Date: Fri, 21 Jan 2005 13:55:58 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Andrea Arcangeli <andrea@cpushare.com>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       Roland McGrath <roland@redhat.com>
Subject: Re: seccomp for 2.6.11-rc1-bk8
Message-ID: <20050121125558.GA5596@elte.hu>
References: <20050121100606.GB8042@dualathlon.random> <20050121120325.GA2934@elte.hu> <20050121124701.GA5179@elte.hu>
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* Ingo Molnar <mingo@elte.hu> wrote:

> > > This is the seccomp patch ported to 2.6.11-rc1-bk8, that I need for
> > > Cpushare (until trusted computing will hit the hardware market). 
> > > [...]
> > 
> > why do you need any kernel code for this? This seems to be a limited
> > ptrace implementation: restricting untrusted userspace code to only be
> > able to exec read/write/sigreturn.
> > 
> > So this patch, unless i'm missing something, duplicates in essence what
> > ptrace can do [...]
> 
> there's one thing ptrace wont do: if the ptrace parent dies
> unexpectedly and the child was 'running' (there is a small window
> where the child might not be stopped and where this may happen) then
> the child can get runaway. While i think this is theoretical (UML
> doesnt suffer from this problem), it is simple to fix - find below a
> proof-of-concept patch that introduces PTRACE_ATTACH_JAIL - ptraced
> children can never escape out of such a jail. (barely tested - but you
> get the idea.)

maybe this could even be fit into existing ptrace semantics, without any
need for PTRACE_ATTACH_JAIL. What we need is to catch the case where a
ptraced child is running (i.e. the signal_wake_up() has already been
done, and the parent is waiting for the child to stop again), and the
ptrace parent is killed unexpectedly.  Would it be a correct fix to just
unconditionally stop the child in this case (and leave it hanging in
such a state)? Or to kill it right away?

	Ingo
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