vlan: allow nested vlan_do_receive()

commit 2425717b27eb (net: allow vlan traffic to be received under bond)
broke ARP processing on vlan on top of bonding.

       +-------+
eth0 --| bond0 |---bond0.103
eth1 --|       |
       +-------+

52870.115435: skb_gro_reset_offset <-napi_gro_receive
52870.115435: dev_gro_receive <-napi_gro_receive
52870.115435: napi_skb_finish <-napi_gro_receive
52870.115435: netif_receive_skb <-napi_skb_finish
52870.115435: get_rps_cpu <-netif_receive_skb
52870.115435: __netif_receive_skb <-netif_receive_skb
52870.115436: vlan_do_receive <-__netif_receive_skb
52870.115436: bond_handle_frame <-__netif_receive_skb
52870.115436: vlan_do_receive <-__netif_receive_skb
52870.115436: arp_rcv <-__netif_receive_skb
52870.115436: kfree_skb <-arp_rcv

Packet is dropped in arp_rcv() because its pkt_type was set to
PACKET_OTHERHOST in the first vlan_do_receive() call, since no eth0.103
exists.

We really need to change pkt_type only if no more rx_handler is about to
be called for the packet.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Reviewed-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/if_vlan.h

@@ -106,7 +106,7 @@ extern struct net_device *__vlan_find_dev_deep(struct net_device *real_dev,
 extern struct net_device *vlan_dev_real_dev(const struct net_device *dev);
 extern u16 vlan_dev_vlan_id(const struct net_device *dev);
 
-extern bool vlan_do_receive(struct sk_buff **skb);
+extern bool vlan_do_receive(struct sk_buff **skb, bool last_handler);
 extern struct sk_buff *vlan_untag(struct sk_buff *skb);
 
 #else
@@ -128,9 +128,9 @@ static inline u16 vlan_dev_vlan_id(const struct net_device *dev)
 	return 0;
 }
 
-static inline bool vlan_do_receive(struct sk_buff **skb)
+static inline bool vlan_do_receive(struct sk_buff **skb, bool last_handler)
 {
-	if ((*skb)->vlan_tci & VLAN_VID_MASK)
+	if (((*skb)->vlan_tci & VLAN_VID_MASK) && last_handler)
 		(*skb)->pkt_type = PACKET_OTHERHOST;
 	return false;
 }

net/8021q/vlan_core.c

@@ -4,7 +4,7 @@
 #include <linux/netpoll.h>
 #include "vlan.h"
 
-bool vlan_do_receive(struct sk_buff **skbp)
+bool vlan_do_receive(struct sk_buff **skbp, bool last_handler)
 {
 	struct sk_buff *skb = *skbp;
 	u16 vlan_id = skb->vlan_tci & VLAN_VID_MASK;
@@ -13,7 +13,10 @@ bool vlan_do_receive(struct sk_buff **skbp)
 
 	vlan_dev = vlan_find_dev(skb->dev, vlan_id);
 	if (!vlan_dev) {
-		if (vlan_id)
+		/* Only the last call to vlan_do_receive() should change
+		 * pkt_type to PACKET_OTHERHOST
+		 */
+		if (vlan_id && last_handler)
 			skb->pkt_type = PACKET_OTHERHOST;
 		return false;
 	}

net/core/dev.c

@@ -3283,18 +3283,18 @@ another_round:
 ncls:
 #endif
 
+	rx_handler = rcu_dereference(skb->dev->rx_handler);
 	if (vlan_tx_tag_present(skb)) {
 		if (pt_prev) {
 			ret = deliver_skb(skb, pt_prev, orig_dev);
 			pt_prev = NULL;
 		}
-		if (vlan_do_receive(&skb))
+		if (vlan_do_receive(&skb, !rx_handler))
 			goto another_round;
 		else if (unlikely(!skb))
 			goto out;
 	}
 
-	rx_handler = rcu_dereference(skb->dev->rx_handler);
 	if (rx_handler) {
 		if (pt_prev) {
 			ret = deliver_skb(skb, pt_prev, orig_dev);