linux-kernel - Re: [v3.11][Regression] HID: hyperv: convert alloc+memcpy to memdup

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Message-ID: <5237A5D5.8010006@canonical.com>
Date:	Mon, 16 Sep 2013 20:44:05 -0400
From:	Joseph Salisbury <joseph.salisbury@...onical.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
CC:	thomas@...3r.de, Jiri Kosina <jkosina@...e.cz>, list@...osl.org,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	LKML <linux-kernel@...r.kernel.org>, open@...osl.org,
	HID CORE LAYER <linux-input@...r.kernel.org>,
	devel@...uxdriverproject.org
Subject: Re: [v3.11][Regression] HID: hyperv: convert alloc+memcpy to memdup

On 09/16/2013 05:05 PM, Dan Carpenter wrote:
> On Mon, Sep 16, 2013 at 04:49:29PM -0400, Joseph Salisbury wrote:
>> On 09/16/2013 04:38 PM, Dan Carpenter wrote:
>>> On Mon, Sep 16, 2013 at 01:42:35PM -0400, Joseph Salisbury wrote:
>>>> Reverting the patch changes the driver back to useing kzalloc() and
>>>> memcpy() instead of  kmemdup.  Doing so has uncovered another bug, which
>>>> causes an oops on memcpy()[1].  We are in the process of bisecting that
>>>> one now and will provide the results.
>>> The two bugs are the same it's that the code has shifted a little.  Mark
>>> the commit as buggy and continue with the git bisect.
>>>
>>> regards,
>>> dan carpenter
>> Can you explain a little further?  Mark commit a4a23f6 as bad?  An
>> initial bisect already reported that was the first bad commit, so it
>> can't be marked bad.  The oops on memcpy() happens after commit a4a23f6
>> is reverted.  The oops on memcpy() did not happen before a4a23f6 was
>> committed, so I assume this new oops was introduced by a change later.
>>
>> Right now I'm bisecting down the oops on memcpy() by updating the bisect
>> with good or bad, depending if the test kernel hit the oops.  I then
>> revert a4a23f6, so that revert is the HEAD of the tree each time before
>> building the kernel again(As long as the commit spit out by bisect is
>> after when a4a23f6 was introduced).
> Yep.  Please continue bisecting the memcpy() oops.
>
> kmemdup() is just a kzalloc() followed by a memcpy().  When we split it
> apart by reverting the patch then we would expect the oops to move to
> the memcpy() part.  Somehow "desc" is a bogus pointer, but I don't
> immediately see how that is possible.
>
> regards,
> dan carpenter

Thanks for the details.  We'll continue the bisect and let you know how
it goes.

Thanks again,

Joe
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