linux-kernel - [PATCH] watchdog: mena21_wdt: Fix a possible data race in a21_wdt_set

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Date:   Tue,  8 May 2018 11:18:25 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     morbidrsa@...il.com, wim@...ux-watchdog.org, linux@...ck-us.net
Cc:     linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH] watchdog: mena21_wdt: Fix a possible data race in a21_wdt_set_timeout

The write operation to "wdt->timeout" is protected by
the lock on line 118, but the read operation to
this data on line 105 is not protected by the lock.
Thus, there may exist a data race for "wdt->timeout".

To fix this data race, the read operation to "wdt->timeout" 
should be also protected by the lock.

Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
---
 drivers/watchdog/mena21_wdt.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/watchdog/mena21_wdt.c b/drivers/watchdog/mena21_wdt.c
index 25d5d2b8cfbe..05ca69042829 100644
--- a/drivers/watchdog/mena21_wdt.c
+++ b/drivers/watchdog/mena21_wdt.c
@@ -102,14 +102,15 @@ static int a21_wdt_set_timeout(struct watchdog_device *wdt,
 		return -EINVAL;
 	}
 
+	mutex_lock(&drv->lock);
+
 	if (timeout == 30 && wdt->timeout == 1) {
+		mutex_unlock(&drv->lock);
 		dev_err(wdt->parent,
 			"Transition from fast to slow mode not allowed\n");
 		return -EINVAL;
 	}
 
-	mutex_lock(&drv->lock);
-
 	if (timeout == 1)
 		gpio_set_value(drv->gpios[GPIO_WD_FAST], 1);
 	else
-- 
2.17.0