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Date:   Wed, 13 Jan 2021 14:40:26 +0000
From:   "hch@infradead.org" <hch@infradead.org>
To:     Trond Myklebust <trondmy@hammerspace.com>
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        "pgoetz@math.utexas.edu" <pgoetz@math.utexas.edu>,
        "chuck.lever@oracle.com" <chuck.lever@oracle.com>
Subject: Re: nfsd vurlerability submit
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On Wed, Jan 13, 2021 at 02:34:45PM +0000, Trond Myklebust wrote:
> On Wed, 2021-01-13 at 08:12 +0000, Christoph Hellwig wrote:
> > FYI, if people really want to use some sort of subtree exports, for
> > XFS
> > (and probably ext4) we encode the project id into the file handle and
> > use the hierarchical project ID inheritance that we already use for
> > project quotas.
> 
> You'd basically need something along the lines of a NetApp qtree.
> 
> i.e. a persisted tag that can label all the files and directories in a
> subtree, and that is used to enforce a set of rules that are generally
> normally associated with filesystems. So no renames from objects inside
> the subtree to directories that lie outside it. No hard links that
> cross the subtree boundary.

That is the XFS project ID, which ext4 has also picked up a few years
ago.