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From: Peter Rosin <peda@axentia.se>
To: Liam Beguin <liambeguin@gmail.com>,
	jic23@kernel.org, lars@metafoo.de, pmeerw@pmeerw.net
Cc: linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org,
	devicetree@vger.kernel.org, robh+dt@kernel.org
Subject: Re: [PATCH v6 08/13] iio: afe: rescale: reduce risk of integer overflow
Date: Fri, 23 Jul 2021 23:17:47 +0200	[thread overview]
Message-ID: <9e0e4398-873e-b5c0-0f0c-50a186ed2228@axentia.se> (raw)
In-Reply-To: <20210721030613.3105327-9-liambeguin@gmail.com>

On 2021-07-21 05:06, Liam Beguin wrote:
> From: Liam Beguin <lvb@xiphos.com>
> 
> Reduce the risk of integer overflow by doing the scale calculation with
> 64bit integers and looking for a Greatest Common Divider for both parts
> of the fractional value when required.
> 
> Signed-off-by: Liam Beguin <lvb@xiphos.com>
> ---
>  drivers/iio/afe/iio-rescale.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
> index 6f6a711ae3ae..35fa3b4e53e0 100644
> --- a/drivers/iio/afe/iio-rescale.c
> +++ b/drivers/iio/afe/iio-rescale.c
> @@ -21,12 +21,21 @@
>  int rescale_process_scale(struct rescale *rescale, int scale_type,
>  			  int *val, int *val2)
>  {
> -	unsigned long long tmp;
> +	s64 tmp, tmp2;
> +	u32 factor;
>  
>  	switch (scale_type) {
>  	case IIO_VAL_FRACTIONAL:
> -		*val *= rescale->numerator;
> -		*val2 *= rescale->denominator;
> +		if (check_mul_overflow(*val, rescale->numerator, (s32 *)&tmp) ||
> +		    check_mul_overflow(*val2, rescale->denominator, (s32 *)&tmp2)) {
> +			tmp = (s64)*val * rescale->numerator;
> +			tmp2 = (s64)*val2 * rescale->denominator;
> +			factor = gcd(tmp, tmp2);

Hi!

Reiterating that gcd() only works for unsigned operands, so this is broken for
negative values.

Cheers,
Peter

> +			tmp = div_s64(tmp, factor);
> +			tmp2 = div_s64(tmp2, factor);
> +		}
> +		*val = tmp;
> +		*val2 = tmp2;
>  		return scale_type;
>  	case IIO_VAL_INT:
>  		*val *= rescale->numerator;
> 

  reply	other threads:[~2021-07-23 21:17 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-21  3:06 [PATCH v6 00/13] iio: afe: add temperature rescaling support Liam Beguin
2021-07-21  3:06 ` [PATCH v6 01/13] iio: inkern: apply consumer scale on IIO_VAL_INT cases Liam Beguin
2021-07-21  3:06 ` [PATCH v6 02/13] iio: inkern: apply consumer scale when no channel scale is available Liam Beguin
2021-07-21  3:06 ` [PATCH v6 03/13] iio: inkern: make a best effort on offset calculation Liam Beguin
2021-07-21  3:06 ` [PATCH v6 04/13] iio: afe: rescale: expose scale processing function Liam Beguin
2021-07-21  3:06 ` [PATCH v6 05/13] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support Liam Beguin
2021-07-23 21:16   ` Peter Rosin
2021-07-28  0:21     ` Liam Beguin
2021-07-28  7:19       ` Peter Rosin
2021-07-29 15:56         ` Liam Beguin
2021-07-30  6:49           ` Peter Rosin
2021-07-30  7:01             ` Peter Rosin
2021-07-30 20:01               ` Liam Beguin
2021-07-30 19:57             ` Liam Beguin
2021-07-31 17:47         ` Jonathan Cameron
2021-07-21  3:06 ` [PATCH v6 06/13] iio: afe: rescale: add offset support Liam Beguin
2021-07-21  3:06 ` [PATCH v6 07/13] iio: test: add basic tests for the iio-rescale driver Liam Beguin
2021-07-24  8:40   ` kernel test robot
2021-07-21  3:06 ` [PATCH v6 08/13] iio: afe: rescale: reduce risk of integer overflow Liam Beguin
2021-07-23 21:17   ` Peter Rosin [this message]
2021-07-28  0:07     ` Liam Beguin
2021-07-28  7:47       ` Peter Rosin
2021-07-29 16:02         ` Liam Beguin
2021-07-21  3:06 ` [PATCH v6 09/13] iio: afe: rescale: fix precision on fractional log scale Liam Beguin
2021-07-23 21:20   ` Peter Rosin
2021-07-28  0:26     ` Liam Beguin
2021-07-28  7:58       ` Peter Rosin
2021-07-29 16:19         ` Liam Beguin
2021-07-21  3:06 ` [PATCH v6 10/13] iio: afe: rescale: add RTD temperature sensor support Liam Beguin
2021-07-21  3:06 ` [PATCH v6 11/13] iio: afe: rescale: add temperature transducers Liam Beguin
2021-07-21  3:06 ` [PATCH v6 12/13] dt-bindings: iio: afe: add bindings for temperature-sense-rtd Liam Beguin
2021-07-21  3:06 ` [PATCH v6 13/13] dt-bindings: iio: afe: add bindings for temperature transducers Liam Beguin
2021-07-23 22:59   ` Rob Herring

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