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[198.48.202.89]) by smtp.gmail.com with ESMTPSA id f10sm3621606qto.31.2021.08.01.12.40.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 01 Aug 2021 12:40:17 -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 v7 07/13] iio: afe: rescale: reduce risk of integer overflow Date: Sun, 1 Aug 2021 15:39:54 -0400 Message-Id: <20210801194000.3646303-8-liambeguin@gmail.com> X-Mailer: git-send-email 2.30.1.489.g328c10930387 In-Reply-To: <20210801194000.3646303-1-liambeguin@gmail.com> References: <20210801194000.3646303-1-liambeguin@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 623744da269a..abd7ad73d1ce 100644 --- a/drivers/iio/afe/iio-rescale.c +++ b/drivers/iio/afe/iio-rescale.c @@ -21,15 +21,24 @@ int rescale_process_scale(struct rescale *rescale, int scale_type, int *val, int *val2) { - unsigned long long tmp; + s64 tmp, tmp2; + u32 factor; u32 mult; u32 rem; u32 neg; 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(abs(tmp), abs(tmp2)); + tmp = div_s64(tmp, factor); + tmp2 = div_s64(tmp2, factor); + } + *val = tmp; + *val2 = tmp2; return scale_type; case IIO_VAL_INT: *val *= rescale->numerator; -- 2.30.1.489.g328c10930387