Re: [PATCH v6 08/13] iio: afe: rescale: reduce risk of integer overflow
From: Peter Rosin <hidden>
Date: 2021-07-23 21:17:56
Also in:
linux-iio, lkml
On 2021-07-21 05:06, Liam Beguin wrote:
quoted hunk ↗ jump to hunk
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 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;