Fix a bug in OneAndZeros unpadding

Introduced in b13c0cc8590199d, it could only trigger if the block size
was more than 256 bytes. In that case an invalid padding could be accepted.

OSS-Fuzz 11608 (https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=11608)

1 files changed, 10 insertions, 0 deletions

diff --git a/src/lib/utils/ct_utils.h b/src/lib/utils/ct_utils.h
index eb510baa2..9243d6701 100644
--- a/src/lib/utils/ct_utils.h
+++ b/src/lib/utils/ct_utils.h
@@ -125,6 +125,16 @@ class Mask
          }
 
       /**
+      * Return a Mask<T> which is set if m is set
+      */
+      template<typename U>
+      static Mask<T> expand(Mask<U> m)
+         {
+         static_assert(sizeof(U) < sizeof(T), "sizes ok");
+         return ~Mask<T>::is_zero(m.value());
+         }
+
+      /**
       * Return a Mask<T> which is set if v is == 0 or cleared otherwise
       */
       static Mask<T> is_zero(T x)