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

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Date:	Mon, 11 Apr 2016 10:44:45 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	chunfeng yun <chunfeng.yun@...iatek.com>
cc:	Felipe Balbi <felipe.balbi@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<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 Mon, 11 Apr 2016, chunfeng yun wrote:

> On Mon, 2016-04-11 at 08:07 +0300, Felipe Balbi wrote:
> > Hi,
> > 
> > chunfeng yun <chunfeng.yun@...iatek.com> writes:
> > > On Fri, 2016-04-08 at 07:07 -0700, 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?
> > > It's misc/usbtest.c
> > 
> > that'll do what you ask it to do with the userspace tool testusb. Are
> > you trying to pass a size of 0 ?
> > 
> No, I just ran "testusb -t10" which called test_ctrl_queue().
> In this function, sub-case 8 passed a parameter @len as 0 to
> simple_alloc_urb(), and then it tried to allocate a 0-length buffer.

That should be easy enough to fix.  Just skip the calls that allocate 
the buffer if the length would be 0.

Alan Stern