Filesystem Security

Filesystem Races Break the Link Between Checks and Use

A process checks that a path is safe, records a reassuring result, then opens the path a fraction of a second later. Those two operations can look like one security decision in source code. The filesystem sees two separate events, with an interval in which names, links, directories, mounts, or permissions may change. That interval is the basis of time-of-check to time-of-use races. The issue is not limited to unusually slow systems or large timing gaps. When an attacker can influence the relevant namespace concurrently, even a small gap can separate the object that passed a check from the object that receives the privileged operation.