bonding: pass link-local packets to bonding master also.

Commit b89f04c6 ("bonding: deliver link-local packets with
skb->dev set to link that packets arrived on") changed the behavior
of how link-local-multicast packets are processed. The change in
the behavior broke some legacy use cases where these packets are
expected to arrive on bonding master device also.

This patch passes the packet to the stack with the link it arrived
on as well as passes to the bonding-master device to preserve the
legacy use case.

Fixes: b89f04c6 ("bonding: deliver link-local packets with skb->dev set to link that packets arrived on")
Reported-by: Michal Soltys <soltys@ziu.info>
Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -1170,9 +1170,26 @@ static rx_handler_result_t bond_handle_frame(struct sk_buff **pskb)
 		}
 	}
 
-	/* don't change skb->dev for link-local packets */
-	if (is_link_local_ether_addr(eth_hdr(skb)->h_dest))
+	/* Link-local multicast packets should be passed to the
+	 * stack on the link they arrive as well as pass them to the
+	 * bond-master device. These packets are mostly usable when
+	 * stack receives it with the link on which they arrive
+	 * (e.g. LLDP) they also must be available on master. Some of
+	 * the use cases include (but are not limited to): LLDP agents
+	 * that must be able to operate both on enslaved interfaces as
+	 * well as on bonds themselves; linux bridges that must be able
+	 * to process/pass BPDUs from attached bonds when any kind of
+	 * STP version is enabled on the network.
+	 */
+	if (is_link_local_ether_addr(eth_hdr(skb)->h_dest)) {
+		struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);
+
+		if (nskb) {
+			nskb->dev = bond->dev;
+			netif_rx(nskb);
+		}
 		return RX_HANDLER_PASS;
+	}
 	if (bond_should_deliver_exact_match(skb, slave, bond))
 		return RX_HANDLER_EXACT;