linux-kernel - [PATCH] hwmon: (f71882fg) prevent possible division by zero

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Date:   Wed, 10 May 2023 07:35:37 -0700
From:   Nikita Zhandarovich <n.zhandarovich@...tech.ru>
To:     Jean Delvare <jdelvare@...e.com>
CC:     Nikita Zhandarovich <n.zhandarovich@...tech.ru>,
        Guenter Roeck <linux@...ck-us.net>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, <linux-hwmon@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <lvc-project@...uxtesting.org>
Subject: [PATCH] hwmon: (f71882fg) prevent possible division by zero

In the unlikely event that something goes wrong with the device and
its registers, the fan_from_reg() function may return 0. This value
will cause a division-by-zero error in the show_pwm() function.

To prevent this, test the value of
fan_from_reg(data->fan_full_speed[nr]) against 0 before performing
the division. If the division-by-zero error is avoided, assign 0 to
the val variable.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: df9ec2dae094 ("hwmon: (f71882fg) Reorder symbols to get rid of a few forward declarations")
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@...tech.ru>
---
 drivers/hwmon/f71882fg.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/f71882fg.c b/drivers/hwmon/f71882fg.c
index 70121482a617..27207ec6f7fe 100644
--- a/drivers/hwmon/f71882fg.c
+++ b/drivers/hwmon/f71882fg.c
@@ -1096,8 +1096,11 @@ static ssize_t show_pwm(struct device *dev,
 		val = data->pwm[nr];
 	else {
 		/* RPM mode */
-		val = 255 * fan_from_reg(data->fan_target[nr])
-			/ fan_from_reg(data->fan_full_speed[nr]);
+		if (fan_from_reg(data->fan_full_speed[nr]))
+			val = 255 * fan_from_reg(data->fan_target[nr])
+				/ fan_from_reg(data->fan_full_speed[nr]);
+		else
+			val = 0;
 	}
 	mutex_unlock(&data->update_lock);
 	return sprintf(buf, "%d\n", val);
-- 
2.25.1