From: Ming Lei <ming.lei@redhat.com>
To: "yukuai (C)" <yukuai3@huawei.com>
Cc: axboe@kernel.dk, josef@toxicpanda.com, hch@infradead.org,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
nbd@other.debian.org, yi.zhang@huawei.com
Subject: Re: [PATCH v5 5/6] nbd: convert to use blk_mq_find_and_get_req()
Date: Wed, 15 Sep 2021 11:46:21 +0800 [thread overview]
Message-ID: <YUFsja+cIxhFY7c0@T590> (raw)
In-Reply-To: <60f68f6b-5fff-6a39-b77b-4bbb86f1c87e@huawei.com>
On Wed, Sep 15, 2021 at 11:36:47AM +0800, yukuai (C) wrote:
> On 2021/09/15 11:16, Ming Lei wrote:
> > On Wed, Sep 15, 2021 at 09:54:09AM +0800, yukuai (C) wrote:
> > > On 2021/09/14 22:37, Ming Lei wrote:
> > > > On Tue, Sep 14, 2021 at 05:19:31PM +0800, yukuai (C) wrote:
> > > > > On 在 2021/09/14 15:46, Ming Lei wrote:
> > > > >
> > > > > > If the above can happen, blk_mq_find_and_get_req() may not fix it too, just
> > > > > > wondering why not take the following simpler way for avoiding the UAF?
> > > > > >
> > > > > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> > > > > > index 5170a630778d..dfa5cce71f66 100644
> > > > > > --- a/drivers/block/nbd.c
> > > > > > +++ b/drivers/block/nbd.c
> > > > > > @@ -795,9 +795,13 @@ static void recv_work(struct work_struct *work)
> > > > > > work);
> > > > > > struct nbd_device *nbd = args->nbd;
> > > > > > struct nbd_config *config = nbd->config;
> > > > > > + struct request_queue *q = nbd->disk->queue;
> > > > > > struct nbd_cmd *cmd;
> > > > > > struct request *rq;
> > > > > > + if (!percpu_ref_tryget(&q->q_usage_counter))
> > > > > > + return;
> > > > > > +
> > > > > > while (1) {
> > > > > > cmd = nbd_read_stat(nbd, args->index);
> > > > > > if (IS_ERR(cmd)) {
> > > > > > @@ -813,6 +817,7 @@ static void recv_work(struct work_struct *work)
> > > > > > if (likely(!blk_should_fake_timeout(rq->q)))
> > > > > > blk_mq_complete_request(rq);
> > > > > > }
> > > > > > + blk_queue_exit(q);
> > > > > > nbd_config_put(nbd);
> > > > > > atomic_dec(&config->recv_threads);
> > > > > > wake_up(&config->recv_wq);
> > > > > >
> > > > >
> > > > > Hi, Ming
> > > > >
> > > > > This apporch is wrong.
> > > > >
> > > > > If blk_mq_freeze_queue() is called, and nbd is waiting for all
> > > > > request to complete. percpu_ref_tryget() will fail here, and deadlock
> > > > > will occur because request can't complete in recv_work().
> > > >
> > > > No, percpu_ref_tryget() won't fail until ->q_usage_counter is zero, when
> > > > it is perfectly fine to do nothing in recv_work().
> > > >
> > >
> > > Hi Ming
> > >
> > > This apporch is a good idea, however we should not get q_usage_counter
> > > in reccv_work(), because It will block freeze queue.
> > >
> > > How about get q_usage_counter in nbd_read_stat(), and put in error path
> > > or after request completion?
> >
> > OK, looks I missed that nbd_read_stat() needs to wait for incoming reply
> > first, so how about the following change by partitioning nbd_read_stat()
> > into nbd_read_reply() and nbd_handle_reply()?
>
> Hi, Ming
>
> The change looks good to me.
>
> Do you want to send a patch to fix this?
I guess you may add inflight check or sort of change in nbd_read_stat(), so feel
free to fold it into your series.
Thanks,
Ming
next prev parent reply other threads:[~2021-09-15 3:46 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-09 14:12 [PATCH v5 0/6] handle unexpected message from server Yu Kuai
2021-09-09 14:12 ` [PATCH v5 1/6] nbd: don't handle response without a corresponding request message Yu Kuai
2021-09-14 0:54 ` Ming Lei
2021-09-09 14:12 ` [PATCH v5 2/6] nbd: make sure request completion won't concurrent Yu Kuai
2021-09-14 0:57 ` Ming Lei
2021-09-14 3:11 ` yukuai (C)
2021-09-09 14:12 ` [PATCH v5 3/6] nbd: check sock index in nbd_read_stat() Yu Kuai
2021-09-09 14:12 ` [PATCH v5 4/6] blk-mq: export two symbols to get request by tag Yu Kuai
2021-09-09 14:12 ` [PATCH v5 5/6] nbd: convert to use blk_mq_find_and_get_req() Yu Kuai
2021-09-14 1:11 ` Ming Lei
2021-09-14 3:11 ` yukuai (C)
2021-09-14 6:44 ` Ming Lei
2021-09-14 7:13 ` yukuai (C)
2021-09-14 7:46 ` Ming Lei
2021-09-14 9:08 ` yukuai (C)
2021-09-14 9:12 ` yukuai (C)
2021-09-14 14:33 ` Ming Lei
2021-09-14 9:19 ` yukuai (C)
2021-09-14 14:37 ` Ming Lei
2021-09-15 1:54 ` yukuai (C)
2021-09-15 3:16 ` Ming Lei
2021-09-15 3:36 ` yukuai (C)
2021-09-15 3:46 ` Ming Lei [this message]
2021-09-09 14:12 ` [PATCH v5 6/6] nbd: don't start request if nbd_queue_rq() failed Yu Kuai
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