Implement BufferHubProducer::attachBuffer

1/ Introduce new kOpProducerQueueInsertBuffer operation to insert a
   standalone ProducerChannel into a ProducerQueueChannel.
2/ Introduce some PDX security check against channel_id spoofing.

Bug: 69981968
Bug: 79224574
Test: buffer_hub_queue-test, libgui_test
Change-Id: I3c13e2897476c34e6e939756b079fe3440937236

16 files changed, 312 insertions, 19 deletions

diff --git a/libs/gui/Android.bp b/libs/gui/Android.bp
index b29c1d5157..ef3e592c09 100644
--- a/libs/gui/Android.bp
+++ b/libs/gui/Android.bp
@@ -123,6 +123,7 @@ cc_library_shared {
         "android.hardware.graphics.common@1.1",
         "libsync",
         "libbinder",
+        "libbufferhub",
         "libbufferhubqueue",  // TODO(b/70046255): Remove this once BufferHub is integrated into libgui.
         "libpdx_default_transport",
         "libcutils",
@@ -149,6 +150,7 @@ cc_library_shared {
                 "BufferHubProducer.cpp",
             ],
             exclude_shared_libs: [
+                "libbufferhub",
                 "libbufferhubqueue",
                 "libpdx_default_transport",
             ],
diff --git a/libs/gui/BufferHubProducer.cpp b/libs/gui/BufferHubProducer.cpp
index 2bc194aead..06d597ccfa 100644
--- a/libs/gui/BufferHubProducer.cpp
+++ b/libs/gui/BufferHubProducer.cpp
@@ -18,6 +18,7 @@
 #include <gui/BufferHubProducer.h>
 #include <inttypes.h>
 #include <log/log.h>
+#include <private/dvr/detached_buffer.h>
 #include <system/window.h>
 #include <ui/DetachedBufferHandle.h>
 
@@ -363,13 +364,86 @@ status_t BufferHubProducer::detachNextBuffer(sp<GraphicBuffer>* out_buffer, sp<F
     return error;
 }
 
