netdev - [PATCH net 1/5] mptcp: set remote_deny_join

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Message-Id: <20250912-net-mptcp-pm-uspace-deny_join_id0-v1-1-40171884ade8@kernel.org>
Date: Fri, 12 Sep 2025 14:52:20 +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 1/5] mptcp: set remote_deny_join_id0 on SYN recv

When a SYN containing the 'C' flag (deny join id0) was received, this
piece of information was not propagated to the path-manager.

Even if this flag is mainly set on the server side, a client can also
tell the server it cannot try to establish new subflows to the client's
initial IP address and port. The server's PM should then record such
info when received, and before sending events about the new connection.

Fixes: df377be38725 ("mptcp: add deny_join_id0 in mptcp_options_received")
Reviewed-by: Mat Martineau <martineau@...nel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
 net/mptcp/subflow.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 3f1b62a9fe889ab1ac07f2a210b9de050436b37e..f31a3a79531a2e160598111d3b0765eee2e599fb 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -883,6 +883,10 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,

 			ctx->subflow_id = 1;
 			owner = mptcp_sk(ctx->conn);
+
+			if (mp_opt.deny_join_id0)
+				WRITE_ONCE(owner->pm.remote_deny_join_id0, true);
+
 			mptcp_pm_new_connection(owner, child, 1);

 			/* with OoO packets we can reach here without ingress

-- 
2.51.0