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. Fixes: 8713107221a8 ("HID: pidff: Rescale time values to match field units") Cc: stable@vger.kernel.org Signed-off-by: Shengzhuo Wei --- drivers/hid/usbhid/hid-pidff.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/hid/usbhid/hid-pidff.c b/drivers/hid/usbhid/hid-pidff.c index 22951b7ecd17..1a2fffcf204e 100644 --- a/drivers/hid/usbhid/hid-pidff.c +++ b/drivers/hid/usbhid/hid-pidff.c @@ -354,9 +354,9 @@ static u32 pidff_rescale_time(u16 time, struct hid_field *field) int exponent = field->unit_exponent; pr_debug("time field exponent: %d\n", exponent); - for (; exponent < FF_TIME_EXPONENT; exponent++) + for (; scaled_time && exponent < FF_TIME_EXPONENT; exponent++) scaled_time *= 10; - for (; exponent > FF_TIME_EXPONENT; exponent--) + for (; scaled_time && exponent > FF_TIME_EXPONENT; exponent--) scaled_time /= 10; pr_debug("time calculated from %d to %d\n", time, scaled_time); --- base-commit: d135ab453a7400a34930bdda1ef4bdc8acfac80e change-id: 20261028-b4-pidff-rescale-exponent-1d5c4e218e6d Best regards, -- Shengzhuo Wei