linux-kernel - Re: Compat 32-bit syscall entry from 64-bit task!? [was: Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF]

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Message-ID: <CAMnK33Xy0hGh=PoKs+JtPqftaPOhWAOHxbOGpsbHgGYgnauu4g@mail.gmail.com>
Date:	Mon, 23 Jan 2012 14:23:18 -0800
From:	Chris Evans <scarybeasts@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Indan Zupancic <indan@....nu>, Andi Kleen <andi@...stfloor.org>,
	Jamie Lokier <jamie@...reable.org>,
	Andrew Lutomirski <luto@....edu>,
	Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org,
	keescook@...omium.org, john.johansen@...onical.com,
	serge.hallyn@...onical.com, coreyb@...ux.vnet.ibm.com,
	pmoore@...hat.com, eparis@...hat.com, djm@...drot.org,
	torvalds@...ux-foundation.org, segoon@...nwall.com,
	rostedt@...dmis.org, jmorris@...ei.org, avi@...hat.com,
	penberg@...helsinki.fi, viro@...iv.linux.org.uk, mingo@...e.hu,
	akpm@...ux-foundation.org, khilman@...com, borislav.petkov@....com,
	amwang@...hat.com, ak@...ux.intel.com, eric.dumazet@...il.com,
	gregkh@...e.de, dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com,
	Roland McGrath <mcgrathr@...omium.org>
Subject: Re: Compat 32-bit syscall entry from 64-bit task!? [was: Re:
 [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF]

On Mon, Jan 23, 2012 at 8:56 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 01/18, Chris Evans wrote:
>>
>> Thanks, Oleg. Seems like this would be a nice change to have. As we
>> can see, people do use ptrace() as a security technology.
>
> OK, I'll send it.
>
>> With this in place, you can also (where possible) set up the tracee
>> with PR_SET_PDEATHSIG==SIGKILL. And then, you have defences again
>> either of the tracer or tracee dying from a stray SIGKILL.
>
> This can only help if the tracer is the natural parent, is it enough?
>
> Indan suggested PTRACE_O_SIGKILL_ON_DEATH, perhaps it makes sense.

Yeah, this takes care of all cases.

One caveat I can think of with the implementation: in the parent
exit() path, the child's SIGKILL needs to be delivered _before_ the
tracer is detached. Otherwise it might feasible wake up and run for a
bit :)


Cheers
Chris

>
> Oleg.
>
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