linux-kernel - Re: [PATCH] iio: adc: Fix potential integer overflow

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Message-ID: <8be2f082-eb0d-24db-305a-a917e67ab371@embeddedor.com>
Date:   Sat, 22 Sep 2018 12:31:58 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: adc: Fix potential integer overflow



On 9/22/18 8:42 AM, Jonathan Cameron wrote:
> On Tue, 18 Sep 2018 07:53:14 -0500
> "Gustavo A. R. Silva" <gustavo@...eddedor.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@...eddedor.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.
> 
> So that moves it from a fix to a warning suppression change.
> I have no problem with those, but description needs to reflect that.
> 
> Let me know if I've missed something, if not I'm happy to apply
> this and will put some text in the message to explain the above
> reasoning.
> 

Hi Jonathan,

I think you are right. Plase, feel free to update the commit log.

Thanks
--
Gustavo