Re: [PATCH] usbnet: Fix use-after-free on disconnect

[Lukas Wunner <lukas@wunner.de>]

On Wed, Apr 13, 2022 at 08:59:48PM +0200, Oliver Neukum wrote:
> On 13.04.22 16:16, Lukas Wunner wrote:
> > Jann Horn reports a use-after-free on disconnect of a USB Ethernet
> > (ax88179_178a.c).  Oleksij Rempel has witnessed the same issue with a
> > different driver (ax88172a.c).
> 
> I see. Very good catch
> 
> > --- a/drivers/net/usb/usbnet.c
> > +++ b/drivers/net/usb/usbnet.c
> > @@ -469,6 +469,9 @@ static enum skb_state defer_bh(struct usbnet *dev, struct sk_buff *skb,
> >   */
> >  void usbnet_defer_kevent (struct usbnet *dev, int work)
> >  {
> > +	if (dev->intf->condition == USB_INTERFACE_UNBINDING)
> > +		return;
> 
> But, no, you cannot do this. This is a very blatant layering violation.
> You cannot use states internal to usb core like that in a driver.

Why do you think it's internal?

enum usb_interface_condition is defined in include/linux/usb.h
for everyone to see and use.  If it was meant to be private,
I'd expect it to be marked as such or live in drivers/usb/core/usb.h.

Adding Greg to clarify.


> I see two options.
> 1. A dedicated flag in usbnet (then please with the correct smp barriers)
> 2. You introduce an API to usb core to query this.

I'd definitely prefer option 2 as I'd hate to duplicate functionality.

What do you have in mind?  A simple accessor to return intf->condition
or something like usb_interface_unbinding() which returns a bool?

Thanks,

Lukas