IntEQ: Recognizing benign integer overflows via equivalence checking across multiple precisions

Abstract

Integer overow (IO) vulnerabilities can be exploited by attackers to compromise computer systems. In the mean time, IOs can be used intentionally by programmers for benign purposes such as hashing and random number generation. Hence, differentiating exploitable and harmful IOs from intentional and benign ones is an important challenge. It allows reducing the number of false positives produced by IO vulnerability detection techniques, helping developers or security analysts to focus on fixing critical IOs without inspecting the numerous false alarms. The dificulty of recognizing benign IOs mainly lies in inferring the intent of programmers from source code. In this paper, we present a novel technique to recognize benign IOs via equivalence checking across multiple preci-sions. We determine if an IO is benign by comparing the effects of an overowed integer arithmetic operation in the actual world (with limited precision) and the same operation in the ideal world (with suficient precision to evade the IO). Specifically, we first extract the data ow path from the overowed integer arithmetic operation to a security-related program point (i.e., sink) and then create a new version of the path using more precise types with suficient bits to represent integers so that the IO can be avoided. Using theorem proving we check whether these two versions are equivalent, that is, if they yield the same values at the sink under all possible inputs. If so, the IO is benign. We implement a prototype, named IntEQ, based on the GCC compiler and the Z3 solver, and evaluate it using 26 harmful IO vulnerabilities from 20 real-world programs, and 444 benign IOs from SPECINT 2000, SPECINT 2006, and 7 real-world applications. The experimental results show that IntEQ does not misclassify any harmful IO bugs (no false negatives) and recognizes 355 out of 444 (about 79.95%) benign IOs, whereas the state of the art can only recognize 19 benign IOs.