Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 852 insertions, 0 deletions

diff --git a/tools/fuzzing/ipc/IPCFuzzController.cpp b/tools/fuzzing/ipc/IPCFuzzController.cpp
new file mode 100644
index 0000000000..860175cf17
--- /dev/null
+++ b/tools/fuzzing/ipc/IPCFuzzController.cpp
@@ -0,0 +1,852 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "IPCFuzzController.h"
+#include "mozilla/Fuzzing.h"
+#include "mozilla/SpinEventLoopUntil.h"
+#include "mozilla/SyncRunnable.h"
+
+#include "nsIThread.h"
+#include "nsThreadUtils.h"
+
+#include "mozilla/ipc/MessageChannel.h"
+#include "mozilla/ipc/MessageLink.h"
+#include "mozilla/ipc/ProtocolUtils.h"
+#include "mozilla/ipc/NodeChannel.h"
+#include "mozilla/ipc/NodeController.h"
+
+#include "mozilla/ipc/PIdleScheduler.h"
+#include "mozilla/ipc/PBackground.h"
+#include "mozilla/dom/PContent.h"
+
+using namespace mojo::core::ports;
+using namespace mozilla::ipc;
+
+// Sync inject means that the actual fuzzing takes place on the I/O thread
+// and hence it injects directly into the target NodeChannel. In async mode,
+// we run the fuzzing on a separate thread and dispatch the runnable that
+// injects the message back to the I/O thread. Both approaches seem to work
+// and have advantages and disadvantages. Blocking the I/O thread means no
+// IPC between other processes will interfere with our fuzzing in the meantime
+// but blocking could also cause hangs when such IPC is required during the
+// fuzzing runtime for some reason.
+//#define MOZ_FUZZ_IPC_SYNC_INJECT 1
+
+// For debugging purposes, it can be helpful to synchronize after each message
+// rather than after each iteration, to see which messages are particularly
+// slow or cause a hang. Without this, synchronization will occur at the end
+// of each iteration as well as after each constructor message.
+//#define MOZ_FUZZ_IPC_SYNC_AFTER_EACH_MSG
+
+namespace mozilla {
+namespace fuzzing {
+
+IPCFuzzController::IPCFuzzController() : mMutex("IPCFuzzController") {
+  InitializeIPCTypes();
+
+  // We use 6 bits for port index selection without wrapping, so we just
+  // create 64 empty rows in our port matrix. Not all of these rows will
+  // be used though.
+  portNames.resize(64);
+
+  // This is our port / toplevel actor ordering. Add new toplevel actors
+  // here to support them in the fuzzer. Do *NOT* change the order of
+  // these, as it will invalidate our fuzzing corpus.
+  portNameToIndex["PContent"] = 0;
+  portNameToIndex["PBackground"] = 1;
+  portNameToIndex["PBackgroundStarter"] = 2;
+  portNameToIndex["PCompositorManager"] = 3;
+  portNameToIndex["PImageBridge"] = 4;
+  portNameToIndex["PProcessHangMonitor"] = 5;
+  portNameToIndex["PProfiler"] = 6;
+  portNameToIndex["PVRManager"] = 7;
+  portNameToIndex["PCanvasManager"] = 8;
+}
+
+// static
+IPCFuzzController& IPCFuzzController::instance() {
+  static IPCFuzzController ifc;
+  return ifc;
+}
+
+void IPCFuzzController::InitializeIPCTypes() {
+  const char* cons = "Constructor";
+  size_t cons_len = strlen(cons);
+
+  for (uint32_t start = 0; start < LastMsgIndex; ++start) {
+    uint32_t i;
+    for (i = (start << 16) + 1; i < ((start + 1) << 16); ++i) {
+      const char* name = IPC::StringFromIPCMessageType(i);
+
+      if (name[0] == '<') break;
+
+      size_t len = strlen(name);
+      if (len > cons_len && !memcmp(cons, name + len - cons_len, cons_len)) {
+        constructorTypes.insert(i);
+      }
+    }
+
+    validMsgTypes[(ProtocolId)start] = i - ((start << 16) + 1);
+  }
+}
+
+bool IPCFuzzController::GetRandomIPCMessageType(ProtocolId pId,
+                                                uint16_t typeOffset,
+                                                uint32_t* type) {
+  auto pIdEntry = validMsgTypes.find(pId);
+  if (pIdEntry == validMsgTypes.end()) {
+    return false;
+  }
+
+  *type =
+      ((uint32_t)pIdEntry->first << 16) + 1 + (typeOffset % pIdEntry->second);
+  return true;
+}
+
+void IPCFuzzController::OnActorConnected(IProtocol* protocol) {
+  if (!XRE_IsParentProcess()) {
+    return;
+  }
+
+#ifdef FUZZ_DEBUG
+  MOZ_FUZZING_NYX_PRINTF("INFO: [OnActorConnected] ActorID %d Protocol: %s\n",
+                         protocol->Id(), protocol->GetProtocolName());
+#endif
+
+  MessageChannel* channel = protocol->ToplevelProtocol()->GetIPCChannel();
+
+  Maybe<PortName> portName = channel->GetPortName();
+  if (portName) {
+    MOZ_FUZZING_NYX_DEBUG(
+        "DEBUG: IPCFuzzController::OnActorConnected() Mutex try\n");
+    // Called on background threads and modifies `actorIds`.
