netdev - Re: [PATCH v2 net-next] tcp: be less liberal in TSEcr received while in SYN

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Message-ID: <CADVnQynMnDaDBkKy9c+DVRL6mf=bmpzjiyVEgxX0df-5iRS8Mg@mail.gmail.com>
Date: Tue, 25 Feb 2025 15:52:23 -0500
From: Neal Cardwell <ncardwell@...gle.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Kuniyuki Iwashima <kuniyu@...zon.com>, Simon Horman <horms@...nel.org>, 
	netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Yong-Hao Zou <yonghaoz1994@...il.com>, "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
Subject: Re: [PATCH v2 net-next] tcp: be less liberal in TSEcr received while
 in SYN_RECV state

On Tue, Feb 25, 2025 at 12:10 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> Yong-Hao Zou mentioned that linux was not strict as other OS in 3WHS,
> for flows using TCP TS option (RFC 7323)
>
> As hinted by an old comment in tcp_check_req(),
> we can check the TSEcr value in the incoming packet corresponds
> to one of the SYNACK TSval values we have sent.
>
> In this patch, I record the oldest and most recent values
> that SYNACK packets have used.
>
> Send a challenge ACK if we receive a TSEcr outside
> of this range, and increase a new SNMP counter.
>
> nstat -az | grep TSEcrRejected
> TcpExtTSEcrRejected            0                  0.0
>
> Due to TCP fastopen implementation, do not apply yet these checks
> for fastopen flows.
>
> v2: No longer use req->num_timeout, but treq->snt_tsval_first
>     to detect when first SYNACK is prepared. This means
>     we make sure to not send an initial zero TSval.
>     Make sure MPTCP and TCP selftests are passing.
>     Change MIB name to TcpExtTSEcrRejected
>
> v1: https://lore.kernel.org/netdev/CADVnQykD8i4ArpSZaPKaoNxLJ2if2ts9m4As+=Jvdkrgx1qMHw@mail.gmail.com/T/
>
> Reported-by: Yong-Hao Zou <yonghaoz1994@...il.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Matthieu Baerts (NGI0) <matttbe@...nel.org>
> ---

Reviewed-by: Neal Cardwell <ncardwell@...gle.com>

Thanks, Eric!

neal