-status_t BufferHubProducer::attachBuffer(int* /* out_slot */,
-                                         const sp<GraphicBuffer>& /* buffer */) {
-    // With this BufferHub backed implementation, we assume (for now) all buffers
-    // are allocated and owned by the BufferHub. Thus the attempt of transfering
-    // ownership of a buffer to the buffer queue is intentionally unsupported.
-    LOG_ALWAYS_FATAL("BufferHubProducer::attachBuffer not supported.");
-    return INVALID_OPERATION;
+status_t BufferHubProducer::attachBuffer(int* out_slot, const sp<GraphicBuffer>& buffer) {
+    // In the BufferHub design, all buffers are allocated and owned by the BufferHub. Thus only
+    // GraphicBuffers that are originated from BufferHub can be attached to a BufferHubProducer.
+    ALOGV("queueBuffer: buffer=%p", buffer.get());
+
+    if (out_slot == nullptr) {
+        ALOGE("attachBuffer: out_slot cannot be NULL.");
+        return BAD_VALUE;
+    }
+    if (buffer == nullptr || !buffer->isDetachedBuffer()) {
+        ALOGE("attachBuffer: invalid GraphicBuffer.");
+        return BAD_VALUE;
+    }
+
+    std::unique_lock<std::mutex> lock(mutex_);
+
+    if (connected_api_ == kNoConnectedApi) {
+        ALOGE("attachBuffer: BufferQueue has no connected producer");
+        return NO_INIT;
+    }
+
+    // Before attaching the buffer, caller is supposed to call
+    // IGraphicBufferProducer::setGenerationNumber to inform the
+    // BufferHubProducer the next generation number.
+    if (buffer->getGenerationNumber() != generation_number_) {
+        ALOGE("attachBuffer: Mismatched generation number, buffer: %u, queue: %u.",
+              buffer->getGenerationNumber(), generation_number_);
+        return BAD_VALUE;
+    }
+
+    // Creates a BufferProducer from the GraphicBuffer.
+    std::unique_ptr<DetachedBufferHandle> detached_handle = buffer->takeDetachedBufferHandle();
+    if (detached_handle == nullptr) {
+        ALOGE("attachBuffer: DetachedBufferHandle cannot be NULL.");
+        return BAD_VALUE;
+    }
+    auto detached_buffer = DetachedBuffer::Import(std::move(detached_handle->handle()));
+    if (detached_buffer == nullptr) {
+        ALOGE("attachBuffer: DetachedBuffer cannot be NULL.");
+        return BAD_VALUE;
+    }
+    auto status_or_handle = detached_buffer->Promote();
+    if (!status_or_handle.ok()) {
+        ALOGE("attachBuffer: Failed to promote a DetachedBuffer into a BufferProducer, error=%d.",
+              status_or_handle.error());
+        return BAD_VALUE;
+    }
+    std::shared_ptr<BufferProducer> buffer_producer =
+            BufferProducer::Import(status_or_handle.take());
+    if (buffer_producer == nullptr) {
+        ALOGE("attachBuffer: Failed to import BufferProducer.");
+        return BAD_VALUE;
+    }
+
+    // Adds the BufferProducer into the Queue.
+    auto status_or_slot = queue_->InsertBuffer(buffer_producer);
+    if (!status_or_slot.ok()) {
+        ALOGE("attachBuffer: Failed to insert buffer, error=%d.", status_or_slot.error());
+        return BAD_VALUE;
+    }
+
+    size_t slot = status_or_slot.get();
+    ALOGV("attachBuffer: returning slot %zu.", slot);
+    if (slot >= static_cast<size_t>(max_buffer_count_)) {
+        ALOGE("attachBuffer: Invalid slot: %zu.", slot);
+        return BAD_VALUE;
+    }
+
+    // The just attached buffer should be in dequeued state according to IGraphicBufferProducer
+    // interface. In BufferHub's language the buffer should be in Gained state.
+    buffers_[slot].mGraphicBuffer = buffer;
+    buffers_[slot].mBufferState.attachProducer();
+    buffers_[slot].mEglFence = EGL_NO_SYNC_KHR;
+    buffers_[slot].mFence = Fence::NO_FENCE;
+    buffers_[slot].mRequestBufferCalled = true;
+    buffers_[slot].mAcquireCalled = false;
+    buffers_[slot].mNeedsReallocation = false;
+
+    *out_slot = static_cast<int>(slot);
+    return NO_ERROR;
 }
 
 status_t BufferHubProducer::queueBuffer(int slot, const QueueBufferInput& input,
diff --git a/libs/gui/tests/IGraphicBufferProducer_test.cpp b/libs/gui/tests/IGraphicBufferProducer_test.cpp
index e5a4adbaba..c20e8fca21 100644
--- a/libs/gui/tests/IGraphicBufferProducer_test.cpp
+++ b/libs/gui/tests/IGraphicBufferProducer_test.cpp
@@ -787,10 +787,31 @@ TEST_P(IGraphicBufferProducerTest,
 
     ASSERT_OK(mProducer->disconnect(TEST_API));
 
-    if (GetParam() == USE_BUFFER_QUEUE_PRODUCER) {
-        // TODO(b/69981968): Implement BufferHubProducer::attachBuffer
-        ASSERT_EQ(NO_INIT, mProducer->attachBuffer(&slot, buffer));
+    ASSERT_EQ(NO_INIT, mProducer->attachBuffer(&slot, buffer));
+}
+
+TEST_P(IGraphicBufferProducerTest, DetachThenAttach_Succeeds) {
+    int slot = -1;
+    sp<Fence> fence;
+    sp<GraphicBuffer> buffer;
+
+    setupDequeueRequestBuffer(&slot, &fence, &buffer);
+    ASSERT_TRUE(buffer != nullptr);
+
+    ASSERT_OK(mProducer->detachBuffer(slot));
+    EXPECT_OK(buffer->initCheck());
+
+    if (GetParam() == USE_BUFFER_HUB_PRODUCER) {
+        // For a GraphicBuffer backed by BufferHub, once detached from an IGBP, it should have
+        // isDetachedBuffer() set. Note that this only applies to BufferHub.
+        EXPECT_TRUE(buffer->isDetachedBuffer());
+    } else {
+        EXPECT_FALSE(buffer->isDetachedBuffer());
     }
+
+    EXPECT_OK(mProducer->attachBuffer(&slot, buffer));
+    EXPECT_FALSE(buffer->isDetachedBuffer());
+    EXPECT_OK(buffer->initCheck());
 }
 
