[bug#32465] Add iptables service

[Julien Lepiller <julien@lepiller.eu>]

Hi,

it's not directly an answer to arun's patch (it is great), but I 
recently came accross firemason 
(http://www.cs.yale.edu/homes/zhai-ennan/firemason.pdf and 
https://github.com/BillHallahan/FireMason) and I thought we could 
implement something similar. Basically, we declare a list of rules in 
the iptables service, and we let other services extend that. A rule 
would be a specification, independent of the order in which they are 
specified. "Any packet that matches this rule must be rejected".

Of course, this means that we may have conflicting specifications, for 
instance "any packet from this ip must be dropped" and "any packet 
entering on this port must be accepted" are in conflict for packets 
entering on this port from this ip address. All we need is a mechanism 
to explicit these cases (when a packet may be dropped or accepted at the 
same time), such as "repair: packets from this ip on this port must be 
dropped", so the service will effectively see these rules: "any packet 
from this ip must be dropped" and "any packet entering on this port but 
not this ip must be accepted", then translated to:

-A INPUT -s ! <ip> -p tcp --dport <port> -j ACCEPT
-A INPUT -s <ip> ACCEPT

(see how they are independent from the order in which they are 
declared?)

The hard part is to detect a conflict between two rules and give hints 
to the user as to how to fix that.

Of course, we should provide a mechanism to load files as a fallback, in 
which case additional rules from services should be ignored.

What do you think?



PS: Arun, in your patch for the manual you say: "This is the service 
type to set up an iptables coniguration". This should be 
"configuration".