Analysing installation scenarios of Debian packages

Abstract

The Debian distribution includes more than 28 thousand maintainer scripts, almost all of them are written in Posix shell. These scripts are executed with root privileges at installation, update, and removal of a package, which make them critical for system maintenance. While Debian policy provides guidance for package maintainers producing the scripts, few tools exist to check the compliance of a script to it. We report on the application of a formal verication approach based on symbolic execution to nd violations of some non-trivial properties required by Debian policy in maintainer scripts. We present our methodology and give an overview of our toolchain. We obtained promising results: our toolchain is eective in analysing a large set of Debian maintainer scripts and it pointed out over 150 policy violations that lead to reports (more than half already xed) on the Debian Bug Tracking system.