Sorry, just dropped in here, and saw the question.
I have myself several AP's using DD-WRT on a OPT1 interface, captive portal enabled on OPT1.
Of course, I wouldn't like it that my 'clients' could hammer on my AP's.
Can I presume that the IP of your AP = 192.168.1.2 ?
Open the web interface of your DD-WRT
Goto Administartion => Shell
Paste this code into the "fire wall" block.
Save.
#!/bin/sh
/usr/sbin/iptables -N logdrop
/usr/sbin/iptables -F logdrop
/usr/sbin/iptables -A logdrop -j LOG
/usr/sbin/iptables -A logdrop -j DROP
/usr/sbin/iptables -I INPUT -i br0 -s 192.168.1.0/24 -p tcp --dport 80 -j logdrop
/usr/sbin/iptables -I INPUT -i br0 -s 192.168.1.0/24 -p tcp --dport 22 -j logdrop
/usr/sbin/iptables -I INPUT -i br0 -s 192.168.1.0/24 -p tcp --dport 23 -j logdrop
## end
With this code, YOU can administer your AP from the LAN interface (192.168.0.0/24) - [DO NOT forget to ADD to Services => Captive Portal => Allowed IP addresses => Direction = Both IP = 192.168.1.2 and hit Save. - This way the AP itself can now communicate with the net to play games, update the time, have a chat, and answer to YOU when you want to login from anywhere except 192.168.1.0/24 ]
No one, coming form the subnet 192.168.1.0/24 can access the DD-WRT interfaces.