linux-kernel - Re: [PATCH] usb: hub: avoid possible division by zero

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Date:	Sat, 23 Nov 2013 18:26:12 +0100
From:	Johannes Thumshirn <morbidrsa@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Lan Tianyu <tianyu.lan@...el.com>,
	Xenia Ragiadakou <burzalodowa@...il.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: hub: avoid possible division by zero

On Sat, Nov 23, 2013 at 09:20:10AM -0800, Greg Kroah-Hartman wrote:
> On Sat, Nov 23, 2013 at 05:31:34PM +0100, Johannes Thumshirn wrote:
> > Avoid possible division by zero in led_work, if hdev->maxchild is 0.
> >
> > See also:
> > http://buildbot.llvm.linuxfoundation.org/checker/scan-build-latest/report-b65939.html#EndPath
> >
> > Signed-off-by: Johannes Thumshirn <morbidrsa@...il.com>
> > ---
> >  drivers/usb/core/hub.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> > index a7c04e2..8c7aa4e 100644
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -453,7 +453,8 @@ static void led_work (struct work_struct *work)
> >  	unsigned		changed = 0;
> >  	int			cursor = -1;
> >
> > -	if (hdev->state != USB_STATE_CONFIGURED || hub->quiescing)
> > +	if (hdev->state != USB_STATE_CONFIGURED || hub->quiescing
> > +		|| hdev->maxchild == 0)
>
> And how can maxchild ever be equal to 0?
>
> Look at where it is assigned (it comes from bNbrPorts in the
> descriptor), in hub_configure() and if it is set to 0, the creation of
> the structure fails and then this code will never run, right?
>
> So I don't think this is needed, and your checker needs to be fixed.
>
> sorry,

Args, sorry for the noise. Should've checked that better.
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