[PATCH 5.15.y] mptcp: pm: send ACK on an active subflow

["Matthieu Baerts (NGI0)" <matttbe@kernel.org>]

commit c07cc3ed895f9bfe0c53b5ed6be710c133b4271c upstream.

Taking the first one on the list doesn't work in some cases, e.g. if the
initial subflow is being removed. Pick another one instead of not
sending anything.

Fixes: 84dfe3677a6f ("mptcp: send out dedicated ADD_ADDR packet")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
[ Conflicts in pm_netlink.c, because the code has been refactored in
  commit f5360e9b314c ("mptcp: introduce and use mptcp_pm_send_ack()")
  which is difficult to backport in this version. The same adaptations
  have been applied: iterating over all subflows, and send the ACK on
  the first active subflow. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/pm_netlink.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 5622dd05087c..c77e596c477c 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -684,16 +684,18 @@ void mptcp_pm_nl_addr_send_ack(struct mptcp_sock *msk)
 		return;
 
 	__mptcp_flush_join_list(msk);
-	subflow = list_first_entry_or_null(&msk->conn_list, typeof(*subflow), node);
-	if (subflow) {
-		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
+	mptcp_for_each_subflow(msk, subflow) {
+		if (__mptcp_subflow_active(subflow)) {
+			struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
 
-		spin_unlock_bh(&msk->pm.lock);
-		pr_debug("send ack for %s\n",
-			 mptcp_pm_should_add_signal(msk) ? "add_addr" : "rm_addr");
+			spin_unlock_bh(&msk->pm.lock);
+			pr_debug("send ack for %s\n",
+				 mptcp_pm_should_add_signal(msk) ? "add_addr" : "rm_addr");
 
-		mptcp_subflow_send_ack(ssk);
-		spin_lock_bh(&msk->pm.lock);
+			mptcp_subflow_send_ack(ssk);
+			spin_lock_bh(&msk->pm.lock);
+			break;
+		}
 	}
 }
 
-- 
2.45.2