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Thu, 29 Oct 2026 21:22:57 -0700 (PDT) Received: from com-75606.corp.openai.org ([199.47.143.5]) by smtp.gmail.com with ESMTPSA id 006d021491bc7-714f2a818b9sm1094944eaf.1.2026.10.29.21.22.56 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 29 Oct 2026 21:22:57 -0700 (PDT) From: Kyle Zeng To: mptcp@lists.linux.dev Cc: Matthieu Baerts , Mat Martineau , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, outbounddisclosures@openai.com Subject: [PATCH] mptcp: pm: kernel: use RCU to free endpoint listeners Date: Thu, 29 Oct 2026 21:22:55 -0700 Message-ID: <20261030042255.74216-1-kylebot@openai.com> X-Mailer: git-send-email 2.55.0 X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" mptcp_pm_nl_create_listen_socket() starts the TCP listener directly instead of going through mptcp_listen(). It consequently misses setting SOCK_RCU_FREE on the parent MPTCP socket. tcp_child_process() can invoke the listener's subflow_data_ready() callback without holding the MPTCP parent lock or a reference to the parent. An authenticated MP_JOIN racing with endpoint teardown can therefore access the parent after its last reference has been dropped. The ADD_ADDR error path can also close an already published listener. Set SOCK_RCU_FREE before __inet_listen_sk() publishes the TCP listener, matching mptcp_listen(). This protects the parent on every subsequent close path, including a failed endpoint addition. Fixes: 1729cf186d8a ("mptcp: create the listening socket for new port") Cc: stable@vger.kernel.org Signed-off-by: Kyle Zeng Reviewed-by: Matthieu Baerts (NGI0) --- I have a reproducer for this issue and can share via DM net/mptcp/pm_kernel.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/mptcp/pm_kernel.c b/net/mptcp/pm_kernel.c index 1a7750813235..f7396628490e 100644 --- a/net/mptcp/pm_kernel.c +++ b/net/mptcp/pm_kernel.c @@ -906,6 +906,7 @@ static int mptcp_pm_nl_create_listen_socket(struct sock= *sk, * old status is known (TCP_CLOSE). */ inet_sk_state_store(newsk, TCP_LISTEN); + sock_set_flag(newsk, SOCK_RCU_FREE); lock_sock(ssk); WRITE_ONCE(mptcp_subflow_ctx(ssk)->pm_listener, true); err =3D __inet_listen_sk(ssk, backlog); base-commit: d89e1d186ec9271bf78e62771779e9fc03bf0fc3 --=20 2.56.0