linux-kernel - Re: [PATCH 2/2] device property: fix UAF in device_get_next_child

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Message-ID: <Z0huCS4Z7dkgpCQ8@smile.fi.intel.com>
Date: Thu, 28 Nov 2024 15:20:09 +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 2/2] device property: fix UAF in
 device_get_next_child_node()

On Wed, Nov 27, 2024 at 09:39:35PM -0800, Dmitry Torokhov wrote:
> fwnode_get_next_child_node() always drops reference to the node passed
> as the "child" argument,

As commented previously,it might be just a documentation bug. So, please
elaborate on the use case before this patch that leads to an issue.

> which makes "child" pointer no longer valid
> and we can not use it to scan the secondary node in case there are no
> more children in primary one.
> 
> Also, it is not obvious whether it is safe to pass children of the
> secondary node to fwnode_get_next_child_node() called on the primary
> node in subsequent calls to device_get_next_child_node().
> 
> Fix the issue by checking whether the child node passed in is indeed a
> child of primary or secondary node, and do not call
> fwnode_get_next_child_node() for the wrong parent node. Also set the
> "child" to NULL after unsuccessful call to fwnode_get_next_child_node()
> on primary node to make sure secondary node's children are scanned from
> the beginning.

To me it sounds over complicated. Why not just take reference to the child once
more and put it after we find next in either cases? Current solution provides
a lot of duplication and makes function less understandable.

-- 
With Best Regards,
Andy Shevchenko