From: Andrea Arcangeli aarcange@redhat.com Subject: 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: 29ec90660d68 ("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 ---

fs/userfaultfd.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/userfaultfd.c~userfaultfd-check-vm_maywrite-was-set-after-verifying-the-uffd-is-registered +++ a/fs/userfaultfd.c @@ -1566,7 +1566,6 @@ static int userfaultfd_unregister(struct cond_resched();

BUG_ON(!vma_can_userfault(vma)); - WARN_ON(!(vma->vm_flags & VM_MAYWRITE));

/* * Nothing to do: this vma is already registered into this @@ -1575,6 +1574,8 @@ static int userfaultfd_unregister(struct if (!vma->vm_userfaultfd_ctx.ctx) goto skip;

+ WARN_ON(!(vma->vm_flags & VM_MAYWRITE)); + if (vma->vm_start > start) start = vma->vm_start; vma_end = min(end, vma->vm_end); _