From: walter harms <wharms@bfs.de>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>,
"Igor M. Liplianin" <liplianin@me.by>,
linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-janitors@vger.kernel.org
Subject: Re: [patch 2/2] [media] ds3000: off by one in ds3000_read_snr()
Date: Thu, 19 Jan 2012 11:26:41 +0100 [thread overview]
Message-ID: <4F17EFE1.3060804@bfs.de> (raw)
In-Reply-To: <20120119093327.GI3356@mwanda>
Am 19.01.2012 10:33, schrieb Dan Carpenter:
> 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@oracle.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.
>
I do not have the hardware either so this is pure theoretical.
Access to the data field depends on the value of dvbs2_noise_reading/tmp
even when the data are reasonable like 50/100 snr_reading would become 0
and the index suddenly is -1.
just my 2 cents.
re,
wh
>> 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
>
next prev parent reply other threads:[~2012-01-19 10:26 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-17 7:30 [patch 2/2] [media] ds3000: off by one in ds3000_read_snr() Dan Carpenter
2012-01-18 17:06 ` walter harms
2012-01-19 9:33 ` Dan Carpenter
2012-01-19 10:26 ` walter harms [this message]
2012-01-19 12:22 ` Dan Carpenter
2012-01-21 15:58 ` Dan Carpenter
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