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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Fri, 3 May 2019 13:41:25 -0400
Message-ID: <CAOQ4uxjztNzH7EbK7o2vkhzzjULkEVKnnedep9GbTSyOhRV-3g@mail.gmail.com>
Subject: Re: [PATCH] overlayfs: ignore empty NFSv4 ACLs in ext4 upperdir
To:     "J. Bruce Fields" <bfields@fieldses.org>
Cc:     NeilBrown <neilb@suse.com>,
        Andreas Gruenbacher <agruenba@redhat.com>,
        Miklos Szeredi <miklos@szeredi.hu>,
        =?UTF-8?Q?Andreas_Gr=C3=BCnbacher?= <andreas.gruenbacher@gmail.com>,
        Patrick Plagwitz <Patrick_Plagwitz@web.de>,
        "linux-unionfs@vger.kernel.org" <linux-unionfs@vger.kernel.org>,
        Linux NFS list <linux-nfs@vger.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Vivek Goyal <vgoyal@redhat.com>
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On Fri, May 3, 2019 at 1:31 PM J. Bruce Fields <bfields@fieldses.org> wrote=
:
>
> On Fri, May 03, 2019 at 01:26:01PM -0400, Amir Goldstein wrote:
> > On Fri, May 3, 2019 at 12:03 PM J. Bruce Fields <bfields@fieldses.org> =
wrote:
> > >
> > > On Thu, May 02, 2019 at 12:02:33PM +1000, NeilBrown wrote:
> > > > On Tue, Dec 06 2016, J. Bruce Fields wrote:
> > > >
> > > > > On Tue, Dec 06, 2016 at 02:18:31PM +0100, Andreas Gruenbacher wro=
te:
> > > > >> On Tue, Dec 6, 2016 at 11:08 AM, Miklos Szeredi <miklos@szeredi.=
hu> wrote:
> > > > >> > On Tue, Dec 6, 2016 at 12:24 AM, Andreas Gr=C3=BCnbacher
> > > > >> > <andreas.gruenbacher@gmail.com> wrote:
> > > > >> >> 2016-12-06 0:19 GMT+01:00 Andreas Gr=C3=BCnbacher <andreas.gr=
uenbacher@gmail.com>:
> > > > >> >
> > > > >> >>> It's not hard to come up with a heuristic that determines if=
 a
> > > > >> >>> system.nfs4_acl value is equivalent to a file mode, and to i=
gnore the
> > > > >> >>> attribute in that case. (The file mode is transmitted in its=
 own
> > > > >> >>> attribute already, so actually converting .) That way, overl=
ayfs could
> > > > >> >>> still fail copying up files that have an actual ACL. It's st=
ill an
> > > > >> >>> ugly hack ...
> > > > >> >>
> > > > >> >> Actually, that kind of heuristic would make sense in the NFS =
client
> > > > >> >> which could then hide the "system.nfs4_acl" attribute.
> > > > >> >
> > > > >> > Even simpler would be if knfsd didn't send the attribute if no=
t
> > > > >> > necessary.  Looks like there's code actively creating the nfs4=
_acl on
> > > > >> > the wire even if the filesystem had none:
> > > > >> >
> > > > >> >     pacl =3D get_acl(inode, ACL_TYPE_ACCESS);
> > > > >> >     if (!pacl)
> > > > >> >         pacl =3D posix_acl_from_mode(inode->i_mode, GFP_KERNEL=
);
> > > > >> >
> > > > >> > What's the point?
> > > > >>
> > > > >> That's how the protocol is specified.
> > > > >
> > > > > Yep, even if we could make that change to nfsd it wouldn't help t=
he
> > > > > client with the large number of other servers that are out there
> > > > > (including older knfsd's).
> > > > >
> > > > > --b.
> > > > >
> > > > >> (I'm not saying that that's very helpful.)
> > > > >>
> > > > >> Andreas
> > > >
> > > > Hi everyone.....
> > > >  I have a customer facing this problem, and so stumbled onto the em=
ail
> > > >  thread.
> > > >  Unfortunately it didn't resolve anything.  Maybe I can help kick t=
hings
> > > >  along???
> > > >
> > > >  The core problem here is that NFSv4 and ext4 use different and lar=
gely
> > > >  incompatible ACL implementations.  There is no way to accurately
> > > >  translate from one to the other in general (common specific exampl=
es
> > > >  can be converted).
> > > >
> > > >  This means that either:
> > > >    1/ overlayfs cannot use ext4 for upper and NFS for lower (or vic=
e
> > > >       versa) or
> > > >    2/ overlayfs need to accept that sometimes it cannot copy ACLs, =
and
> > > >       that is OK.
> > > >
> > > >  Silently not copying the ACLs is probably not a good idea as it mi=
ght
> > > >  result in inappropriate permissions being given away.  So if the
> > > >  sysadmin wants this (and some clearly do), they need a way to
> > > >  explicitly say "I accept the risk".
> > >
> > > So, I feel like silently copying ACLs up *also* carries a risk, if th=
at
> > > means switching from server-enforcement to client-enforcement of thos=
e
> > > permissions.
> > >
> > > Sorry, I know we had another thread recently about permissions in thi=
s
> > > situation, and I've forgotten the conclusion.
> > >
> > > Out of curiosity, what's done with selinux labels?
> > >
> >
> > overlayfs calls security_inode_copy_up_xattr(name) which
> > can fail (<0) allow (0) or skip(1).
> >
> > selinux_inode_copy_up_xattr() as well as smack_inode_copy_up_xattr()
> > skip their own xattr on copy up and fail any other xattr copy up.
>
> If it's OK to silently skip copying up security labels, maybe it's OK to
> silently skip NFSv4 ACLs too?
>

I think overlayfs inode security context is taken from overlayfs
mount parameters (i.e. per container context) and therefore
the lower security. xattr are ignored (CC Vivek).

Thanks,
Amir.