linux-kernel - Re: [PATCH] usb: core: buffer: avoid NULL pointer dereferrence

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Message-ID: <Pine.LNX.4.44L0.1604081120190.2069-100000@iolanthe.rowland.org>
Date:	Fri, 8 Apr 2016 11:21:05 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
cc:	Chunfeng Yun <chunfeng.yun@...iatek.com>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-usb@...r.kernel.org>, <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH] usb: core: buffer: avoid NULL pointer dereferrence

On Fri, 8 Apr 2016, Greg Kroah-Hartman wrote:

> On Fri, Apr 08, 2016 at 05:08:03PM +0800, Chunfeng Yun wrote:
> > NULL pointer dereferrence will happen when class driver
> > wants to allocate zero length buffer and pool_max[0]
> > can't be used, so skip reserved pool in this case.
> 
> Why would a driver want to allocate a 0 length buffer?  What driver does
> this?
> 
> Shouldn't we fix that issue instead?

And even if a driver does want to allocate a 0-length buffer, shouldn't 
the function simply return early instead of running through all its 
calculations?

Alan Stern