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Subject: Re: [PATCH v2] nvme-tcp: Check if request has started before
 processing it
To:     "Ewan D. Milne" <emilne@redhat.com>,
        Daniel Wagner <dwagner@suse.de>
Cc:     linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org,
        Jens Axboe <axboe@fb.com>, Hannes Reinecke <hare@suse.de>,
        Keith Busch <kbusch@kernel.org>, Christoph Hellwig <hch@lst.de>
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 <6b51a989-5551-e243-abda-5872411ec3ff@grimberg.me>
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 <2fc7a320c86f75507584453dd2fbd744de5c170d.camel@redhat.com>
From:   Sagi Grimberg <sagi@grimberg.me>
Message-ID: <ed3ccac0-79ed-fe10-89eb-d403820b4c6a@grimberg.me>
Date:   Tue, 30 Mar 2021 10:34:25 -0700
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>> It is, but in this situation, the controller is sending a second
>> completion that results in a use-after-free, which makes the
>> transport irrelevant. Unless there is some other flow (which is
>> unclear
>> to me) that causes this which is a bug that needs to be fixed rather
>> than hidden with a safeguard.
>>
> 
> The kernel should not crash regardless of any network traffic that is
> sent to the system.  It should not be possible to either intentionally
> of mistakenly contruct packets that will deny service in this way.

This is not specific to nvme-tcp. I can build an rdma or pci controller
that can trigger the same crash... I saw a similar patch from Hannes
implemented in the scsi level, and not the individual scsi transports..

I would also mention, that a crash is not even the scariest issue that
we can see here, because if the request happened to be reused we are
in the silent data corruption realm...