 #if USE_BUFFER_HUB_AS_BUFFER_QUEUE
diff --git a/libs/vr/libbufferhub/buffer_hub_client.cpp b/libs/vr/libbufferhub/buffer_hub_client.cpp
index 159f2bd1b3..577cba9572 100644
--- a/libs/vr/libbufferhub/buffer_hub_client.cpp
+++ b/libs/vr/libbufferhub/buffer_hub_client.cpp
@@ -42,11 +42,13 @@ LocalChannelHandle BufferHubClient::TakeChannelHandle() {
 BufferHubBuffer::BufferHubBuffer(LocalChannelHandle channel_handle)
     : Client{pdx::default_transport::ClientChannel::Create(
           std::move(channel_handle))},
-      id_(-1) {}
+      id_(-1),
+      cid_(-1) {}
 BufferHubBuffer::BufferHubBuffer(const std::string& endpoint_path)
     : Client{pdx::default_transport::ClientChannelFactory::Create(
           endpoint_path)},
-      id_(-1) {}
+      id_(-1),
+      cid_(-1) {}
 
 BufferHubBuffer::~BufferHubBuffer() {
   if (metadata_header_ != nullptr) {
@@ -136,6 +138,7 @@ int BufferHubBuffer::ImportBuffer() {
   }
 
   id_ = new_id;
+  cid_ = buffer_desc.buffer_cid();
   buffer_state_bit_ = buffer_desc.buffer_state_bit();
 
   // Note that here the buffer state is mapped from shared memory as an atomic
diff --git a/libs/vr/libbufferhub/include/private/dvr/buffer_hub_client.h b/libs/vr/libbufferhub/include/private/dvr/buffer_hub_client.h
index 0ea77c85fb..b71f5dcba6 100644
--- a/libs/vr/libbufferhub/include/private/dvr/buffer_hub_client.h
+++ b/libs/vr/libbufferhub/include/private/dvr/buffer_hub_client.h
@@ -107,8 +107,14 @@ class BufferHubBuffer : public pdx::Client {
   IonBuffer* buffer() { return &buffer_; }
   const IonBuffer* buffer() const { return &buffer_; }
 
+  // Gets ID of the buffer client. All BufferHubBuffer clients derived from the
+  // same buffer in bufferhubd share the same buffer id.
   int id() const { return id_; }
 
+  // Gets the channel id of the buffer client. Each BufferHubBuffer client has
+  // its system unique channel id.
+  int cid() const { return cid_; }
+
   // Returns the buffer buffer state.
   uint64_t buffer_state() { return buffer_state_->load(); };
 
