mptcp: subflows garbage collection

The msk can close MP_JOIN subflows if the initial handshake
fails. Currently such subflows are kept alive in the
conn_list until the msk itself is closed.

Beyond the wasted memory, we could end-up sending the
DATA_FIN and the DATA_FIN ack on such socket, even after a
reset.

Fixes: 43b54c6e ("mptcp: Use full MPTCP-level disconnect state machine")
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/mptcp/protocol.c

@@ -1383,6 +1383,20 @@ static void pm_work(struct mptcp_sock *msk)
 	spin_unlock_bh(&msk->pm.lock);
 }
 
+static void __mptcp_close_subflow(struct mptcp_sock *msk)
+{
+	struct mptcp_subflow_context *subflow, *tmp;
+
+	list_for_each_entry_safe(subflow, tmp, &msk->conn_list, node) {
+		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
+
+		if (inet_sk_state_load(ssk) != TCP_CLOSE)
+			continue;
+
+		__mptcp_close_ssk((struct sock *)msk, ssk, subflow, 0);
+	}
+}
+
 static void mptcp_worker(struct work_struct *work)
 {
 	struct mptcp_sock *msk = container_of(work, struct mptcp_sock, work);
@@ -1400,6 +1414,9 @@ static void mptcp_worker(struct work_struct *work)
 	mptcp_clean_una(sk);
 	mptcp_check_data_fin_ack(sk);
 	__mptcp_flush_join_list(msk);
+	if (test_and_clear_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags))
+		__mptcp_close_subflow(msk);
+
 	__mptcp_move_skbs(msk);
 
 	if (msk->pm.status)

net/mptcp/protocol.h

@@ -90,6 +90,7 @@
 #define MPTCP_WORK_RTX		2
 #define MPTCP_WORK_EOF		3
 #define MPTCP_FALLBACK_DONE	4
+#define MPTCP_WORK_CLOSE_SUBFLOW 5
 
 struct mptcp_options_received {
 	u64	sndr_key;

net/mptcp/subflow.c

@@ -272,9 +272,15 @@ static bool subflow_thmac_valid(struct mptcp_subflow_context *subflow)
 
 void mptcp_subflow_reset(struct sock *ssk)
 {
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	struct sock *sk = subflow->conn;
+
 	tcp_set_state(ssk, TCP_CLOSE);
 	tcp_send_active_reset(ssk, GFP_ATOMIC);
 	tcp_done(ssk);
+	if (!test_and_set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &mptcp_sk(sk)->flags) &&
+	    schedule_work(&mptcp_sk(sk)->work))
+		sock_hold(sk);
 }
 
 static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)