[PATCH 4.19 009/196] hwmon: (max6697) Fix underflow when writing limit attributes

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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Guenter Roeck <linux@xxxxxxxxxxxx>

[ Upstream commit cbf7467828cd4ec7ceac7a8b5b5ddb2f69f07b0e ]

Using DIV_ROUND_CLOSEST() on an unbound value can result in underflows.
Indeed, module test scripts report:

temp1_max: Suspected underflow: [min=0, read 255000, written -9223372036854775808]
temp1_crit: Suspected underflow: [min=0, read 255000, written -9223372036854775808]

Fix by introducing an extra set of clamping.

Fixes: 5372d2d71c46 ("hwmon: Driver for Maxim MAX6697 and compatibles")
Reviewed-by: Tzung-Bi Shih <tzungbi@xxxxxxxxxx>
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/hwmon/max6697.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/hwmon/max6697.c b/drivers/hwmon/max6697.c
index 6df28fe0577da..7e7f59c68ce6e 100644
--- a/drivers/hwmon/max6697.c
+++ b/drivers/hwmon/max6697.c
@@ -314,6 +314,7 @@ static ssize_t set_temp(struct device *dev,
 		return ret;
 
 	mutex_lock(&data->update_lock);
+	temp = clamp_val(temp, -1000000, 1000000);	/* prevent underflow */
 	temp = DIV_ROUND_CLOSEST(temp, 1000) + data->temp_offset;
 	temp = clamp_val(temp, 0, data->type == max6581 ? 255 : 127);
 	data->temp[nr][index] = temp;
-- 
2.43.0







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