linux-kernel - Re: [PATCH v2] device property: fix of node refcount leak in fwnode_graph_get_next

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Date:   Tue, 22 Nov 2022 14:54:36 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Yang Yingliang <yangyingliang@...wei.com>
Cc:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        djrscally@...il.com, heikki.krogerus@...ux.intel.com,
        sakari.ailus@...ux.intel.com, gregkh@...uxfoundation.org,
        rafael@...nel.org
Subject: Re: [PATCH v2] device property: fix of node refcount leak in
 fwnode_graph_get_next_endpoint()

On Tue, Nov 22, 2022 at 08:00:39PM +0800, Yang Yingliang wrote:
> The 'parent' returned by fwnode_graph_get_port_parent()
> with refcount incremented when 'prev' is not null, it

NULL

> needs be put when finish using it.
> 
> Because the parent is const, introduce a new variable to
> store the returned fwnode, then put it before returning
> from fwnode_graph_get_next_endpoint().

...

>  fwnode_graph_get_next_endpoint(const struct fwnode_handle *fwnode,
>  			       struct fwnode_handle *prev)
>  {
> +	struct fwnode_handle *ep, *port_parent = NULL;
>  	const struct fwnode_handle *parent;
> -	struct fwnode_handle *ep;
>  
>  	/*
>  	 * If this function is in a loop and the previous iteration returned
>  	 * an endpoint from fwnode->secondary, then we need to use the secondary
>  	 * as parent rather than @fwnode.
>  	 */
> -	if (prev)
> -		parent = fwnode_graph_get_port_parent(prev);
> -	else
> +	if (prev) {
> +		port_parent = fwnode_graph_get_port_parent(prev);
> +		parent = port_parent;
> +	} else {
>  		parent = fwnode;
> +	}
>  	if (IS_ERR_OR_NULL(parent))
>  		return NULL;
>  
>  	ep = fwnode_call_ptr_op(parent, graph_get_next_endpoint, prev);
> -	if (ep)
> +	if (ep) {
> +		fwnode_handle_put(port_parent);
>  		return ep;
> +	}
>  
> -	return fwnode_graph_get_next_endpoint(parent->secondary, NULL);
> +	ep = fwnode_graph_get_next_endpoint(parent->secondary, NULL);
> +	fwnode_handle_put(port_parent);
> +	return ep;

It seems too complicated for the simple fix.

As I said, just drop const qualifier and add fwnode_handle_get() in the 'else'
branch. This will allow you to drop if (prev) at the end.

-- 
With Best Regards,
Andy Shevchenko