Substantially increase coverage in BOLT11 deserialization fuzzer

Author: TheBlueMatt

fuzz/src/bolt11_deser.rs

@@ -8,25 +8,58 @@
 // licenses.
 
 use bitcoin::bech32::{u5, FromBase32, ToBase32};
+use bitcoin::secp256k1::{Secp256k1, SecretKey};
 use crate::utils::test_logger;
-use lightning_invoice::RawDataPart;
+use std::str::FromStr;
+use lightning_invoice::{Bolt11Invoice, RawBolt11Invoice, RawDataPart, RawHrp, RawTaggedField, TaggedField};
 
 #[inline]
 pub fn do_test<Out: test_logger::Output>(data: &[u8], _out: Out) {
-	let bech32 = data.iter().map(|x| u5::try_from_u8(x % 32).unwrap()).collect::<Vec<_>>();
-	let invoice = match RawDataPart::from_base32(&bech32) {
-		Ok(invoice) => invoice,
-		Err(_) => return,
-	};
-
-	// Our encoding is not worse than the input
-	assert!(invoice.to_base32().len() <= bech32.len());
-
-	// Our serialization is loss-less
-	assert_eq!(
-		RawDataPart::from_base32(&invoice.to_base32()).expect("faild parsing out own encoding"),
-		invoice
-	);
+	// Read a fake HRP length byte
+	let hrp_len = std::cmp::min(*data.get(0).unwrap_or(&0) as usize, data.len());
+	if let Ok(s) = std::str::from_utf8(&data[..hrp_len]) {
+		let hrp = match RawHrp::from_str(s) {
+			Ok(hrp) => hrp,
+			Err(_) => return,
+		};
+		let bech32 = data.iter()
+			.skip(hrp_len)
+			.map(|x| u5::try_from_u8(x % 32).unwrap())
+			.collect::<Vec<_>>();
+		let invoice_data = match RawDataPart::from_base32(&bech32) {
+			Ok(invoice) => invoice,
+			Err(_) => return,
+		};
+
+		// Our data encoding is not worse than the input
+		assert!(invoice_data.to_base32().len() <= bech32.len());
+
+		// Our data serialization is loss-less
+		assert_eq!(
+			RawDataPart::from_base32(&invoice_data.to_base32()).expect("faild parsing out own encoding"),
+			invoice_data
+		);
+
+		if invoice_data.tagged_fields.iter().any(|field| matches!(field, RawTaggedField::KnownSemantics(TaggedField::PayeePubKey(_)))) {
+			// We could forge a signature using the fact that signing is insecure in fuzz mode, but
+			// easier to just skip and rely on the fact that no-PayeePubKey invoices do pubkey
+			// recovery
+			return;
+		}
+
+		let raw_invoice = RawBolt11Invoice { hrp, data: invoice_data };
+		let signed_raw_invoice = match raw_invoice.sign(|hash| {
+			let private_key = SecretKey::from_slice(&[42; 32]).unwrap();
+			Ok::<_, ()>(Secp256k1::new().sign_ecdsa_recoverable(hash, &private_key))
+		}) {
+			Ok(inv) => inv,
+			Err(_) => return,
+		};
+
+		if let Ok(invoice) = Bolt11Invoice::from_signed(signed_raw_invoice) {
+			invoice.amount_milli_satoshis();
+		}
+	}
 }
 
 pub fn bolt11_deser_test<Out: test_logger::Output>(data: &[u8], out: Out) {