Commit 49b09ae0bf57 for kernel

commit 49b09ae0bf57b4230187d4cdd0a370558e44a6e8
Author: Kyle Zeng <kylebot@openai.com>
Date:   Thu Oct 29 21:22:55 2026 -0700

    mptcp: pm: kernel: use RCU to free endpoint listeners

    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 <kylebot@openai.com>
    Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
    Link: https://patch.msgid.link/20261030042255.74216-1-kylebot@openai.com
    Signed-off-by: Paolo Abeni <pabeni@redhat.com>

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 = __inet_listen_sk(ssk, backlog);