Re: [PATCH RFC] blk-mq: fix potential uaf for 'queue_hw_ctx'

[yukuai (C)]

在 2022/02/24 10:15, Ming Lei 写道:
> > Hi, Ming
> >
> > If blk_mq_quiesce_queue() is called from __blk_mq_update_nr_hw_queues()
> > first, and then swithing elevator to none won't trigger the problem.
> > However, what if blk_mq_unquiesce_queue() from switching elevator
> > decrease quiesce_depth to 0 first, and then blk_mq_quiesce_queue() is
> > called from __blk_mq_update_nr_hw_queues(), it seems to me such
> > concurrent scenarios still exist.
>
> No, the scenario won't exist, once blk_mq_quiesce_queue() returns, it is
> guaranteed that:
>
> - in-progress run queue is drained
> - no new run queue can be started

I understand that... What I mean about the concurrent scenario is that
reading queue_hw_ctx in blk_mq_run_hw_queues(), not the actual run
queue blk_mq_run_hw_queue():

t1                              t2
elevator_switch
 blk_mq_quiesce_queue -> quiesce_depth = 1
 blk_mq_unquiesce_queue-> quiesce_depth = 0
  blk_mq_run_hw_queues
                                 __blk_mq_update_nr_hw_queues
                                  blk_mq_quiesce_queue
   queue_for_each_hw_ctx
   -> quiesce_queue can't prevent reading queue_hw_ctx
    blk_mq_run_hw_queue
    //need_run is always false, nothing to do

Am I missing something about blk_mq_quiesce_queue ?

Thanks,
Kuai