linux-ext4 - Re: [PATCH v2 01/11] rbtree: Fix rbtree_postorder_for_each_entry

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Date:	Thu, 7 Nov 2013 13:38:00 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Cody P Schafer <cody@...ux.vnet.ibm.com>
Cc:	EXT4 <linux-ext4@...r.kernel.org>, Jan Kara <jack@...e.cz>,
	rostedt@...dmis.org, Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 01/11] rbtree: Fix
 rbtree_postorder_for_each_entry_safe() iterator

On Wed,  6 Nov 2013 17:42:30 -0800 Cody P Schafer <cody@...ux.vnet.ibm.com> wrote:

> The iterator rbtree_postorder_for_each_entry_safe() relies on pointer
> underflow behavior when testing for loop termination. In particular
> it expects that
>   &rb_entry(NULL, type, field)->field
> is NULL. But the result of this expression is not defined by a C standard
> and some gcc versions (e.g. 4.3.4) assume the above expression can never
> be equal to NULL. The net result is an oops because the iteration is not
> properly terminated.
> 
> Fix the problem by modifying the iterator to avoid pointer underflows.

So the sole caller is in zswap.c.  Is that code actually generating oopses?

IOW, is there any need to fix this in 3.12 or earlier?
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