Re: [PATCH v4] seccomp: add ptrace options for suspend/resume

From: Andy Lutomirski <luto@amacapital.net>
To: Serge Hallyn <serge.hallyn@ubuntu.com>
Cc: Oleg Nesterov <oleg@redhat.com>,
	Tycho Andersen <tycho.andersen@canonical.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	Kees Cook <keescook@chromium.org>, Will Drewry <wad@chromium.org>,
	Roland McGrath <roland@hack.frob.com>,
	Pavel Emelyanov <xemul@parallels.com>
Subject: Re: [PATCH v4] seccomp: add ptrace options for suspend/resume
Date: Wed, 10 Jun 2015 10:42:01 -0700	[thread overview]
Message-ID: <CALCETrWYc2ZqGWzrNQMHdwQ-_sAy8AhkMdJWABEpwMP2qbSO8A@mail.gmail.com> (raw)
In-Reply-To: <20150610172931.GD4069@ubuntumail>

On Wed, Jun 10, 2015 at 10:29 AM, Serge Hallyn <serge.hallyn@ubuntu.com> wrote:
> Quoting Andy Lutomirski (luto@amacapital.net):
>> On Wed, Jun 10, 2015 at 9:31 AM, Oleg Nesterov <oleg@redhat.com> wrote:
>> > On 06/09, Andy Lutomirski wrote:
>> >>
>> >> On Tue, Jun 9, 2015 at 5:49 PM, Tycho Andersen
>> >> >
>> >> > @@ -556,6 +556,15 @@ static int ptrace_setoptions(struct task_struct *child, unsigned long data)
>> >> >         if (data & ~(unsigned long)PTRACE_O_MASK)
>> >> >                 return -EINVAL;
>> >> >
>> >> > +       if (unlikely(data & PTRACE_O_SUSPEND_SECCOMP)) {
>> >
>> > Well, we should do this if
>> >
>> >                         (data & O_SUSPEND) && !(flags & O_SUSPEND)
>> >
>> > or at least if
>> >
>> >                         (data ^ flags) & O_SUSPEND
>> >
>> >
>> >> > +               if (!config_enabled(CONFIG_CHECKPOINT_RESTORE) ||
>> >> > +                   !config_enabled(CONFIG_SECCOMP))
>> >> > +                       return -EINVAL;
>> >> > +
>> >> > +               if (!capable(CAP_SYS_ADMIN))
>> >> > +                       return -EPERM;
>> >>
>> >> I tend to think that we should also require that current not be using
>> >> seccomp.  Otherwise, in principle, there's a seccomp bypass for
>> >> privileged-but-seccomped programs.
>> >
>> > Andy, I simply can't understand why do we need any security check at all.
>> >
>> > OK, yes, in theory we can have a seccomped CAP_SYS_ADMIN process, seccomp
>> > doesn't filter ptrace, you hack that process and force it to attach to
>> > another CAP_SYS_ADMIN/seccomped process, etc, etc... Looks too paranoid
>> > to me.
>>
>> I've sometimes considered having privileged processes I write fork and
>> seccomp their child.  Of course, if you're allowing ptrace through
>> your seccomp filter, you open a giant can of worms, but I think we
>> should take the more paranoid approach to start and relax it later as
>
> I really do intend to look at your old proposed tree for improving that...
> have only done a once-over so far, though.

Don't read it yet.  It's unnecessarily complicated due to the mess
that is x86's entry code, and I want to clean up the entry code first.

--Andy