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

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Message-ID: <1290669242.2798.110.camel@edumazet-laptop>
Date:	Thu, 25 Nov 2010 08:14:02 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Марк Коренберг 
	<socketpair@...il.com>
Cc:	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: Simple kernel attack using socketpair. easy, 100%
 reproductiblle, works under guest. no way to protect :(

Le jeudi 25 novembre 2010 à 07:28 +0100, Eric Dumazet a écrit :

> 
> Since you obviously read recent mails on this subject yesterday, why
> dont you Cc netdev ?
> 
> There is a very easy way to protect against this actually.
> 
> A patch was posted yesterday, and need some adjustements.
> 
> 
> diff --git a/net/unix/garbage.c b/net/unix/garbage.c
> index c8df6fd..40df93d 100644
> --- a/net/unix/garbage.c
> +++ b/net/unix/garbage.c
> @@ -259,9 +259,16 @@ static void inc_inflight_move_tail(struct unix_sock *u)
>  }
>  
>  static bool gc_in_progress = false;
> +#define UNIX_INFLIGHT_TRIGGER_GC 2000
>  
>  void wait_for_unix_gc(void)
>  {
> +	/*
> +	 * If number of inflight sockets is insane,
> +	 * force a garbage collect right now.
> +	 */
> +	if (unix_tot_inflight > UNIX_INFLIGHT_TRIGGER_GC && !gc_in_progress)
> +		unix_gc();
>  	wait_event(unix_gc_wait, gc_in_progress == false);
>  }
>  
> 

Hmm... it seems its another problem, chains are very long so we hit a
NMI watchdog.

I guess we should limit to a very small number, like 64, or rewrite the
garbage collector to a better algo.



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