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Subject: Re: [PATCH v2] nvme-tcp: Check if request has started before
 processing it
To:     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>
References: <20210301175601.116405-1-dwagner@suse.de>
 <6b51a989-5551-e243-abda-5872411ec3ff@grimberg.me>
 <20210311094345.ogm2lxqfuszktuhp@beryllium.lan>
From:   Sagi Grimberg <sagi@grimberg.me>
Message-ID: <70af5b02-10c1-ab0b-1dfc-5906216871b4@grimberg.me>
Date:   Mon, 15 Mar 2021 10:16:13 -0700
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> Hi Sagi,
> 
> On Fri, Mar 05, 2021 at 11:57:30AM -0800, Sagi Grimberg wrote:
>> Daniel, again, there is nothing specific about this to nvme-tcp,
>> this is a safeguard against a funky controller (or a different
>> bug that is hidden by this).
> 
> As far I can tell, the main difference between nvme-tcp and FC/NVMe,
> nvme-tcp has not a FW or a big driver which filter out some noise from a
> misbehaving controller. I haven't really checked the other transports
> but I wouldn't surprised they share the same properties as FC/NVMe.
> 
>> The same can happen in any other transport so I would suggest that if
>> this is a safeguard we want to put in place, we should make it a
>> generic one.
>>
>> i.e. nvme_tag_to_rq() that _all_ transports call consistently.
> 
> Okay, I'll review all the relevant code and see what could made more
> generic and consistent.
> 
> Though I think nvme-tcp plays in a different league as it is exposed to
> normal networking traffic and this is a very hostile environment.

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.