linux-kernel - Re: [RFC PATCH 09/27] vfs: Allow mounting to other namespaces

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Message-ID: <20190217001440.GS2217@ZenIV.linux.org.uk>
Date:   Sun, 17 Feb 2019 00:14:41 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     David Howells <dhowells@...hat.com>
Cc:     keyrings@...r.kernel.org, trond.myklebust@...merspace.com,
        sfrench@...ba.org, linux-security-module@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, rgb@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 09/27] vfs: Allow mounting to other namespaces

On Fri, Feb 15, 2019 at 04:08:46PM +0000, David Howells wrote:
> Currently sys_move_mount() and sys_mount(MS_MOVE) prevent the caller from
> moving a mount into a namespace not their own.  Relax this such that any
> mount can be mounted onto any given mountpoint provided that the source
> mount is either detached or the same namespace as the destination.
> 
> This permits container namespaces to be built from the outside rather than
> from the inside.

I'm looking forward to your analysis of security implications, as well as
the proof that attach_recursive_mnt() won't get confused by that...