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Date:   Thu, 25 Apr 2019 12:45:00 -0400
From:   "bfields@fieldses.org" <bfields@fieldses.org>
To:     Trond Myklebust <trondmy@hammerspace.com>
Cc:     "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
        "Anna.Schumaker@netapp.com" <Anna.Schumaker@netapp.com>
Subject: Re: [PATCH 6/9] NFSv4: Convert the NFS client idmapper to use the
 container user namespace
Message-ID: <20190425164500.GA9015@fieldses.org>
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On Thu, Apr 25, 2019 at 04:40:18PM +0000, Trond Myklebust wrote:
> On Thu, 2019-04-25 at 11:33 -0400, bfields@fieldses.org wrote:
> > On Thu, Apr 25, 2019 at 03:00:22PM +0000, Trond Myklebust wrote:
> > > The assumption is that if you have enough privileges to mount a
> > > filesystem using the NFS client, then you would also have enough
> > > privileges to run a userspace client, so there is little point in
> > > restricting the NFS client.
> > > 
> > > So the guiding principle is that a NFS client mount that is started
> > > in
> > > a container should behave as if it were started by a process in a
> > > "real
> > > VM". That means that the root uid/gid in the container maps to a
> > > root
> > > uid/gid on the wire.
> > > Ditto, if there is a need to run the idmapper in the container,
> > > then
> > > the expectation is that processes running as 'user' with uid 'u',
> > > will
> > > see their creds mapped correctly by the idmapper. Again, that's
> > > what
> > > you would see if the process were running in a VM instead of a
> > > container.
> > > 
> > > Does that all make sense?
> > 
> > Yes, thanks!
> > 
> > I thought there was a problem that the idmapper depended on
> > keyring usermodehelper calls that it was hard to pass namespace
> > information to.  Did that get fixed and I missed it or or forgot?
> 
> No, you are correct, and so we assume the container is using rpc.idmapd
> (and rpc.gssd) if it is running NFSv4 with RPCSEC_GSS.
> 
> If the keyring upcall gets fixed, then we may allow it to be used in
> future kernels.

OK, got it.  Is there anything we lose by using idmapd?  (IDMAP_NAMESZ
might be a limitation?)

--b.