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

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Message-ID: <20131123172010.GA8018@kroah.com>
Date:	Sat, 23 Nov 2013 09:20:10 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Johannes Thumshirn <morbidrsa@...il.com>
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 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,

greg k-h
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