[PATCH 4.4 309/312] macvlan: Fix potential use-after free for broadcasts

[Greg Kroah-Hartman]

From: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

commit 260916dfb48c374f7840f3b86e69afd3afdb6e96 upstream.

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@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/net/macvlan.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -305,6 +305,8 @@ static void macvlan_process_broadcast(st
 
 		rcu_read_unlock();
 
+		if (src)
+			dev_put(src->dev);
 		kfree_skb(skb);
 
 		cond_resched();
@@ -312,6 +314,7 @@ static void macvlan_process_broadcast(st
 }
 
 static void macvlan_broadcast_enqueue(struct macvlan_port *port,
+				      const struct macvlan_dev *src,
 				      struct sk_buff *skb)
 {
 	struct sk_buff *nskb;
@@ -321,8 +324,12 @@ static void macvlan_broadcast_enqueue(st
 	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;
 	}
@@ -432,8 +439,7 @@ static rx_handler_result_t macvlan_handl
 			goto out;
 		}
 
-		MACVLAN_SKB_CB(skb)->src = src;
-		macvlan_broadcast_enqueue(port, skb);
+		macvlan_broadcast_enqueue(port, src, skb);
 
 		return RX_HANDLER_PASS;
 	}