Re: [PATCH v2] HID: pidff: bound the unit exponent rescaling loop

[sashiko-bot@kernel.org]

> pidff_rescale_time() walks the device-provided unit exponent one step
> at a time, allowing extreme values to cause billions of iterations
> while ff->mutex is held. In a UHID test with an INT_MIN exponent,
> EVIOCSFF took 3.1 to 4.3 seconds to upload a finite-duration effect.
> 
> Stop rescaling once scaled_time becomes zero, since further
> multiplication or division by 10 cannot change the result. The u32
> value becomes zero within 32 multiplications by 10, and the u16
> input within 5 divisions. This bounds the loops while preserving
> their results for all exponents, including wraparound.
> 
> Also warn during initialization if the duration field's unit exponent
> is outside the range -8 to 0. This helps identify unusual device
> descriptors without logging on every effect upload or changing the
> rescaling result.
> 
> Fixes: 8713107221a8 ("HID: pidff: Rescale time values to match field units")
> Reviewed-by: Tomasz Pakuła <tomasz.pakula.oficjalny@gmail.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Shengzhuo Wei <me@cherr.cc>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261102-b4-pidff-rescale-exponent-v2-1-a75bcca65fd0@cherr.cc?part=1