netdev - Re: linux 5.17.1 disregarding ACK values resulting in stalled TCP connections

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Message-ID: <20220407102657.GB16047@breakpoint.cc>
Date:   Thu, 7 Apr 2022 12:26:57 +0200
From:   Florian Westphal <fw@...len.de>
To:     Jozsef Kadlecsik <kadlec@...filter.org>
Cc:     Florian Westphal <fw@...len.de>,
        Neal Cardwell <ncardwell@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Jaco Kroon <jaco@....co.za>, netfilter-devel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: linux 5.17.1 disregarding ACK values resulting in stalled TCP
 connections

Jozsef Kadlecsik <kadlec@...filter.org> wrote:
> I'd merge the two conditions so that it'd cover both original condition 
> branches:
> 
> diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
> index 8ec55cd72572..87375ce2f995 100644
> --- a/net/netfilter/nf_conntrack_proto_tcp.c
> +++ b/net/netfilter/nf_conntrack_proto_tcp.c
> @@ -556,33 +556,26 @@ static bool tcp_in_window(struct nf_conn *ct,
>  			}
>  
>  		}
> -	} else if (((state->state == TCP_CONNTRACK_SYN_SENT
> -		     && dir == IP_CT_DIR_ORIGINAL)
> -		   || (state->state == TCP_CONNTRACK_SYN_RECV
> -		     && dir == IP_CT_DIR_REPLY))
> -		   && after(end, sender->td_end)) {
> +	} else if (tcph->syn &&
> +		   ((after(end, sender->td_end) &&
> +		     (state->state == TCP_CONNTRACK_SYN_SENT ||
> +		      state->state == TCP_CONNTRACK_SYN_RECV)) ||
> +		    (dir == IP_CT_DIR_REPLY &&
> +		     state->state == TCP_CONNTRACK_SYN_SENT))) {

Thats what I did as well, I merged the two branches but I made the
2nd clause stricter to also consider the after() test; it would no
longer re-init for syn-acks when sequence did not advance.

Then, dir == IP_CT_DIR_REPLY && state == SYN_SENT is already covered
by earlier test and can be elided.

I'm fine with your version though, will you submit a patch?