Re: [RFC PATCH 2/9] ublk_drv: refactor ublk_cancel_queue()

Ming Lei
2022-08-29T03:01:37Z

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@linux.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,
Ming