Re: [PATCH] driver core: take parent lock on deferred probe

[Alan Stern]

On Tue, Oct 13, 2026 at 07:43:08PM +0200, Danilo Krummrich wrote:
> On Tue Oct 13, 2026 at 4:06 PM CEST, Johan Hovold wrote:
> > +void bus_probe_device_deferred(struct device *dev)
> > +{
> > +	if (dev->parent && dev->bus->need_parent_lock)
> > +		device_lock(dev->parent);
> 
> This looks like it has the same potential UAF as the other patch.  It's quite
> unfortunate we need the whole need_parent_lock thing just for USB.  IIUC the
> main reason USB needs this is because interface devices share resources of USB
> devices and we need to keep the locking order to avoid inversions, right?  Is
> there more to this from the USB side of things?

That's pretty much it.

> I think we can probably do something like this
> 
> 	struct device *parent = NULL;
> 
> 	scoped_guard(device, dev) {
> 		if (dev->p->dead)
> 			return;
> 	
> 		if (dev->bus->need_parent_lock)
> 			parent = get_device(dev->parent);
> 	}
> 
> to avoid the problem, but it's still a bit ugly.
> 
> > +	__bus_probe_device(dev);
> > +	if (dev->parent && dev->bus->need_parent_lock)
> > +		device_unlock(dev->parent);
> > +}

Wouldn't it be simpler just to make each USB interface take a reference 
to its parent device?  And likewise for USB devices, if needed?

Alan Stern