From: =?iso-8859-1?q?R=E9mi_Denis-Courmont?= <rdenis@simphalempin.com>
Organization: Remlab.net
To: Andi Kleen <andi@firstfloor.org>
Subject: Re: RFC: Network privilege separation.
Date: Mon, 12 Jan 2009 22:15:27 +0200
User-Agent: KMail/1.9.9
Cc: Valdis.Kletnieks@vt.edu, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Michael Stone <michael@laptop.org>, linux-kernel@vger.kernel.org,
       netdev@vger.kernel.org
References: <1231307334-9542-1-git-send-email-michael@laptop.org> <200901122147.57731.rdenis@simphalempin.com> <20090112201435.GC23848@one.firstfloor.org>
In-Reply-To: <20090112201435.GC23848@one.firstfloor.org>
MIME-Version: 1.0
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 8BIT
Content-Disposition: inline
Message-Id: <200901122215.27842.rdenis@simphalempin.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1439
Lines: 39

Le lundi 12 janvier 2009 22:14:35 Andi Kleen, vous avez ?crit?:
> > Expanding the heap,
>
> That's a problem agreed  Ok you can just always use very
> bss arrays sized for the worst case.
>
> > Getting timestamps.
>
> At least on 64bit that's done in ring 3 only with a vsyscall.
>
> > Waiting on futexes,
> > catching signals, polling file descriptors. Seeking, doing vectorized
> > I/O. Cloning.
>
> That all can be done by the frontend reading/feeding
> data into the pipe. But it shouldn't directly access the user data
> to be immune against attacks.

What's the point of writing a parser (that could also have bugs) when the 
kernel can do it? One could argue that shared futexes could be dangerous, but 
not the rest?

> > Codecs don't like to read/write raw video through a pipe...
>
> I don't think that's given. It would need some restructuring,
> but I think the end result would be likely worth it.

A normal DVD would be over 30 megabytes per seconds once decoded, just for the 
video. And remember vmsplice() is not allowed by SECCOMP. Media players have 
assembly-coded memory copy optimizations (like the kernel) for some reason.

-- 
R?mi Denis-Courmont
http://www.remlab.net/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/