bonding: fix error handling if slave is busy (v2)

If slave device already has a receive handler registered, then the
error unwind of bonding device enslave function is broken.

The following will leave a pointer to freed memory in the slave
device list, causing a later kernel panic.
# modprobe dummy
# ip li add dummy0-1 link dummy0 type macvlan
# modprobe bonding
# echo +dummy0 >/sys/class/net/bond0/bonding/slaves

The fix is to detach the slave (which removes it from the list)
in the unwind path.
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Reviewed-by: Nicolas de Pesloüan <nicolas.2p.debian@free.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -1822,7 +1822,7 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
 				 "but new slave device does not support netpoll.\n",
 				 bond_dev->name);
 			res = -EBUSY;
-			goto err_close;
+			goto err_detach;
 		}
 	}
 #endif
@@ -1831,7 +1831,7 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
 
 	res = bond_create_slave_symlinks(bond_dev, slave_dev);
 	if (res)
-		goto err_close;
+		goto err_detach;
 
 	res = netdev_rx_handler_register(slave_dev, bond_handle_frame,
 					 new_slave);
@@ -1852,6 +1852,11 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
 err_dest_symlinks:
 	bond_destroy_slave_symlinks(bond_dev, slave_dev);
 
+err_detach:
+	write_lock_bh(&bond->lock);
+	bond_detach_slave(bond, new_slave);
+	write_unlock_bh(&bond->lock);
+
 err_close:
 	dev_close(slave_dev);