Update error deserialization in compliance with BOLT #1

fuzz/Cargo.toml

@@ -60,6 +60,10 @@ path = "fuzz_targets/msg_ping_target.rs"
 name = "msg_pong_target"
 path = "fuzz_targets/msg_pong_target.rs"
 
+[[bin]]
+name = "msg_error_message_target"
+path = "fuzz_targets/msg_error_message_target.rs"
+
 [[bin]]
 name = "msg_accept_channel_target"
 path = "fuzz_targets/msg_targets/msg_accept_channel_target.rs"
@@ -119,7 +123,3 @@ path = "fuzz_targets/msg_targets/msg_update_fail_htlc_target.rs"
 [[bin]]
 name = "msg_channel_reestablish_target"
 path = "fuzz_targets/msg_targets/msg_channel_reestablish_target.rs"
-
-[[bin]]
-name = "msg_error_message_target"
-path = "fuzz_targets/msg_targets/msg_error_message_target.rs"

fuzz/fuzz_targets/msg_error_message_target.rs

@@ -8,12 +8,14 @@ use lightning::util::reset_rng_state;
 
 use lightning::ln::msgs::{MsgEncodable, MsgDecodable};
 
-mod utils;
-
 #[inline]
 pub fn do_test(data: &[u8]) {
 	reset_rng_state();
-	test_msg!(msgs::ErrorMessage, data);
+	if let Ok(msg) = msgs::ErrorMessage::decode(data){
+		let enc = msg.encode();
+		assert_eq!(&data[0..32], &enc[0..32]);
+		assert_eq!(&data[34..enc.len()], &enc[34..]);
+	}
 }
 
 #[cfg(feature = "afl")]

fuzz/fuzz_targets/msg_targets/gen_target.sh

@@ -1,4 +1,4 @@
-for target in CommitmentSigned FundingCreated FundingLocked FundingSigned OpenChannel RevokeAndACK Shutdown UpdateAddHTLC UpdateFailHTLC UpdateFailMalformedHTLC UpdateFee UpdateFulfillHTLC AcceptChannel ClosingSigned ChannelReestablish ErrorMessage; do
+for target in CommitmentSigned FundingCreated FundingLocked FundingSigned OpenChannel RevokeAndACK Shutdown UpdateAddHTLC UpdateFailHTLC UpdateFailMalformedHTLC UpdateFee UpdateFulfillHTLC AcceptChannel ClosingSigned ChannelReestablish; do
 	tn=$(echo $target | sed 's/\([a-z0-9]\)\([A-Z]\)/\1_\2/g')
 	fn=msg_$(echo $tn | tr '[:upper:]' '[:lower:]')_target.rs
 	cat msg_target_template.txt | sed s/MSG_TARGET/$target/ > $fn

src/ln/msgs.rs

@@ -5,7 +5,7 @@ use bitcoin::network::serialize::{deserialize,serialize};
 use bitcoin::blockdata::script::Script;
 
 use std::error::Error;
-use std::fmt;
+use std::{cmp, fmt};
 use std::result::Result;
 
 use util::{byte_utils, internal_traits, events};
@@ -1626,11 +1626,9 @@ impl MsgDecodable for ErrorMessage {
 		if v.len() < 34 {
 			return Err(DecodeError::ShortRead);
 		}
-		let len = byte_utils::slice_to_be16(&v[32..34]);
-		if v.len() < 34 + len as usize {
-			return Err(DecodeError::ShortRead);
-		}
-		let data = match String::from_utf8(v[34..34 + len as usize].to_vec()) {
+		// Unlike most messages, BOLT 1 requires we truncate our read if the value is out of range
+		let len = cmp::min(byte_utils::slice_to_be16(&v[32..34]) as usize, v.len() - 34);
+		let data = match String::from_utf8(v[34..34 + len].to_vec()) {
 			Ok(s) => s,
 			Err(_) => return Err(DecodeError::BadText),
 		};