[PATCH net v2 2/4] vxlan: Fix error path in __vxlan_dev_create()

[Petr Machata]

When a failure occurs in rtnl_configure_link(), the current code
calls unregister_netdevice() to roll back the earlier call to
register_netdevice(), and jumps to errout, which calls
vxlan_fdb_destroy().

However unregister_netdevice() calls transitively ndo_uninit, which is
vxlan_uninit(), and that already takes care of deleting the default FDB
entry by calling vxlan_fdb_delete_default(). Since the entry added
earlier in __vxlan_dev_create() is exactly the default entry, the
cleanup code in the errout block always leads to double free and thus a
panic.

Besides, since vxlan_fdb_delete_default() always destroys the FDB entry
with notification enabled, the deletion of the default entry is notified
even before the addition was notified.

Instead, before calling unregister_netdevice(), destroy the default FDB
entry by hand, which solves both problems.

Fixes: 0241b836732f ("vxlan: fix default fdb entry netlink notify ordering 
during netdev create")
Signed-off-by: Petr Machata <pe...@mellanox.com>
---

Notes:
    v2:
    
    - Delete the default entry before calling unregister_netdevice(). That
      takes care of former patch #3, hence tweak the commit message to
      mention that problem as well.

 drivers/net/vxlan.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index c9956c08edf5..f29bf7d3e682 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -3282,14 +3282,15 @@ static int __vxlan_dev_create(struct net *net, struct 
net_device *dev,
        }
 
        err = register_netdevice(dev);
-       if (err)
-               goto errout;
+       if (err) {
+               if (f)
+                       vxlan_fdb_destroy(vxlan, f, false);
+               return err;
+       }
 
        err = rtnl_configure_link(dev, NULL);
-       if (err) {
-               unregister_netdevice(dev);
+       if (err)
                goto errout;
-       }
 
        /* notify default fdb entry */
        if (f)
@@ -3297,9 +3298,15 @@ static int __vxlan_dev_create(struct net *net, struct 
net_device *dev,
 
        list_add(&vxlan->next, &vn->vxlan_list);
        return 0;
+
 errout:
+       /* unregister_netdevice() destroys the default FDB entry with deletion
+        * notification. But the addition notification was not sent yet, so
+        * destroy the entry by hand here.
+        */
        if (f)
                vxlan_fdb_destroy(vxlan, f, false);
+       unregister_netdevice(dev);
        return err;
 }
 
-- 
2.4.11