Commit 1d05b91a authored Dec 15, 2020 by Uwe Kleine-König Committed by Greg Kroah-Hartman Jan 19, 2021

hwmon: (pwm-fan) Ensure that calculation doesn't discard big period values



[ Upstream commit 1eda52334e6d13eb1a85f713ce06dd39342b5020 ]

With MAX_PWM being defined to 255 the code

	unsigned long period;
	...
	period = ctx->pwm->args.period;
	state.duty_cycle = DIV_ROUND_UP(pwm * (period - 1), MAX_PWM);

calculates a too small value for duty_cycle if the configured period is
big (either by discarding the 64 bit value ctx->pwm->args.period or by
overflowing the multiplication). As this results in a too slow fan and
so maybe an overheating machine better be safe than sorry and error out
in .probe.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20201215092031.152243-1-u.kleine-koenig@pengutronix.de


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 1229d433

drivers/hwmon/pwm-fan.c

+11 −1

Original line number	Diff line number	Diff line
		@@ -330,8 +330,18 @@ static int pwm_fan_probe(struct platform_device *pdev)

		ctx->pwm_value = MAX_PWM;

		/* Set duty cycle to maximum allowed and enable PWM output */
		pwm_init_state(ctx->pwm, &state);
		/*
		* __set_pwm assumes that MAX_PWM * (period - 1) fits into an unsigned
		* long. Check this here to prevent the fan running at a too low
		* frequency.
		*/
		if (state.period > ULONG_MAX / MAX_PWM + 1) {
		dev_err(dev, "Configured period too big\n");
		return -EINVAL;
		}

		/* Set duty cycle to maximum allowed and enable PWM output */
		state.duty_cycle = ctx->pwm->args.period - 1;
		state.enabled = true;