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Date:   Fri, 17 Feb 2017 09:19:53 -0800
From:   James Bottomley <>
To:     "Eric W. Biederman" <>
Cc:     Vivek Goyal <>,
        Amir Goldstein <>,
        Djalal Harouni <>, Chris Mason <>,
        Theodore Tso <>,
        Josh Triplett <>,
        Andy Lutomirski <>,
        Seth Forshee <>,
        linux-fsdevel <>,
        linux-kernel <>,
        LSM List <>,
        Dongsu Park <>,
        David Herrmann <>,
        Miklos Szeredi <>,
        Alban Crequy <>,
        Al Viro <>,
        "Serge E. Hallyn" <>, Phil Estes <>
Subject: Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount

On Fri, 2017-02-17 at 14:57 +1300, Eric W. Biederman wrote:
> I think I am missing something but I completely do not understand 
> that subthread that says use file marks and perform the work in the 
> vfs. The problem is that fundamentally we need multiple mappings and 
> I don't see a mark on a file (even an inherited mark) providing the 
> mapping so I don't see the point.

The point of the mark is that it's a statement by the system
administrator that the underlying subtree is safe to be mounted by an
unprivileged container in the containers user view (i.e. with
current_user_ns() == s_user_ns).  For the unprivileged container
there's no real arbitrary s_user_ns use case because the unprivileged
container must prove it can set up the mapping, so it would likely
always be mounting from within a user_ns with the mapping it wanted.


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