netdev - Re: [PATCH 1/1] netfilter: Add possibility to turn off netfilters defrag per netns

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Message-ID: <alpine.DEB.2.00.1201050959030.5244@blackhole.kfki.hu>
Date:	Thu, 5 Jan 2012 10:11:28 +0100 (CET)
From:	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
To:	Hans Schillstrom <hans.schillstrom@...csson.com>
cc:	Pablo Neira Ayuso <pablo@...filter.org>,
	Jan Engelhardt <jengelh@...ozas.de>,
	Patrick McHardy <kaber@...sh.net>,
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/1] netfilter: Add possibility to turn off netfilters
 defrag per netns

On Thu, 5 Jan 2012, Hans Schillstrom wrote:

> On Wednesday 04 January 2012 22:40:09 Jozsef Kadlecsik wrote:
> > On Wed, 4 Jan 2012, Hans Schillstrom wrote:
> > 
> > > On Wednesday, January 04, 2012 19:05:10 Jozsef Kadlecsik wrote:
> > > > On Wed, 4 Jan 2012, Pablo Neira Ayuso wrote:
> > > > 
> > > > > On Wed, Jan 04, 2012 at 12:48:35PM +0100, Hans Schillstrom wrote:
> > > > > > I like that idea, an "early" table at prio -500 with PREROUTING.
> > > > > > There is also a need for a new flag "--allfrags"
> > > > > > i.e. all fragments needs to be sorted out and sent to same dest for defrag.
> > > > > > 
> > > > > > ex.
> > > > > > iptables -t early -A PREROUTING -i eth0 --allfrags -j NOTRACK
> > > > > 
> > > > > New tables add too much overhead. We have discussed this before with
> > > > > Patrick.
> > > > > 
> > > > > Since this still remains specific to your needs, I think you can
> > > > > remove nf_conntrack module in your setup.
> > > > > 
> > > > > I don't come with one sane setup that may want selectively defragment
> > > > > some traffic yes and other not.
> > > > > 
> > > > > Am I missing anything else?
> > > > 
> > > > I agree. If you don't want defragmentation at all, then make sure you 
> > > > don't load the nf_conntrack module directly/indirectly. Conntrack doesn't 
> > > > work without defragmentation anyway.
> > > 
> > > We are using LXC and it's only in the container that holds the external 
> > > interface that can't have defragmentation.
> > > The problem is if it's loaded you have it in all namespaces :-(
> > 
> > Conntrack is per net namespaces. You may have one container with conntrack 
> > enabled and another one without conntrack.
> 
> How do you disable conntrack per netns ?
> I can't see how to do it except for NOTRACK
> Then the nf_defrag issue is still there...

OK, I see. Conntrack is per net namespace but it's enabled globally.
 
So at the moment I think the best solution is something like your patch 
variant (but the condition is wrong, it should be "&& !skb->nfct"):

--- a/net/ipv4/netfilter/nf_defrag_ipv4.c
+++ b/net/ipv4/netfilter/nf_defrag_ipv4.c
@@ -74,6 +74,14 @@ static unsigned int ipv4_conntrack_defrag(unsigned int
hooknum,
...
+       const struct net_device *dev = (hooknum == NF_INET_LOCAL_OUT ?
+                                       out : in);
+
+       /* No defrag and not Previously seen (loopback)? */
+       if (dev_net(dev)->ct.sysctl_notrac_defrag && skb->nfct) {
+               /* Attach fake conntrack entry. as in NOTRACK */
+               skb->nfct = &nf_ct_untracked_get()->ct_general;
+               skb->nfctinfo = IP_CT_NEW;
+               nf_conntrack_get(skb->nfct);
+               return NF_ACCEPT;
+       }
...

Best regards,
Jozsef
-
E-mail  : kadlec@...ckhole.kfki.hu, kadlecsik.jozsef@...ner.mta.hu
PGP key : http://www.kfki.hu/~kadlec/pgp_public_key.txt
Address : Wigner Research Centre for Physics, Hungarian Academy of Sciences
          H-1525 Budapest 114, POB. 49, Hungary
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