Can anyone tell me how I can block a TV that's on my wifi from accessing anything outside the LAN?

I do want the TV to be able to access local PCs however, so I can use its inbuilt apps to play videos from a local DLNA server on my HTPC.

But I don't want it to be able to access its firmware server, ad servers, or anything else outside my house.

My router is a TP-Link TL-WDR3600 v1 running DD-WRT v3.0-r46788 std.