From a7eb38aac8b6b3400cebba9b09fefca1c04cfbb3 Mon Sep 17 00:00:00 2001
From: Kamran Khan <kamranrkhan@google.com>
Date: Thu, 10 Dec 2020 21:26:44 -0800
Subject: [PATCH] Use checked sub

---
 src/ctap/apdu.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/ctap/apdu.rs b/src/ctap/apdu.rs
index 7a65fd2..66dde63 100644
--- a/src/ctap/apdu.rs
+++ b/src/ctap/apdu.rs
@@ -174,7 +174,8 @@ impl TryFrom<&[u8]> for APDU {
                 return Err(ApduStatusCode::SW_WRONG_LENGTH);
             }
 
-            let extended_apdu_le_len: usize = payload.len() - extended_apdu_lc - 3;
+            let extended_apdu_le_len: usize =
+                payload.len().checked_sub(extended_apdu_lc + 3).unwrap_or(0);
             if extended_apdu_le_len > 3 {
                 return Err(ApduStatusCode::SW_WRONG_LENGTH);
             }