linux-kernel - Re: [PATCHv3 0/2] capability controlled user-namespaces

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Date:   Mon, 8 Jan 2018 00:24:52 -0600
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     James Morris <james.l.morris@...cle.com>
Cc:     Mahesh Bandewar
         (महेश बंडेवार) <maheshb@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        Kernel-hardening <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Serge Hallyn <serge@...lyn.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        Mahesh Bandewar <mahesh@...dewar.net>
Subject: Re: [PATCHv3 0/2] capability controlled user-namespaces

On Mon, Jan 08, 2018 at 11:35:26AM +1100, James Morris wrote:
> On Tue, 2 Jan 2018, Mahesh Bandewar (महेश बंडेवार) wrote:
> 
> > On Sat, Dec 30, 2017 at 12:31 AM, James Morris
> > <james.l.morris@...cle.com> wrote:
> > > On Wed, 27 Dec 2017, Mahesh Bandewar (महेश बंडेवार) wrote:
> > >
> > >> Hello James,
> > >>
> > >> Seems like I missed your name to be added into the review of this
> > >> patch series. Would you be willing be pull this into the security
> > >> tree? Serge Hallyn has already ACKed it.
> > >
> > > Sure!
> > >
> > Thank you James.
> 
> I'd like to see what Eric Biederman thinks of this.
> 
> Also, why do we need the concept of a controlled user-ns at all, if the 
> default whitelist maintains existing behavior?

In past discussions two uses have been brought up:

1. if an 0-day is discovered which is exacerbated by a specific
privilege in user namespaces, that privilege could be turned off until a
reboot with a fixed kernel is scheduled, without fully disabling all
containers.

2. some systems may be specifically designed to run software which
only requires a few capabilities in a userns.  In that case all others
could be disabled.