linux-kernel - Re: [PATCH 1/2] device property: do not leak child nodes when using NULL/error pointers

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Message-ID: <Z0hsbNqXSkQjsR1v@smile.fi.intel.com>
Date: Thu, 28 Nov 2024 15:13:16 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Daniel Scally <djrscally@...il.com>, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] device property: do not leak child nodes when using
 NULL/error pointers

On Wed, Nov 27, 2024 at 09:39:34PM -0800, Dmitry Torokhov wrote:
> The documentation to various API calls that locate children for a given
> fwnode (such as fwnode_get_next_available_child_node() or
> device_get_next_child_node()) states that the reference to the node
> passed in "child" argument is dropped unconditionally, however the
> change that added checks for the main node to be NULL or error pointer
> broke this promise.

This commit message doesn't explain a use case. Hence it might be just
a documentation issue, please elaborate.

> Add missing fwnode_handle_put() calls to restore the documented
> behavior.

...

While at it, please fix the kernel-doc (missing Return section).

>  {
> +	if (IS_ERR_OR_NULL(fwnode) ||

Unneeded check as fwnode_has_op() has it already.

> +	    !fwnode_has_op(fwnode, get_next_child_node)) {
> +		fwnode_handle_put(child);
> +		return NULL;
> +	}

>  	return fwnode_call_ptr_op(fwnode, get_next_child_node, child);

Now it's useless to call the macro, you can simply take the direct call.

>  }

...

> @@ struct fwnode_handle *device_get_next_child_node(const struct device *dev,
>  	const struct fwnode_handle *fwnode = dev_fwnode(dev);
>  	struct fwnode_handle *next;

> -	if (IS_ERR_OR_NULL(fwnode))
> +	if (IS_ERR_OR_NULL(fwnode)) {
> +		fwnode_handle_put(child);
>  		return NULL;
> +	}

>  	/* Try to find a child in primary fwnode */
>  	next = fwnode_get_next_child_node(fwnode, child);

So, why not just moving the original check (w/o dropping the reference) here?
Wouldn't it have the same effect w/o explicit call to the fwnode_handle_put()?

-- 
With Best Regards,
Andy Shevchenko