vxlan: set needed headroom correctly

commit 9dc2ad10 upstream.

vxlan_setup is called when allocating the net_device, i.e. way before
vxlan_newlink (or vxlan_dev_configure) is called. This means
vxlan->default_dst is actually unset in vxlan_setup and the condition that
sets needed_headroom always takes the else branch.

Set the needed_headrom at the point when we have the information about
the address family available.

Fixes: e4c7ed41 ("vxlan: add ipv6 support")
Fixes: 2853af6a ("vxlan: use dev->needed_headroom instead of dev->hard_header_len")
CC: Cong Wang <cwang@twopensource.com>
Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[ luis: backported to 3.16:
  - initialise needed_headrom in vxlan_newlink() instead of
    vxlan_dev_configure() ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/net/vxlan.c

@@ -2251,10 +2251,6 @@ static void vxlan_setup(struct net_device *dev)
 
 	eth_hw_addr_random(dev);
 	ether_setup(dev);
-	if (vxlan->default_dst.remote_ip.sa.sa_family == AF_INET6)
-		dev->needed_headroom = ETH_HLEN + VXLAN6_HEADROOM;
-	else
-		dev->needed_headroom = ETH_HLEN + VXLAN_HEADROOM;
 
 	dev->netdev_ops = &vxlan_netdev_ops;
 	dev->destructor = free_netdev;
@@ -2651,8 +2647,12 @@ static int vxlan_newlink(struct net *net, struct net_device *dev,
 
 		dev->needed_headroom = lowerdev->hard_header_len +
 				       (use_ipv6 ? VXLAN6_HEADROOM : VXLAN_HEADROOM);
-	} else if (use_ipv6)
+	} else if (use_ipv6) {
 		vxlan->flags |= VXLAN_F_IPV6;
+		dev->needed_headroom = ETH_HLEN + VXLAN6_HEADROOM;
+	} else {
+		dev->needed_headroom = ETH_HLEN + VXLAN_HEADROOM;
+	}
 
 	if (data[IFLA_VXLAN_TOS])
 		vxlan->tos  = nla_get_u8(data[IFLA_VXLAN_TOS]);