Re: [PATCH] xfs: fix use-after-free on CIL context on shutdown

[Christoph Hellwig <hch@infradead.org>]

On Thu, Jun 11, 2020 at 12:45:03PM +1000, 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.
> 
> Fixes: 0e7ab7efe7745 ("xfs: Throttle commits on delayed background CIL push")
> Reported-by: Yu Kuai <yukuai3@huawei.com>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>