Re: [PATCH v2] seccomp: add ptrace options for suspend/resume

From: Tycho Andersen <tycho.andersen@canonical.com>
To: Kees Cook <keescook@chromium.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
	Andy Lutomirski <luto@amacapital.net>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	Will Drewry <wad@chromium.org>,
	Roland McGrath <roland@hack.frob.com>,
	Pavel Emelyanov <xemul@parallels.com>,
	"Serge E. Hallyn" <serge.hallyn@ubuntu.com>
Subject: Re: [PATCH v2] seccomp: add ptrace options for suspend/resume
Date: Tue, 9 Jun 2015 15:52:27 -0600	[thread overview]
Message-ID: <20150609215227.GG2045@hopstrocity> (raw)
In-Reply-To: <CAGXu5jLC-DcS-Mg5OTM-LEkuOKMMGrV2tq+Lky1Mxh_rDLa4Bg@mail.gmail.com>

On Tue, Jun 09, 2015 at 02:45:49PM -0700, Kees Cook wrote:
> On Tue, Jun 9, 2015 at 2:22 PM, Tycho Andersen
> <tycho.andersen@canonical.com> wrote:
> > Hi Kees, Andy,
> >
> > On Fri, Jun 05, 2015 at 11:16:50PM +0200, Oleg Nesterov wrote:
> >> Hi Tycho,
> >>
> >> On 06/04, Tycho Andersen wrote:
> >> > > > +#ifdef CONFIG_CHECKPOINT_RESTORE
> >> > > > +bool may_suspend_seccomp(void)
> >> > > > +{
> >> > > > +       if (!capable(CAP_SYS_ADMIN))
> >> > > > +               return false;
> >> > > > +
> >> > > > +       if (current->seccomp.mode != SECCOMP_MODE_DISABLED)
> >> > > > +               return false;
> >> > >
> >> > > Heh. OK, I won't argue with the new check too ;)
> >> >
> >> > Actually now that I think about it I agree with you, these checks
> >> > don't seem necessary. Even inside a user namespace, if you can ptrace
> >> > a process you can make it do whatever you want irrespective of
> >> > seccomp, as long as it has the necessary capabilities. Once the
> >> > seccomp checks are run after ptrace, they'll be enforced so you
> >> > couldn't have it call whatever you want in the first place.
> >>
> >> Good ;)
> >>
> >> > Still, perhaps I'm missing something...
> >>
> >> Kees, Andy?
> >
> > Any thoughts on removing may_suspend_seccomp() all together?
> 
> As in, just open-code the check? That would be fine by me.

Sorry, I meant getting rid of any checks entirely. Using my argument
above I've managed to convince myself they don't add any value. You
guys know a lot more about this than I do, though.

Tycho