A Low-Overhead, Value-Tracking Approach to Information Flow Security

Abstract. We present a hybrid approach to information flow security where security violations are detected at execution time. We track se-cure values and secure locations at run time to prevent problems such as password disclosure in C programs. This analysis is safe in the presence of pointer aliasing. Such problems are hard to solve using static analysis (or lead to many false positives). Our technique works on programs with annotations that identify values and locations that need to be secure. We instrument the annotated program with statements that capture rel-evant information flow with assertions that detect any violation. This instrumentation does not interfere with the safe assignment of values to variables in the program. The instrumented assertions are invoked only when relevant values or locations are involved. We demonstrate the ap-plicability of our approach by analysing various Linux utilities such as su, sudo, passwd, ftp and ssh. Our experiments show that for safe exe-cutions the overhead introduced by our instrumentation is, on average, less than 1%