[PATCH 3.16 029/328] vxlan: fix default fdb entry netlink notify ordering during netdev create

[Ben Hutchings]

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Roopa Prabhu <roopa@xxxxxxxxxxxxxxxxxxx>

commit 0241b836732f5f43c3f0fd9e9073c1fb24ea6757 upstream.

Problem:
In vxlan_newlink, a default fdb entry is added before register_netdev.
The default fdb creation function also notifies user-space of the
fdb entry on the vxlan device which user-space does not know about yet.
(RTM_NEWNEIGH goes before RTM_NEWLINK for the same ifindex).

This patch fixes the user-space netlink notification ordering issue
with the following changes:
- decouple fdb notify from fdb create.
- Move fdb notify after register_netdev.
- Call rtnl_configure_link in vxlan newlink handler to notify
userspace about the newlink before fdb notify and
hence avoiding the user-space race.

Fixes: afbd8bae9c79 ("vxlan: add implicit fdb entry for default destination")
Signed-off-by: Roopa Prabhu <roopa@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.16:
 - Drop changes to vxlan_changelink()
 - Drop last argument to vxlan_fdb_destroy()
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2614,6 +2614,7 @@ static int vxlan_newlink(struct net *net
 	struct vxlan_net *vn = net_generic(net, vxlan_net_id);
 	struct vxlan_dev *vxlan = netdev_priv(dev), *tmp;
 	struct vxlan_rdst *dst = &vxlan->default_dst;
+	struct vxlan_fdb *f = NULL;
 	__u32 vni;
 	int err;
 	bool use_ipv6 = false;
@@ -2751,27 +2752,38 @@ static int vxlan_newlink(struct net *net
 
 	/* create an fdb entry for a valid default destination */
 	if (!vxlan_addr_any(&vxlan->default_dst.remote_ip)) {
-		err = vxlan_fdb_update(vxlan, all_zeros_mac,
+		err = vxlan_fdb_create(vxlan, all_zeros_mac,
 				       &vxlan->default_dst.remote_ip,
 				       NUD_REACHABLE|NUD_PERMANENT,
-				       NLM_F_EXCL|NLM_F_CREATE,
 				       vxlan->dst_port,
 				       vxlan->default_dst.remote_vni,
 				       vxlan->default_dst.remote_ifindex,
-				       NTF_SELF);
+				       NTF_SELF, &f);
 		if (err)
 			return err;
 	}
 
 	err = register_netdevice(dev);
+	if (err)
+		goto errout;
+
+	err = rtnl_configure_link(dev, NULL);
 	if (err) {
-		vxlan_fdb_delete_default(vxlan);
-		return err;
+		unregister_netdevice(dev);
+		goto errout;
 	}
 
+	/* notify default fdb entry */
+	if (f)
+		vxlan_fdb_notify(vxlan, f, first_remote_rtnl(f), RTM_NEWNEIGH);
+
 	list_add(&vxlan->next, &vn->vxlan_list);
 
 	return 0;
+errout:
+	if (f)
+		vxlan_fdb_destroy(vxlan, f);
+	return err;
 }
 
 static void vxlan_dellink(struct net_device *dev, struct list_head *head)