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

From: Jakub Kicinski <[email-masked]>
Date: Tue, 18 Jul 2023 19:58:27 -0700

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?