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

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Date:   Tue, 21 Feb 2017 11:57:27 +0900
From:   "J. R. Okajima" <hooanon05g@...il.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     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@...r.kernel.org, linux-kernel@...r.kernel.org,
        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

James Bottomley:
> I realised as I was trimming down the vestigial inode properties in the
> patch that actually shiftfs does use the i_ino from the underlying for
> userspace.  The reason why is that it comes from the getattr call in
> stat and that's fully what the underlying filesystem returns (including
> the inode number).

Let me make sure.
- shiftfs has its own inode, but it will never be visible to userspace.
- the inode attr visible to users are equivalent to the underlying one,
  includeing dev:ino pair.
right?
If so, I am afraid it will make users confused. The dev:ino pair is a
system-wide identity, but shiftfs creates the same dev:ino pair with
different owner. Though I don't know whether the actual application or
LSM exists or not who will be damaged by this situation.
For git-status case which I wrote previously, it might not be a problem
as long as dev:ino is unchanged from git index.
But such filesystem looks weird.


J. R. Okajima