linux-kernel - Re: [PATCH] mtd: nand: mxc_nand: fix a possible NULL dereference

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Date:	Thu, 12 Nov 2015 11:14:18 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	LABBE Corentin <montjoie.mailing@...il.com>
Cc:	LABBE Corentin <clabbe.montjoie@...il.com>, baruch@...s.co.il,
	computersforpeace@...il.com, dwmw2@...radead.org,
	fransklaver@...il.com, k.kozlowski.k@...il.com,
	luis@...ethencourt.com, s.hauer@...gutronix.de,
	linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org
Subject: Re: [PATCH] mtd: nand: mxc_nand: fix a possible NULL dereference

Hello,

On Thu, Nov 12, 2015 at 11:03:28AM +0100, LABBE Corentin wrote:
> On Thu, Nov 12, 2015 at 09:19:09AM +0100, Uwe Kleine-König wrote:
> > Hello Corentin,
> > 
> > On Thu, Nov 12, 2015 at 08:46:55AM +0100, LABBE Corentin wrote:
> > > of_match_device could return NULL, and so cause a NULL pointer
> > > dereference later.
> > > 
> > > Signed-off-by: LABBE Corentin <clabbe.montjoie@...il.com>
> > > ---
> > >  drivers/mtd/nand/mxc_nand.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/mtd/nand/mxc_nand.c b/drivers/mtd/nand/mxc_nand.c
> > > index 136e73a..9e42431 100644
> > > --- a/drivers/mtd/nand/mxc_nand.c
> > > +++ b/drivers/mtd/nand/mxc_nand.c
> > > @@ -1464,8 +1464,7 @@ static int __init mxcnd_probe_dt(struct mxc_nand_host *host)
> > >  {
> > >  	struct device_node *np = host->dev->of_node;
> > >  	struct mxc_nand_platform_data *pdata = &host->pdata;
> > > -	const struct of_device_id *of_id =
> > > -		of_match_device(mxcnd_dt_ids, host->dev);
> > > +	const struct of_device_id *of_id;
> > >  	int buswidth;
> > >  
> > >  	if (!np)
> > > @@ -1482,6 +1481,9 @@ static int __init mxcnd_probe_dt(struct mxc_nand_host *host)
> > >  
> > >  	pdata->width = buswidth / 8;
> > >  
> > > +	of_id = of_match_device(mxcnd_dt_ids, host->dev);
> > > +	if (!of_id)
> > > +		return -ENODEV;
> > 
> > You should return 1 here instead of -ENODEV. Also this check should
> > better be done instead of
> > 
> > 	if (!np)
> > 		return 1;
> > 
> > at the start of the function.
> 
> Are you sure for the "1" value ? It seems a very bad error value.
> And I found plenty of case where if (!np) return -Esomething and no example of return 1

This is not an error value. The semantic is:

	0	everything ok, initialized from dt
	1	device was not probed by dt -> fall back to board-file stuff
	<0	error that should abort probing

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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