@@ -170,6 +176,7 @@ class BufferHubBuffer : public pdx::Client {
   // for logging and debugging purposes only and should not be used for lookup
   // or any other functional purpose as a security precaution.
   int id_;
+  int cid_;
   uint64_t buffer_state_bit_{0ULL};
   IonBuffer buffer_;
   IonBuffer metadata_buffer_;
diff --git a/libs/vr/libbufferhub/include/private/dvr/bufferhub_rpc.h b/libs/vr/libbufferhub/include/private/dvr/bufferhub_rpc.h
index f4918c497e..088a235e7e 100644
--- a/libs/vr/libbufferhub/include/private/dvr/bufferhub_rpc.h
+++ b/libs/vr/libbufferhub/include/private/dvr/bufferhub_rpc.h
@@ -164,10 +164,11 @@ class BufferDescription {
  public:
   BufferDescription() = default;
   BufferDescription(const IonBuffer& buffer, const IonBuffer& metadata, int id,
-                    uint64_t buffer_state_bit,
+                    int buffer_cid, uint64_t buffer_state_bit,
                     const FileHandleType& acquire_fence_fd,
                     const FileHandleType& release_fence_fd)
       : id_(id),
+        buffer_cid_(buffer_cid),
         buffer_state_bit_(buffer_state_bit),
         buffer_(buffer, id),
         metadata_(metadata, id),
@@ -180,6 +181,9 @@ class BufferDescription {
   // ID of the buffer client. All BufferHubBuffer clients derived from the same
   // buffer in bufferhubd share the same buffer id.
   int id() const { return id_; }
+  // Channel ID of the buffer client. Each BufferHubBuffer client has its system
+  // unique channel id.
+  int buffer_cid() const { return buffer_cid_; }
   // State mask of the buffer client. Each BufferHubBuffer client backed by the
   // same buffer channel has uniqued state bit among its siblings. For a
   // producer buffer the bit must be kProducerStateBit; for a consumer the bit
@@ -193,6 +197,7 @@ class BufferDescription {
 
  private:
   int id_{-1};
+  int buffer_cid_{-1};
   uint64_t buffer_state_bit_{0};
   // Two IonBuffers: one for the graphic buffer and one for metadata.
   NativeBufferHandle<FileHandleType> buffer_;
@@ -202,7 +207,7 @@ class BufferDescription {
   FileHandleType acquire_fence_fd_;
   FileHandleType release_fence_fd_;
 
-  PDX_SERIALIZABLE_MEMBERS(BufferDescription<FileHandleType>, id_,
+  PDX_SERIALIZABLE_MEMBERS(BufferDescription<FileHandleType>, id_, buffer_cid_,
                            buffer_state_bit_, buffer_, metadata_,
                            acquire_fence_fd_, release_fence_fd_);
 
@@ -381,6 +386,7 @@ struct BufferHubRPC {
     kOpCreateConsumerQueue,
     kOpGetQueueInfo,
     kOpProducerQueueAllocateBuffers,
+    kOpProducerQueueInsertBuffer,
     kOpProducerQueueRemoveBuffer,
     kOpConsumerQueueImportBuffers,
     // TODO(b/77153033): Separate all those RPC operations into subclasses.
@@ -430,6 +436,8 @@ struct BufferHubRPC {
                     std::vector<std::pair<LocalChannelHandle, size_t>>(
                         uint32_t width, uint32_t height, uint32_t layer_count,
                         uint32_t format, uint64_t usage, size_t buffer_count));
+  PDX_REMOTE_METHOD(ProducerQueueInsertBuffer, kOpProducerQueueInsertBuffer,
+                    size_t(int buffer_cid));
   PDX_REMOTE_METHOD(ProducerQueueRemoveBuffer, kOpProducerQueueRemoveBuffer,
                     void(size_t slot));
   PDX_REMOTE_METHOD(ConsumerQueueImportBuffers, kOpConsumerQueueImportBuffers,
diff --git a/libs/vr/libbufferhubqueue/buffer_hub_queue_client.cpp b/libs/vr/libbufferhubqueue/buffer_hub_queue_client.cpp
index 8feb1cd803..1f2c51765d 100644
--- a/libs/vr/libbufferhubqueue/buffer_hub_queue_client.cpp
+++ b/libs/vr/libbufferhubqueue/buffer_hub_queue_client.cpp
@@ -524,6 +524,40 @@ Status<void> ProducerQueue::AddBuffer(
   return BufferHubQueue::Enqueue({buffer, slot, 0ULL});
 }
 
