From 4bcd615fad6adddc68b058d498b30a9e0e0db77a Mon Sep 17 00:00:00 2001 From: Guenter Roeck Date: Mon, 25 Sep 2017 09:17:01 -0700 Subject: [PATCH] watchdog: Fix potential kref imbalance when opening watchdog If a watchdog driver's open function sets WDOG_HW_RUNNING with the expectation that the watchdog can not be stopped, but then stops the watchdog anyway in its stop function, kref_get() wil not be called in watchdog_open(). If the watchdog then stops on close, WDOG_HW_RUNNING will be cleared and kref_put() will be called, causing a kref imbalance. As result the character device data structure will be released, which in turn will cause the system to crash on the next call to watchdog_open(). Fixes: ee142889e32f5 ("watchdog: Introduce WDOG_HW_RUNNING flag") Signed-off-by: Guenter Roeck Signed-off-by: Wim Van Sebroeck --- drivers/watchdog/watchdog_dev.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c index 1e971a5..12fe47d 100644 --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -769,6 +769,7 @@ static int watchdog_open(struct inode *inode, struct file *file) { struct watchdog_core_data *wd_data; struct watchdog_device *wdd; + bool hw_running; int err; /* Get the corresponding watchdog device */ @@ -788,7 +789,8 @@ static int watchdog_open(struct inode *inode, struct file *file) * If the /dev/watchdog device is open, we don't want the module * to be unloaded. */ - if (!watchdog_hw_running(wdd) && !try_module_get(wdd->ops->owner)) { + hw_running = watchdog_hw_running(wdd); + if (!hw_running && !try_module_get(wdd->ops->owner)) { err = -EBUSY; goto out_clear; } @@ -799,7 +801,7 @@ static int watchdog_open(struct inode *inode, struct file *file) file->private_data = wd_data; - if (!watchdog_hw_running(wdd)) + if (!hw_running) kref_get(&wd_data->kref); /* dev/watchdog is a virtual (and thus non-seekable) filesystem */ -- 2.7.4