netdev - Re: PROBLEM: pppol2tp over pppoe NULL pointer dereference

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Date:	Thu, 03 Nov 2011 09:47:44 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Misha Labjuk <spiked.yar@...il.com>,
	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: PROBLEM: pppol2tp over pppoe NULL pointer dereference

Le jeudi 03 novembre 2011 à 02:35 +0400, Misha Labjuk a écrit :
> Thanks!!  Panic disappeared.
> 

Here is the official patch submission again (not mangled this time),
thanks !

[PATCH] l2tp: fix race in l2tp_recv_dequeue()

Misha Labjuk reported panics occurring in l2tp_recv_dequeue()

If we release reorder_q.lock, we must not keep a dangling pointer (tmp),
since another thread could manipulate reorder_q.

Instead we must restart the scan at beginning of list.

Reported-by: Misha Labjuk <spiked.yar@...il.com>
Tested-by: Misha Labjuk <spiked.yar@...il.com>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
 net/l2tp/l2tp_core.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

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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