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

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

Le vendredi 26 novembre 2010 à 12:38 +0800, Shan Wei a écrit :
> Eric Dumazet wrote, at 11/25/2010 10:11 PM:
> > Le jeudi 25 novembre 2010 à 13:35 +0500, Марк Коренберг a écrit :
> >> quick and dirty fix will be not to allow to pass unix socket inside
> >> unix socket. I think it would not break much applications.
> > 
> > Really, if it was not needed, net/unix/garbage.c would not exist at
> > all...
> > 
> > It is needed by some apps.
> > 
> > 
> > [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>
> 
> This problem is same as that reported with title "Unix socket local DOS (OOM)", right?
> After applied this patch, this program can be killed now. but still eat 100% cpu. 
> 

Not the same problem, but a different one. 

In this case, we queue files on top of another and never give a chance
to free them, unless the program dies (and full memory eaten)

And yes, its eating 100% cpu, since it has no sleep inside, like

for (;;) ;