netdev - Re: [PATCH net-next 0/3] net: handle the exp removal problem with ovs upcall properly

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Date: Tue, 18 Jul 2023 19:58:27 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Pablo Neira Ayuso <pablo@...filter.org>, Florian Westphal <fw@...len.de>
Cc: Xin Long <lucien.xin@...il.com>, network dev <netdev@...r.kernel.org>,
 dev@...nvswitch.org, davem@...emloft.net, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Pravin B Shelar
 <pshelar@....org>, Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang
 <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, Marcelo Ricardo
 Leitner <marcelo.leitner@...il.com>, Davide Caratti <dcaratti@...hat.com>,
 Aaron Conole <aconole@...hat.com>
Subject: Re: [PATCH net-next 0/3] net: handle the exp removal problem with
 ovs upcall properly

On Sun, 16 Jul 2023 17:09:16 -0400 Xin Long wrote:
> With the OVS upcall, the original ct in the skb will be dropped, and when
> the skb comes back from userspace it has to create a new ct again through
> nf_conntrack_in() in either OVS __ovs_ct_lookup() or TC tcf_ct_act().
> 
> However, the new ct will not be able to have the exp as the original ct
> has taken it away from the hash table in nf_ct_find_expectation(). This
> will cause some flow never to be matched, like:
> 
>   'ip,ct_state=-trk,in_port=1 actions=ct(zone=1)'
>   'ip,ct_state=+trk+new+rel,in_port=1 actions=ct(commit,zone=1)'
>   'ip,ct_state=+trk+new+rel,in_port=1 actions=ct(commit,zone=2),normal'
> 
> if the 2nd flow triggers the OVS upcall, the 3rd flow will never get
> matched.
> 
> OVS conntrack works around this by adding its own exp lookup function to
> not remove the exp from the hash table and saving the exp and its master
> info to the flow keys instead of create a real ct. But this way doesn't
> work for TC act_ct.
> 
> The patch 1/3 allows nf_ct_find_expectation() not to remove the exp from
> the hash table if tmpl is set with IPS_CONFIRMED when doing lookup. This
> allows both OVS conntrack and TC act_ct to have a simple and clear fix
> for this problem in the patch 2/3 and 3/3.

Florian, Pablo, any opinion on these? 
Would you prefer to take them via netfilter?