronization, but the locking is insufficient.

Double-checked locking refers to the situation where a programmer checks to see if a resource has been initialized, grabs a lock, checks again to see if the resource has been initialized, and then performs the initialization if it has not occurred yet. This should not be done, as it is not guaranteed to work in all languages and on all architectures. In summary, other threads may not be operating inside the synchronous block and are not guaranteed to see the operations execute in the same order as they would appear inside the synchronous block.

Skutki

• Integrity, Other

  Modify Application Data; Alter Execution Logic

Zapobieganie

• Implementation

  While double-checked locking can be achieved in some languages, it is inherently flawed in Java before 1.5, and cannot be achieved without compromising platform independence. Before Java 1.5, only use of the synchronized keyword is known to work. Beginning in Java 1.5, use of the "volatile" keyword allows double-checked locking to work successfully, although there is some debate as to whether it achieves sufficient performance gains. See references.

Słabość nadrzędna

• CWE-667 Improper Locking

Może prowadzić do

• CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition

Kiedy powstaje

• Implementation

Dotyczy

Java

Źródła

1. The "Double-Checked Locking is Broken" Declaration — David Bacon et al
2. JSR 133 (Java Memory Model) FAQ — Jeremy Manson and Brian Goetz
3. The Art of Software Security Assessment — Mark Dowd, John McDonald, Justin Schuh, Chapter 13, "Threading Vulnerabilities", Page 815, Addison Wesley, 2006