From: Pablo Neira Ayuso <pablo@netfilter.org>
To: Florian Westphal <fw@strlen.de>
Cc: Jozsef Kadlecsik <kadlec@netfilter.org>,
Francesco Ruggeri <fruggeri@arista.com>,
open list <linux-kernel@vger.kernel.org>,
netdev <netdev@vger.kernel.org>,
coreteam@netfilter.org, netfilter-devel@vger.kernel.org,
Jakub Kicinski <kuba@kernel.org>,
David Miller <davem@davemloft.net>
Subject: Re: [PATCH nf v2] netfilter: conntrack: connection timeout after re-register
Date: Wed, 14 Oct 2020 10:11:40 +0200 [thread overview]
Message-ID: <20201014081140.GA16515@salvia> (raw)
In-Reply-To: <20201014000628.GA15290@salvia>
On Wed, Oct 14, 2020 at 02:06:28AM +0200, Pablo Neira Ayuso wrote:
> On Fri, Oct 09, 2020 at 10:05:48PM +0200, Florian Westphal wrote:
> > Jozsef Kadlecsik <kadlec@netfilter.org> wrote:
> > > > The "delay unregister" remark was wrt. the "all rules were deleted"
> > > > case, i.e. add a "grace period" rather than acting right away when
> > > > conntrack use count did hit 0.
> > >
> > > Now I understand it, thanks really. The hooks are removed, so conntrack
> > > cannot "see" the packets and the entries become stale.
> >
> > Yes.
> >
> > > What is the rationale behind "remove the conntrack hooks when there are no
> > > rule left referring to conntrack"? Performance optimization? But then the
> > > content of the whole conntrack table could be deleted too... ;-)
> >
> > Yes, this isn't the case at the moment -- only hooks are removed,
> > entries will eventually time out.
> >
> > > > Conntrack entries are not removed, only the base hooks get unregistered.
> > > > This is a problem for tcp window tracking.
> > > >
> > > > When re-register occurs, kernel is supposed to switch the existing
> > > > entries to "loose" mode so window tracking won't flag packets as
> > > > invalid, but apparently this isn't enough to handle keepalive case.
> > >
> > > "loose" (nf_ct_tcp_loose) mode doesn't disable window tracking, it
> > > enables/disables picking up already established connections.
> > >
> > > nf_ct_tcp_be_liberal would disable TCP window checking (but not tracking)
> > > for non RST packets.
> >
> > You are right, mixup on my part.
> >
> > > But both seems to be modified only via the proc entries.
> >
> > Yes, we iterate table on re-register and modify the existing entries.
>
> For iptables-nft, it might be possible to avoid this deregister +
> register ct hooks in the same transaction: Maybe add something like
> nf_ct_netns_get_all() to bump refcounters by one _iff_ they are > 0
> before starting the transaction processing, then call
> nf_ct_netns_put_all() which decrements refcounters and unregister
> hooks if they reach 0.
Hm, scratch that, put_all() would create an imbalance with this
conditional increment.
> The only problem with this approach is that this pulls in the
> conntrack module, to solve that, struct nf_ct_hook in
> net/netfilter/core.c could be used to store the reference to
> ->netns_get_all and ->net_put_all.
>
> Legacy would still be flawed though.
next prev parent reply other threads:[~2020-10-14 8:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-07 19:32 [PATCH nf v2] netfilter: conntrack: connection timeout after re-register Francesco Ruggeri
2020-10-08 23:41 ` Francesco Ruggeri
2020-10-09 6:52 ` Jozsef Kadlecsik
2020-10-09 11:03 ` Florian Westphal
2020-10-09 18:48 ` Jozsef Kadlecsik
2020-10-09 18:55 ` Florian Westphal
2020-10-09 19:49 ` Jozsef Kadlecsik
2020-10-09 20:00 ` Francesco Ruggeri
2020-10-09 20:05 ` Florian Westphal
2020-10-14 0:06 ` Pablo Neira Ayuso
2020-10-14 8:11 ` Pablo Neira Ayuso [this message]
2020-10-14 8:23 ` Florian Westphal
2020-10-14 18:42 ` Francesco Ruggeri
2020-10-14 19:35 ` Florian Westphal
2020-10-20 15:21 ` Pablo Neira Ayuso
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20201014081140.GA16515@salvia \
--to=pablo@netfilter.org \
--cc=coreteam@netfilter.org \
--cc=davem@davemloft.net \
--cc=fruggeri@arista.com \
--cc=fw@strlen.de \
--cc=kadlec@netfilter.org \
--cc=kuba@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=netfilter-devel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).