+Status<size_t> ProducerQueue::InsertBuffer(
+    const std::shared_ptr<BufferProducer>& buffer) {
+  if (buffer == nullptr ||
+      !BufferHubDefs::IsBufferGained(buffer->buffer_state())) {
+    ALOGE(
+        "ProducerQueue::InsertBuffer: Can only insert a buffer when it's in "
+        "gained state.");
+    return ErrorStatus(EINVAL);
+  }
+
+  auto status_or_slot =
+      InvokeRemoteMethod<BufferHubRPC::ProducerQueueInsertBuffer>(
+          buffer->cid());
+  if (!status_or_slot) {
+    ALOGE(
+        "ProducerQueue::InsertBuffer: Failed to insert producer buffer: "
+        "buffer_cid=%d, error: %s.",
+        buffer->cid(), status_or_slot.GetErrorMessage().c_str());
+    return status_or_slot.error_status();
+  }
+
+  size_t slot = status_or_slot.get();
+
+  // Note that we are calling AddBuffer() from the base class to explicitly
+  // avoid Enqueue() the BufferProducer.
+  auto status = BufferHubQueue::AddBuffer(buffer, slot);
+  if (!status) {
+    ALOGE("ProducerQueue::InsertBuffer: Failed to add buffer: %s.",
+          status.GetErrorMessage().c_str());
+    return status.error_status();
+  }
+  return {slot};
+}
+
 Status<void> ProducerQueue::RemoveBuffer(size_t slot) {
   auto status =
       InvokeRemoteMethod<BufferHubRPC::ProducerQueueRemoveBuffer>(slot);
diff --git a/libs/vr/libbufferhubqueue/include/private/dvr/buffer_hub_queue_client.h b/libs/vr/libbufferhubqueue/include/private/dvr/buffer_hub_queue_client.h
index 60e1c4b8a9..df500b493e 100644
--- a/libs/vr/libbufferhubqueue/include/private/dvr/buffer_hub_queue_client.h
+++ b/libs/vr/libbufferhubqueue/include/private/dvr/buffer_hub_queue_client.h
@@ -331,6 +331,13 @@ class ProducerQueue : public pdx::ClientBase<ProducerQueue, BufferHubQueue> {
   pdx::Status<void> AddBuffer(const std::shared_ptr<BufferProducer>& buffer,
                               size_t slot);
 
+  // Inserts a ProducerBuffer into the queue. On success, the method returns the
+  // |slot| number where the new buffer gets inserted. Note that the buffer
+  // being inserted should be in Gain'ed state prior to the call and it's
+  // considered as already Dequeued when the function returns.
+  pdx::Status<size_t> InsertBuffer(
+      const std::shared_ptr<BufferProducer>& buffer);
+
   // Remove producer buffer from the queue.
   pdx::Status<void> RemoveBuffer(size_t slot) override;
 
diff --git a/libs/vr/libbufferhubqueue/tests/buffer_hub_queue-test.cpp b/libs/vr/libbufferhubqueue/tests/buffer_hub_queue-test.cpp
index 47a27344bd..2975f56928 100644
--- a/libs/vr/libbufferhubqueue/tests/buffer_hub_queue-test.cpp
+++ b/libs/vr/libbufferhubqueue/tests/buffer_hub_queue-test.cpp
@@ -181,6 +181,40 @@ TEST_F(BufferHubQueueTest, TestProducerConsumer) {
   }
 }
 
