Computer Sciences Dept.

Defective Error/Pointer Interactions in the Linux Kernel

Cindy Rubio-González and Ben Liblit

Linux run-time errors are represented by integer values referred to as error codes. These values propagate across long function-call chains before being handled. As these error codes propagate, they are often temporarily or permanently encoded into pointer values. Error-valued pointers are not valid memory addresses, and therefore require special care by programmers. Misuse of pointer variables that store error codes can lead to serious problems such as system crashes, data corruption, unexpected results, etc. We use static program analysis to find three classes of bugs relating error-valued pointers: bad dereferences, bad pointer arithmetic, and bad overwrites. Our tool finds 57 true bugs among 52 different Linux file system implementations, the virtual file system (VFS), the memory management module (mm), and 4 drivers.

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