Re: Simple kernel attack using socketpair. easy, 100% reproductiblle, works under guest. no way to protect :(

[Eric Dumazet <eric.dumazet@gmail.com>]

Le lundi 29 novembre 2010 à 09:46 -0800, David Miller a écrit :
> From: Eric Dumazet <eric.dumazet@gmail.com>
> Date: Thu, 25 Nov 2010 15:11:39 +0100
> 
> > [PATCH] af_unix: limit recursion level
> > 
> > Its easy to eat all kernel memory and trigger NMI watchdog, using an
> > exploit program that queues unix sockets on top of others.
> > 
> > lkml ref : http://lkml.org/lkml/2010/11/25/8
> > 
> > This mechanism is used in applications, one choice we have is to have a
> > recursion limit.
> > 
> > Other limits might be needed as well (if we queue other types of files),
> > since the passfd mechanism is currently limited by socket receive queue
> > sizes only.
> > 
> > Add a recursion_level to unix socket, allowing up to 4 levels.
> > 
> > Each time we send an unix socket through sendfd mechanism, we copy its
> > recursion level (plus one) to receiver. This recursion level is cleared
> > when socket receive queue is emptied.
> > 
> > Reported-by: Марк Коренберг <socketpair@gmail.com>
> > Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> 
> Ok, since such deep recursive AF_UNIX fd sends is pretty
> rediculious, it seems this is not likely to hit legitimate
> use cases and thus I've applied this.
> 
> Also queued up for -stable.
> 
> Thanks!

I tested FreeBSD (latest) and got a kernel freeze as well with exploit
program.

I dont know yet how to fully fix this problem.