Device drivers remain a main source of runtime failures in operating systems. To detect bugs in device drivers, fuzzing has been commonly used in practice. However, a main limitation of existing fuzzing approaches is that they cannot effectively test error handling code. Indeed, these fuzzing approaches require effective inputs to cover target code, but much error handling code in drivers is triggered by occasional errors (such as insufficient memory and hardware malfunctions) that are not related to inputs. In this paper, based on software fault injection, we propose a new fuzzing approach named FIZZER, to test error handling code in device drivers. At compile time, FIZZER uses static analysis to recommend possible error sites that can trigger error handling code. During driver execution, by analyzing runtime information, it automatically fuzzes error-site sequences for fault injection to improve code coverage. We evaluate FIZZER on 18 device drivers in Linux 4.19, and in total find 22 real bugs. The code coverage is increased by over 15% compared to normal execution without fuzzing.

Data races are often hard to detect in device drivers, due to the non-determinism of concurrent execution. According to our study of Linux driver patches that fix data races, more than 38% of patches involve a pattern that we call inconsistent lock protection. Specifically, if a variable is accessed within two concurrently executed functions, the sets of locks held around each access are disjoint, at least one of the locksets is non-empty, and at least one of the involved accesses is a write, then a data race may occur. In this paper, we present a runtime analysis approach, named DILP, to detect data races caused by inconsistent lock protection in device drivers. By monitoring driver execution, DILP collects the information about runtime variable accesses and executed functions. Then after driver execution, DILP analyzes the collected information to detect and report data races caused by inconsistent lock protection. We evaluate DILP on 12 device drivers in Linux 4.16.9, and find 25 real data races.

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