From LinuxTag Public Wiki
Parking your car within the area of Messe Berlin is prohibited and your car may be towed away on your own cost. If you have to bring some stuff directly to the exhibition hall, please see Cruising the Area of Messe Berlin for Delivery.
All parking lots around Messe Berlin will be open and usable free of charge. The nearest one to the entrace is P13 and P13a as shown in light blue on the map.