linux-kernel - Re: [PATCH] cgroups: fix possible use after free

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Message-ID: <20090210124527.GA28946@ZenIV.linux.org.uk>
Date:	Tue, 10 Feb 2009 12:45:27 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Paul Menage <menage@...gle.com>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH] cgroups: fix possible use after free

On Tue, Feb 10, 2009 at 02:15:36AM -0800, Paul Menage wrote:
> On Tue, Feb 10, 2009 at 1:31 AM, Li Zefan <lizf@...fujitsu.com> wrote:
> > In cgroup_kill_sb(), root is freed before sb is detached from the list,
> > so another sget() may find this sb and call cgroup_test_super(),
> > which will access the root that has been freed.
> 
> I think that I'd assumed that by the time we get to cgroup_kill_sb()
> there's no chance of the sb being resurrected by sget().

There is none.  grab_super() will fail to get it, so sget() will go
through retry logics.  Which doesn't mean that test won't be called
on it in the meanwhile.
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