kernfs: fix hash calculation in kernfs_rename_ns()

3eef34ad7dc3 ("kernfs: implement kernfs_get_parent(),
kernfs_name/path() and friends") restructured kernfs_rename_ns() such
that new name assignment happens under kernfs_rename_lock;
unfortunately, it mistakenly passed NULL to kernfs_name_hash() to
calculate the new hash if the name hasn't changed, which can lead to
oops.

Fix it by using kn->name and kn->ns when calculating the new hash.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Dan Carpenter dan.carpenter@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/kernfs/dir.c

@@ -1295,7 +1295,7 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
 
 	spin_unlock_irq(&kernfs_rename_lock);
 
-	kn->hash = kernfs_name_hash(new_name, new_ns);
+	kn->hash = kernfs_name_hash(kn->name, kn->ns);
 	kernfs_link_sibling(kn);
 
 	kernfs_put(old_parent);