linux-kernel - RE: [PATCH] usb/core: fix NULL pointer dereference in recursively_mark

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Date:	Tue, 7 Jan 2014 09:16:42 +0000
From:	"Du, ChangbinX" <changbinx.du@...el.com>
To:	'Alan Stern' <stern@...land.harvard.edu>
CC:	"'gregkh@...uxfoundation.org'" <gregkh@...uxfoundation.org>,
	"'sarah.a.sharp@...ux.intel.com'" <sarah.a.sharp@...ux.intel.com>,
	"Lan, Tianyu" <tianyu.lan@...el.com>,
	"'burzalodowa@...il.com'" <burzalodowa@...il.com>,
	"'linux-usb@...r.kernel.org'" <linux-usb@...r.kernel.org>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] usb/core: fix NULL pointer dereference in
 recursively_mark_NOTATTACHED

> > Changbin, after looking more closely I realized there was a second
> > aspect to this race: recursively_mark_NOTATTACHED uses hub->ports[i]
> > while hub_disconnect removes the port devices.  You ought to be able
> > to cause an oops by inserting a delay just after the loop where
> > usb_hub_remove_port_device is called.
> >
> > The updated patch below should fix both problems.  Can you test it?
> >
> > Alan Stern
> >
> 
> Ok, I'll test it today or tomorrow. Please wait my response.

Alan, I cannot cause a panic after inserting a delay just after 
usb_hub_remove_port_device is called, even move the delay after 
kfree(hub->ports). recursively_mark_NOTATTACHED will not access 
hub->ports[i] since maxchild has been set to 0.

Alan, I think your last patch can fix this issue. 
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