mptcp: fix per socket endpoint accounting

Since full-mesh endpoint support, the reception of a single ADD_ADDR
option can cause multiple subflows creation. When such option is
accepted we increment 'add_addr_accepted' by one. When we received
a paired RM_ADDR option, we deleted all the relevant subflows,
decrementing 'add_addr_accepted' by one for each of them.

We have a similar issue for 'local_addr_used'

Fix them moving the pm endpoint accounting outside the subflow
traversal.

Fixes: 1a0d6136 ("mptcp: local addresses fullmesh")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/pm_netlink.c

@@ -711,6 +711,8 @@ static void mptcp_pm_nl_rm_addr_or_subflow(struct mptcp_sock *msk,
 		return;
 
 	for (i = 0; i < rm_list->nr; i++) {
+		bool removed = false;
+
 		list_for_each_entry_safe(subflow, tmp, &msk->conn_list, node) {
 			struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
 			int how = RCV_SHUTDOWN | SEND_SHUTDOWN;
@@ -730,15 +732,19 @@ static void mptcp_pm_nl_rm_addr_or_subflow(struct mptcp_sock *msk,
 			mptcp_close_ssk(sk, ssk, subflow);
 			spin_lock_bh(&msk->pm.lock);
 
+			removed = true;
+			msk->pm.subflows--;
+			__MPTCP_INC_STATS(sock_net(sk), rm_type);
+		}
+		if (!removed)
+			continue;
+
 		if (rm_type == MPTCP_MIB_RMADDR) {
 			msk->pm.add_addr_accepted--;
 			WRITE_ONCE(msk->pm.accept_addr, true);
 		} else if (rm_type == MPTCP_MIB_RMSUBFLOW) {
 			msk->pm.local_addr_used--;
 		}
-			msk->pm.subflows--;
-			__MPTCP_INC_STATS(sock_net(sk), rm_type);
-		}
 	}
 }