linux-kernel - Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount

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Message-ID: <20170207181040.GA18551@infradead.org>
Date:   Tue, 7 Feb 2017 10:10:40 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     James Bottomley <James.Bottomley@...senpartnership.com>,
        Christoph Hellwig <hch@...radead.org>,
        Djalal Harouni <tixxdz@...il.com>, Chris Mason <clm@...com>,
        Theodore Tso <tytso@....edu>,
        Josh Triplett <josh@...htriplett.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andy Lutomirski <luto@...nel.org>,
        Seth Forshee <seth.forshee@...onical.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Dongsu Park <dongsu@...ocode.com>,
        David Herrmann <dh.herrmann@...glemail.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Alban Crequy <alban.crequy@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Serge E. Hallyn" <serge@...lyn.com>, Phil Estes <estesp@...il.com>
Subject: Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount

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.