SmartFix: Fixing Vulnerable Smart Contracts by Accelerating Generate-and-Verify Repair using Statistical Models

We present SmartFix, a new technique for repairing vulnerable smart contracts. There is an urgent need to develop automatic bug-repair techniques for smart contracts, as smart contracts are safety-critical software and manual debugging is burdensome and error-prone. While several repair approaches have been proposed recently, they are unsatisfactory since no existing techniques can achieve high repairability, full automation, and safety guarantee at the same time, posing significant problems for practical use. SmartFix aims to address these shortcomings by using a "generate-and-verify"approach that iteratively enumerates candidate patches while validating their correctness by invoking a safety verifier. However, in this approach, a technical challenge arises as the search space is huge and the verification-based patch validation is expensive. To address this challenge, we present a novel technique for accelerating the generate-and-verify repair procedure using statistical models derived from the verifier's feedback. Experimental results on real-world Ethereum smart contracts show that SmartFix is able to achieve a fix success rate of 94.8% for critical classes of vulnerabilities, far outperforming sGuard, the existing state-of-the-art technique whose success rate is 65.4%.