E-raamat: Value-Range Analysis of C Programs: Towards Proving the Absence of Buffer Overflow Vulnerabilities

Abu erover owoccurswheninputiswrittenintoamemorybu erthatisnot large enough to hold the input. Bu er over ows may allow a malicious person to gain control over a computer system in that a crafted input can trick the defectiveprogramintoexecutingcodethatisencodedintheinputitself.They are recognised as one of the most widespread forms of security vulnerability, and many workarounds, including new processor features, have been proposed to contain the threat. This book describes a static analysis that aims to prove the absence of bu er over ows in C programs. The analysis is conservative in the sense that it locates every possible over ow. Furthermore, it is fully automatic in that it requires no user annotations in the input program. Thekeyideaoftheanalysisistoinferasymbolicstateforeachp- gram point that describes the possible variable valuations that can arise at that point. The program is correct if the inferred values for array indices and pointer o sets lie within the bounds of the accessed bu er. The symbolic state consists of a ?nite set of linear inequalities whose feasible points induce a convex polyhedron that represents an approximation to possible variable valuations. The book formally describes how program operations are mapped to operations on polyhedra and details how to limit the analysis to those p- tionsofstructuresandarraysthatarerelevantforveri cation.Withrespectto operations on string bu ers, we demonstrate how to analyse C strings whose length is determined by anul character within the string.