vxlan: Fix error path in __vxlan_dev_create()

mainline inclusion
from mainline-4.20
commit 6db92468
category: bugfix
bugzilla: 6186
CVE: NA

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

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, move the unregister_netdevice() call after the manual destroy,
which solves both problems.

Fixes: 0241b836 ("vxlan: fix default fdb entry netlink notify ordering during netdev create")
Signed-off-by: NPetr Machata <petrm@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NMao Wenan <maowenan@huawei.com>
Reviewed-by: NWei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/net/vxlan.c

@@ -3190,6 +3190,7 @@ static int __vxlan_dev_create(struct net *net, struct net_device *dev,
 	struct vxlan_net *vn = net_generic(net, vxlan_net_id);
 	struct vxlan_dev *vxlan = netdev_priv(dev);
 	struct vxlan_fdb *f = NULL;
+	bool unregister = false;
 	int err;
 
 	err = vxlan_dev_configure(net, dev, conf, false, extack);
@@ -3215,12 +3216,11 @@ static int __vxlan_dev_create(struct net *net, struct net_device *dev,
 	err = register_netdevice(dev);
 	if (err)
 		goto errout;
+	unregister = true;
 
 	err = rtnl_configure_link(dev, NULL);
-	if (err) {
-		unregister_netdevice(dev);
+	if (err)
 		goto errout;
-	}
 
 	/* notify default fdb entry */
 	if (f)
@@ -3228,9 +3228,16 @@ 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);
+	if (unregister)
+		unregister_netdevice(dev);
 	return err;
 }