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Date: Tue, 7 Feb 2017 10:10:40 -0800
From: Christoph Hellwig <hch@infradead.org>
To: Amir Goldstein <amir73il@gmail.com>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>,
        Christoph Hellwig <hch@infradead.org>,
        Djalal Harouni <tixxdz@gmail.com>, Chris Mason <clm@fb.com>,
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        "Eric W. Biederman" <ebiederm@xmission.com>,
        Andy Lutomirski <luto@kernel.org>,
        Seth Forshee <seth.forshee@canonical.com>,
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        Al Viro <viro@zeniv.linux.org.uk>,
        "Serge E. Hallyn" <serge@hallyn.com>, Phil Estes <estesp@gmail.com>
Subject: Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount
Message-ID: <20170207181040.GA18551@infradead.org>
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On Tue, Feb 07, 2017 at 07:59:00PM +0200, Amir Goldstein wrote:
> I am not even sure that would be enough.
> dentry does not contain information about the mount user came from,
> and sb contains only information about the user ns of the mounter of
> the file system, not the mounter of the bind mount, right?
> I think I am missing some big pieces of the big picture.
> Would love to hear what Eric has to say.

IFF we want to do what shiftfs does properly we need vfsmount + inode,
no need for the dentry.

But maybe we need to go back and decice if we want to allow uid/gid
remapping for arbitrary subtrees anyway.  Another option would be
to require something like a project as used for project quotas as the
root.  This would also be conveniant as it could storge the used
remapping tables.