Fix: Prevent use of uninitialized memory when creating Bezier spline

When Constructing bezier splines from dna, the positions of the
left/right handles were set directly in the internal vectors, by
requesting a reference to them. The problem is that
BezierSpline::handle_positions_left() calls ensure_auto_handles()
before returning the reference. That function does some calculations on
uninitialized memory if the positions array is not yet filled.

Differential Revision: https://developer.blender.org/D13107

3 files changed, 25 insertions, 8 deletions

diff --git a/source/blender/blenkernel/BKE_spline.hh b/source/blender/blenkernel/BKE_spline.hh
index 8509b730709..55a4f6ffcfd 100644
--- a/source/blender/blenkernel/BKE_spline.hh
+++ b/source/blender/blenkernel/BKE_spline.hh
@@ -306,11 +306,23 @@ class BezierSpline final : public Spline {
   blender::Span<HandleType> handle_types_left() const;
   blender::MutableSpan<HandleType> handle_types_left();
   blender::Span<blender::float3> handle_positions_left() const;
-  blender::MutableSpan<blender::float3> handle_positions_left();
+  /**
+   * Get writable access to the hande position.
+   *
+   * \param write_only: pass true for an uninitialized spline, this prevents accessing
+   * uninitialized memory while autogenerating handles.
+   */
+  blender::MutableSpan<blender::float3> handle_positions_left(bool write_only = false);
   blender::Span<HandleType> handle_types_right() const;
   blender::MutableSpan<HandleType> handle_types_right();
   blender::Span<blender::float3> handle_positions_right() const;
-  blender::MutableSpan<blender::float3> handle_positions_right();
+  /**
+   * Get writable access to the hande position.
+   *
+   * \param write_only: pass true for an uninitialized spline, this prevents accessing
+   * uninitialized memory while autogenerating handles.
+   */
+  blender::MutableSpan<blender::float3> handle_positions_right(bool write_only = false);
   void ensure_auto_handles() const;
 
   void translate(const blender::float3 &translation) override;
diff --git a/source/blender/blenkernel/intern/curve_eval.cc b/source/blender/blenkernel/intern/curve_eval.cc
index bb745d5b20d..ff0478f2543 100644
--- a/source/blender/blenkernel/intern/curve_eval.cc
+++ b/source/blender/blenkernel/intern/curve_eval.cc
@@ -225,8 +225,8 @@ static SplinePtr spline_from_dna_bezier(const Nurb &nurb)
   Span<const BezTriple> src_points{nurb.bezt, nurb.pntsu};
   spline->resize(src_points.size());
   MutableSpan<float3> positions = spline->positions();
-  MutableSpan<float3> handle_positions_left = spline->handle_positions_left();
-  MutableSpan<float3> handle_positions_right = spline->handle_positions_right();
+  MutableSpan<float3> handle_positions_left = spline->handle_positions_left(true);
+  MutableSpan<float3> handle_positions_right = spline->handle_positions_right(true);
   MutableSpan<BezierSpline::HandleType> handle_types_left = spline->handle_types_left();
   MutableSpan<BezierSpline::HandleType> handle_types_right = spline->handle_types_right();
   MutableSpan<float> radii = spline->radii();
diff --git a/source/blender/blenkernel/intern/spline_bezier.cc b/source/blender/blenkernel/intern/spline_bezier.cc
index e760bf3495e..166fe0f5464 100644
--- a/source/blender/blenkernel/intern/spline_bezier.cc
+++ b/source/blender/blenkernel/intern/spline_bezier.cc
@@ -142,11 +142,14 @@ Span<float3> BezierSpline::handle_positions_left() const
   this->ensure_auto_handles();
   return handle_positions_left_;
 }
-MutableSpan<float3> BezierSpline::handle_positions_left()
+MutableSpan<float3> BezierSpline::handle_positions_left(const bool write_only)
 {
-  this->ensure_auto_handles();
+  if (!write_only) {
+    this->ensure_auto_handles();
+  }
   return handle_positions_left_;
 }
+
 Span<BezierSpline::HandleType> BezierSpline::handle_types_right() const
 {
   return handle_types_right_;
@@ -160,9 +163,11 @@ Span<float3> BezierSpline::handle_positions_right() const
   this->ensure_auto_handles();
   return handle_positions_right_;
 }
-MutableSpan<float3> BezierSpline::handle_positions_right()
+MutableSpan<float3> BezierSpline::handle_positions_right(const bool write_only)
 {
-  this->ensure_auto_handles();
+  if (!write_only) {
+    this->ensure_auto_handles();
+  }
   return handle_positions_right_;
 }