linux-kernel - Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF

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Message-ID: <20120112164751.GA24802@redhat.com>
Date:	Thu, 12 Jan 2012 17:47:51 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	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,
	jmorris@...ei.org, scarybeasts@...il.com, avi@...hat.com,
	penberg@...helsinki.fi, viro@...iv.linux.org.uk, luto@....edu,
	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
Subject: Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using
	BPF

On 01/12, Steven Rostedt wrote:
>
> On Thu, 2012-01-12 at 17:14 +0100, Oleg Nesterov wrote:
>
> > May be this needs something like LSM_UNSAFE_SECCOMP, or perhaps
> > cap_bprm_set_creds() should take seccomp.mode == 2 into account, I dunno.
> >
> > OTOH, currently seccomp.mode == 1 doesn't allow to exec at all.
>
> I've never used seccomp, so I admit I'm totally ignorant on this topic.

me too ;)

> But looking at seccomp from the outside, the biggest advantage to this
> would be the ability for normal processes to be able to limit tasks it
> kicks off. If I want to run a task in a sandbox, I don't want to be root
> to do so.
>
> I guess a web browser doesn't perform an exec to run java programs. But
> it would be nice if I could execute something from the command line that
> I could run in a sand box.
>
> What's the problem with making sure that the setuid isn't set before
> doing an execv? Only fail when setuid (or some other magic) is enabled
> on the file being exec'd.

I agree. That is why I mentioned LSM_UNSAFE_SECCOMP/cap_bprm_set_creds.
Just I do not know what would be the most simple/clean way to do this.


And in any case I agree that the current seccomp_check_exec() looks
strange. Btw, it does
{
	if (current->seccomp.mode != 2)
		return 0;
	/* We can rely on the task refcount for the filter. */
	if (!current->seccomp.filter)
		return -EPERM;

How it is possible to have seccomp.filter == NULL with mode == 2?

Oleg.

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