Re: [PATCH v4] hwmon: (isl28022) Fix integer overflow in power calculation on 32-bit

[Guenter Roeck]

On Fri, Apr 10, 2026 at 12:26:19AM +0000, Pradhan, Sanman wrote:
> From: Sanman Pradhan <psanman@xxxxxxxxxxx>
> 
> isl28022_read_power() computes:
> 
>   *val = ((51200000L * ((long)data->gain)) /
>           (long)data->shunt) * (long)regval;
> 
> On 32-bit platforms, 'long' is 32 bits. With gain=8 and shunt=10000
> (the default configuration):
> 
>   (51200000 * 8) / 10000 = 40960
>   40960 * 65535 = 2,684,313,600
> 
> This exceeds LONG_MAX (2,147,483,647), resulting in signed integer
> overflow.
> 
> Additionally, dividing before multiplying by regval loses precision
> unnecessarily.
> 
> Use u64 arithmetic with div_u64() and multiply before dividing to
> retain precision. The intermediate product cannot overflow u64
> (worst case: 51200000 * 8 * 65535 = 26843136000000). Power is
> inherently non-negative, so unsigned types are the natural fit.
> Cap the result to LONG_MAX before returning it through the hwmon
> callback.
> 
> Fixes: 39671a14df4f2 ("hwmon: (isl28022) new driver for ISL28022 power monitor")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Sanman Pradhan <psanman@xxxxxxxxxxx>

Applied.

Thanks,
Guenter