Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] xfs: fix use-after-free on CIL context on shutdown
To:     Dave Chinner <david@fromorbit.com>
CC:     <darrick.wong@oracle.com>, <linux-xfs@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <yi.zhang@huawei.com>
References: <20200611013952.2589997-1-yukuai3@huawei.com>
 <20200611022848.GQ2040@dread.disaster.area>
 <20200611024503.GR2040@dread.disaster.area>
From:   "yukuai (C)" <yukuai3@huawei.com>
Message-ID: <9d13cb34-5625-ed84-71f5-ad48204589a1@huawei.com>
Date:   Tue, 16 Jun 2020 09:16:09 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
 Thunderbird/60.8.0
MIME-Version: 1.0
In-Reply-To: <20200611024503.GR2040@dread.disaster.area>
Content-Type: text/plain; charset="gbk"; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 2020/6/11 10:45, Dave Chinner wrote:
> 
> From: Dave Chinner <dchinner@redhat.com>
> 
> xlog_wait() on the CIL context can reference a freed context if the
> waiter doesn't get scheduled before the CIL context is freed. This
> can happen when a task is on the hard throttle and the CIL push
> aborts due to a shutdown. This was detected by generic/019:
> 
> thread 1			thread 2
> 
> __xfs_trans_commit
>   xfs_log_commit_cil
>    <CIL size over hard throttle limit>
>    xlog_wait
>     schedule
> 				xlog_cil_push_work
> 				wake_up_all
> 				<shutdown aborts commit>
> 				xlog_cil_committed
> 				kmem_free
> 
>     remove_wait_queue
>      spin_lock_irqsave --> UAF
> 
> Fix it by moving the wait queue to the CIL rather than keeping it in
> in the CIL context that gets freed on push completion. Because the
> wait queue is now independent of the CIL context and we might have
> multiple contexts in flight at once, only wake the waiters on the
> push throttle when the context we are pushing is over the hard
> throttle size threshold.

Hi, Dave,

How do you think about the following fix:

1. use autoremove_wake_func(), and remove remove_wait_queue() to
avoid UAF.
2. add finish_wait().

@@ -576,12 +576,13 @@ xlog_wait(
                 __releases(lock)
  {
         DECLARE_WAITQUEUE(wait, current);
+       wait.func = autoremove_wake_function;

         add_wait_queue_exclusive(wq, &wait);
         __set_current_state(TASK_UNINTERRUPTIBLE);
         spin_unlock(lock);
         schedule();
-       remove_wait_queue(wq, &wait);
+       finish_wait(wq, &wait);
  }

Best regards!
Yu Kuai