vxlan: fix race between flush and incoming learning

It is possible for a packet to arrive during vxlan_stop(), and
have a dynamic entry created. Close this by checking if device
is up.

 CPU1                             CPU2
vxlan_stop
  vxlan_flush
     hash_lock acquired
                                  vxlan_encap_recv
                                     vxlan_snoop
                                        waiting for hash_lock
     hash_lock relased
  vxlan_flush done
                                        hash_lock acquired
                                        vxlan_fdb_create

This is a day-one bug in vxlan goes back to 3.7.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 7 deletions

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index 3b1d2ee7156b..577a069a6dde 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -571,7 +571,6 @@ static void vxlan_snoop(struct net_device *dev,
 {
         struct vxlan_dev *vxlan = netdev_priv(dev);
         struct vxlan_fdb *f;
-        int err;
 
         f = vxlan_find_mac(vxlan, src_mac);
         if (likely(f)) {
@@ -588,12 +587,15 @@ static void vxlan_snoop(struct net_device *dev,
         } else {
                 /* learned new entry */
                 spin_lock(&vxlan->hash_lock);
-                err = vxlan_fdb_create(vxlan, src_mac, src_ip,
-                                       NUD_REACHABLE,
-                                       NLM_F_EXCL|NLM_F_CREATE,
-                                       vxlan->dst_port,
-                                       vxlan->default_dst.remote_vni,
-                                       0, NTF_SELF);
+
+                /* close off race between vxlan_flush and incoming packets */
+                if (netif_running(dev))
+                        vxlan_fdb_create(vxlan, src_mac, src_ip,
+                                         NUD_REACHABLE,
+                                         NLM_F_EXCL|NLM_F_CREATE,
+                                         vxlan->dst_port,
+                                         vxlan->default_dst.remote_vni,
+                                         0, NTF_SELF);
                 spin_unlock(&vxlan->hash_lock);
         }
 }