Race Conditions, Files, and Security Flaws; or the Tortoise and the Hare Redux

A pernicious type of security problem, race conditions create a timing interval in which the manipulation of resources allows an attacker to gain privileges, read and alter protected files, and violate the security policy of the site. The majority of these conditions found on applications and system programs in the UNIX operating system arise during file system manipulation and file accesses. This paper discusses why race conditions arise, presents some examples, and explores ways to alleviate the problem of their occurrence in programs, both through modification of system calls and careful programming. A tool to scan for potential race conditions, as well as a library function to analyze the environment dynamically at run time (and thus detect such conditions) are presented.