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Re: Announce: NetKeeper Firewall For Linux

To: hadi@xxxxxxxxxx
Subject: Re: Announce: NetKeeper Firewall For Linux
From: Emmanuel Fleury <fleury@xxxxxxxxx>
Date: Thu, 06 Nov 2003 11:26:16 +0100
Cc: "David S. Miller" <davem@xxxxxxxxxx>, netfilter-devel@xxxxxxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx, Mikkel Christiansen <mixxel@xxxxxxxxx>
In-reply-to: <1068089345.1020.17.camel@xxxxxxxxxxxxxxxx>
Organization: Aalborg University -- Computer Science Dept.
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On Thu, 2003-11-06 at 04:29, jamal wrote:
> Yes, i think you missed my point ;-> 

Oops ! :)

> You guys are doing a great job at coming up with some good packet
> classification algorithm(s). I wanna encourage you to continue doing
> that. 
> OTOH, I have spent a lot of time thinking and coming up with a good
> architecture for the action part (that follows classification). So it
> will be a shame if you miss that because you happened to see one
> good thing in the old code.
Putting the two together will result in some good things. You trying to
> redo what i am doing will mean you are always a few steps behind[1]. Now
> if you can do it better than what i have, then you can convert me 
> too - thats the way opensource works. 

Ok, actually we were so focused on the classification scheme that we
didn't really try to do something nice for the actions... In a matter of
facts, we have only one action (log) and it is not even implemented. 

So, we will definitely look at your code to avoid us to have to think
about this part (and avoid to have to recode the actions). 

> Anything that requires "connection setup" to dynamically add rules is a
> candidate. Think Voip SIP Proxy server for example which will insert
> rules; think any authentication schemes that are needed before
> installing rules, think tcp-splicing etc.

Ok, but you are speaking about non permanent rules (aka dynamic rules). 

The idea we have to handle stateful inspection is to have the core
filter (totally static) plus some "state" nodes placed inside the IDD
which are calling a function to evaluate the "state" of the packet
(based on some informations given by the packet header and a database of
the open connections). When reaching the terminals, one of the action
can be to change the state of the connection.

I guess that what you describe can be handled by such mechanism 
(better than changing the ruleset each time). As it is handled outside
of the IDD, this take only the time of the look-up in the database and
the time to modify the database (when necessary).

But, I over simplified things here, this scheme is far from being ready
at this point. We should investigate it more in depth (we need more

> I think thats a design issue. For example while u32 classifier may not
> process as fast as you (lookups would take longer relatively ) - its
> insertion time is independent of the complexity of the rules.
> Lakshman (sp?) had a good paper on the tradeoffs between memory space
> used, lookup times and insertion times (there was another variable) and
> i think he may have proved you cant have all of them work well at the
> same time.

Ok. Could you give more details about the references of this paper from
Lakshman ?

> So if you add rule #50000 while there are already 49999 existing
> it will take over an hour to install in the worst case, did i understand
> this correctly?

Yes (I messed up things in the following paragraph), you are totally
right here. I totally forgot that you have to deal with rule-overlapping
which is actually making things incredibly sequential).

> > Of course your question was about taking one of this big filters and
> > then add one tiny winy rule to it. So, I guess the time to do so would
> > be at most 1s (in the very worst case, I would say).

I am wrong here, terribly wrong. The thing is that is you add a rule at
the end of your filter, you will not have to rebuild it, but inserting a
rule randomly in the list is... bad. For now, we don't have any good
algorithm to insert a rule, so we just rebuild the whole thing.

> > When coding in the kernel, we are coding with the idea that: 
> >    « The kernel should defend itself against user-space. »
> > 
> > So, when the user say: "Commit". 
> > 
> > The kernel will first check the decision diagram for safety (no NULL
> > pointers, out of range variables, no loops, etc) and depending of the
> > tests, will take the decision to commit or not.
> That sounds more like still a user space problem ;->


Users shouldn't be able to break the kernel just by misconfiguring it.

> I saw in your paper briefly that you have infact a checker for something
> like this. 

If you are speaking about the "network access verifier", it is something
totally different. But, I might have misunderstood you.

> In my view the most important issues in priority order are:
> lookup speed regardless of table size, insert/delete rate regardless of
> table size, Capacity (should be able to go to the hundreds of thousands
> of flows), memory use for storage purposes - although i dont really care
> very much about these since memory is cheap these days.

Ok, I think we have to work on the insert/delete part. I know for a fact
that insert/delete inside the IDD is not an option (as the complexity of
this operation is too high), so we will look at some other way to handle

> > PS: I would like also to say here that we got a really great feed back
> > from the nf-hipac team. So, thank a lot to Michael Bellion and Thomas
> > Heinz.
> > 
> I am sorry i confused you with them;-> I suppose you are both from .dk.

No, Michael and Thomas are from Germany. Mikkel Christiansen is from
Denmark and I'm from France (working in Denmark currently).

> [1]I briefly looked at your paper and it seems the only action you had
> initially was DENY or ACCEPT.

We can extend this without any problem.

> Looking at your code you now have an action dispatcher that seems
> to be exactly like the old one i have (you havent implemented code
> around it but you have the hooks in place). This is why i made the
> comment. 

Actually, as I said, we were just no so concerned about the handling of
the actions, so we just did it in the most natural way (for us). It is a
good sign that we are meeting your very first implementation. 

Emmanuel Fleury

Computer Science Department, |  Office: B1-201
Aalborg University,          |  Phone:  +45 96 35 72 23
Fredriks Bajersvej 7E,       |  Fax:    +45 98 15 98 89
9220 Aalborg East, Denmark   |  Email:  fleury@xxxxxxxxx

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