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

[David Miller <davem@davemloft.net>]

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!