CapAssess: An Endeavor to Assess and Enhance Linux Capabilities Utilization

The Linux capabilities mechanism divides the root privileges to provide more fine-grained access control, but its effectiveness depends on proper implementation and configuration. The scattered enforcement of capabilities in the kernel and its sporadic usage in programs pose challenges in gathering assessment information. To address this, we propose three tools for diagnosing potential problems in its design, implementation, and utilization. First, we employ LLVM/Clang to examine the capabilities enforcement in the kernel to map capabilities checks to files. This is the first attempt to explore the interaction between capabilities and other mechanisms, such as UGO. Second, We propose a pattern-based method to identify the sensitive kernel functions protected by capabilities, quanti-fying the overlap problem of capabilities. Third, we employ a customized fuzzing approach to determine the minimal set of capabilities required by programs, offering insight for secure usage. Additionally, Our study is further guided by international access management standards, providing structured criteria for the assessment. Leveraging data collected by our tools, we identify imperfections of capabilities and reported to stakeholders. To the best of our knowledge, this is the first systematic assessment of Linux capabilities.