Subject: Re: PROBLEM: pppol2tp over pppoe NULL pointer dereference

From: "Jorge Boncompte [DTI2]" <[email-masked]>
Date: Wed, 02 Nov 2011 16:54:30 +0100

El 02/11/2011 8:07, Eric Dumazet escribió:
> Le mercredi 02 novembre 2011 à 09:04 +0400, Misha Labjuk a écrit :
>> 2011/11/2 Eric Dumazet <[email-masked]>:
>>>
>>> On what kind of NIC this is happening ?
>>>
>>
>> Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit
>> Ethernet controller (rev 02)
>> Kernel driver in use: r8169
> 
> OK thanks, could you try the following patch as well ?
> 
> If we release reorder_q.lock, we must not keep a dangling pointer (tmp)
> and restart the whole loop.
> 
> diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
> index 34b2dde..bf8d50c 100644
> --- a/net/l2tp/l2tp_core.c
> +++ b/net/l2tp/l2tp_core.c
> @@ -397,6 +397,7 @@ static void l2tp_recv_dequeue(struct l2tp_session *session)
>  	 * expect to send up next, dequeue it and any other
>  	 * in-sequence packets behind it.
>  	 */
> +start:
>  	spin_lock_bh(&session->reorder_q.lock);
>  	skb_queue_walk_safe(&session->reorder_q, skb, tmp) {
>  		if (time_after(jiffies, L2TP_SKB_CB(skb)->expires)) {
> @@ -433,7 +434,7 @@ static void l2tp_recv_dequeue(struct l2tp_session *session)
>  		 */
>  		spin_unlock_bh(&session->reorder_q.lock);
>  		l2tp_recv_dequeue_skb(session, skb);
> -		spin_lock_bh(&session->reorder_q.lock);
> +		goto start;
>  	}
>  
>  out:
> 
> 
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> 
> 

	I've been using this same exact patch on an old kernel since a while ago. I had
one system that crashed here, now decommissioned. After some testing I was
unable to reproduce the bug in another systems but on the one that exhibited the
problem it fixed the crashes.

	Regards,
		Jorge
-- 
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Jorge Boncompte - Ingenieria y Gestion de RED
DTI2 - Desarrollo de la Tecnologia de las Comunicaciones
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