Place Your Locks Well: Understanding and Detecting Lock Misuse Bugs

Modern multi-threaded software systems commonly leverage locks to prevent concurrency bugs. Nevertheless, due to the complexity of writing the correct concurrent code, using locks itself is often error-prone. In this work, we investigate a general variety of lock misuses. Our characteristic study of existing CVE IDs reveals that lock misuses can inflict concurrency errors and even severe security issues, such as denial-of-service and memory corruption. To alleviate the threats, we present a practical static analysis framework, namely Lockpick, which consists of two core stages to effectively detect misused locks. More specifically, Lockpick first conducts path-sensitive typestate analysis, tracking lock-state transitions and interactions to identify sequential typestate violations. Guided by the preceding results, Lockpick then performs concurrency-aware detection to pinpoint various lock misuse errors, effectively reasoning about the thread interleavings of interest. The results are encouraging—we have used Lockpick to uncover 203 unique and confirmed lock misuses across a broad spectrum of impactful open-source systems, such as OpenSSL, the Linux kernel, PostgreSQL, MariaDB, FFmpeg, Apache HTTPd, and FreeBSD. Three exciting results are that those confirmed lock misuses are long-latent, hiding for 7.4 years on average; in total, 16 CVE IDs have been assigned for the severe errors uncovered; and Lockpick can flag many real bugs missed by the previous tools with significantly fewer false positives.