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

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Date:	Tue, 17 Sep 2013 00:05:04 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Joseph Salisbury <joseph.salisbury@...onical.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 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
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