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[198.48.202.89]) by smtp.gmail.com with ESMTPSA id t125sm1932847qkf.41.2021.07.14.20.12.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Jul 2021 20:12:40 -0700 (PDT) From: Liam Beguin 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 v5 04/10] iio: afe: rescale: reduce risk of integer overflow Date: Wed, 14 Jul 2021 23:12:09 -0400 Message-Id: <20210715031215.1534938-5-liambeguin@gmail.com> X-Mailer: git-send-email 2.30.1.489.g328c10930387 In-Reply-To: <20210715031215.1534938-1-liambeguin@gmail.com> References: <20210715031215.1534938-1-liambeguin@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org From: Liam Beguin 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 --- 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 774eb3044edd..4c3cfd4d5181 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 +68,16 @@ 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; + if (check_mul_overflow(*val, rescale->numerator, (s32 *)&tmp) || + check_mul_overflow(*val2, rescale->denominator, (s32 *)&tmp2)) { + factor = gcd(tmp, tmp2); + do_div(tmp, factor); + do_div(tmp2, factor); + } + *val = tmp; + *val2 = tmp2; return ret; case IIO_VAL_INT: *val *= rescale->numerator; -- 2.30.1.489.g328c10930387