netdev - Re: [PATCH net-next 3/3] openvswitch: set IPS_CONFIRMED in tmpl status only when commit is set in conntrack

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Message-ID: <d35d01d9-83de-4862-85a7-574a6c4dc8f5@ovn.org>
Date: Mon, 17 Jun 2024 22:10:31 +0200
From: Ilya Maximets <i.maximets@....org>
To: Xin Long <lucien.xin@...il.com>, network dev <netdev@...r.kernel.org>,
 dev@...nvswitch.org
Cc: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
 Jiri Pirko <jiri@...nulli.us>, Davide Caratti <dcaratti@...hat.com>,
 Florian Westphal <fw@...len.de>, Jamal Hadi Salim <jhs@...atatu.com>,
 Eric Dumazet <edumazet@...gle.com>, Cong Wang <xiyou.wangcong@...il.com>,
 kuba@...nel.org, Paolo Abeni <pabeni@...hat.com>, davem@...emloft.net,
 Pablo Neira Ayuso <pablo@...filter.org>, Aaron Conole <aconole@...hat.com>,
 i.maximets@....org
Subject: Re: [PATCH net-next 3/3] openvswitch: set IPS_CONFIRMED in tmpl
 status only when commit is set in conntrack

On 7/16/23 23:09, Xin Long wrote:
> By not setting IPS_CONFIRMED in tmpl that allows the exp not to be removed
> from the hashtable when lookup, we can simplify the exp processing code a
> lot in openvswitch conntrack.
> 
> Signed-off-by: Xin Long <lucien.xin@...il.com>
> ---
>  net/openvswitch/conntrack.c | 78 +++++--------------------------------
>  1 file changed, 10 insertions(+), 68 deletions(-)
> 
> diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
> index 331730fd3580..fa955e892210 100644
> --- a/net/openvswitch/conntrack.c
> +++ b/net/openvswitch/conntrack.c
> @@ -455,45 +455,6 @@ static int ovs_ct_handle_fragments(struct net *net, struct sw_flow_key *key,
>  	return 0;
>  }
>  
> -static struct nf_conntrack_expect *
> -ovs_ct_expect_find(struct net *net, const struct nf_conntrack_zone *zone,
> -		   u16 proto, const struct sk_buff *skb)
> -{
> -	struct nf_conntrack_tuple tuple;
> -	struct nf_conntrack_expect *exp;
> -
> -	if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb), proto, net, &tuple))
> -		return NULL;
> -
> -	exp = __nf_ct_expect_find(net, zone, &tuple);
> -	if (exp) {
> -		struct nf_conntrack_tuple_hash *h;
> -
> -		/* Delete existing conntrack entry, if it clashes with the
> -		 * expectation.  This can happen since conntrack ALGs do not
> -		 * check for clashes between (new) expectations and existing
> -		 * conntrack entries.  nf_conntrack_in() will check the
> -		 * expectations only if a conntrack entry can not be found,
> -		 * which can lead to OVS finding the expectation (here) in the
> -		 * init direction, but which will not be removed by the
> -		 * nf_conntrack_in() call, if a matching conntrack entry is
> -		 * found instead.  In this case all init direction packets
> -		 * would be reported as new related packets, while reply
> -		 * direction packets would be reported as un-related
> -		 * established packets.
> -		 */
> -		h = nf_conntrack_find_get(net, zone, &tuple);
> -		if (h) {
> -			struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(h);
> -
> -			nf_ct_delete(ct, 0, 0);
> -			nf_ct_put(ct);
> -		}
> -	}
> -
> -	return exp;
> -}
> -
>  /* This replicates logic from nf_conntrack_core.c that is not exported. */
>  static enum ip_conntrack_info
>  ovs_ct_get_info(const struct nf_conntrack_tuple_hash *h)
> @@ -852,36 +813,16 @@ static int ovs_ct_lookup(struct net *net, struct sw_flow_key *key,
>  			 const struct ovs_conntrack_info *info,
>  			 struct sk_buff *skb)
>  {
> -	struct nf_conntrack_expect *exp;
> -
> -	/* If we pass an expected packet through nf_conntrack_in() the
> -	 * expectation is typically removed, but the packet could still be
> -	 * lost in upcall processing.  To prevent this from happening we
> -	 * perform an explicit expectation lookup.  Expected connections are
> -	 * always new, and will be passed through conntrack only when they are
> -	 * committed, as it is OK to remove the expectation at that time.
> -	 */
> -	exp = ovs_ct_expect_find(net, &info->zone, info->family, skb);
> -	if (exp) {
> -		u8 state;
> -
> -		/* NOTE: New connections are NATted and Helped only when
> -		 * committed, so we are not calling into NAT here.
> -		 */
> -		state = OVS_CS_F_TRACKED | OVS_CS_F_NEW | OVS_CS_F_RELATED;
> -		__ovs_ct_update_key(key, state, &info->zone, exp->master);

Hi, Xin, others.

Unfortunately, it seems like removal of this code broke the expected behavior.
OVS in userspace expects that SYN packet of a new related FTP connection will
get +new+rel+trk flags, but after this patch we're only getting +rel+trk and not
new.  This is a problem because we need to commit this connection with the label
and we do that for +new packets.  If we can't get +new packet we'll have to commit
every single +rel+trk packet, which doesn't make a lot of sense.  And it's a
significant behavior change regardless.

Could you, please, take a look?

The issue can be reproduced by running check-kernel tests in OVS repo.
'FTP SNAT orig tuple' tests fail 100% of the time.

Best regards, Ilya Maximets.