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    SubjectRe: [patch 2/2] [media] ds3000: off by one in ds3000_read_snr()


    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
    >


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