Use test_msg_exact in channl_update fuzz testing

Gossip messages should always use `test_msg_exact` to ensure they
round-trip during signature validation.

Author: TheBlueMatt

fuzz/src/msg_targets/gen_target.sh

@@ -39,14 +39,17 @@ GEN_TEST lightning::ln::msgs::ChannelReestablish test_msg_simple ""
 
 GEN_TEST lightning::ln::msgs::DecodedOnionErrorPacket test_msg ""
 
+# Gossip messages need to use `test_msg_exact` to ensure that messages
+# round-trip exactly when doing signature validation.
 GEN_TEST lightning::ln::msgs::ChannelAnnouncement test_msg_exact ""
 GEN_TEST lightning::ln::msgs::NodeAnnouncement test_msg_exact ""
+GEN_TEST lightning::ln::msgs::ChannelUpdate test_msg_exact ""
+
 GEN_TEST lightning::ln::msgs::QueryShortChannelIds test_msg ""
 GEN_TEST lightning::ln::msgs::ReplyChannelRange test_msg ""
 
 GEN_TEST lightning::ln::msgs::ErrorMessage test_msg_hole ", 32, 2"
 GEN_TEST lightning::ln::msgs::WarningMessage test_msg_hole ", 32, 2"
-GEN_TEST lightning::ln::msgs::ChannelUpdate test_msg_hole ", 108, 1"
 
 GEN_TEST lightning::ln::channel_state::ChannelDetails test_msg_simple ""
 

fuzz/src/msg_targets/mod.rs

@@ -25,11 +25,11 @@ pub mod msg_channel_reestablish;
 pub mod msg_decoded_onion_error_packet;
 pub mod msg_channel_announcement;
 pub mod msg_node_announcement;
+pub mod msg_channel_update;
 pub mod msg_query_short_channel_ids;
 pub mod msg_reply_channel_range;
 pub mod msg_error_message;
 pub mod msg_warning_message;
-pub mod msg_channel_update;
 pub mod msg_channel_details;
 pub mod msg_open_channel_v2;
 pub mod msg_accept_channel_v2;

fuzz/src/msg_targets/msg_channel_update.rs

@@ -17,11 +17,11 @@ use crate::utils::test_logger;
 
 #[inline]
 pub fn msg_channel_update_test<Out: test_logger::Output>(data: &[u8], _out: Out) {
-	test_msg_hole!(lightning::ln::msgs::ChannelUpdate, data, 108, 1);
+	test_msg_exact!(lightning::ln::msgs::ChannelUpdate, data);
 }
 
 #[no_mangle]
 pub extern "C" fn msg_channel_update_run(data: *const u8, datalen: usize) {
 	let data = unsafe { std::slice::from_raw_parts(data, datalen) };
-	test_msg_hole!(lightning::ln::msgs::ChannelUpdate, data, 108, 1);
+	test_msg_exact!(lightning::ln::msgs::ChannelUpdate, data);
 }