+TEST_F(BufferHubQueueTest, TestInsertBuffer) {
+  ASSERT_TRUE(CreateProducerQueue(config_builder_.Build(), UsagePolicy{}));
+
+  consumer_queue_ = producer_queue_->CreateConsumerQueue();
+  ASSERT_TRUE(consumer_queue_ != nullptr);
+  EXPECT_EQ(producer_queue_->capacity(), 0);
+  EXPECT_EQ(consumer_queue_->capacity(), 0);
+
+  std::shared_ptr<BufferProducer> p1 = BufferProducer::Create(
+      kBufferWidth, kBufferHeight, kBufferFormat, kBufferUsage, 0);
+  ASSERT_TRUE(p1 != nullptr);
+
+  // Inserting a posted buffer will fail.
+  DvrNativeBufferMetadata meta;
+  EXPECT_EQ(p1->PostAsync(&meta, LocalHandle()), 0);
+  auto status_or_slot = producer_queue_->InsertBuffer(p1);
+  EXPECT_FALSE(status_or_slot.ok());
+  EXPECT_EQ(status_or_slot.error(), EINVAL);
+
+  // Inserting a gained buffer will succeed.
+  std::shared_ptr<BufferProducer> p2 = BufferProducer::Create(
+      kBufferWidth, kBufferHeight, kBufferFormat, kBufferUsage);
+  ASSERT_TRUE(p2 != nullptr);
+  status_or_slot = producer_queue_->InsertBuffer(p2);
+  EXPECT_TRUE(status_or_slot.ok());
+  // This is the first buffer inserted, should take slot 0.
+  size_t slot = status_or_slot.get();
+  EXPECT_EQ(slot, 0);
+
+  // Wait and expect the consumer to kick up the newly inserted buffer.
+  WaitAndHandleOnce(consumer_queue_.get(), kTimeoutMs);
+  EXPECT_EQ(consumer_queue_->capacity(), 1ULL);
+}
+
 TEST_F(BufferHubQueueTest, TestRemoveBuffer) {
   ASSERT_TRUE(CreateProducerQueue(config_builder_.Build(), UsagePolicy{}));
   DvrNativeBufferMetadata mo;
diff --git a/libs/vr/libpdx/private/pdx/service.h b/libs/vr/libpdx/private/pdx/service.h
index 13aa3e90d7..15fa327e45 100644
--- a/libs/vr/libpdx/private/pdx/service.h
+++ b/libs/vr/libpdx/private/pdx/service.h
@@ -59,9 +59,18 @@ class Channel : public std::enable_shared_from_this<Channel> {
   virtual ~Channel() {}
 
   /*
+   * Accessors to the pid of the last active client.
+   */
+  pid_t GetActiveProcessId() const { return client_pid_; }
+  void SetActiveProcessId(pid_t pid) { client_pid_ = pid; }
+
+  /*
    * Utility to get a shared_ptr reference from the channel context pointer.
    */
   static std::shared_ptr<Channel> GetFromMessageInfo(const MessageInfo& info);
+
+ private:
+  pid_t client_pid_ = 0;
 };
 
 /*
diff --git a/libs/vr/libpdx_uds/service_endpoint.cpp b/libs/vr/libpdx_uds/service_endpoint.cpp
index 32d40e8371..ecbfdba7c4 100644
--- a/libs/vr/libpdx_uds/service_endpoint.cpp
+++ b/libs/vr/libpdx_uds/service_endpoint.cpp
@@ -521,6 +521,9 @@ Status<void> Endpoint::ReceiveMessageForChannel(
   info.flags = 0;
   info.service = service_;
   info.channel = GetChannelState(channel_id);
+  if (info.channel != nullptr) {
+    info.channel->SetActiveProcessId(request.cred.pid);
+  }
   info.send_len = request.send_len;
   info.recv_len = request.max_recv_len;
   info.fd_count = request.file_descriptors.size();
diff --git a/services/vr/bufferhubd/detached_buffer_channel.cpp b/services/vr/bufferhubd/detached_buffer_channel.cpp
index a5cf68dcfd..306180578f 100644
--- a/services/vr/bufferhubd/detached_buffer_channel.cpp
+++ b/services/vr/bufferhubd/detached_buffer_channel.cpp
@@ -109,6 +109,7 @@ Status<BufferDescription<BorrowedHandle>> DetachedBufferChannel::OnImport(
   return BufferDescription<BorrowedHandle>{buffer_,
                                            metadata_buffer_,
                                            buffer_id(),
+                                           channel_id(),
                                            /*buffer_state_bit=*/0,
                                            BorrowedHandle{},
                                            BorrowedHandle{}};
diff --git a/services/vr/bufferhubd/producer_channel.cpp b/services/vr/bufferhubd/producer_channel.cpp
index b6977aaa63..97af660e5d 100644
--- a/services/vr/bufferhubd/producer_channel.cpp
+++ b/services/vr/bufferhubd/producer_channel.cpp
@@ -236,9 +236,13 @@ bool ProducerChannel::HandleMessage(Message& message) {
 
