Setuid Demystified
by Hao Chen and David Wagner (University of California at Berkeley), Drew Dean (SRI International)
Access control in Unix systems is mainly based on user IDs, yet the system calls that modify user IDs (uid-setting system calls), such as setuid, are poorly designed, insufficiently documented, and widely misunderstood and misused. This has caused many security vulnerabilities in application programs. We propose to make progress on the setuid mystery through two approaches. First, we study kernel sources and compare the semantics of the uid-setting system calls in three major Unix systems: Linux, Solaris, and FreeBSD. Second, we develop a formal model of user IDs as a Finite State Automaton (FSA) and develop new techniques for automatic construction of such models. We use the resulting FSA to uncover pitfalls in the Unix API of the uid-setting system calls, to identify differences in the semantics of these calls among various Unix systems, to detect inconsistency in the handling of user IDs within an OS kernel, and to check the proper usage of these calls in programs automatically.

Finally, we provide general guidelines on the proper usage of the uid-setting system calls, and we propose a high-level API that is more comprehensible, usable, and portable than the usual Unix API.

Download the paper in PDF format here.

Spotlight

Bash Shellshock bug: More attacks, more patches

Posted on 29 September 2014.  |  As vendors scramble to issue patches for the GNU Bash Shellshock bug and companies rush to implement them, attackers around the world are probing systems for the hole it opens.


Weekly newsletter

Reading our newsletter every Monday will keep you up-to-date with security news.
  



Daily digest

Receive a daily digest of the latest security news.
  

DON'T
MISS

Tue, Sep 30th
    COPYRIGHT 1998-2014 BY HELP NET SECURITY.   // READ OUR PRIVACY POLICY // ABOUT US // ADVERTISE //