Add libbinder_ndk systemapi support for injecting RPC binder accessors

This allows libbinder_ndk to set up client connections to binder RPC
services underneath the libbinder_ndk service manager APIs.

It requires callbacks to be added to the local process to get connection
information that the client is responsible for obtaining.
Once these callbacks are added to libbinder, any client elswhere in the
process using the service manager APIs will be able to get and use a
binder for the service in the same way they do for kernel binder
services.

Test: atest binderRpcTest vm_accessor_test
Bug: 358427181
Change-Id: I528e84bac40efe13884a68ed851ecfb14dd27daa

Author: devinmoore-goog

libs/binder/IServiceManager.cpp

@@ -157,12 +157,21 @@ class CppBackendShim : public IServiceManager {
 
 class AccessorProvider {
 public:
-    AccessorProvider(RpcAccessorProvider&& provider) : mProvider(std::move(provider)) {}
-    sp<IBinder> provide(const String16& name) { return mProvider(name); }
+    AccessorProvider(std::set<std::string>&& instances, RpcAccessorProvider&& provider)
+          : mInstances(std::move(instances)), mProvider(std::move(provider)) {}
+    sp<IBinder> provide(const String16& name) {
+        if (mInstances.count(String8(name).c_str()) > 0) {
+            return mProvider(name);
+        } else {
+            return nullptr;
+        }
+    }
+    const std::set<std::string>& instances() { return mInstances; }
 
 private:
     AccessorProvider() = delete;
 
+    std::set<std::string> mInstances;
     RpcAccessorProvider mProvider;
 };
 
@@ -318,10 +327,32 @@ sp<IServiceManager> getServiceManagerShimFromAidlServiceManagerForTests(
     return sp<CppBackendShim>::make(sp<BackendUnifiedServiceManager>::make(sm));
 }
 
-std::weak_ptr<AccessorProvider> addAccessorProvider(RpcAccessorProvider&& providerCallback) {
+// gAccessorProvidersMutex must be locked already
+static bool isInstanceProvidedLocked(const std::string& instance) {
+    return gAccessorProviders.end() !=
+            std::find_if(gAccessorProviders.begin(), gAccessorProviders.end(),
+                         [&instance](const AccessorProviderEntry& entry) {
+                             return entry.mProvider->instances().count(instance) > 0;
+                         });
+}
+
+std::weak_ptr<AccessorProvider> addAccessorProvider(std::set<std::string>&& instances,
+                                                    RpcAccessorProvider&& providerCallback) {
+    if (instances.empty()) {
+        ALOGE("Set of instances is empty! Need a non empty set of instances to provide for.");
+        return std::weak_ptr<AccessorProvider>();
+    }
     std::lock_guard<std::mutex> lock(gAccessorProvidersMutex);
+    for (const auto& instance : instances) {
+        if (isInstanceProvidedLocked(instance)) {
+            ALOGE("The instance %s is already provided for by a previously added "
+                  "RpcAccessorProvider.",
+                  instance.c_str());
+            return std::weak_ptr<AccessorProvider>();
+        }
+    }
     std::shared_ptr<AccessorProvider> provider =
-            std::make_shared<AccessorProvider>(std::move(providerCallback));
+            std::make_shared<AccessorProvider>(std::move(instances), std::move(providerCallback));
     std::weak_ptr<AccessorProvider> receipt = provider;
     gAccessorProviders.push_back(AccessorProviderEntry(std::move(provider)));
 
@@ -331,8 +362,9 @@ std::weak_ptr<AccessorProvider> addAccessorProvider(RpcAccessorProvider&& provid
 status_t removeAccessorProvider(std::weak_ptr<AccessorProvider> wProvider) {
     std::shared_ptr<AccessorProvider> provider = wProvider.lock();
     if (provider == nullptr) {
-        ALOGE("The provider supplied to removeAccessorProvider has already been removed.");
-        return NAME_NOT_FOUND;
+        ALOGE("The provider supplied to removeAccessorProvider has already been removed or the "
+              "argument to this function was nullptr.");
+        return BAD_VALUE;
     }
     std::lock_guard<std::mutex> lock(gAccessorProvidersMutex);
     size_t sizeBefore = gAccessorProviders.size();

libs/binder/include/binder/IServiceManager.h

@@ -24,6 +24,7 @@
 #include <utils/String16.h>
 #include <utils/Vector.h>
 #include <optional>
+#include <set>
 
 namespace android {
 
@@ -224,20 +225,36 @@ LIBBINDER_EXPORTED bool checkPermission(const String16& permission, pid_t pid, u
 typedef std::function<status_t(const String16& name, sockaddr* outAddr, socklen_t addrSize)>
         RpcSocketAddressProvider;
 
-typedef std::function<sp<IBinder>(const String16& name)> RpcAccessorProvider;
+/**
+ * This callback provides a way for clients to get access to remote services by
+ * providing an Accessor object from libbinder that can connect to the remote
+ * service over sockets.
+ *
+ * \param instance name of the service that the callback will provide an
+ *        Accessor for. The provided accessor will be used to set up a client
+ *        RPC connection in libbinder in order to return a binder for the
+ *        associated remote service.
+ *
+ * \return IBinder of the Accessor object that libbinder implements.
+ *         nullptr if the provider callback doesn't know how to reach the
+ *         service or doesn't want to provide access for any other reason.
+ */
+typedef std::function<sp<IBinder>(const String16& instance)> RpcAccessorProvider;
 
 class AccessorProvider;
 
 /**
- * Register an accessor provider for the service manager APIs.
+ * Register a RpcAccessorProvider for the service manager APIs.
  *
+ * \param instances that the RpcAccessorProvider knows about and can provide an
+ *        Accessor for.
  * \param provider callback that generates Accessors.
  *
  * \return A pointer used as a recept for the successful addition of the
  *         AccessorProvider. This is needed to unregister it later.
  */
 [[nodiscard]] LIBBINDER_EXPORTED std::weak_ptr<AccessorProvider> addAccessorProvider(
-        RpcAccessorProvider&& providerCallback);
+        std::set<std::string>&& instances, RpcAccessorProvider&& providerCallback);
 
 /**
  * Remove an accessor provider using the pointer provided by addAccessorProvider

libs/binder/ndk/Android.bp

@@ -95,6 +95,7 @@ cc_library {
         "persistable_bundle.cpp",
         "process.cpp",
         "service_manager.cpp",
+        "binder_rpc.cpp",
     ],
 
     static_libs: [