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/[email protected]
Cc: <[email protected]>
Fixes: 29ec90660d68 ("userfaultfd: shmem/hugetlbfs: only allow to register VM_MAYWRITE vmas")
Signed-off-by: Andrea Arcangeli <[email protected]>
Reported-by: [email protected]
Acked-by: Mike Rapoport <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Acked-by: Peter Xu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index cd58939dc977e481930053f37e3137394265d75e..7a85e609fc276f28dd80c8dc481e383094d1dfe9 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1566,7 +1566,6 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
                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 userfaultfd_ctx *ctx,
                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);