From: "yukuai (C)" <yukuai3@huawei.com>
To: Ming Lei <ming.lei@redhat.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 09:54:09 +0800 [thread overview]
Message-ID: <8f1849a3-6bf2-6b14-7ef9-4969a9a5425b@huawei.com> (raw)
In-Reply-To: <YUCzr2ysb+vJ1x0W@T590>
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?
Thanks
Kuai
next prev parent reply other threads:[~2021-09-15 1:54 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) [this message]
2021-09-15 3:16 ` Ming Lei
2021-09-15 3:36 ` yukuai (C)
2021-09-15 3:46 ` Ming Lei
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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