How can I programmatically manage iptables rules on the fly?
I need to query existing rules, as well as being able to easily add and delete rules. I haven't found any API's for doing this. Is there something that I'm missing?
The closest I've come to a solution is using iptables-save | iptables-xml for querying and manually calling the iptables command itself to add/delete rules. Another solution I've considered is simply regenerating the entire ruleset out of my application's database and flushing the whole chain, then applying it again. But I want to avoid this as I don't want to drop any packets -- unless there's a way to atomically do this. I'm wondering if there's a better way.
An API in C would be great; however, as I'm planning to build this into a stand-alone suid program, libraries that do this in ANY language are fine too.
Answer
From the netfilter FAQ:
The answer unfortunately is: No.
Now you might think 'but what about libiptc?'. As has been pointed out numerous times on the mailinglist(s), libiptc was NEVER meant to be used as a public interface. We don't guarantee a stable interface, and it is planned to remove it in the next incarnation of linux packet filtering. libiptc is way too low-layer to be used reasonably anyway.
We are well aware that there is a fundamental lack for such an API, and we are working on improving that situation. Until then, it is recommended to either use system() or open a pipe into stdin of iptables-restore. The latter will give you a way better performance.