linux-kernel - Re: [RFC PATCH 2/9] ublk_drv: refactor ublk_cancel

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Date:   Mon, 29 Aug 2022 12:50:26 +0800
From:   Ziyang Zhang <ZiyangZhang@...ux.alibaba.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     axboe@...nel.dk, xiaoguang.wang@...ux.alibaba.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        joseph.qi@...ux.alibaba.com
Subject: Re: [RFC PATCH 2/9] ublk_drv: refactor ublk_cancel_queue()

On 2022/8/29 11:01, Ming Lei wrote:
> On Wed, Aug 24, 2022 at 01:47:37PM +0800, ZiyangZhang wrote:
>> Assume only a few FETCH_REQ ioucmds are sent to ublk_drv, then the
>> ubq_daemon exits, We have to call io_uring_cmd_done() for all ioucmds
>> received so that io_uring ctx will not leak.
>>
>> ublk_cancel_queue() may be called before START_DEV or after STOP_DEV,
>> we decrease ubq->nr_io_ready and clear UBLK_IO_FLAG_ACTIVE so that we
>> won't call io_uring_cmd_done() twice for one ioucmd to avoid UAF. Also
>> clearing UBLK_IO_FLAG_ACTIVE makes the code more reasonable.
>>
>> Signed-off-by: ZiyangZhang <ZiyangZhang@...ux.alibaba.com>
>> ---
>>  drivers/block/ublk_drv.c | 11 ++++++++---
>>  1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
>> index c39b67d7133d..e08f636b0b9d 100644
>> --- a/drivers/block/ublk_drv.c
>> +++ b/drivers/block/ublk_drv.c
>> @@ -967,18 +967,23 @@ static void ublk_cancel_queue(struct ublk_queue *ubq)
>>  {
>>  	int i;
>>  
>> -	if (!ublk_queue_ready(ubq))
>> +	if (!ubq->nr_io_ready)
>>  		return;
>>  
>>  	for (i = 0; i < ubq->q_depth; i++) {
>>  		struct ublk_io *io = &ubq->ios[i];
>>  
>> -		if (io->flags & UBLK_IO_FLAG_ACTIVE)
>> +		if (io->flags & UBLK_IO_FLAG_ACTIVE) {
>> +			pr_devel("%s: done old cmd: qid %d tag %d\n",
>> +					__func__, ubq->q_id, i);
>>  			io_uring_cmd_done(io->cmd, UBLK_IO_RES_ABORT, 0);
>> +			io->flags &= ~UBLK_IO_FLAG_ACTIVE;
>> +			ubq->nr_io_ready--;
>> +		}
>>  	}
>>  
>>  	/* all io commands are canceled */
>> -	ubq->nr_io_ready = 0;
>> +	WARN_ON_ONCE(ubq->nr_io_ready);
> 
> The change looks fine, but suggest to add comment like the
> following given the above WARN_ON_ONCE() change isn't obvious.
> 
> ```
> 1) ublk_cancel_dev() is called before sending START_DEV(), ->mutex
> provides protection on above update.
> 
> 2) ublk_cancel_dev() is called after sending START_DEV(), disk is
> deleted first, UBLK_IO_RES_ABORT is returned so that any new io
> command can't be issued to driver, so updating on io flags and
> nr_io_ready is safe here
> 
> Also ->nr_io_ready is guaranteed to become zero after ublk_cance_queue
> returns since request queue is either frozen or not present in both two cases.
> 
> ```
> 

Thanks for your advice, Ming.

Regards,
Zhang