- By default, access is denied.
- Traffic destined for anywhere but to a select few services (i.e., TCP or UDP ports) is blocked by the local firewall.
- NTP
- IMAP(S)
- POP(S)
- OpenVPN
- IPsec
- HTTP(S) traffic caught by firewall, redirected to the mesh node's client IP and port.
- iptables -t nat -A PREROUTING -i wlan0 -p tcp --dport 80 -j REDIRECT --to-port 31337
- iptables -t nat -A PREROUTING -i wlan0 -p tcp --dport 443 -j REDIRECT --to-port 31338
- We'd have to add an extra bit in there --destination 10.x.x.1
- A web server listening on the redirect ports (31337/TCP and 31338/TCP) uses URI rewriting to point everything to a special URI:
- The web server listening on ports 31337/TCP and 31338/TCP serves a page to the client. The client reads the text ("This is a wireless mesh, stuff about OPSEC, click here to pass through to the directory of services.") and clicks a button.
- It'd be nice if the page also optionally displayed a message "There is a gateway to the public Net, so you can browse outside of this mesh." if a gateway route existed and had been propagated.
- When the button is clicked the firewall is updated to permit that MAC address to send traffic.
- ipset -A capo_sessions_ipset CLIENT_IP,CLIENT_MAC
- Yes, MAC spoofing to bypass this is trivial. This isn't to prevent people from getting online if they don't have a valid room number, it's to force them to see a message from the admin and then kick them over to a directory of services curated by the node's software.
- Set a timeout on the client IP? 10 minutes? 60 minutes? 5 minutes (same as DHCP lease time)?
- ipset -D capo_sessinos_ipset CLIENT_IP
- Captive::Portal includes a script (capo-ctl.pl) which already does this. In fact, you're supposed to run it from cron every ten minutes or so to clean out idle sessions.
- Captive::Portal requires iptables (have it), ipset (need to compile and install it), and a rule in /etc/sudoers so it can run without privileges but still carry out privileged tasks.
- fping is used to test idle sessions (have it).
- A CGI script that implements a captive portal is included in Captive::Portal, it's called capo.cgi and runs under Apache.
- Basics of coding with this module:
my $capo = Captive::Portal->new(cfg_file=>$cfg_file);
while (my $eq = CGI::Fast->new){
$capo->run($q);
}
- capo-ctl.pl is included with the module and manipulates the currently running IPtables rules (as well as backing store of Captive::Portal) with the ipset utility
- Everything Captive::Portal relies on the same configuration file (by default, config.pl).
- mock-server.pl is a script that pulls the HTML from a URI (say, a web server listening on wlan0) and spits it to stdout for testing.
- Used for testing your setup without needing a client.
- test-server.pl implements a very simple HTTP server so you can test your capi.cgi script without having to configure Apache.
- We might have to modify capo.cgi to use the DBI Perl module to access the SQLite databases that hold the directories of services users can reach.
- We may have either modify or subclass the Captive::Portal class and add support for extracting and using the IP address of the client interface (wlan0:1) rather than just the physical interface (wlan0). It's been a long time since I've done OO under Perl but it's certainly possible.
- config.pl should be configured for no authentication (i.e., just a click-through).
