From 1eda52334e6d13eb1a85f713ce06dd39342b5020 Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>

Date: Tue, 15 Dec 2020 10:20:30 +0100

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

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Git-commit: 1eda52334e6d13eb1a85f713ce06dd39342b5020

Patch-mainline: v5.11-rc3

References: git-fixes

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>

Acked-by: Takashi Iwai <tiwai@suse.de>

---

 drivers/hwmon/pwm-fan.c | 12 +++++++++++-

 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c

index 777439f48c14..111a91dc6b79 100644

--- a/drivers/hwmon/pwm-fan.c

+++ b/drivers/hwmon/pwm-fan.c

@@ -334,8 +334,18 @@ 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;

-- 

2.26.2