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: Tue, 14 Sep 2021 15:13:38 +0800 [thread overview]
Message-ID: <374c6b37-b4b2-fe01-66be-ca2dbbc283e9@huawei.com> (raw)
In-Reply-To: <YUBE4BJ7+kN1c4l8@T590>
On 2021/09/14 14:44, Ming Lei wrote:
> On Tue, Sep 14, 2021 at 11:11:06AM +0800, yukuai (C) wrote:
>> On 2021/09/14 9:11, Ming Lei wrote:
>>> On Thu, Sep 09, 2021 at 10:12:55PM +0800, Yu Kuai wrote:
>>>> blk_mq_tag_to_rq() can only ensure to return valid request in
>>>> following situation:
>>>>
>>>> 1) client send request message to server first
>>>> submit_bio
>>>> ...
>>>> blk_mq_get_tag
>>>> ...
>>>> blk_mq_get_driver_tag
>>>> ...
>>>> nbd_queue_rq
>>>> nbd_handle_cmd
>>>> nbd_send_cmd
>>>>
>>>> 2) client receive respond message from server
>>>> recv_work
>>>> nbd_read_stat
>>>> blk_mq_tag_to_rq
>>>>
>>>> If step 1) is missing, blk_mq_tag_to_rq() will return a stale
>>>> request, which might be freed. Thus convert to use
>>>> blk_mq_find_and_get_req() to make sure the returned request is not
>>>> freed.
>>>
>>> But NBD_CMD_INFLIGHT has been added for checking if the reply is
>>> expected, do we still need blk_mq_find_and_get_req() for covering
>>> this issue? BTW, request and its payload is pre-allocated, so there
>>> isn't real use-after-free.
>>
>> Hi, Ming
>>
>> Checking NBD_CMD_INFLIGHT relied on the request founded by tag is valid,
>> not the other way round.
>>
>> nbd_read_stat
>> req = blk_mq_tag_to_rq()
>> cmd = blk_mq_rq_to_pdu(req)
>> mutex_lock(cmd->lock)
>> checking NBD_CMD_INFLIGHT
>
> Request and its payload is pre-allocated, and either req->ref or cmd->lock can
> serve the same purpose here. Once cmd->lock is held, you can check if the cmd is
> inflight or not. If it isn't inflight, just return -ENOENT. Is there any
> problem to handle in this way?
Hi, Ming
in nbd_read_stat:
1) get a request by tag first
2) get nbd_cmd by the request
3) hold cmd->lock and check if cmd is inflight
If we want to check if the cmd is inflight in step 3), we have to do
setp 1) and 2) first. As I explained in patch 0, blk_mq_tag_to_rq()
can't make sure the returned request is not freed:
nbd_read_stat
blk_mq_sched_free_requests
blk_mq_free_rqs
blk_mq_tag_to_rq
-> get rq before clear mapping
blk_mq_clear_rq_mapping
__free_pages -> rq is freed
blk_mq_request_started -> UAF
Thanks,
Kuai
next prev parent reply other threads:[~2021-09-14 7:13 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) [this message]
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
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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