Subject: Re: [RFC PATCH net-next 1/2] devlink: Hold a reference on parent device

From: Ido Schimmel <[email-masked]>
Date: Wed, 21 Jun 2023 18:35:15 +0300

On Wed, Jun 21, 2023 at 01:48:36PM +0200, Jiri Pirko wrote:
> Mon, Jun 19, 2023 at 02:50:14PM CEST, [email-masked] wrote:
> >@@ -91,6 +92,7 @@ static void devlink_release(struct work_struct *work)
> > 
> > 	mutex_destroy(&devlink->lock);
> > 	lockdep_unregister_key(&devlink->lock_key);
> >+	put_device(devlink->dev);
> 
> In this case I think you have to make sure this is called before
> devlink_free() ends. After the caller of devlink_free() returns (most
> probably .remove callback), nothing stops module from being removed.
> 
> I don't see other way. Utilize complete() here and wait_for_completion()
> at the end of devlink_free().

I might be missing something, but how can I do something like
wait_for_completion(&devlink->comp) at the end of devlink_free()? After
I call devlink_put() the devlink instance can be freed and the
wait_for_completion() call will result in a UAF.

> 
> If the completion in devlink_put() area rings a bell for you, let me save
> you the trouble looking it up:
> 9053637e0da7 ("devlink: remove the registration guarantee of references")
> This commit removed that. But it is a different usage.
> 
> 
> 
> > 	kfree(devlink);
> > }
> > 
> >@@ -204,6 +206,7 @@ struct devlink *devlink_alloc_ns(const struct devlink_ops *ops,
> > 	if (ret < 0)
> > 		goto err_xa_alloc;
> > 
> >+	get_device(dev);
> > 	devlink->dev = dev;
> > 	devlink->ops = ops;
> > 	xa_init_flags(&devlink->ports, XA_FLAGS_ALLOC);
> >-- 
> >2.40.1
> >