hwmon: (lm80) fix a missing check of the status of SMBus read

BugLink: https://bugs.launchpad.net/bugs/1818813

[ Upstream commit c9c63915 ]

If lm80_read_value() fails, it returns a negative number instead of the
correct read data. Therefore, we should avoid using the data if it
fails.

The fix checks if lm80_read_value() fails, and if so, returns with the
error number.
Signed-off-by: Kangjie Lu <kjlu@umn.edu>
[groeck: One variable for return values is enough]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/hwmon/lm80.c

@@ -360,9 +360,11 @@ static ssize_t set_fan_div(struct device *dev, struct device_attribute *attr,
 	struct i2c_client *client = data->client;
 	unsigned long min, val;
 	u8 reg;
-	int err = kstrtoul(buf, 10, &val);
-	if (err < 0)
-		return err;
+	int rv;
+
+	rv = kstrtoul(buf, 10, &val);
+	if (rv < 0)
+		return rv;
 
 	/* Save fan_min */
 	mutex_lock(&data->update_lock);
@@ -390,8 +392,11 @@ static ssize_t set_fan_div(struct device *dev, struct device_attribute *attr,
 		return -EINVAL;
 	}
 
-	reg = (lm80_read_value(client, LM80_REG_FANDIV) &
-	       ~(3 << (2 * (nr + 1)))) | (data->fan_div[nr] << (2 * (nr + 1)));
+	rv = lm80_read_value(client, LM80_REG_FANDIV);
+	if (rv < 0)
+		return rv;
+	reg = (rv & ~(3 << (2 * (nr + 1))))
+	    | (data->fan_div[nr] << (2 * (nr + 1)));
 	lm80_write_value(client, LM80_REG_FANDIV, reg);
 
 	/* Restore fan_min */