DDRace: Finding Concurrency UAF Vulnerabilities in Linux Drivers with Directed Fuzzing

Concurrency use-after-free (UAF) vulnerabilities account for a large portion of UAF vulnerabilities in Linux drivers. Many solutions have been proposed to find either concurrency bugs or UAF vulnerabilities, but few of them can be directly applied to efficiently find concurrency UAF vulnerabilities. In this paper, we propose the first concurrency directed greybox fuzzing solution DDRace to discover concurrency UAF vulnerabilities efficiently in Linux drivers. First, we identify candidate use-after-free locations as target sites and extract the relevant concurrency elements to reduce the exploration space of directed fuzzing. Second, we design a novel vulnerability related distance metric and an interleaving priority scheme to guide the fuzzer to better explore UAF vulnerabilities and thread interleavings. Lastly, to make test cases reproducible, we design an adaptive kernel state migration scheme to assist continuous fuzzing. We have implemented a prototype of DDRace, and evaluated it on upstream Linux drivers. Results show that DDRace is effective at discovering concurrency use-after-free vulnerabilities. It finds 4 unknown vulnerabilities and 8 known ones, which is more effective than other state-of-the-art solutions.