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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:     Jens Axboe <axboe@fb.com>, Christoph Hellwig <hch@lst.de>,
        linux-nvme@lists.infradead.org, Daniel Wagner <dwagner@suse.de>,
        linux-kernel@vger.kernel.org
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 <5b45835b-eb81-29e8-e319-a8509474e27f@grimberg.me>
From:   Hannes Reinecke <hare@suse.de>
Message-ID: <a18701ad-6880-37bb-7978-7ea6b7079c9e@suse.de>
Date:   Tue, 16 Feb 2021 09:51:00 +0100
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On 2/15/21 10:23 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.
> 
> And this doesn't help because the command can have been easily reused
> and started... What is this protecting against? Note that none of the
> other transports checks that, why should tcp?

Because it's particularly easy to spoof packets on tcp.
All other nvme-of transports are layered on top of other transports 
which do some sanity checks already, so it becomes really hard to inject 
invalid NVMe-oF frames for those.
NVMe-TCP has none of these protections, making it really easy to inject 
faulty frames (or, heaven forbid, running a packet fuzzer).

And crashing the machine on invalid frames is always a bad idea; I would 
have expected NVMe-TCP to drop them.

Cheers,

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