linux-kernel - Re: [PATCH v6 0/1] ns: introduce binfmt

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Message-ID: <1541081413.2853.6.camel@HansenPartnership.com>
Date:   Thu, 01 Nov 2018 07:10:13 -0700
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     Laurent Vivier <laurent@...ier.eu>,
        kernel list <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        containers@...ts.linux-foundation.org, dima@...sta.com,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v6 0/1] ns: introduce binfmt_misc namespace

On Thu, 2018-11-01 at 04:51 +0100, Jann Horn wrote:
> On Thu, Nov 1, 2018 at 3:59 AM James Bottomley
> <James.Bottomley@...senpartnership.com> wrote:
> > 
> > On Tue, 2018-10-16 at 11:52 +0200, Laurent Vivier wrote:
> > > Hi,
> > > 
> > > Any comment on this last version?
> > > 
> > > Any chance to be merged?
> > 
> > I've got a use case for this:  I went to one of the Graphene talks
> > in Edinburgh and it struck me that we seem to keep reinventing the
> > type of sandboxing that qemu-user already does.  However if you
> > want to do an x86 on x86 sandbox, you can't currently use the
> > binfmt_misc mechanism because that has you running *every* binary
> > on the system emulated. Doing it per user namespace fixes this
> > problem and allows us to at least cut down on all the pointless
> > duplication.
> 
> Waaaaaait. What? qemu-user does not do "sandboxing". qemu-user makes
> your code slower and *LESS* secure. As far as I know, qemu-user is
> only intended for purposes like development and testing.

Sandboxing is about protecting the cloud service provider (and other
tenants) from horizontal attack by reducing calls to the shared kernel.
 I think it's pretty indisputable that full emulation is an effective
sandbox in that regard.

We can argue for about bugginess vs completeness, but technologically
qemu-user already has most of the system calls, which seems to be a
significant problem with other sandboxes.  I also can't dispute it's
slower, but that's a tradeoff for people to make.

James