netdev - Re: use-after-free in usbnet

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Message-ID: <Pine.LNX.4.44L0.1203211031490.1369-100000@iolanthe.rowland.org>
Date:	Wed, 21 Mar 2012 10:35:22 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ming Lei <tom.leiming@...il.com>
cc:	netdev@...r.kernel.org, <linux-usb@...r.kernel.org>,
	Fedora Kernel Team <kernel-team@...oraproject.org>,
	Dave Jones <davej@...hat.com>
Subject: 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

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