linux-kernel - Re: [PATCH 2/2] usb: fail on usb_hub_create_port

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Date:	Tue, 20 Aug 2013 14:18:57 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Krzysztof Mazur <krzysiek@...lesie.net>
cc:	linux-usb@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>,
	Daniel J Blueman <daniel@...ascale-asia.com>
Subject: Re: [PATCH 2/2] usb: fail on usb_hub_create_port_device() errors

On Tue, 20 Aug 2013, Krzysztof Mazur wrote:

> Ignoring usb_hub_create_port_device() errors cause later NULL pointer
> deference when uninitialized hub->ports[i] entries are dereferenced
> after port memory allocation error.
> 
> Signed-off-by: Krzysztof Mazur <krzysiek@...lesie.net>
> ---
> I'm not sure if failing in that case is a good idea, but other solutions
> are more complex.
> 
> I tried also changing hdev->maxchild and skiping initialization
> of later ports, but it didn't work because in some cases
> hub->descriptor->bNbrPorts is used instead of hdev->maxchild.
> With simulated usb_hub_create_port_device() failure I have an Oops
> in hub_power_on().

I think this patch is correct.  However, we also should change the 
other places that refer to bNbrPorts; make them use maxchild instead.

> Another possible solution is allowing for uninitialized ports and
> checking for hub->ports[i] == NULL.

No, if we can't allocate memory for all the ports then the whole thing 
should fail.

Alan Stern

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