Fix scid_utils::is_valid* false positive

cargo bench was able to find an scid of 0 as a valid fake scid

Author: valentinewallace

lightning/src/ln/channelmanager.rs

@@ -2313,7 +2313,7 @@ impl<M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelManager<M, T, K, F
 						None => { // unknown_next_peer
 							// Note that this is likely a timing oracle for detecting whether an scid is a
 							// phantom.
-							if fake_scid::is_valid_phantom(&self.fake_scid_rand_bytes, *short_channel_id) {
+							if fake_scid::is_valid_phantom(&self.fake_scid_rand_bytes, *short_channel_id, &self.genesis_hash) {
 								None
 							} else {
 								break Some(("Don't have available channel for forwarding as requested.", 0x4000 | 10, None));
@@ -3202,7 +3202,7 @@ impl<M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelManager<M, T, K, F
 										}
 										if let PendingHTLCRouting::Forward { onion_packet, .. } = routing {
 											let phantom_secret_res = self.keys_manager.get_node_secret(Recipient::PhantomNode);
-											if phantom_secret_res.is_ok() && fake_scid::is_valid_phantom(&self.fake_scid_rand_bytes, short_chan_id) {
+											if phantom_secret_res.is_ok() && fake_scid::is_valid_phantom(&self.fake_scid_rand_bytes, short_chan_id, &self.genesis_hash) {
 												let phantom_shared_secret = SharedSecret::new(&onion_packet.public_key.unwrap(), &phantom_secret_res.unwrap()).secret_bytes();
 												let next_hop = match onion_utils::decode_next_payment_hop(phantom_shared_secret, &onion_packet.hop_data, onion_packet.hmac, payment_hash) {
 													Ok(res) => res,

lightning/src/util/scid_utils.rs

@@ -73,7 +73,7 @@ pub(crate) mod fake_scid {
 	use core::convert::TryInto;
 	use core::ops::Deref;
 
-	const TEST_SEGWIT_ACTIVATION_HEIGHT: u32 = 0;
+	const TEST_SEGWIT_ACTIVATION_HEIGHT: u32 = 1;
 	const MAINNET_SEGWIT_ACTIVATION_HEIGHT: u32 = 481_824;
 	const MAX_TX_INDEX: u32 = 2_500;
 	const MAX_NAMESPACES: u8 = 8; // We allocate 3 bits for the namespace identifier.
@@ -151,12 +151,13 @@ pub(crate) mod fake_scid {
 	}
 
 	/// Returns whether the given fake scid falls into the given namespace.
-	pub fn is_valid_phantom(fake_scid_rand_bytes: &[u8; 32], scid: u64) -> bool {
+	pub fn is_valid_phantom(fake_scid_rand_bytes: &[u8; 32], scid: u64, genesis_hash: &BlockHash) -> bool {
 		let block_height = scid_utils::block_from_scid(&scid);
 		let tx_index = scid_utils::tx_index_from_scid(&scid);
 		let namespace = Namespace::Phantom;
 		let valid_vout = namespace.get_encrypted_vout(block_height, tx_index, fake_scid_rand_bytes);
-		valid_vout == scid_utils::vout_from_scid(&scid) as u8
+		block_height >= segwit_activation_height(genesis_hash)
+			&& valid_vout == scid_utils::vout_from_scid(&scid) as u8
 	}
 
 	#[cfg(test)]
@@ -194,11 +195,12 @@ pub(crate) mod fake_scid {
 		fn test_is_valid_phantom() {
 			let namespace = Namespace::Phantom;
 			let fake_scid_rand_bytes = [0; 32];
+			let testnet_genesis = genesis_block(Network::Testnet).header.block_hash();
 			let valid_encrypted_vout = namespace.get_encrypted_vout(0, 0, &fake_scid_rand_bytes);
-			let valid_fake_scid = scid_utils::scid_from_parts(0, 0, valid_encrypted_vout as u64).unwrap();
-			assert!(is_valid_phantom(&fake_scid_rand_bytes, valid_fake_scid));
-			let invalid_fake_scid = scid_utils::scid_from_parts(0, 0, 12).unwrap();
-			assert!(!is_valid_phantom(&fake_scid_rand_bytes, invalid_fake_scid));
+			let valid_fake_scid = scid_utils::scid_from_parts(1, 0, valid_encrypted_vout as u64).unwrap();
+			assert!(is_valid_phantom(&fake_scid_rand_bytes, valid_fake_scid, &testnet_genesis));
+			let invalid_fake_scid = scid_utils::scid_from_parts(1, 0, 12).unwrap();
+			assert!(!is_valid_phantom(&fake_scid_rand_bytes, invalid_fake_scid, &testnet_genesis));
 		}
 
 		#[test]