Messages in this thread | | | Subject | Re: [PATCH v2] nvme-tcp: Check if request has started before processing it | From | "Ewan D. Milne" <> | Date | Wed, 31 Mar 2021 17:01:41 -0400 |
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On Wed, 2021-03-31 at 09:11 +0200, Hannes Reinecke wrote: > On 3/31/21 1:28 AM, Keith Busch wrote: > > On Tue, Mar 30, 2021 at 10:34:25AM -0700, Sagi Grimberg wrote: > > > > > > > > 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.. > > > > If scsi wants this too, this could be made generic at the blk-mq > > level. > > We just need to make something like blk_mq_tag_to_rq(), but return > > NULL > > if the request isn't started. > > > > > 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... > > > > If this does happen, I think we have to come up with some way to > > mitigate it. We're not utilizing the full 16 bits of the > > command_id, so > > maybe we can append something like a generation sequence number > > that can > > be checked for validity. > > > > ... which will be near impossible. > We can protect against crashing on invalid frames. > We can _not_ protect against maliciously crafted packets referencing > any > random _existing_ tag; that's what TLS is for. > > What we can do, though, is checking the 'state' field in the tcp > request, and only allow completions for commands which are in a state > allowing for completions. > > Let's see if I can whip up a patch.
That would be great. BTW in the crash dump I am looking at now, it looks like pdu->command_id was zero in nvme_tcp_recv_data(), and blk_mq_tag_to_rq() returned a request struct that had not been used. So I think we do need to check that the tag was actually allocated.
-Ewan
> > Cheers, > > Hannes
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