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    SubjectRe: [PATCH] iio: adc: Fix potential integer overflow
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    On 09/24/2018 07:18 PM, Lars-Peter Clausen wrote:
    > On 09/22/2018 03:42 PM, Jonathan Cameron wrote:
    >> On Tue, 18 Sep 2018 07:53:14 -0500
    >> "Gustavo A. R. Silva" <gustavo@embeddedor.com> wrote:
    >>
    >>> Cast factor to s64 in order to give the compiler complete information
    >>> about the proper arithmetic to use and avoid a potential integer
    >>> overflow. Notice that such variable is being used in a context
    >>> that expects an expression of type s64 (64 bits, signed).
    >>>
    >>> Addresses-Coverity-ID: 1324146 ("Unintentional integer overflow")
    >>> Fixes: e13d757279bb ("iio: adc: Add QCOM SPMI PMIC5 ADC driver")
    >>> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
    >>> ---
    >>> drivers/iio/adc/qcom-vadc-common.c | 2 +-
    >>> 1 file changed, 1 insertion(+), 1 deletion(-)
    >>>
    >>> diff --git a/drivers/iio/adc/qcom-vadc-common.c b/drivers/iio/adc/qcom-vadc-common.c
    >>> index dcd7fb5..e360e27 100644
    >>> --- a/drivers/iio/adc/qcom-vadc-common.c
    >>> +++ b/drivers/iio/adc/qcom-vadc-common.c
    >>> @@ -282,7 +282,7 @@ static int qcom_vadc_scale_code_voltage_factor(u16 adc_code,
    >>> voltage = div64_s64(voltage, data->full_scale_code_volt);
    >>> if (voltage > 0) {
    >>> voltage *= prescale->den;
    >>> - temp = prescale->num * factor;
    >>> + temp = prescale->num * (s64)factor;
    >> So factor is an unsigned int so could be 32 bits. In reality it only
    >> takes a small set of values between 1 and 1000
    >>
    >> Maximum numerator is 10 so a maximum of 10,000.
    >>
    >> Hence this is a false positive, be it one that would be very hard
    >> for a static checker to identify.
    >
    > I think the reason why it complains is because temp is s64. So it infers
    > that the idea was that the result of the multiplication can be larger
    > than 64 bit. For 32bit * 32bit -> 32bit it should not complain.

    "lager than 32 bit"

    >
    >>
    >> So that moves it from a fix to a warning suppression change.
    >> I have no problem with those, but description needs to reflect that.
    >
    > Maybe just change the type of temp to u32. There is also
    > mul_u64_u32_div() which could be used here to further simplify things.
    >

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