Re: [PATCH nf-next] netfilter: xt_socket: add XT_SOCKET_NOWILDCARD flag

[Eric Dumazet <eric.dumazet@gmail.com>]

On Tue, 2013-06-04 at 11:10 +0200, Jesper Dangaard Brouer wrote:
> On Mon, 03 Jun 2013 15:57:29 -0700
> Eric Dumazet <eric.dumazet@gmail.com> wrote:
> 
> > From: Eric Dumazet <edumazet@google.com>
> > 
> > xt_socket module can be a nice replacement to conntrack module
> > in some cases (SYN filtering for example)
> > 
> > But it lacks the ability to match the 3rd packet of TCP
> > handshake (ACK coming from the client).
> > 
> > Add a XT_SOCKET_NOWILDCARD flag to disable the wildcard mechanism
> 
> Sorry, but I'm not sure I understand your description.
> 
> What is the effect of adding the XT_SOCKET_NOWILDCARD flag?
> It almost sound like it adds the ability to match the 3rd packet of TCP
> handshake (ACK coming from the client), is that the case?
> 

Well, if the found socket happens to be a LISTEN socket, we ignore the
socket if it was bound to 0.0.0.0

Thats the wildcard thing in xt_socket. Not clear why its there, but
thing is : we apparently have to keep this behavior by default.

So yes, the ACK packet from the client is not matched by current
xt_socket.

After my patch, it is matched.

I CCed you because you mentioned using conntrack for SYN filtering :
xt_socket can be a way to do the same thing without the conntrack
overhead, for locally terminated traffic.