linux-kernel - [PATCH net 4/5] mptcp: tfo: record 'deny join id0' info

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Message-Id: <20250912-net-mptcp-pm-uspace-deny_join_id0-v1-4-40171884ade8@kernel.org>
Date: Fri, 12 Sep 2025 14:52:23 +0200
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: Mat Martineau <martineau@...nel.org>, Geliang Tang <geliang@...nel.org>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>, Donald Hunter <donald.hunter@...il.com>, 
 Florian Westphal <fw@...len.de>, Kishen Maloor <kishen.maloor@...el.com>, 
 Shuah Khan <shuah@...nel.org>, Dmytro Shytyi <dmytro@...tyi.net>
Cc: netdev@...r.kernel.org, mptcp@...ts.linux.dev, 
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
 "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
Subject: [PATCH net 4/5] mptcp: tfo: record 'deny join id0' info

When TFO is used, the check to see if the 'C' flag (deny join id0) was
set was bypassed.

This flag can be set when TFO is used, so the check should also be done
when TFO is used.

Note that the set_fully_established label is also used when a 4th ACK is
received. In this case, deny_join_id0 will not be set.

Fixes: dfc8d0603033 ("mptcp: implement delayed seq generation for passive fastopen")
Reviewed-by: Mat Martineau <martineau@...nel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
 net/mptcp/options.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 2a8ea28442b271675411d190604073f779bee7fa..1103b3341a70560f563bfb21ca143ce2f2c60321 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -985,13 +985,13 @@ static bool check_fully_established(struct mptcp_sock *msk, struct sock *ssk,
 		return false;
 	}

-	if (mp_opt->deny_join_id0)
-		WRITE_ONCE(msk->pm.remote_deny_join_id0, true);
-
 	if (unlikely(!READ_ONCE(msk->pm.server_side)))
 		pr_warn_once("bogus mpc option on established client sk");

 set_fully_established:
+	if (mp_opt->deny_join_id0)
+		WRITE_ONCE(msk->pm.remote_deny_join_id0, true);
+
 	mptcp_data_lock((struct sock *)msk);
 	__mptcp_subflow_fully_established(msk, subflow, mp_opt);
 	mptcp_data_unlock((struct sock *)msk);

-- 
2.51.0