[PATCH net 2/5] vxlan: Don't double-free default FDB entry 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.

Fix by skipping the rollback code and just returning.

Fixes: 0241b836732f ("vxlan: fix default fdb entry netlink notify ordering 
during netdev create")
Signed-off-by: Petr Machata <pe...@mellanox.com>
---
 drivers/net/vxlan.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index c9956c08edf5..139741617b90 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)
@@ -3298,8 +3299,8 @@ static int __vxlan_dev_create(struct net *net, struct 
net_device *dev,
        list_add(&vxlan->next, &vn->vxlan_list);
        return 0;
 errout:
-       if (f)
-               vxlan_fdb_destroy(vxlan, f, false);
+       unregister_netdevice(dev);
+       /* the all_zeros_mac entry was deleted at vxlan_uninit */
        return err;
 }
 
-- 
2.4.11