IB/mlx4: Avoid null pointer dereference in mlx4_ib_scan_netdevs()

When Ethernet netdev is not present for a port (e.g. when the link
layer type of the port is InfiniBand) it's possible to dereference a
null pointer when we do netdevice scanning.

To fix that, we move a section of code that needs to run only when
netdev is present to a proper if () statement.

Fixes: ad4885d2 ("IB/mlx4: Build the port IBoE GID table properly under bonding")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/mlx4/main.c

@@ -1789,32 +1789,35 @@ static void mlx4_ib_scan_netdevs(struct mlx4_ib_dev *ibdev,
 			port_state = (netif_running(curr_netdev) && netif_carrier_ok(curr_netdev)) ?
 						IB_PORT_ACTIVE : IB_PORT_DOWN;
 			mlx4_ib_set_default_gid(ibdev, curr_netdev, port);
-		} else {
-			reset_gid_table(ibdev, port);
-		}
-		/* if using bonding/team and a slave port is down, we don't the bond IP
-		 * based gids in the table since flows that select port by gid may get
-		 * the down port.
+			/* if using bonding/team and a slave port is down, we
+			 * don't the bond IP based gids in the table since
+			 * flows that select port by gid may get the down port.
 			 */
 			if (curr_master && (port_state == IB_PORT_DOWN)) {
 				reset_gid_table(ibdev, port);
-			mlx4_ib_set_default_gid(ibdev, curr_netdev, port);
+				mlx4_ib_set_default_gid(ibdev,
+							curr_netdev, port);
 			}
-		/* if bonding is used it is possible that we add it to masters
-		 * only after IP address is assigned to the net bonding
-		 * interface.
+			/* if bonding is used it is possible that we add it to
+			 * masters only after IP address is assigned to the
+			 * net bonding interface.
 			*/
 			if (curr_master && (old_master != curr_master)) {
 				reset_gid_table(ibdev, port);
-			mlx4_ib_set_default_gid(ibdev, curr_netdev, port);
+				mlx4_ib_set_default_gid(ibdev,
+							curr_netdev, port);
 				mlx4_ib_get_dev_addr(curr_master, ibdev, port);
 			}
 
 			if (!curr_master && (old_master != curr_master)) {
 				reset_gid_table(ibdev, port);
-			mlx4_ib_set_default_gid(ibdev, curr_netdev, port);
+				mlx4_ib_set_default_gid(ibdev,
+							curr_netdev, port);
 				mlx4_ib_get_dev_addr(curr_netdev, ibdev, port);
 			}
+		} else {
+			reset_gid_table(ibdev, port);
+		}
 	}
 
 	spin_unlock(&iboe->lock);