[PATCH v5 04/10] iio: afe: rescale: reduce risk of integer overflow
From: Liam Beguin <hidden>
Date: 2021-07-15 03:12:49
Also in:
linux-iio, lkml
Subsystem:
iio subsystem and drivers, iio unit converter, the rest · Maintainers:
Jonathan Cameron, Peter Rosin, Linus Torvalds
From: Liam Beguin <redacted> 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 <redacted> --- 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