After shutdown, for fallback MPTCP sockets, we always have

write_seq == snd_una+1

The above will foul OUTQ ioctl(). Keep snd_una in sync with
write_seq even after shutdown.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/protocol.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 29b6f57b917e..3fef1b4e7780 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2690,6 +2690,7 @@ static void __mptcp_check_send_data_fin(struct sock *sk)
 	 * state now
 	 */
 	if (__mptcp_check_fallback(msk)) {
+		WRITE_ONCE(msk->snd_una, msk->write_seq);
 		if ((1 << sk->sk_state) & (TCPF_CLOSING | TCPF_LAST_ACK)) {
 			inet_sk_state_store(sk, TCP_CLOSE);
 			mptcp_close_wake_up(sk);
-- 
2.33.1