Lazy Programs Leak Secrets

To preserve confidentiality, information-flow control (IFC) restricts how untrusted code handles secret data. While promising, IFC systems are not perfect; they can still leak sensitive information via covert channels. In this work, we describe a novel exploit of lazy evaluation to reveal secrets in IFC systems. Specifically, we show that lazy evaluation might transport information through the internal timing covert channel, a channel present in systems with concurrency and shared resources. We illustrate our claim with an attack for LIO , a concurrent IFC system for Haskell. We propose a countermeasure based on restricting the implicit sharing caused by lazy evaluation.