Fixed panic in bitmap assign_mut (#1078)

* fix oob access in bitmap assign

* undo changes and fix root cause

src/bitmap/immutable.rs

@@ -239,7 +239,12 @@ impl Bitmap {
     pub fn make_mut(self) -> MutableBitmap {
         match self.into_mut() {
             Either::Left(data) => {
-                MutableBitmap::from_vec(data.bytes.as_ref().to_vec(), data.length)
+                if data.offset > 0 {
+                    // we have to recreate the bytes because a MutableBitmap does not have an `offset`.
+                    data.iter().collect()
+                } else {
+                    MutableBitmap::from_vec(data.bytes.as_ref().to_vec(), data.length)
+                }
             }
             Either::Right(data) => data,
         }

tests/it/bitmap/assign_ops.rs

@@ -18,6 +18,24 @@ fn basics() {
     );
 }
 
+#[test]
+fn binary_assign_oob() {
+    // this check we don't have an oob access if the bitmaps are size T + 1
+    // and we do some slicing.
+    let a = MutableBitmap::from_iter(std::iter::repeat(true).take(65));
+    let b = MutableBitmap::from_iter(std::iter::repeat(true).take(65));
+
+    let a: Bitmap = a.into();
+    let a = a.slice(10, 20);
+
+    let b: Bitmap = b.into();
+    let b = b.slice(10, 20);
+
+    let mut a = a.make_mut();
+
+    binary_assign(&mut a, &b, |x: u64, y| x & y);
+}
+
 #[test]
 fn fast_paths() {
     let b = MutableBitmap::from([true, false]);