ebtables on mac80211

ebtables on mac80211

[Wilco Baan Hofman]

Hi,

I'm looking to implement hooks to ebtables in the mac80211 wireless
stack.

I'm trying to find the best approach for doing this.. basically what I
want to be able to have is clients being able to communicate, but not
ARP spoofing the gateway or setting up a rogue DHCP.

As it's currently implemented, there's some sort of internal bridge
functionality within the wireless stack in net/mac80211/rx.c at around
ieee802_deliver_skb(), where every ethernet packet essentially gets
routed among wireless clients.

If I understand ebtables correctly, an forward event is triggered for
every packet to every interface, right? So essentially, this should do
the same, except that for every wireless client would be a forward from
the wireless interface to the wireless interface.

What would be the best way to implement this and in what way would it be
acceptable upstream?

Best regards,

Wilco Baan Hofman

[Bridge] ebtables on mac80211

[Wilco Baan Hofman]

Hi,

I'm looking to implement hooks to ebtables in the mac80211 wireless
stack.

I'm trying to find the best approach for doing this.. basically what I
want to be able to have is clients being able to communicate, but not
ARP spoofing the gateway or setting up a rogue DHCP.

As it's currently implemented, there's some sort of internal bridge
functionality within the wireless stack in net/mac80211/rx.c at around
ieee802_deliver_skb(), where every ethernet packet essentially gets
routed among wireless clients.

If I understand ebtables correctly, an forward event is triggered for
every packet to every interface, right? So essentially, this should do
the same, except that for every wireless client would be a forward from
the wireless interface to the wireless interface.

What would be the best way to implement this and in what way would it be
acceptable upstream?

Best regards,

Wilco Baan Hofman

Re: [Bridge] ebtables on mac80211

[Bart De Schuymer]

Op 12/04/2012 0:34, Wilco Baan Hofman schreef:
> Hi,
>
> I'm looking to implement hooks to ebtables in the mac80211 wireless
> stack.
>
> I'm trying to find the best approach for doing this.. basically what I
> want to be able to have is clients being able to communicate, but not
> ARP spoofing the gateway or setting up a rogue DHCP.
>
> As it's currently implemented, there's some sort of internal bridge
> functionality within the wireless stack in net/mac80211/rx.c at around
> ieee802_deliver_skb(), where every ethernet packet essentially gets
> routed among wireless clients.
>
> If I understand ebtables correctly, an forward event is triggered for
> every packet to every interface, right? So essentially, this should do
> the same, except that for every wireless client would be a forward from
> the wireless interface to the wireless interface.
>
> What would be the best way to implement this and in what way would it be
> acceptable upstream?
You can add a new ebtables table, requiring minimal changes to the 
userland tool. You can start by adding a table called something like 
"filter-wireless" with a built-in chain on NF_BR_FORWARD. See 
net/bridge/netfilter/ebtable_broute.c: it contains the code that adds 
the broute table with a built-in chain on NF_BR_BROUTING. This approach 
has minimal impact since it doesn't use netfilter hooks (no call to 
nf_register_hooks) and uses a built-in chain that ebtables understands.
If you want to use the netfilter infrastructure, you'll probably need a 
new protocol family. See net/bridge/netfilter/ebtable_filter.c in that case.

cheers,
Bart


-- 
Bart De Schuymer
www.artinalgorithms.be

Re: [Bridge] ebtables on mac80211

[Bart De Schuymer]

Op 12/04/2012 0:34, Wilco Baan Hofman schreef:
> Hi,
>
> I'm looking to implement hooks to ebtables in the mac80211 wireless
> stack.
>
> I'm trying to find the best approach for doing this.. basically what I
> want to be able to have is clients being able to communicate, but not
> ARP spoofing the gateway or setting up a rogue DHCP.
>
> As it's currently implemented, there's some sort of internal bridge
> functionality within the wireless stack in net/mac80211/rx.c at around
> ieee802_deliver_skb(), where every ethernet packet essentially gets
> routed among wireless clients.
>
> If I understand ebtables correctly, an forward event is triggered for
> every packet to every interface, right? So essentially, this should do
> the same, except that for every wireless client would be a forward from
> the wireless interface to the wireless interface.
>
> What would be the best way to implement this and in what way would it be
> acceptable upstream?
You can add a new ebtables table, requiring minimal changes to the 
userland tool. You can start by adding a table called something like 
"filter-wireless" with a built-in chain on NF_BR_FORWARD. See 
net/bridge/netfilter/ebtable_broute.c: it contains the code that adds 
the broute table with a built-in chain on NF_BR_BROUTING. This approach 
has minimal impact since it doesn't use netfilter hooks (no call to 
nf_register_hooks) and uses a built-in chain that ebtables understands.
If you want to use the netfilter infrastructure, you'll probably need a 
new protocol family. See net/bridge/netfilter/ebtable_filter.c in that case.

cheers,
Bart


-- 
Bart De Schuymer
www.artinalgorithms.be