[MACVLAN]: Prevent nesting macvlan devices

Don't allow to nest macvlan devices since it will cause lockdep
warnings and isn't really useful for anything.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index 2e4bcd5654c..e8dc2f44fec 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -384,6 +384,13 @@ static int macvlan_newlink(struct net_device *dev,
         if (lowerdev == NULL)
                 return -ENODEV;
 
+        /* Don't allow macvlans on top of other macvlans - its not really
+         * wrong, but lockdep can't handle it and its not useful for anything
+         * you couldn't do directly on top of the real device.
+         */
+        if (lowerdev->rtnl_link_ops == dev->rtnl_link_ops)
+                return -ENODEV;
+
         if (!tb[IFLA_MTU])
                 dev->mtu = lowerdev->mtu;
         else if (dev->mtu > lowerdev->mtu)