[Bro-Dev] changing Notice::policy mechanism

Seth Hall seth at icir.org
Thu Nov 1 13:35:17 PDT 2012

I've discussed changing the Notice::policy notice handling mechanism with a few people and I think that generally everyone agrees that the current mechanism, while very powerful, sucks from a usability perspective.  This is a good thing to address now since we're either on the precipice of repeating a mistake to more frameworks or adapting to a style that is easier to understand.  I'm going to give an example of how I think it could work in an evented model now.  Please shoot holes. :)

These implement the decidedly silly case of sending a notice to an email if the SSH connection originated locally.

event Notice::policy(n: Notice::Info) 
	if ( n$note == SSH::Login &&
	     Site::is_local_host(n$id$orig_h) )
		add n$actions[Notice::ACTION_EMAIL];

That would be replacement to the current model of this:

redef Notice::policy += {
	[$pred(n: Notice::Info) = { 
		return ( n$note == SSH::Login && Site::is_local_host(n$id$orig_h) );
	 $action = Notice::ACTION_EMAIL],

Here are some random thoughts about these two approaches in no particular order:

 - The evented model (top one) is more Bro-y and easier which is a BIG plus.

 - The PolicyItem model (bottom one) has the ability to halt further processing with the $halt attribute of PolicyItems.  I don't think I'm convinced that this is a huge issue.

 - The evented model has latency from the event queue, but I don't think this is a huge issue.  The latency is normally ok.  Jon, is it an issue for the file analysis framework?  I don't remember.  The actions being applied would be processed through an event queue too so they will be processed after the policy events anyway.

 - Code block prioritization is built into the evented model using the &priority attribute.  It's specifically implemented for PolicyItem model.

Any thoughts?


Seth Hall
International Computer Science Institute
(Bro) because everyone has a network

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