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watchdog: Fix potential kref imbalance when opening watchdog

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[ 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>
This commit is contained in:
Guenter Roeck 2017-09-25 09:17:01 -07:00 committed by Greg Kroah-Hartman
parent 32dc29cf72
commit 6ad31f8583
1 changed files with 4 additions and 2 deletions
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6
drivers/watchdog/watchdog_dev.c
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@ -760,6 +760,7 @@ 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 */
@ -779,7 +780,8 @@ 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;
}
@ -790,7 +792,7 @@ 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 */