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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Apr 14, 2022 at 12:58:58PM +0200, Lukas Wunner wrote:
> 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.

Because we didn't think people would do crazy things like this.

> Adding Greg to clarify.

Oliver is right.  Also what prevents the condition from changing _right_
after you tested for it?

thanks,

greg k-h