linux-kernel - Re: [PATCH] mm: fix use-after-free in sys_remap_file

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Message-ID: <20131213062427.GH8167@moon>
Date:	Fri, 13 Dec 2013 10:24:27 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michel Lespinasse <walken@...gle.com>,
	Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
	PaX Team <pageexec@...email.hu>,
	Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH] mm: fix use-after-free in sys_remap_file_pages

On Thu, Dec 12, 2013 at 10:41:18PM -0500, Rik van Riel wrote:
> 
> If the vma has been freed by the time the code jumps to the
> out label (because it was freed by a function called from
> mmap_region), surely it will also already have been freed
> by the time this patch dereferences it?
> 
> Also, setting vma = NULL to avoid the if (vma) branch at
> the out: label is unnecessarily obfuscated. Lets make things
> clear by documenting what is going on, and having a label
> after that dereference.

This patch is a bit easier to read, at least for me. And if
I understand the code flow right, the issue is due to
remap_file_pages -> mmap_region -> find_vma_links -> do_munmap.
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