software node: Handle software node injection to an existing device properly

The function software_node_notify() - the function that creates
and removes the symlinks between the node and the device - was
called unconditionally in device_add_software_node() and
device_remove_software_node(), but it needs to be called in
those functions only in the special case where the node is
added to a device that has already been registered.

This fixes NULL pointer dereference that happens if
device_remove_software_node() is used with device that was
never registered.

Fixes: b622b24519f5 ("software node: Allow node addition to already existing device")
Reported-and-tested-by: Dominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
---
 drivers/base/swnode.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

On Wed, Jun 23, 2021 at 3:14 PM Heikki Krogerus
<heikki.krogerus@linux.intel.com> wrote:
>
> The function software_node_notify() - the function that creates
> and removes the symlinks between the node and the device - was
> called unconditionally in device_add_software_node() and
> device_remove_software_node(), but it needs to be called in
> those functions only in the special case where the node is
> added to a device that has already been registered.
>
> This fixes NULL pointer dereference that happens if
> device_remove_software_node() is used with device that was
> never registered.
>
> Fixes: b622b24519f5 ("software node: Allow node addition to already existing device")
> Reported-and-tested-by: Dominik Brodowski <linux@dominikbrodowski.net>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>

Applied, thanks!

It may not make it into 5.13 though due to the timing.

> ---
>  drivers/base/swnode.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
> index 3cc11b813f28c..d1f1a82401207 100644
> --- a/drivers/base/swnode.c
> +++ b/drivers/base/swnode.c
> @@ -1045,7 +1045,15 @@ int device_add_software_node(struct device *dev, const struct software_node *nod
>         }
>
>         set_secondary_fwnode(dev, &swnode->fwnode);
> -       software_node_notify(dev, KOBJ_ADD);
> +
> +       /*
> +        * If the device has been fully registered by the time this function is
> +        * called, software_node_notify() must be called separately so that the
> +        * symlinks get created and the reference count of the node is kept in
> +        * balance.
> +        */
> +       if (device_is_registered(dev))
> +               software_node_notify(dev, KOBJ_ADD);
>
>         return 0;
>  }
> @@ -1065,7 +1073,8 @@ void device_remove_software_node(struct device *dev)
>         if (!swnode)
>                 return;
>
> -       software_node_notify(dev, KOBJ_REMOVE);
> +       if (device_is_registered(dev))
> +               software_node_notify(dev, KOBJ_REMOVE);
>         set_secondary_fwnode(dev, NULL);
>         kobject_put(&swnode->kobj);
>  }
> @@ -1119,8 +1128,7 @@ int software_node_notify(struct device *dev, unsigned long action)
>
>         switch (action) {
>         case KOBJ_ADD:
> -               ret = sysfs_create_link_nowarn(&dev->kobj, &swnode->kobj,
> -                                              "software_node");
> +               ret = sysfs_create_link(&dev->kobj, &swnode->kobj, "software_node");
>                 if (ret)
>                         break;
>
> --
> 2.30.2
>