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

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Message-ID: <75602dce-0780-e51a-c8c9-d1820ddf3e2b@huawei.com>
Date:   Tue, 22 Nov 2022 21:12:41 +0800
From:   Yang Yingliang <yangyingliang@...wei.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.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 2022/11/22 20:54, Andy Shevchenko wrote:
> 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.

fwnode is const, fwnode_handle_get doesn't accept this type.

>