 BufferDescription<BorrowedHandle> ProducerChannel::GetBuffer(
     uint64_t buffer_state_bit) {
-  return {
-      buffer_,          metadata_buffer_,           buffer_id(),
-      buffer_state_bit, acquire_fence_fd_.Borrow(), release_fence_fd_.Borrow()};
+  return {buffer_,
+          metadata_buffer_,
+          buffer_id(),
+          channel_id(),
+          buffer_state_bit,
+          acquire_fence_fd_.Borrow(),
+          release_fence_fd_.Borrow()};
 }
 
 Status<BufferDescription<BorrowedHandle>> ProducerChannel::OnGetBuffer(
diff --git a/services/vr/bufferhubd/producer_channel.h b/services/vr/bufferhubd/producer_channel.h
index 67fdf150a0..10a4ce7c71 100644
--- a/services/vr/bufferhubd/producer_channel.h
+++ b/services/vr/bufferhubd/producer_channel.h
@@ -43,6 +43,8 @@ class ProducerChannel : public BufferHubChannel {
 
   ~ProducerChannel() override;
 
+  uint64_t buffer_state() const { return buffer_state_->load(); }
+
   bool HandleMessage(Message& message) override;
   void HandleImpulse(Message& message) override;
 
diff --git a/services/vr/bufferhubd/producer_queue_channel.cpp b/services/vr/bufferhubd/producer_queue_channel.cpp
index c0c48c2dc1..88f5508307 100644
--- a/services/vr/bufferhubd/producer_queue_channel.cpp
+++ b/services/vr/bufferhubd/producer_queue_channel.cpp
@@ -76,6 +76,11 @@ bool ProducerQueueChannel::HandleMessage(Message& message) {
           message);
       return true;
 
+    case BufferHubRPC::ProducerQueueInsertBuffer::Opcode:
+      DispatchRemoteMethod<BufferHubRPC::ProducerQueueInsertBuffer>(
+          *this, &ProducerQueueChannel::OnProducerQueueInsertBuffer, message);
+      return true;
+
     case BufferHubRPC::ProducerQueueRemoveBuffer::Opcode:
       DispatchRemoteMethod<BufferHubRPC::ProducerQueueRemoveBuffer>(
           *this, &ProducerQueueChannel::OnProducerQueueRemoveBuffer, message);
@@ -278,6 +283,81 @@ ProducerQueueChannel::AllocateBuffer(Message& message, uint32_t width,
   return {{std::move(buffer_handle), slot}};
 }
 
