Ensure Amount uses checked ops

substrate/serai/primitives/src/amount.rs

@@ -1,6 +1,4 @@
-use core::{
-  ops::{Add, Mul},
-};
+use core::ops::{Add, Sub, Mul};
 
 use scale::{Encode, Decode, MaxEncodedLen};
 use scale_info::TypeInfo;
@@ -21,13 +19,21 @@ pub const COIN: Amount = Amount(1_000_000_00);
 impl Add for Amount {
   type Output = Amount;
   fn add(self, other: Amount) -> Amount {
-    Amount(self.0 + other.0)
+    // Explicitly use checked_add so even if range checks are disabled, this is still checked
+    Amount(self.0.checked_add(other.0).unwrap())
+  }
+}
+
+impl Sub for Amount {
+  type Output = Amount;
+  fn sub(self, other: Amount) -> Amount {
+    Amount(self.0.checked_sub(other.0).unwrap())
   }
 }
 
 impl Mul for Amount {
   type Output = Amount;
   fn mul(self, other: Amount) -> Amount {
-    Amount(self.0 * other.0)
+    Amount(self.0.checked_mul(other.0).unwrap())
   }
 }