linux-kernel - Re: [patch v8 3/7] nbd: check sock index in nbd_read

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Date:   Wed, 22 Sep 2021 20:21:26 +0800
From:   "yukuai (C)" <yukuai3@...wei.com>
To:     Ming Lei <ming.lei@...hat.com>
CC:     <josef@...icpanda.com>, <axboe@...nel.dk>, <hch@...radead.org>,
        <linux-block@...r.kernel.org>, <nbd@...er.debian.org>,
        <linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>
Subject: Re: [patch v8 3/7] nbd: check sock index in nbd_read_stat()

On 2021/09/22 17:22, Ming Lei wrote:
> On Sun, Sep 19, 2021 at 06:34:28PM +0800, yukuai (C) wrote:
>> On 2021/09/16 17:33, Yu Kuai wrote:
>>> The sock that clent send request in nbd_send_cmd() and receive reply
>>> in nbd_read_stat() should be the same.
>>>
>>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
>>> ---
>>>    drivers/block/nbd.c | 4 ++++
>>>    1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
>>> index 614c6ab2b8fe..c724a5bd7fa4 100644
>>> --- a/drivers/block/nbd.c
>>> +++ b/drivers/block/nbd.c
>>> @@ -746,6 +746,10 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
>>>    		ret = -ENOENT;
>>>    		goto out;
>>>    	}
>>> +	if (cmd->index != index) {
>>> +		dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d from different sock %d (expected %d)",
>>> +			tag, index, cmd->index);
>>> +	}
>>>    	if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
>>>    		dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
>>>    			req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
>>>
>>
>> Hi, Ming
>>
>> Any suggestions about this patch?
> 
> I think this one relies on nbd protocol between server and client, and
> does the protocol require both request and reply xmitted via same
> socket?
> 

I searched nbd-server source code, and found that socket_read() and
send_reply->socket_write() are always come in pares and using the same
socket.

BTW, if server reply a read request from a unexpected sock, then
nbd_read_stat() might stuck in receiving the read data. And for worse,
nbd_read_stat() can mistake the normal reply message for the read data
afterwards and corrupt client.

Thanks,
Kuai