Re: use-after-free in usbnet

On Wed, 21 Mar 2012, Ming Lei wrote:

Looks it is a general issue about usb_hcd_unlink_urb.

Alan, how about increasing URB reference count before calling unlink1
inside usb_hcd_unlink_urb to fix this kind of problem?

No, that won't fix the problem.  The URB could complete and be
deallocated even before usb_hcd_unlink_urb() is called, so nothing that
function can do will prevent the error.

It is the caller's responsibility to make sure that the URB does not 
get freed before usb_unlink_urb() or usb_kill_urb() returns.  We 
probably should mention this in the kerneldoc...

Alan Stern