vxlan: fix snooping for link-local IPv6 addresses

If VXLAN is run over link-local IPv6 addresses, it is necessary to store
the ifindex in the FDB entries. Otherwise, the used interface is undefined
and unicast communication will most likely fail.

Support for link-local IPv4 addresses should be possible as well, but as
the semantics aren't as well defined as for IPv6, and there doesn't seem to
be much interest in having the support, it's not implemented for now.
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/vxlan.c

@@ -957,16 +957,24 @@ static int vxlan_fdb_dump(struct sk_buff *skb, struct netlink_callback *cb,
  */
 static bool vxlan_snoop(struct net_device *dev,
 			union vxlan_addr *src_ip, const u8 *src_mac,
-			__be32 vni)
+			u32 src_ifindex, __be32 vni)
 {
 	struct vxlan_dev *vxlan = netdev_priv(dev);
 	struct vxlan_fdb *f;
+	u32 ifindex = 0;
+
+#if IS_ENABLED(CONFIG_IPV6)
+	if (src_ip->sa.sa_family == AF_INET6 &&
+	    (ipv6_addr_type(&src_ip->sin6.sin6_addr) & IPV6_ADDR_LINKLOCAL))
+		ifindex = src_ifindex;
+#endif
 
 	f = vxlan_find_mac(vxlan, src_mac, vni);
 	if (likely(f)) {
 		struct vxlan_rdst *rdst = first_remote_rcu(f);
 
-		if (likely(vxlan_addr_equal(&rdst->remote_ip, src_ip)))
+		if (likely(vxlan_addr_equal(&rdst->remote_ip, src_ip) &&
+			   rdst->remote_ifindex == ifindex))
 			return false;
 
 		/* Don't migrate static entries, drop packets */
@@ -993,7 +1001,7 @@ static bool vxlan_snoop(struct net_device *dev,
 					 vxlan->cfg.dst_port,
 					 vni,
 					 vxlan->default_dst.remote_vni,
-					 0, NTF_SELF);
+					 ifindex, NTF_SELF);
 		spin_unlock(&vxlan->hash_lock);
 	}
 
@@ -1264,6 +1272,7 @@ static bool vxlan_set_mac(struct vxlan_dev *vxlan,
 			  struct sk_buff *skb, __be32 vni)
 {
 	union vxlan_addr saddr;
+	u32 ifindex = skb->dev->ifindex;
 
 	skb_reset_mac_header(skb);
 	skb->protocol = eth_type_trans(skb, vxlan->dev);
@@ -1285,7 +1294,7 @@ static bool vxlan_set_mac(struct vxlan_dev *vxlan,
 	}
 
 	if ((vxlan->cfg.flags & VXLAN_F_LEARN) &&
-	    vxlan_snoop(skb->dev, &saddr, eth_hdr(skb)->h_source, vni))
+	    vxlan_snoop(skb->dev, &saddr, eth_hdr(skb)->h_source, ifindex, vni))
 		return false;
 
 	return true;
@@ -1994,7 +2003,8 @@ static void vxlan_encap_bypass(struct sk_buff *skb, struct vxlan_dev *src_vxlan,
 	}
 
 	if (dst_vxlan->cfg.flags & VXLAN_F_LEARN)
-		vxlan_snoop(skb->dev, &loopback, eth_hdr(skb)->h_source, vni);
+		vxlan_snoop(skb->dev, &loopback, eth_hdr(skb)->h_source, 0,
+			    vni);
 
 	u64_stats_update_begin(&tx_stats->syncp);
 	tx_stats->tx_packets++;