linux-kernel - Re: static analysis bug report in drivers/staging/iio/dac/ad5380.c

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Message-ID: <1f73a6d5-9e77-6f2f-8fcf-ec87f5ffa54d@metafoo.de>
Date:   Thu, 15 Aug 2019 13:40:35 +0200
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Colin Ian King <colin.king@...onical.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Peter Meerwald-Stadler <pmeerw@...erw.ne>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Stefan Popa <stefan.popa@...log.com>,
        linux-iio@...r.kernel.org,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: static analysis bug report in drivers/staging/iio/dac/ad5380.c

On 8/15/19 12:21 PM, Colin Ian King wrote:
> Hi,
> 
> Static analysis with Coverity Scan has detected a potential assignment
> bug in ad5380.c:
> 
> 217        case IIO_CHAN_INFO_CALIBBIAS:
> 218                ret = regmap_read(st->regmap,
> AD5380_REG_OFFSET(chan->address),
> 219                                        val);
> 220                if (ret)
> 221                        return ret;
> 222                *val >>= chan->scan_type.shift;
> 
> CID 43178 (#1 of 1): Unused value (UNUSED_VALUE)assigned_pointer:
> Assigning value from val - (1 << chan->scan_type.realbits) / 2 to val
> here, but that stored value is not used.
> 
> 223                val -= (1 << chan->scan_type.realbits) / 2;
> 224                return IIO_VAL_INT;
> 
> val is a pointer and so updating it before a return is probably not the
> intention.  I suspect the intention was probably:
> 
> 		   *val -= (1 << chan->scan_type.realbits) / 2;
> 
> However, I'm not confident about this as the following case has:
> 
> 225        case IIO_CHAN_INFO_SCALE:
> 226                *val = 2 * st->vref;
> 227                *val2 = chan->scan_type.realbits;
> 228                return IIO_VAL_FRACTIONAL_LOG2;
> 
> which may imply the update maybe to *val2 instead, e.g.:
> 
> 		*val2 -= (1 << chan->scan_type.realbits) / 2;
> 
> Any ideas?

Updating changing val to *val is the right fix in this case.