Set parent namespace for linker-namespaces

This change allows applications to share RTLD_GLOBAL
native libraries between namespaces associated with
different classloaders.

The rule is - if a library is GLOBAL within namespace
associated with parent classloader, it is shared
with namespace associated with this classloader

Note that the sharing happens on create_namespace
event, which is tied to createClassloader in case of
application classloaders created by the framework, for
custom application classloaders it is tied to first
loadLibrary() event.

Bug: http://b/28560538
Bug: https://code.google.com/p/android/issues/detail?id=208458
Change-Id: I7ee701166f8ec5eff033b7acc0f80c7aa4ec5bda
(cherry picked from commit 24db75c1)

libnativeloader/dlext_namespaces.h

@@ -83,7 +83,8 @@ extern struct android_namespace_t* android_create_namespace(const char* name,
                                                             const char* ld_library_path,
                                                             const char* default_library_path,
                                                             uint64_t type,
-                                                            const char* permitted_when_isolated_path);
+                                                            const char* permitted_when_isolated_path,
+                                                            android_namespace_t* parent);
 
 __END_DECLS
 

libnativeloader/native_loader.cpp

@@ -97,11 +97,14 @@ class LibraryNamespaces {
       namespace_type |= ANDROID_NAMESPACE_TYPE_SHARED;
     }
 
+    android_namespace_t* parent_ns = FindParentNamespaceByClassLoader(env, class_loader);
+
     ns = android_create_namespace("classloader-namespace",
                                   nullptr,
                                   library_path.c_str(),
                                   namespace_type,
-                                  permitted_path.c_str());
+                                  permitted_path.c_str(),
+                                  parent_ns);
 
     if (ns != nullptr) {
       namespaces_.push_back(std::make_pair(env->NewWeakGlobalRef(class_loader), ns));
@@ -198,6 +201,29 @@ class LibraryNamespaces {
     return initialized_;
   }
 
+  jobject GetParentClassLoader(JNIEnv* env, jobject class_loader) {
+    jclass class_loader_class = env->FindClass("java/lang/ClassLoader");
+    jmethodID get_parent = env->GetMethodID(class_loader_class,
+                                            "getParent",
+                                            "()Ljava/lang/ClassLoader;");
+
+    return env->CallObjectMethod(class_loader, get_parent);
+  }
+
+  android_namespace_t* FindParentNamespaceByClassLoader(JNIEnv* env, jobject class_loader) {
+    jobject parent_class_loader = GetParentClassLoader(env, class_loader);
+
+    while (parent_class_loader != nullptr) {
+      android_namespace_t* ns = FindNamespaceByClassLoader(env, parent_class_loader);
+      if (ns != nullptr) {
+        return ns;
+      }
+
+      parent_class_loader = GetParentClassLoader(env, parent_class_loader);
+    }
+    return nullptr;
+  }
+
   bool initialized_;
   std::vector<std::pair<jweak, android_namespace_t*>> namespaces_;
   std::string public_libraries_;