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Subject: Re: [PATCH] nvme-tcp: Check if request has started before processing
 it
To:     Sagi Grimberg <sagi@grimberg.me>, Keith Busch <kbusch@kernel.org>
Cc:     Daniel Wagner <dwagner@suse.de>, linux-nvme@lists.infradead.org,
        linux-kernel@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
        Jens Axboe <axboe@fb.com>
References: <20210212181738.79274-1-dwagner@suse.de>
 <c3a682d3-58f7-f5cc-caaa-75c36ca464e2@grimberg.me>
 <20210212210929.GA3851@redsun51.ssa.fujisawa.hgst.com>
 <ddf87227-1ad3-b8be-23ba-460433f70a85@grimberg.me>
From:   Hannes Reinecke <hare@suse.de>
Message-ID: <73e4914e-f867-c899-954d-4b61ae2b4c33@suse.de>
Date:   Sat, 13 Feb 2021 09:46:41 +0100
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On 2/12/21 10:49 PM, Sagi Grimberg wrote:
> 
>>>> blk_mq_tag_to_rq() will always return a request if the command_id is
>>>> in the valid range. Check if the request has been started. If we
>>>> blindly process the request we might double complete a request which
>>>> can be fatal.
>>>
>>> How did you get to this one? did the controller send a completion for
>>> a completed/bogus request?
>>
>> If that is the case, then that must mean it's possible the driver could
>> have started the command id just before the bogus completion check. Data
>> iorruption, right?
> 
> Yes, which is why I don't think this check is very useful..

I actually view that as a valid protection against spoofed frames.
Without it it's easy to crash the machine by injecting fake completions 
with random command ids.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
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