We present \textsc{MemFix}, an automated technique for fixing memory
deallocation errors in C programs. \textsc{MemFix} aims to fix
memory-leak, double-free, and use-after-free errors, which occur
when developers fail to properly deallocate memory objects.
\textsc{MemFix} attempts to fix these errors by finding a set of
free-statements that correctly deallocate all allocated objects
without causing double-frees and use-after-frees. The key insight
behind \textsc{MemFix} is that finding such a set of deallocation
statements corresponds to solving an exact cover problem derived
from a variant of typestate static analysis. We formally present
the technique and experimentally show that \textsc{MemFix} is able to fix
real errors found in open-source programs. Because \textsc{MemFix} is
based on a sound static analysis, the generated patches guarantee to
fix the original errors without introducing new errors.