Description of problem:
Upstream commit dab5855 ("perf_counter: Add mmap event hooks to mprotect()") is fundamentally wrong as mprotect_fixup() can free 'vma' due to merging. Fix the problem by moving perf_event_mmap() hook to mprotect_fixup(). In certain scenario, a local, unprivileged user could use this flaw to trigger a denial of service.
*** This bug has been marked as a duplicate of bug 651671 ***