bonding: fix PACKET_ORIGDEV regression

This patch fixes a subtle PACKET_ORIGDEV regression which was a side
effect of fixes introduced by:

6a9e461f bonding: pass link-local packets to bonding master also.

... to:

b89f04c6 bonding: deliver link-local packets with skb->dev set to link that packets arrived on

While 6a9e461f restored pre-b89f04c6 presence of link-local
packets on bonding masters (which is required e.g. by linux bridges
participating in spanning tree or needed for lab-like setups created
with group_fwd_mask) it also caused the originating device
information to be lost due to cloning.

Maciej Żenczykowski proposed another solution that doesn't require
packet cloning and retains original device information - instead of
returning RX_HANDLER_PASS for all link-local packets it's now limited
only to packets from inactive slaves.

At the same time, packets passed to bonding masters retain correct
information about the originating device and PACKET_ORIGDEV can be used
to determine it.

This elegantly solves all issues so far:

- link-local packets that were removed from bonding masters
- LLDP daemons being forced to explicitly bind to slave interfaces
- PACKET_ORIGDEV having no effect on bond interfaces

Fixes: 6a9e461f (bonding: pass link-local packets to bonding master also.)
Reported-by: Vincent Bernat <vincent@bernat.ch>
Signed-off-by: Michal Soltys <soltys@ziu.info>
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -1183,29 +1183,22 @@ static rx_handler_result_t bond_handle_frame(struct sk_buff **pskb)
 		}
 	}
 
-	/* 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.
+	/*
+	 * For packets determined by bond_should_deliver_exact_match() call to
+	 * be suppressed we want to make an exception for link-local packets.
+	 * This is necessary for e.g. LLDP daemons to be able to monitor
+	 * inactive slave links without being forced to bind to them
+	 * explicitly.
+	 *
+	 * At the same time, packets that are passed to the bonding master
+	 * (including link-local ones) can have their originating interface
+	 * determined via PACKET_ORIGDEV socket option.
 	 */
-	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;
-			nskb->queue_mapping = 0;
-			netif_rx(nskb);
-		}
+	if (bond_should_deliver_exact_match(skb, slave, bond)) {
+		if (is_link_local_ether_addr(eth_hdr(skb)->h_dest))
 			return RX_HANDLER_PASS;
-	}
-	if (bond_should_deliver_exact_match(skb, slave, bond))
 		return RX_HANDLER_EXACT;
+	}
 
 	skb->dev = bond->dev;