From 2fd0cbb81487a69149167ccfa0053b6f8aaa2d66 Mon Sep 17 00:00:00 2001
From: Jeffrey Czyz <jkczyz@gmail.com>
Date: Wed, 15 Feb 2023 20:17:18 -0600
Subject: [PATCH] Fix amount overflow in Invoice building

An overflow can occur when multiplying the offer amount by the requested
quantity when no amount is given in the request. Return an error instead
of overflowing.
---
 lightning/src/offers/invoice.rs | 37 +++++++++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

diff --git a/lightning/src/offers/invoice.rs b/lightning/src/offers/invoice.rs
index d1b1e99bad3..4fdcf4e125f 100644
--- a/lightning/src/offers/invoice.rs
+++ b/lightning/src/offers/invoice.rs
@@ -148,7 +148,8 @@ impl<'a> InvoiceBuilder<'a> {
 			Some(amount_msats) => amount_msats,
 			None => match invoice_request.contents.offer.amount() {
 				Some(Amount::Bitcoin { amount_msats }) => {
-					amount_msats * invoice_request.quantity().unwrap_or(1)
+					amount_msats.checked_mul(invoice_request.quantity().unwrap_or(1))
+						.ok_or(SemanticError::InvalidAmount)?
 				},
 				Some(Amount::Currency { .. }) => return Err(SemanticError::UnsupportedCurrency),
 				None => return Err(SemanticError::MissingAmount),
@@ -782,7 +783,7 @@ mod tests {
 	use crate::ln::features::{BlindedHopFeatures, Bolt12InvoiceFeatures};
 	use crate::offers::invoice_request::InvoiceRequestTlvStreamRef;
 	use crate::offers::merkle::{SignError, SignatureTlvStreamRef, self};
-	use crate::offers::offer::{OfferBuilder, OfferTlvStreamRef};
+	use crate::offers::offer::{OfferBuilder, OfferTlvStreamRef, Quantity};
 	use crate::offers::parse::{ParseError, SemanticError};
 	use crate::offers::payer::PayerTlvStreamRef;
 	use crate::offers::refund::RefundBuilder;
@@ -1172,6 +1173,38 @@ mod tests {
 		assert_eq!(tlv_stream.amount, Some(1001));
 	}
 
+	#[test]
+	fn builds_invoice_with_quantity_from_request() {
+		let invoice = OfferBuilder::new("foo".into(), recipient_pubkey())
+			.amount_msats(1000)
+			.supported_quantity(Quantity::Unbounded)
+			.build().unwrap()
+			.request_invoice(vec![1; 32], payer_pubkey()).unwrap()
+			.quantity(2).unwrap()
+			.build().unwrap()
+			.sign(payer_sign).unwrap()
+			.respond_with_no_std(payment_paths(), payment_hash(), now()).unwrap()
+			.build().unwrap()
+			.sign(recipient_sign).unwrap();
+		let (_, _, _, tlv_stream, _) = invoice.as_tlv_stream();
+		assert_eq!(invoice.amount_msats(), 2000);
+		assert_eq!(tlv_stream.amount, Some(2000));
+
+		match OfferBuilder::new("foo".into(), recipient_pubkey())
+			.amount_msats(1000)
+			.supported_quantity(Quantity::Unbounded)
+			.build().unwrap()
+			.request_invoice(vec![1; 32], payer_pubkey()).unwrap()
+			.quantity(u64::max_value()).unwrap()
+			.build_unchecked()
+			.sign(payer_sign).unwrap()
+			.respond_with_no_std(payment_paths(), payment_hash(), now())
+		{
+			Ok(_) => panic!("expected error"),
+			Err(e) => assert_eq!(e, SemanticError::InvalidAmount),
+		}
+	}
+
 	#[test]
 	fn builds_invoice_with_fallback_address() {
 		let script = Script::new();