From cc15831d0a2c0c9128a3e972273317fe32bf8b52 Mon Sep 17 00:00:00 2001
From: Jeff <138259519+jdotc1@users.noreply.github.com>
Date: Thu, 22 Oct 2026 19:13:54 -0400
Subject: [PATCH] BUG: Reject transform parameter counts that exceed the metric
 limit

ObjectToObjectMetric::GetNumberOfParameters returned the moving
transform's 64-bit IdentifierType count through the metric's unsigned
int NumberOfParametersType, so a dense displacement field with more
than 2^32 - 1 parameters was silently truncated. Callers then sized the
derivative from the truncated count and wrote past its end.

Throw instead when the count does not fit. This makes the overflow a
clear error; widening the metric API remains open.

Addresses #6949.
---
 .../include/itkObjectToObjectMetric.hxx       |   8 +-
 .../Numerics/Optimizersv4/test/CMakeLists.txt |   1 +
 .../test/itkObjectToObjectMetricGTest.cxx     | 130 ++++++++++++++++++
 3 files changed, 138 insertions(+), 1 deletion(-)
 create mode 100644 Modules/Numerics/Optimizersv4/test/itkObjectToObjectMetricGTest.cxx

diff --git a/Modules/Numerics/Optimizersv4/include/itkObjectToObjectMetric.hxx b/Modules/Numerics/Optimizersv4/include/itkObjectToObjectMetric.hxx
index b4bca4d43da..39c98c4a7d6 100644
--- a/Modules/Numerics/Optimizersv4/include/itkObjectToObjectMetric.hxx
+++ b/Modules/Numerics/Optimizersv4/include/itkObjectToObjectMetric.hxx
@@ -121,7 +121,13 @@ typename ObjectToObjectMetric<TFixedDimension, TMovingDimension, TVirtualImage,
   ObjectToObjectMetric<TFixedDimension, TMovingDimension, TVirtualImage, TParametersValueType>::GetNumberOfParameters()
     const
 {
-  return this->m_MovingTransform->GetNumberOfParameters();
+  const auto numberOfParameters = this->m_MovingTransform->GetNumberOfParameters();
+  if (numberOfParameters > NumericTraits<NumberOfParametersType>::max())
+  {
+    itkExceptionMacro("Moving transform has " << numberOfParameters << " parameters, exceeding the metric limit of "
+                                              << NumericTraits<NumberOfParametersType>::max());
+  }
+  return static_cast<NumberOfParametersType>(numberOfParameters);
 }
 
 template <unsigned int TFixedDimension,
diff --git a/Modules/Numerics/Optimizersv4/test/CMakeLists.txt b/Modules/Numerics/Optimizersv4/test/CMakeLists.txt
index 94f2d321bbf..bf77ff8791c 100644
--- a/Modules/Numerics/Optimizersv4/test/CMakeLists.txt
+++ b/Modules/Numerics/Optimizersv4/test/CMakeLists.txt
@@ -39,6 +39,7 @@ set(
   ITKOptimizersv4GTests
   itkGradientDescentOptimizerv4ObserverGTest.cxx
   itkMultiGradientOptimizerv4GTest.cxx
+  itkObjectToObjectMetricGTest.cxx
   itkWindowConvergenceMonitoringFunctionGTest.cxx
 )
 creategoogletestdriver(ITKOptimizersv4 "${ITKOptimizersv4-Test_LIBRARIES}" "${ITKOptimizersv4GTests}")
diff --git a/Modules/Numerics/Optimizersv4/test/itkObjectToObjectMetricGTest.cxx b/Modules/Numerics/Optimizersv4/test/itkObjectToObjectMetricGTest.cxx
new file mode 100644
index 00000000000..315f47d4403
--- /dev/null
+++ b/Modules/Numerics/Optimizersv4/test/itkObjectToObjectMetricGTest.cxx
@@ -0,0 +1,130 @@
+/*=========================================================================
+ *
+ *  Copyright NumFOCUS
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *         https://www.apache.org/licenses/LICENSE-2.0.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *=========================================================================*/
+
+// First include the header file to be tested:
+#include "itkObjectToObjectMetric.h"
+
+#include "itkGTest.h"
+#include "itkIdentityTransform.h"
+#include <limits>
+
+namespace
+{
+class CountTransform : public itk::IdentityTransform<double, 3>
+{
+public:
+  ITK_DISALLOW_COPY_AND_MOVE(CountTransform);
+  using Self = CountTransform;
+  using Superclass = itk::IdentityTransform<double, 3>;
+  using Pointer = itk::SmartPointer<Self>;
+  using NumberOfParametersType = Superclass::NumberOfParametersType;
+  itkNewMacro(Self);
+  itkOverrideGetNameOfClassMacro(CountTransform);
+
+  void
+  SetCount(NumberOfParametersType count)
+  {
+    m_Count = count;
+  }
+
+  NumberOfParametersType
+  GetNumberOfParameters() const override
+  {
+    return m_Count;
+  }
+
+protected:
+  CountTransform() = default;
+  ~CountTransform() override = default;
+
+private:
+  NumberOfParametersType m_Count{};
+};
+
+class CountMetric : public itk::ObjectToObjectMetric<3, 3>
+{
+public:
+  ITK_DISALLOW_COPY_AND_MOVE(CountMetric);
+  using Self = CountMetric;
+  using Superclass = itk::ObjectToObjectMetric<3, 3>;
+  using Pointer = itk::SmartPointer<Self>;
+  itkNewMacro(Self);
+  itkOverrideGetNameOfClassMacro(CountMetric);
+
+  MeasureType
+  GetValue() const override
+  {
+    return 0.0;
+  }
+
+  void
+  GetDerivative(DerivativeType & derivative) const override
+  {
+    derivative.SetSize(0);
+  }
+
+  void
+  GetValueAndDerivative(MeasureType & value, DerivativeType & derivative) const override
+  {
+    value = this->GetValue();
+    this->GetDerivative(derivative);
+  }
+
+  bool
+  SupportsArbitraryVirtualDomainSamples() const override
+  {
+    return false;
+  }
+
+protected:
+  CountMetric() = default;
+  ~CountMetric() override = default;
+};
+} // namespace
+
+TEST(ObjectToObjectMetric, PreservesRepresentableParameterCounts)
+{
+  const auto transform = CountTransform::New();
+  const auto metric = CountMetric::New();
+  metric->SetMovingTransform(transform);
+  using CountType = CountMetric::NumberOfParametersType;
+  for (const CountType count : { CountType{ 0 }, CountType{ 17 }, std::numeric_limits<CountType>::max() })
+  {
+    transform->SetCount(count);
+    EXPECT_EQ(metric->GetNumberOfParameters(), count);
+  }
+}
+
+TEST(ObjectToObjectMetric, RejectsParameterCountOverflow)
+{
+  using TransformCountType = CountTransform::NumberOfParametersType;
+  using MetricCountType = CountMetric::NumberOfParametersType;
+  if constexpr (std::numeric_limits<TransformCountType>::digits <= std::numeric_limits<MetricCountType>::digits)
+  {
+    GTEST_SKIP() << "The transform count type is not wider than the metric count type";
+  }
+  else
+  {
+    const auto transform = CountTransform::New();
+    const auto metric = CountMetric::New();
+    metric->SetMovingTransform(transform);
+    const auto maximum = static_cast<TransformCountType>(std::numeric_limits<MetricCountType>::max());
+    transform->SetCount(maximum + TransformCountType{ 1 });
+    EXPECT_THROW(metric->GetNumberOfParameters(), itk::ExceptionObject);
+  }
+}