ovl: verify upper dentry in ovl_remove_and_whiteout()

ovl: verify upper dentry in ovl_remove_and_whiteout()

Orabug: 26175588

The upper dentry may become stale before we call ovl_lock_rename_workdir.
For example, someone could (mistakenly or maliciously) manually unlink(2)
it directly from upperdir.

To ensure it is not stale, let's lookup it after ovl_lock_rename_workdir
and and check if it matches the upper dentry.

Essentially, it is the same problem and similar solution as in
commit 11f3710417d0 ("ovl: verify upper dentry before unlink and rename").

Signed-off-by: Maxim Patlasov <mpatlasov@virtuozzo.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org>
(cherry picked from commit cfc9fde0b07c3b44b570057c5f93dda59dca1c94)
Signed-off-by: Somasundaram Krishnasamy <somasundaram.krishnasamy@oracle.com>
Reviewed-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>
Reviewed-by:  Ethan Zhao <ethan.zhao@oracle.com>