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From: Liam Beguin <liambeguin@gmail.com>
To: liambeguin@gmail.com, peda@axentia.se, 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: [PATCH v3 04/10] iio: afe: rescale: reduce risk of integer overflow
Date: Wed, 30 Jun 2021 21:00:28 -0400	[thread overview]
Message-ID: <20210701010034.303088-5-liambeguin@gmail.com> (raw)
In-Reply-To: <20210701010034.303088-1-liambeguin@gmail.com>

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.

Signed-off-by: Liam Beguin <lvb@xiphos.com>
---
 drivers/iio/afe/iio-rescale.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index 774eb3044edd..98bcb5d418d6 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -39,7 +39,8 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
 			    int *val, int *val2, long mask)
 {
 	struct rescale *rescale = iio_priv(indio_dev);
-	unsigned long long tmp;
+	s64 tmp, tmp2;
+	u32 factor;
 	int ret;
 
 	switch (mask) {
@@ -67,8 +68,11 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
 		}
 		switch (ret) {
 		case IIO_VAL_FRACTIONAL:
-			*val *= rescale->numerator;
-			*val2 *= rescale->denominator;
+			tmp = (s64)*val * rescale->numerator;
+			tmp2 = (s64)*val2 * rescale->denominator;
+			factor = gcd(tmp, tmp2);
+			*val = tmp / factor;
+			*val2 = tmp2 / factor;
 			return ret;
 		case IIO_VAL_INT:
 			*val *= rescale->numerator;
-- 
2.30.1.489.g328c10930387


  parent reply	other threads:[~2021-07-01  1:01 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-01  1:00 [PATCH v3 00/10] iio: afe: add temperature rescaling support Liam Beguin
2021-07-01  1:00 ` [PATCH v3 01/10] iio: inkern: apply consumer scale on IIO_VAL_INT cases Liam Beguin
2021-07-01  1:00 ` [PATCH v3 02/10] iio: inkern: apply consumer scale when no channel scale is available Liam Beguin
2021-07-01  1:00 ` [PATCH v3 03/10] iio: inkern: make a best effort on offset calculation Liam Beguin
2021-07-04 16:26   ` Jonathan Cameron
2021-07-04 18:03     ` Liam Beguin
2021-07-01  1:00 ` Liam Beguin [this message]
2021-07-04 16:36   ` [PATCH v3 04/10] iio: afe: rescale: reduce risk of integer overflow Jonathan Cameron
2021-07-05  4:23     ` Liam Beguin
2021-07-05  8:29       ` Jonathan Cameron
2021-07-01  1:00 ` [PATCH v3 05/10] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support Liam Beguin
2021-07-04 16:37   ` Jonathan Cameron
2021-07-01  1:00 ` [PATCH v3 06/10] iio: afe: rescale: add offset support Liam Beguin
2021-07-04 16:53   ` Jonathan Cameron
2021-07-05  4:27     ` Liam Beguin
2021-07-01  1:00 ` [PATCH v3 07/10] iio: afe: rescale: add RTD temperature sensor support Liam Beguin
2021-07-01  1:00 ` [PATCH v3 08/10] iio: afe: rescale: add temperature transducers Liam Beguin
2021-07-01  1:00 ` [PATCH v3 09/10] dt-bindings: iio: afe: add bindings for temperature-sense-rtd Liam Beguin
2021-07-04 17:02   ` Jonathan Cameron
2021-07-05  4:31     ` Liam Beguin
2021-07-01  1:00 ` [PATCH v3 10/10] dt-bindings: iio: afe: add bindings for temperature transducers Liam Beguin

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