Fix use-after-free bug in nmslib engine query path

CHANGELOG.md

@@ -16,7 +16,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ### Features
 * Add parent join support for lucene knn [#1182](https://github.com/opensearch-project/k-NN/pull/1182)
 ### Enhancements
-### Bug Fixes 
+### Bug Fixes
+* Fix use-after-free case on nmslib search path [#1305](https://github.com/opensearch-project/k-NN/pull/1305)
 ### Infrastructure
 * Upgrade gradle to 8.4 [1289](https://github.com/opensearch-project/k-NN/pull/1289)
 ### Documentation

jni/include/nmslib_wrapper.h

@@ -48,10 +48,10 @@ namespace knn_jni {
         struct IndexWrapper {
             explicit IndexWrapper(const std::string& spaceType) {
                 // Index gets constructed with a reference to data (see above) but is otherwise unused
-                similarity::ObjectVector data;
                 space.reset(similarity::SpaceFactoryRegistry<float>::Instance().CreateSpace(spaceType, similarity::AnyParams()));
                 index.reset(similarity::MethodFactoryRegistry<float>::Instance().CreateMethod(false, "hnsw", spaceType, *space, data));
             }
+            similarity::ObjectVector data;
             std::unique_ptr<similarity::Space<float>> space;
             std::unique_ptr<similarity::Index<float>> index;
         };

jni/tests/nmslib_wrapper_test.cpp

@@ -21,6 +21,17 @@
 using ::testing::NiceMock;
 using ::testing::Return;
 
+TEST(NmslibIndexWrapperSearchTest, BasicAssertions) {
+    similarity::initLibrary();
+    knn_jni::nmslib_wrapper::IndexWrapper indexWrapper = knn_jni::nmslib_wrapper::IndexWrapper("l2");
+    int k = 10;
+    int dim = 2;
+    std::unique_ptr<float> rawQueryvector(new float[dim]);
+    std::unique_ptr<similarity::Object> queryObject(new similarity::Object(-1, -1, dim*sizeof(float), rawQueryvector.get()));
+    similarity::KNNQuery<float> knnQuery(*(indexWrapper.space), queryObject.get(), k);
+    indexWrapper.index->Search((similarity::KNNQuery<float> *)nullptr);
+}
+
 TEST(NmslibCreateIndexTest, BasicAssertions) {
     // Initialize nmslib
     similarity::initLibrary();