This is a note to let you know that I've just added the patch titled
watchdog: set cdev owner before adding
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
watchdog-set-cdev-owner-before-adding.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 42efbf53dca3da639292319459e90732193af19c
Author: Curtis Klein <curtis.klein@xxxxxxx>
Date: Tue Dec 5 11:05:22 2023 -0800
watchdog: set cdev owner before adding
[ Upstream commit 38d75297745f04206db9c29bdd75557f0344c7cc ]
When the new watchdog character device is registered, it becomes
available for opening. This creates a race where userspace may open the
device before the character device's owner is set. This results in an
imbalance in module_get calls as the cdev_get in cdev_open will not
increment the reference count on the watchdog driver module.
This causes problems when the watchdog character device is released as
the module loader's reference will also be released. This makes it
impossible to open the watchdog device later on as it now appears that
the module is being unloaded. The open will fail with -ENXIO from
chrdev_open.
The legacy watchdog device will fail with -EBUSY from the try_module_get
in watchdog_open because it's module owner is the watchdog core module
so it can still be opened but it will fail to get a refcount on the
underlying watchdog device driver.
Fixes: 72139dfa2464 ("watchdog: Fix the race between the release of watchdog_core_data and cdev")
Signed-off-by: Curtis Klein <curtis.klein@xxxxxxx>
Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20231205190522.55153-1-curtis.klein@xxxxxxx
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Wim Van Sebroeck <wim@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 808896c9e1c2..686c9f0f3d63 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -980,6 +980,7 @@ static int watchdog_cdev_register(struct watchdog_device *wdd)
/* Fill in the data structures */
cdev_init(&wd_data->cdev, &watchdog_fops);
+ wd_data->cdev.owner = wdd->ops->owner;
/* Add the device */
err = cdev_device_add(&wd_data->cdev, &wd_data->dev);
@@ -994,8 +995,6 @@ static int watchdog_cdev_register(struct watchdog_device *wdd)
return err;
}
- wd_data->cdev.owner = wdd->ops->owner;
-
/* Record time of most recent heartbeat as 'just before now'. */
wd_data->last_hw_keepalive = ktime_sub(ktime_get(), 1);
