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From:   Rick Macklem <rmacklem@uoguelph.ca>
To:     Tom Talpey <tom@talpey.com>,
        Chuck Lever III <chuck.lever@oracle.com>
CC:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: NFSv4.1/4.2 server returns same sessionid after
 DestroySession/CreateSession
Thread-Topic: NFSv4.1/4.2 server returns same sessionid after
 DestroySession/CreateSession
Thread-Index: AQHYlKIG8hnDNDQzXUuZ/p7iJwgH2615RPsAgAAqTQCAAAlZgIAAKIvmgAAL34CAAAlvaQ==
Date:   Mon, 11 Jul 2022 21:55:44 +0000
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Tom Talpey <tom@talpey.com> wrote:=0A=
> On 7/11/2022 4:43 PM, Rick Macklem wrote:=0A=
> >>>> CREATE_SESSION has a built-in reply cache to thwart replay attacks.=
=0A=
> >>>> It can legitimately return the same sessionid as a previous request.=
=0A=
> >>>> Granted, DESTROY_SESSION is supposed to wipe that reply cache...=0A=
> > Well, I just re-read the RFC and I don't see anything that says Destroy=
Session=0A=
> > affects the CreateSession reply cache.=0A=
> =0A=
> It actually does, but I think it's problematic:=0A=
> =0A=
> =0A=
> 18.37.3.  DESCRIPTION=0A=
> =0A=
>     The DESTROY_SESSION operation closes the session and discards the=0A=
>     session's reply cache, if any.  Any remaining connections associated=
=0A=
>     with the session are immediately disassociated.  If the connection=0A=
>     has no remaining associated sessions, the connection MAY be closed by=
=0A=
>     the server.  Locks, delegations, layouts, wants, and the lease, which=
=0A=
>     are all tied to the client ID, are not affected by DESTROY_SESSION.=
=0A=
When I read "discards the session's reply cache" I think I somehow read it=
=0A=
as "discards the create_session reply cache", but it pretty obviously is re=
ferring=0A=
to what is cached for the session's slots.=0A=
=0A=
> What about the reply to DESTROY_SESSION itself? I guess the idea is=0A=
> that if the client misses the reply and reconnects/retransmits, it=0A=
> gets NFSERR_BAD_SESSION and figures it out. Maybe not worth taking=0A=
> to IETF, since you found the root cause!=0A=
Yep, the reply to DestroySession doesn't get cached but, as you note, the=
=0A=
client usually can just ignore a NFS4ERR_BAD_SESSION reply and assume it=0A=
is a retry, since it wanted to get rid of the session anyhow.=0A=
=0A=
rick=0A=
=0A=
Tom.=0A=