[PATCH 2.4] TCP window tracking: core implementation

[Roberto Nibali]

Hello Willy,

>> Could you batch my patchset for your next -hf series, please? I'll try
>> to get you a tcpdump with erroneous behaviour regarding window tracking,
>> so you can verify this as well.
> 
> No, and I'm sorry to insist in this direction : the -hf tree is only a
> *selection* of patches from next mainline version(s). It's targetted at

Stupid me, I didn't mean -hf series, I meant the experimental 2.4.x 
kernel series we're going to start.

> the users who cannot risk an upgrade to the next -pre-something, but who
> still need security or stability fixes. Under no circumstance should I
> add new features to this tree.

Of course. Although tcp window tracking could be seen as a security fix.

> I'm currently thinking about another tree (something like 2.4-enterprise)
> which would host those patches absolutely needed for people with higher
> expectations than "normal" users. Nflog, window-tracking, epoll, and

I'm probably going to drop the nflog stuff, since it is not really used 
in 2.4.x. Also the tcp window tracking can happily live without it.

> jiffies64 immediately come to mind, but possibly a small bunch of others
> too. And I hope to count you among the patch contributors ;-)

Sure thing.

>> This is of course possible but could potentially lead to a lot of
>> exception code. I reckon that it's safe enough to fallback to classic
>> packet filtering when dealing with non-RFC conform TCP clients or
>> applications. Meanwhile I've found the problem with the NOTRACK hanging
>> and will propose a fix in another thread I've started.
> 
> OK, I don't have much idea about how to proceed with the NOTRACK yet
> because in the past I could not get it to work along with window-tracking.
> So of course I'm interested :-)

It's not supposed to work with window tracking other than not 
influencing it. I use the NOTRACK feature to simulate the old ipchains 
or ipfwadm behaviour. So when using NOTRACK you need to map the TCP 
states into to filter rules yourself. While window tracking (looking at 
TCP) is an n-tuple (n>7) check on the skb, NOTRACK is a simple 5 to 
7-tuple check with no memory constraints:

<srcIP, srcPORT, destIP, destPORT, proto, (TCPflags, interface)>

I'll send you the semantics off-list.

Best regards,
Roberto Nibali, ratz
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