linux-kernel - Re: [patch 2/2] [media] ds3000: off by one in ds3000_read

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Message-ID: <20120119093327.GI3356@mwanda>
Date:	Thu, 19 Jan 2012 12:33:27 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	walter harms <wharms@....de>
Cc:	Mauro Carvalho Chehab <mchehab@...radead.org>,
	"Igor M. Liplianin" <liplianin@...by>, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [patch 2/2] [media] ds3000: off by one in ds3000_read_snr()

On Wed, Jan 18, 2012 at 06:06:46PM +0100, walter harms wrote:
> 
> 
> Am 17.01.2012 08:30, schrieb Dan Carpenter:
> > This is a static checker patch and I don't have the hardware to test
> > this, so please review it carefully.  The dvbs2_snr_tab[] array has 80
> > elements so when we cap it at 80, that's off by one.  I would have
> > assumed that the test was wrong but in the lines right before we have
> > the same test but use "snr_reading - 1" as the array offset.  I've done
> > the same thing here.
> > 
> > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> > 
> > diff --git a/drivers/media/dvb/frontends/ds3000.c b/drivers/media/dvb/frontends/ds3000.c
> > index af65d01..3f5ae0a 100644
> > --- a/drivers/media/dvb/frontends/ds3000.c
> > +++ b/drivers/media/dvb/frontends/ds3000.c
> > @@ -681,7 +681,7 @@ static int ds3000_read_snr(struct dvb_frontend *fe, u16 *snr)
> >  			snr_reading = dvbs2_noise_reading / tmp;
> >  			if (snr_reading > 80)
> >  				snr_reading = 80;
> > -			*snr = -(dvbs2_snr_tab[snr_reading] / 1000);
> > +			*snr = -(dvbs2_snr_tab[snr_reading - 1] / 1000);
> >  		}
> >  		dprintk("%s: raw / cooked = 0x%02x / 0x%04x\n", __func__,
> >  				snr_reading, *snr);
> 
> hi dan,
> 
> perhaps it is more useful to do it in the check above ?

It looks like the check is correct but we need to shift all the
values by one.  Again, I don't have this hardware, I'm just going by
the context.

> thinking about that why not replace the number (80) with ARRAY_SIZE() ?

That would be a cleanup, yes but it could go in a separate patch.

regards,
dan carpenter


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