linux-kernel - Re: [PATCH 5/7] seccomp_filter: Document what seccomp

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Date:	Fri, 06 May 2011 09:35:37 -0400
From:	Eric Paris <eparis@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Will Drewry <wad@...omium.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	kees.cook@...onical.com, agl@...omium.org, jmorris@...ei.org,
	Randy Dunlap <rdunlap@...otime.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 5/7] seccomp_filter: Document what seccomp_filter is and
 how it works.

On Fri, 2011-05-06 at 07:53 -0400, Steven Rostedt wrote:
> On Thu, 2011-05-05 at 02:21 -0700, Will Drewry wrote:
> 
> > In particular, if the userspace code wants to stage some filters and
> > apply them all at once, when ready, I'm not sure that it makes sense
> > to me to put that complexity in the kernel itself.  For instance,
> > Eric's second sample showed a call that took an array of ints and
> > coalesced them into "fd == %d || ...".  That simple example shows that
> > we could easily get by with a pretty minimal kernel-supported
> > interface as long as the richer behavior could live userspace side --
> > even if just in a simple helper library.  It'd be pretty easy to
> > implement a userspace library that exposed add_filter(syscall_nr,
> > filter) and apply_filters() such that it could manage building the
> > final filter string for a given syscall and pushing it to prctl on
> > apply.
> 
> I'm fine with a single kernel call and the "temporary filter" be done in
> userspace. Making the kernel code less complex is better :)

I'm also starting to think a userspace library is a good idea as well.
Everything in the kernel is an && with nothing but SET and APPLY.  We
provide interfaces to build the strings as we go along including UNSET
and stuff like that if there are users....

-Eric

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