netdev - Re: [PATCH net-next] tcp: be less liberal in tsecr received while in SYN

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Message-ID: <CANn89iL-oCk=FqGzeDi4PN_PX6r8tQZ-zwxObi=R_8=9QzkbQw@mail.gmail.com>
Date: Tue, 25 Feb 2025 13:50:26 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Matthieu Baerts <matttbe@...nel.org>
Cc: Paolo Abeni <pabeni@...hat.com>, Kuniyuki Iwashima <kuniyu@...zon.com>, 
	Simon Horman <horms@...nel.org>, Florian Westphal <fw@...len.de>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Jakub Kicinski <kuba@...nel.org>, 
	Yong-Hao Zou <yonghaoz1994@...il.com>, "David S . Miller" <davem@...emloft.net>, 
	Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next] tcp: be less liberal in tsecr received while in
 SYN_RECV state

On Tue, Feb 25, 2025 at 11:51 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Tue, Feb 25, 2025 at 11:48 AM Matthieu Baerts <matttbe@...nel.org> wrote:
> >
> > On 25/02/2025 11:42, Eric Dumazet wrote:
> > > On Tue, Feb 25, 2025 at 11:39 AM Eric Dumazet <edumazet@...gle.com> wrote:
> > >>
> > >
> > >>
> > >> Yes, this would be it :
> > >>
> > >> diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
> > >> index 728bce01ccd3ddb1f374fa96b86434a415dbe2cb..3555567ba4fb1ccd5c5921e39d11ff08f1d0cafd
> > >> 100644
> > >> --- a/net/ipv4/tcp_timer.c
> > >> +++ b/net/ipv4/tcp_timer.c
> > >> @@ -477,8 +477,8 @@ static void tcp_fastopen_synack_timer(struct sock
> > >> *sk, struct request_sock *req)
> > >>          * regular retransmit because if the child socket has been accepted
> > >>          * it's not good to give up too easily.
> > >>          */
> > >> -       inet_rtx_syn_ack(sk, req);
> > >>         req->num_timeout++;
> > >> +       inet_rtx_syn_ack(sk, req);
> > >>         tcp_update_rto_stats(sk);
> > >>         if (!tp->retrans_stamp)
> > >>                 tp->retrans_stamp = tcp_time_stamp_ts(tp);
> > >
> > > Obviously, I need to refine the patch and send a V2 later.

In v2 I will no longer read req->num_timeout

First SYNACK is sent with syn_skb being set.

Subsequent RTX SYNACK have a NULL syn_skb :

tcp_rtx_synack()

res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL, NULL);