Re: [RFC PATCH 1/6] NFSD: Handle @rqstp == NULL in check_nfsd_access()

[Mike Snitzer <snitzer@kernel.org>]

On Thu, Aug 29, 2024 at 07:05:45AM +1000, NeilBrown wrote:
> On Wed, 28 Aug 2024, Mike Snitzer wrote:
> > 
> > So I honestly feel like Chuck's latest revision is perfectly fine.
> > I disagree that "The behavior for LOCALIO is therefore the same as
> > the AUTH_UNIX check below." is inaccurate.  The precondition from the
> > client (used to establish localio and cause rqstp to be NULL in
> > check_nfsd_access) is effectively comparable no?
> > 
> 
> I don't think the correctness of the code is at all related to
> AUTH_UNIX.
> Suppose we did add support for krb5 somehow - would we really need a
> different test?  I think not.
> 
> I think that the reason the code is correct and safe is that we trust
> the client.  We *know* the client will only present an filehandle which
> it has received over the wire and which it verified - with the
> accompanying credential - it was allowed to access.
> 
> Maybe that is what you meant by "The precondition from the client".  I
> agree that does give us sufficient safety.  I don't think AUTH_UNIX is
> relevant.
> 
> /*
>  * If rqstp is NULL, this is a LOCALIO request which will only ever use
>  * filehandle/credential pair for which access has been affirmed (by
>  * ACCESS or OPEN NFS requests) over the wire.  So there is no need for
>  * further checks here.
>  */

Makes sense, and thanks!

> (It wasn't quite this clear to me when I wrote previously - but I always
>  seems to think more clearly in the mornings!)

I haven't been sleeping enough.. tonight, tonight I will!!! ;)

Mike