4.15-stable review patch. If anyone has any objections, please let me know.
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From: Guenter Roeck linux@roeck-us.net
[ Upstream commit 4bcd615fad6adddc68b058d498b30a9e0e0db77a ]
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 linux@roeck-us.net Signed-off-by: Wim Van Sebroeck wim@iguana.be Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/watchdog/watchdog_dev.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
--- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -769,6 +769,7 @@ static int watchdog_open(struct inode *i { 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 *i * 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 *i
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 */