linux-kernel - [34-longterm 208/247] hwmon: (sht15) Fix integer overflow in humidity calculation

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Message-Id: <1308850515-15242-149-git-send-email-paul.gortmaker@windriver.com>
Date:	Thu, 23 Jun 2011 13:34:36 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	stable@...nel.org, linux-kernel@...r.kernel.org
Cc:	stable-review@...nel.org,
	Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
	Jean Delvare <khali@...ux-fr.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [34-longterm 208/247] hwmon: (sht15) Fix integer overflow in humidity calculation

From: Vivien Didelot <vivien.didelot@...oirfairelinux.com>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit ccd32e735de7a941906e093f8dca924bb05c5794 upstream.

An integer overflow occurs in the calculation of RHlinear when the
relative humidity is greater than around 30%. The consequence is a subtle
(but noticeable) error in the resulting humidity measurement.

Signed-off-by: Vivien Didelot <vivien.didelot@...oirfairelinux.com>
Signed-off-by: Jean Delvare <khali@...ux-fr.org>
Cc: Jonathan Cameron <jic23@....ac.uk>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 drivers/hwmon/sht15.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/sht15.c b/drivers/hwmon/sht15.c
index a610e78..38a41d2 100644
--- a/drivers/hwmon/sht15.c
+++ b/drivers/hwmon/sht15.c
@@ -333,11 +333,11 @@ static inline int sht15_calc_humid(struct sht15_data *data)
 
 	const int c1 = -4;
 	const int c2 = 40500; /* x 10 ^ -6 */
-	const int c3 = -2800; /* x10 ^ -9 */
+	const int c3 = -28; /* x 10 ^ -7 */
 
 	RHlinear = c1*1000
 		+ c2 * data->val_humid/1000
-		+ (data->val_humid * data->val_humid * c3)/1000000;
+		+ (data->val_humid * data->val_humid * c3) / 10000;
 	return (temp - 25000) * (10000 + 80 * data->val_humid)
 		/ 1000000 + RHlinear;
 }
-- 
1.7.4.4

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