+Status<size_t> ProducerQueueChannel::OnProducerQueueInsertBuffer(
+    pdx::Message& message, int buffer_cid) {
+  ATRACE_NAME("ProducerQueueChannel::InsertBuffer");
+  ALOGD_IF(TRACE,
+           "ProducerQueueChannel::InsertBuffer: channel_id=%d, buffer_cid=%d",
+           channel_id(), buffer_cid);
+
+  if (capacity_ >= BufferHubRPC::kMaxQueueCapacity) {
+    ALOGE("ProducerQueueChannel::InsertBuffer: reaches kMaxQueueCapacity.");
+    return ErrorStatus(E2BIG);
+  }
+  auto producer_channel = std::static_pointer_cast<ProducerChannel>(
+      service()->GetChannel(buffer_cid));
+  if (producer_channel == nullptr ||
+      producer_channel->channel_type() != BufferHubChannel::kProducerType) {
+    // Rejects the request if the requested buffer channel is invalid and/or
+    // it's not a ProducerChannel.
+    ALOGE(
+        "ProducerQueueChannel::InsertBuffer: Invalid buffer_cid=%d, "
+        "producer_buffer=0x%p, channel_type=%d.",
+        buffer_cid, producer_channel.get(),
+        producer_channel == nullptr ? -1 : producer_channel->channel_type());
+    return ErrorStatus(EINVAL);
+  }
+  if (producer_channel->GetActiveProcessId() != message.GetProcessId()) {
+    // Rejects the request if the requested buffer channel is not currently
+    // connected to the caller this is IPC request. This effectively prevents
+    // fake buffer_cid from being injected.
+    ALOGE(
+        "ProducerQueueChannel::InsertBuffer: Requested buffer channel "
+        "(buffer_cid=%d) is not connected to the calling process (pid=%d). "
+        "It's connected to a different process (pid=%d).",
+        buffer_cid, message.GetProcessId(),
+        producer_channel->GetActiveProcessId());
+    return ErrorStatus(EINVAL);
+  }
+  uint64_t buffer_state = producer_channel->buffer_state();
+  if (!BufferHubDefs::IsBufferGained(buffer_state)) {
+    // Rejects the request if the requested buffer is not in Gained state.
+    ALOGE(
+        "ProducerQueueChannel::InsertBuffer: The buffer (cid=%d, "
+        "state=0x%" PRIx64 ") is not in gained state.",
+        buffer_cid, buffer_state);
+    return ErrorStatus(EINVAL);
+  }
+
+  // Register the to-be-inserted buffer's channel_id into the first empty
+  // buffer slot.
+  size_t slot = 0;
+  for (; slot < BufferHubRPC::kMaxQueueCapacity; slot++) {
+    if (buffers_[slot].expired())
+      break;
+  }
+  if (slot == BufferHubRPC::kMaxQueueCapacity) {
+    ALOGE(
+        "ProducerQueueChannel::AllocateBuffer: Cannot find empty slot for new "
+        "buffer allocation.");
+    return ErrorStatus(E2BIG);
+  }
+
+  buffers_[slot] = producer_channel;
+  capacity_++;
+
+  // Notify each consumer channel about the new buffer.
+  for (auto* consumer_channel : consumer_channels_) {
+    ALOGD(
+        "ProducerQueueChannel::AllocateBuffer: Notified consumer with new "
+        "buffer, buffer_cid=%d",
+        buffer_cid);
+    consumer_channel->RegisterNewBuffer(producer_channel, slot);
+  }
+
+  return {slot};
+}
+
 Status<void> ProducerQueueChannel::OnProducerQueueRemoveBuffer(
     Message& /*message*/, size_t slot) {
   if (buffers_[slot].expired()) {
diff --git a/services/vr/bufferhubd/producer_queue_channel.h b/services/vr/bufferhubd/producer_queue_channel.h
index e825f47774..e4fa24372a 100644
--- a/services/vr/bufferhubd/producer_queue_channel.h
+++ b/services/vr/bufferhubd/producer_queue_channel.h
@@ -38,8 +38,12 @@ class ProducerQueueChannel : public BufferHubChannel {
                                  uint32_t format, uint64_t usage,
                                  size_t buffer_count);
 
-  // Detach a BufferHubProducer indicated by |slot|. Note that the buffer must
-  // be in Gain'ed state for the producer queue to detach.
+  // Inserts a BufferProducer into the queue. Note that the buffer must be in
+  // Gain'ed state for the operation to succeed.
+  pdx::Status<size_t> OnProducerQueueInsertBuffer(pdx::Message& message, int buffer_cid);
+
+  // Removes a BufferProducer indicated by |slot|. Note that the buffer must be
+  // in Gain'ed state for the operation to succeed.
   pdx::Status<void> OnProducerQueueRemoveBuffer(pdx::Message& message,
                                                 size_t slot);