[PATCH] watchdog: core: assign parent with devm registration

[PATCH] watchdog: core: assign parent with devm registration

[Rosen Penev]

If the user did not pass a parent in the struct watchdog_device
then use the device used for devres as parent.

This is quite intuitive and can help avoiding having to
assign parent explicitly in every driver using devres
to add the watchdog_device.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 Linus: hope you don't mind me flat out copying the description from
 https://lore.kernel.org/all/20260427-gpio-mmio-more-v3-1-fe1882351424@kernel.org/
 drivers/watchdog/watchdog_core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
index 8300520688d0..726c85debabc 100644
--- a/drivers/watchdog/watchdog_core.c
+++ b/drivers/watchdog/watchdog_core.c
@@ -440,6 +440,13 @@ int devm_watchdog_register_device(struct device *dev,
 	if (!rcwdd)
 		return -ENOMEM;
 
+	/*
+	 * We are passing the devres device here so if the user did not pass
+	 * another parent, it's this one.
+	 */
+	if (!wdd->parent)
+		wdd->parent = dev;
+
 	ret = watchdog_register_device(wdd);
 	if (!ret) {
 		*rcwdd = wdd;
-- 
2.54.0

Re: [PATCH] watchdog: core: assign parent with devm registration

[Guenter Roeck]

On 5/23/26 19:23, Rosen Penev wrote:
> If the user did not pass a parent in the struct watchdog_device
> then use the device used for devres as parent.
> 
> This is quite intuitive and can help avoiding having to
> assign parent explicitly in every driver using devres
> to add the watchdog_device.
> 
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
>   Linus: hope you don't mind me flat out copying the description from
>   https://lore.kernel.org/all/20260427-gpio-mmio-more-v3-1-fe1882351424@kernel.org/
>   drivers/watchdog/watchdog_core.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
> index 8300520688d0..726c85debabc 100644
> --- a/drivers/watchdog/watchdog_core.c
> +++ b/drivers/watchdog/watchdog_core.c
> @@ -440,6 +440,13 @@ int devm_watchdog_register_device(struct device *dev,
>   	if (!rcwdd)
>   		return -ENOMEM;
>   
> +	/*
> +	 * We are passing the devres device here so if the user did not pass
> +	 * another parent, it's this one.
> +	 */
> +	if (!wdd->parent)
> +		wdd->parent = dev;
> +

I understand that you consider it to be garbage, but in my opinion Sashiko has a
point. If the watchdog device data structure is static, wdd->parent will be retained
over multiple remove/reinsert instantiations of the driver, which in turn would result
in subsequent UAF. That means I can not accept your patch.

Guenter

Re: [PATCH] watchdog: core: assign parent with devm registration

[Linus Walleij]

On Sun, May 24, 2026 at 5:22 PM Guenter Roeck <linux@roeck-us.net> wrote:

> I understand that you consider it to be garbage, but in my opinion Sashiko has a
> point. If the watchdog device data structure is static, wdd->parent will be retained
> over multiple remove/reinsert instantiations of the driver, which in turn would result
> in subsequent UAF. That means I can not accept your patch.

Hm! I wonder if that is a problem for my patch as well. We do have
GPIO dongles that can be plugged in/out repeatedly....

Yours,
Linus Walleij