variable_nat_decode() check for overflow / add test case

Author: rooooooooob

rust/src/address.rs

@@ -6,13 +6,16 @@ use ed25519_bip32::XPub;
 // returns (Number represented, bytes read) if valid encoding
 // or None if decoding prematurely finished
 fn variable_nat_decode(bytes: &[u8]) -> Option<(u64, usize)> {
-    let mut output = 0u64;
+    let mut output = 0u128;
     let mut bytes_read = 0;
     for byte in bytes {
-        output = (output << 7) | (byte & 0x7F) as u64;
+        output = (output << 7) | (byte & 0x7F) as u128;
+        if output > u64::MAX.into() {
+            return None;
+        }
         bytes_read += 1;
         if (byte & 0x80) == 0 {
-            return Some((output, bytes_read));
+            return Some((output as u64, bytes_read));
         }
     }
     None
@@ -695,6 +698,12 @@ mod tests {
         }
     }
 
+    #[test]
+    fn variable_nat_decode_too_big() {
+        let too_big = [129, 255, 255, 255, 255, 255, 255, 255, 255, 255, 127];
+        assert_eq!(None, variable_nat_decode(&too_big));
+    }
+
     #[test]
     fn base_serialize_consistency() {
         let base = BaseAddress::new(