linux-kernel - [PATCH 3.11 110/121] hwmon: (ntc_thermistor) Avoid math overflow

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Message-Id: <1392986945-9693-111-git-send-email-luis.henriques@canonical.com>
Date:	Fri, 21 Feb 2014 12:48:54 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Doug Anderson <dianders@...omium.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.11 110/121] hwmon: (ntc_thermistor) Avoid math overflow

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

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

From: Doug Anderson <dianders@...omium.org>

commit d3d89c468ceebbcf9423d1a3d66c5bf91f569570 upstream.

The ntc thermistor code was doing math whose temporary result might
have overflowed 32-bits.  We need some casts in there to make it safe.

In one example I found:
- pullup_uV: 1800000
- result of iio_read_channel_raw: 3226
- 1800000 * 3226 => 0x15a1cbc80

Signed-off-by: Doug Anderson <dianders@...omium.org>
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/hwmon/ntc_thermistor.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/hwmon/ntc_thermistor.c b/drivers/hwmon/ntc_thermistor.c
index 830a842..4a80a54 100644
--- a/drivers/hwmon/ntc_thermistor.c
+++ b/drivers/hwmon/ntc_thermistor.c
@@ -145,7 +145,7 @@ struct ntc_data {
 static int ntc_adc_iio_read(struct ntc_thermistor_platform_data *pdata)
 {
 	struct iio_channel *channel = pdata->chan;
-	unsigned int result;
+	s64 result;
 	int val, ret;
 
 	ret = iio_read_channel_raw(channel, &val);
@@ -155,10 +155,10 @@ static int ntc_adc_iio_read(struct ntc_thermistor_platform_data *pdata)
 	}
 
 	/* unit: mV */
-	result = pdata->pullup_uv * val;
+	result = pdata->pullup_uv * (s64) val;
 	result >>= 12;
 
-	return result;
+	return (int)result;
 }
 
 static const struct of_device_id ntc_match[] = {
-- 
1.9.0

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