userfaultfd: check VM_MAYWRITE was set after verifying the uffd is registered
Calling UFFDIO_UNREGISTER on virtual ranges not yet registered in uffd could trigger an harmless false positive WARN_ON. Check the vma is already registered before checking VM_MAYWRITE to shut off the false positive warning. Link: http://lkml.kernel.org/r/20181206212028.18726-2-aarcange@redhat.com Cc: <stable@vger.kernel.org> Fixes: 29ec9066 ("userfaultfd: shmem/hugetlbfs: only allow to register VM_MAYWRITE vmas") Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reported-by: syzbot+06c7092e7d71218a2c16@syzkaller.appspotmail.com Acked-by: Mike Rapoport <rppt@linux.ibm.com> Acked-by: Hugh Dickins <hughd@google.com> Acked-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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