Re: [RFC PATCH v2 0/7] Add a root_dir option to nfs.conf

[Trond Myklebust <trondmy@hammerspace.com>]

On Tue, 2019-05-28 at 12:47 -0400, Chuck Lever wrote:
> > On May 28, 2019, at 12:44 PM, Trond Myklebust <
> > trondmy@hammerspace.com> wrote:
> > 
> > On Tue, 2019-05-28 at 11:25 -0400, Steve Dickson wrote:
> > > On 5/21/19 3:58 PM, Trond Myklebust wrote:
> > > > On Tue, 2019-05-21 at 15:06 -0400, Chuck Lever wrote:
> > > > > > On May 21, 2019, at 2:17 PM, Trond Myklebust <
> > > > > > trondmy@hammerspace.com> wrote:
> > > > > > 
> > > > > > On Tue, 2019-05-21 at 13:40 -0400, Chuck Lever wrote:
> > > > > > > Hi Trond -
> > > > > > > 
> > > > > > > > On May 21, 2019, at 8:46 AM, Trond Myklebust <
> > > > > > > > trondmy@gmail.com
> > > > > > > > wrote:
> > > > > > > > 
> > > > > > > > The following patchset adds support for the 'root_dir'
> > > > > > > > configuration
> > > > > > > > option for nfsd in nfs.conf. If a user sets this option
> > > > > > > > to
> > > > > > > > a
> > > > > > > > valid
> > > > > > > > directory path, then nfsd will act as if it is confined
> > > > > > > > to
> > > > > > > > a
> > > > > > > > chroot
> > > > > > > > jail based on that directory. All paths in /etc/exporfs
> > > > > > > > and
> > > > > > > > from
> > > > > > > > exportfs are then resolved relative to that directory.
> > > > > > > 
> > > > > > > What about files under /proc that mountd might access? I
> > > > > > > assume
> > > > > > > these
> > > > > > > pathnames are not affected.
> > > > > > > 
> > > > > > That's why we have 2 threads. One thread is root jailed
> > > > > > using
> > > > > > chroot,
> > > > > > and is used to talk to knfsd. The other thread is not root
> > > > > > jailed
> > > > > > (or
> > > > > > at least not by root_dir) and so has full access to /etc,
> > > > > > /proc,
> > > > > > /var,
> > > > > > ...
> > > > > > 
> > > > > > > Aren't there also one or two other files that maintain
> > > > > > > export
> > > > > > > state
> > > > > > > like /var/lib/nfs/rmtab? Are those affected?
> > > > > > 
> > > > > > See above. They are not affected.
> > > > > > 
> > > > > > > IMHO it could be less confusing to administrators to make
> > > > > > > root_dir an
> > > > > > > [exportfs] option instead of a [mountd] option, if this
> > > > > > > is
> > > > > > > not a
> > > > > > > true
> > > > > > > chroot of mountd.
> > > > > > 
> > > > > > It is neither. I made in a [nfsd] option, since it governs
> > > > > > the
> > > > > > way
> > > > > > that
> > > > > > both exportfs and mountd talk to nfsd.
> > > > > 
> > > > > My point is not about implementation, it's about how this
> > > > > functionality
> > > > > is presented to administrators.
> > > > > 
> > > > > In nfs.conf, [nfsd] looks like it controls what options are
> > > > > passed
> > > > > via
> > > > > rpc.nfsd. That still seems like a confusing admin interface.
> > > > > 
> > > > > IMO admins won't care about who is talking to whom. They will
> > > > > care
> > > > > about
> > > > > how the export pathnames are interpreted. That seems like it
> > > > > belongs
> > > > > squarely with the exportfs interface.
> > > > > 
> > > > 
> > > > With the exportfs interface, yes. However it is not specific to
> > > > the
> > > > exportfs utility, so to me [exportfs] is more confusing than
> > > > what
> > > > exists now.
> > > > 
> > > > OK, so what if we put it in [general] instead, and perhaps
> > > > rename
> > > > it
> > > > "export_rootdir"?
> > > > 
> > > I'm just catching up... my apologies tartness...
> > > 
> > > So setting root_dir effects *all* exports in /etc/exports? 
> > > If that is the case, that one variable can change hundreds
> > > of export... is that what we really want?
> > > 
> > > Wouldn't be better to have a little more granularity? 
> > 
> > Can you explain what you mean? The intention here is that if you
> > have
> > all your exported filesystems set up in a subtree under
> > /mnt/my/exports, then you can remove that unnecessary prefix.
> > 
> > So, for instance, if I'm trying to export /mnt/my/exports/foo and
> > /mnt/my/exports/bar, then I can make those two filesystems appear
> > as
> > /foo, and /bar to the remote clients.
> > 
> > If an admin wants to rearrange all the paths in /etc/exports, and
> > make
> > a custom namespace, then that is possible using bind mounts: just
> > create a directory /my_exports, and use mount --bind to attach the
> > necessary mountpoints into the right spots in /my_exports, then use
> > export_rootdir to remove the /my_exports prefix.
> 
> Just to be clear, do you expect that each mount namespace on a
> Linux NFS server would have its own /etc/exports and /etc/nfs.conf ?
> 
> Maybe you stated that before, and I missed it.

Yes, if you are running in a containerised environment, then you will
have your own /etc/exports, /etc/nfs.conf, etc.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com