netdev - [v2 PATCH 1/2] macvlan: Fix potential use-after free for broadcasts

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Message-ID: <20160601034300.GB31335@gondor.apana.org.au>
Date:	Wed, 1 Jun 2016 11:43:00 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
Cc:	buytenh@...tstofly.org, kaber@...sh.net, netdev@...r.kernel.org,
	jpirko@...hat.com
Subject: [v2 PATCH 1/2] macvlan: Fix potential use-after free for broadcasts

When we postpone a broadcast packet we save the source port in
the skb if it is local.  However, the source port can disappear
before we get a chance to process the packet.

This patch fixes this by holding a ref count on the netdev.

It also delays the skb->cb modification until after we allocate
the new skb as you should not modify shared skbs.

Fixes: 412ca1550cbe ("macvlan: Move broadcasts into a work queue")
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index 2bcf1f3..78a00e3 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -305,11 +305,14 @@ static void macvlan_process_broadcast(struct work_struct *w)
 
 		rcu_read_unlock();
 
+		if (src)
+			dev_put(src->dev);
 		kfree_skb(skb);
 	}
 }
 
 static void macvlan_broadcast_enqueue(struct macvlan_port *port,
+				      const struct macvlan_dev *src,
 				      struct sk_buff *skb)
 {
 	struct sk_buff *nskb;
@@ -319,8 +322,12 @@ static void macvlan_broadcast_enqueue(struct macvlan_port *port,
 	if (!nskb)
 		goto err;
 
+	MACVLAN_SKB_CB(nskb)->src = src;
+
 	spin_lock(&port->bc_queue.lock);
 	if (skb_queue_len(&port->bc_queue) < MACVLAN_BC_QUEUE_LEN) {
+		if (src)
+			dev_hold(src->dev);
 		__skb_queue_tail(&port->bc_queue, nskb);
 		err = 0;
 	}
@@ -429,8 +436,7 @@ static rx_handler_result_t macvlan_handle_frame(struct sk_buff **pskb)
 			goto out;
 		}
 
-		MACVLAN_SKB_CB(skb)->src = src;
-		macvlan_broadcast_enqueue(port, skb);
+		macvlan_broadcast_enqueue(port, src, skb);
 
 		return RX_HANDLER_PASS;
 	}
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt