linux-kernel - Re: [PATCH] blkcg: Fix use-after-free of q->root_blkg and q->root

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Message-ID: <20121018212133.GL13370@google.com>
Date:	Thu, 18 Oct 2012 14:21:33 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Jun'ichi Nomura <j-nomura@...jp.nec.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Vivek Goyal <vgoyal@...hat.com>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH] blkcg: Fix use-after-free of q->root_blkg and
 q->root_rl.blkg

On Wed, Oct 17, 2012 at 05:45:36PM +0900, Jun'ichi Nomura wrote:
> blk_put_rl() does not call blkg_put() for q->root_rl because we
> don't take request list reference on q->root_blkg.
> However, if root_blkg is once attached then detached (freed),
> blk_put_rl() is confused by the bogus pointer in q->root_blkg.
> 
> For example, with !CONFIG_BLK_DEV_THROTTLING &&
> CONFIG_CFQ_GROUP_IOSCHED,
> switching IO scheduler from cfq to deadline will cause system stall
> after the following warning with 3.6:
...
> This patch clears q->root_blkg and q->root_rl.blkg when root blkg
> is destroyed.
> 
> Signed-off-by: Jun'ichi Nomura <j-nomura@...jp.nec.com>
> Acked-by: Vivek Goyal <vgoyal@...hat.com>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Jens Axboe <axboe@...nel.dk>

Acked-by: Tejun Heo <tj@...nel.org>

Jens, this one needs Cc: stable.

Thanks.

-- 
tejun
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