ovl: fail ovl_lock_rename_workdir() if either target is unhashed

As well as checking that the parent hasn't changed after getting the
lock we need to check that the dentry hasn't been unhashed.
Otherwise we might try to rename something that has been removed.

Reported-by: [e-mail]
Fixes: d2c995581c7c ("ovl: Call ovl_create_temp() without lock held.")
Signed-off-by: NeilBrown <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Tested-by: [e-mail]
Reviewed-by: Amir Goldstein <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>

fs/overlayfs/util.c

···
 		goto err;
 	if (trap)
 		goto err_unlock;
-	if (work && work->d_parent != workdir)
+	if (work && (work->d_parent != workdir || d_unhashed(work)))
 		goto err_unlock;
-	if (upper && upper->d_parent != upperdir)
+	if (upper && (upper->d_parent != upperdir || d_unhashed(upper)))
 		goto err_unlock;
 
 	return 0;