From: Guenter Roeck <linux@roeck-us.net>
To: Curtis Klein <curtis.klein@hpe.com>,
wim@linux-watchdog.org, haokexin@gmail.com,
linux-watchdog@vger.kernel.org
Subject: Re: [PATCH] watchdog: set cdev owner before adding
Date: Tue, 5 Dec 2023 11:13:28 -0800 [thread overview]
Message-ID: <a1d11e74-9c8b-463a-a237-dae651f4cda7@roeck-us.net> (raw)
In-Reply-To: <20231205190522.55153-1-curtis.klein@hpe.com>
On 12/5/23 11:05, Curtis Klein wrote:
> 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@hpe.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
> ---
> drivers/watchdog/watchdog_dev.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index 15df74e11a59..e2bd266b1b5b 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -1073,6 +1073,7 @@ 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);
> @@ -1087,8 +1088,6 @@ 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);
> watchdog_set_open_deadline(wd_data);
prev parent reply other threads:[~2023-12-05 19:13 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-05 19:05 [PATCH] watchdog: set cdev owner before adding Curtis Klein
2023-12-05 19:13 ` Guenter Roeck [this message]
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