Maintaining Authorization Hook Placements Across Program Versions

We examine the problem of maintaining security code across program versions. There are now several cases where programmers manually retrofit their programs with security code, such as authorization mechanisms. However, programs evolve, so a challenge for programmers is to determine whether their security code remains correct across multiple versions of the program. The insight of this work is that programmers can use the constraints on the authorization policies that can be enforced in one version of the program to limit their effort in validating authorization hook placements in later versions. We develop a tool we call HEIMDAL to implement this insight, finding that a modest number of authorization constraints require review across several versions of the X window server program.