Messages in this thread | | | From | Hannes Reinecke <> | Subject | Re: [PATCH v2] nvme-tcp: Check if request has started before processing it | Date | Wed, 31 Mar 2021 09:11:59 +0200 |
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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.
Cheers,
Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), GF: Felix Imendörffer
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