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

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Message-ID: <6599ad830902101754w50a64b0ds126510360fdef28e@mail.gmail.com>
Date:	Tue, 10 Feb 2009 17:54:07 -0800
From:	Paul Menage <menage@...gle.com>
To:	Al Viro <viro@...iv.linux.org.uk>
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 5:19 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> So you can't wrap sget() into a mutex that might be grabbed at some
> point of ->kill_sb() or it'll wait forever in that scenario.

Good point.

>
> So no exclusion is needed there at all.  If you don't want later remount
> of the first mount to affect these flags of second one you shouldn't share
> the superblock at all, obviously...

I have plans for some slightly more complex state in that structure -
I'll probably just add a spinlock around accesses to those fields so
that we can avoid exposing any inconsistent state.

Paul
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