In the Linux kernel, the following vulnerability has been resolved:gfs2: Fix potential glock use-after-free on unmountWhen a DLM lockspace is released and there ares still locks in thatlockspace, DLM will unlock those locks automatically. Commitfb6791d100d1b started exploiting this behavior to speed up filesystemunmount: gfs2 would simply free glocks it didn't want to unlock and thenrelease the lockspace. This didn't take the bast callbacks forasynchronous lock contention notifications into account, which remainactive until until a lock is unlocked or its lockspace is released.To prevent those callbacks from accessing deallocated objects, put theglocks that should not be unlocked on the sd_dead_glocks list, releasethe lockspace, and only then free those glocks.As an additional measure, ignore unexpected ast and bast callbacks ifthe receiving glock is dead.
