Allocate and assign the SCID alias after we're certain the channel will survive.

Wait until we're certain that channel creation will be created until we allocate and initialize the outbound SCID alias. This fixes some paths where we might leak an unused outbound SCID alias.

Author: waterson

lightning/src/ln/channelmanager.rs

@@ -5383,13 +5383,11 @@ where
 
 		// Otherwise create the channel right now.
 		let user_channel_id = u128::from_be_bytes(random_bytes);
-		let outbound_scid_alias = self.create_and_insert_outbound_scid_alias();
 		let mut channel = match InboundV1Channel::new(&self.fee_estimator, &self.entropy_source, &self.signer_provider,
 			counterparty_node_id.clone(), &self.channel_type_features(), &peer_state.latest_features, msg, user_channel_id,
-			&self.default_configuration, best_block_height, &self.logger, outbound_scid_alias)
+			&self.default_configuration, best_block_height, &self.logger, /*outbound_scid_alias=*/0)
 		{
 			Err(e) => {
-				self.outbound_scid_aliases.lock().unwrap().remove(&outbound_scid_alias);
 				return Err(MsgHandleErrInternal::from_chan_no_close(e, msg.temporary_channel_id));
 			},
 			Ok(res) => res
@@ -5402,6 +5400,10 @@ where
 		if channel_type.requires_anchors_zero_fee_htlc_tx() {
 			return Err(MsgHandleErrInternal::send_err_msg_no_close("No channels with anchor outputs accepted".to_owned(), msg.temporary_channel_id.clone()));
 		}
+		
+		let outbound_scid_alias = self.create_and_insert_outbound_scid_alias();
+		channel.context.set_outbound_scid_alias(outbound_scid_alias);
+		
 		peer_state.pending_msg_events.push(events::MessageSendEvent::SendAcceptChannel {
 			node_id: counterparty_node_id.clone(),
 			msg: channel.accept_inbound_channel(user_channel_id),