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Date: Tue, 20 Aug 2013 20:50:43 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Brad Spengler <spender@grsecurity.net>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Colin Walters <walters@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: PATCH? fix unshare(NEWPID) && vfork()
Message-ID: <20130820185043.GA24040@redhat.com>
References: <20130819172524.GA22268@redhat.com> <CALCETrW+dEwR38ERQhx25-aw1dhsCE6X+9BQZJhusO88aUxN1A@mail.gmail.com> <20130819183319.GA24846@redhat.com> <CALCETrWrpNszRGCRRMLgiOopcSdDShB3Mck6gRPco=dAZeX3pQ@mail.gmail.com> <20130819184355.GA25362@redhat.com> <CALCETrU4gTfzcpeEo-X7o-yZefKiw9BVNKdcN4fThUeiuZtOOg@mail.gmail.com>
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On 08/20, Andy Lutomirski wrote:
>
> On Mon, Aug 19, 2013 at 11:43 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> > On 08/19, Andy Lutomirski wrote:
> >>
> >> On Mon, Aug 19, 2013 at 11:33 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> >> >
> >> > So do you think this change is fine or not (ignoring the fact it needs
> >> > cleanups) ?
> >>
> >> I think that removing the CLONE_VM check is fine (although there are
> >> some other ones that should probably be removed as well), but I'm not
> >> sure if that check needs replacing with something else.
> >
> > OK, thanks... but I still can't understand.
> >
> > The patch I sent is equivalent to the new one below. I just tried to
> > unify it with another check in do_fork().
>
> I was confused.

Andy, I do not know how much you were confused, but I bet I am confused
much more ;)

> Currently (with or without your patch), vfork() followed by
> unshare(CLONE_NEWUSER) or unshare(CLONE_NEWPID) will unshare the VM.

Could you spell please?

We never unshare the VM. CLONE_VM in sys_unshare() paths just means
"fail unless ->mm is not shared".

Oleg.