mptcp: be careful on subflow status propagation on errors

Currently the subflow error report callback unconditionally
propagates the fallback subflow status to the owning msk.

If the msk is already orphaned, the above prevents the code
from correctly tracking the msk moving to the TCP_CLOSE state
and doing the appropriate cleanup.

All the above causes increasing memory usage over time and
sporadic self-tests failures.

There is a great deal of infrastructure trying to propagate
correctly the fallback subflow status to the owning mptcp socket,
e.g. via mptcp_subflow_eof() and subflow_sched_work_if_closed():
in the error propagation path we need only to cope with unorphaned
sockets.

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/339
Fixes: 15cc1045 ("mptcp: deliver ssk errors to msk")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/subflow.c

@@ -1399,6 +1399,7 @@ void __mptcp_error_report(struct sock *sk)
 	mptcp_for_each_subflow(msk, subflow) {
 		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
 		int err = sock_error(ssk);
+		int ssk_state;
 
 		if (!err)
 			continue;
@@ -1409,7 +1410,14 @@ void __mptcp_error_report(struct sock *sk)
 		if (sk->sk_state != TCP_SYN_SENT && !__mptcp_check_fallback(msk))
 			continue;
 
-		inet_sk_state_store(sk, inet_sk_state_load(ssk));
+		/* We need to propagate only transition to CLOSE state.
+		 * Orphaned socket will see such state change via
+		 * subflow_sched_work_if_closed() and that path will properly
+		 * destroy the msk as needed.
+		 */
+		ssk_state = inet_sk_state_load(ssk);
+		if (ssk_state == TCP_CLOSE && !sock_flag(sk, SOCK_DEAD))
+			inet_sk_state_store(sk, ssk_state);
 		sk->sk_err = -err;
 
 		/* This barrier is coupled with smp_rmb() in mptcp_poll() */