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

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Message-ID: <1326383015.7642.77.camel@gandalf.stny.rr.com>
Date:	Thu, 12 Jan 2012 10:43:35 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Will Drewry <wad@...omium.org>
Cc:	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,
	oleg@...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 Wed, 2012-01-11 at 11:25 -0600, Will Drewry wrote:

> Filter programs may _only_ cross the execve(2) barrier if last filter
> program was attached by a task with CAP_SYS_ADMIN capabilities in its
> user namespace.  Once a task-local filter program is attached from a
> process without privileges, execve will fail.  This ensures that only
> privileged parent task can affect its privileged children (e.g., setuid
> binary).

This means that a non privileged user can not run another program with
limited features? How would a process exec another program and filter
it? I would assume that the filter would need to be attached first and
then the execv() would be performed. But after the filter is attached,
the execv is prevented?

Maybe I don't understand this correctly.

-- Steve
 

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