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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CANn89iJfXJi7CL2ekBo9Zn9KtVTRxwMCZiSxdC21uNfkdNU1Jg@mail.gmail.com>
Date: Tue, 25 Feb 2025 11:11:07 +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 11:09 AM Matthieu Baerts <matttbe@...nel.org> wrote:
>
> Hi Paolo, Eric,
>
> On 25/02/2025 10:59, Paolo Abeni wrote:
> > On 2/24/25 12:06 PM, Eric Dumazet 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 TcpExtTSECR_Rejected
> >> TcpExtTSECR_Rejected            0                  0.0
>
> (...)
>
> > It looks like this change causes mptcp self-test failures:
> >
> > https://netdev-3.bots.linux.dev/vmksft-mptcp/results/6642/1-mptcp-join-sh/stdout
> >
> > ipv6 subflows creation fails due to the added check:
> >
> > # TcpExtTSECR_Rejected            3                  0.0
>
> You have been faster to report the issue :-)
>
> > (for unknown reasons the ipv4 variant of the test is successful)
>
> Please note that it is not the first time the MPTCP test suite caught
> issues with the IPv6 stack. It is likely possible the IPv6 stack is less
> covered than the v4 one in the net selftests. (Even if I guess here the
> issue is only on MPTCP side.)


subflow_prep_synack() does :

 /* clear tstamp_ok, as needed depending on cookie */
if (foc && foc->len > -1)
     ireq->tstamp_ok = 0;

I will double check fastopen code then.