+    MutexAutoLock lock(mMutex);
+    MOZ_FUZZING_NYX_DEBUG(
+        "DEBUG: IPCFuzzController::OnActorConnected() Mutex locked\n");
+    actorIds[*portName].emplace_back(protocol->Id(), protocol->GetProtocolId());
+
+    // Fix the port we will be using for at least the next 5 messages
+    useLastPortName = true;
+    lastActorPortName = *portName;
+
+    // Use this actor for the next 5 messages
+    useLastActor = 5;
+  } else {
+    MOZ_FUZZING_NYX_PRINT("WARNING: No port name on actor?!\n");
+  }
+}
+
+void IPCFuzzController::OnActorDestroyed(IProtocol* protocol) {
+  if (!XRE_IsParentProcess()) {
+    return;
+  }
+
+  MOZ_FUZZING_NYX_PRINTF("INFO: [OnActorDestroyed] ActorID %d Protocol: %s\n",
+                         protocol->Id(), protocol->GetProtocolName());
+
+  MessageChannel* channel = protocol->ToplevelProtocol()->GetIPCChannel();
+
+  Maybe<PortName> portName = channel->GetPortName();
+  if (portName) {
+    MOZ_FUZZING_NYX_DEBUG(
+        "DEBUG: IPCFuzzController::OnActorDestroyed() Mutex try\n");
+    // Called on background threads and modifies `actorIds`.
+    MutexAutoLock lock(mMutex);
+    MOZ_FUZZING_NYX_DEBUG(
+        "DEBUG: IPCFuzzController::OnActorDestroyed() Mutex locked\n");
+
+    for (auto iter = actorIds[*portName].begin();
+         iter != actorIds[*portName].end();) {
+      if (iter->first == protocol->Id() &&
+          iter->second == protocol->GetProtocolId()) {
+        iter = actorIds[*portName].erase(iter);
+      } else {
+        ++iter;
+      }
+    }
+  } else {
+    MOZ_FUZZING_NYX_PRINT("WARNING: No port name on destroyed actor?!\n");
+  }
+}
+
+void IPCFuzzController::AddToplevelActor(PortName name, ProtocolId protocolId) {
+  const char* protocolName = ProtocolIdToName(protocolId);
+  auto result = portNameToIndex.find(protocolName);
+  if (result == portNameToIndex.end()) {
+    MOZ_FUZZING_NYX_PRINTF(
+        "ERROR: [OnActorConnected] Unknown Top-Level Protocol: %s\n",
+        protocolName);
+    MOZ_REALLY_CRASH(__LINE__);
+  }
+  uint8_t portIndex = result->second;
+  portNames[portIndex].push_back(name);
+}
+
+bool IPCFuzzController::ObserveIPCMessage(mozilla::ipc::NodeChannel* channel,
+                                          IPC::Message& aMessage) {
+  if (!mozilla::fuzzing::Nyx::instance().is_enabled("IPC_Generic")) {
+    // Fuzzer is not enabled.
+    return true;
+  }
+
+  if (!XRE_IsParentProcess()) {
+    // For now we only care about things in the parent process.
+    return true;
+  }
+
+  if (aMessage.IsFuzzMsg()) {
+    // Don't observe our own messages. If this is the first fuzzing message,
+    // we also block further non-fuzzing communication on that node.
+    if (!channel->mBlockSendRecv) {
+      MOZ_FUZZING_NYX_PRINTF(
+          "INFO: [NodeChannel::OnMessageReceived] Blocking further "
+          "communication on Port %lu %lu (seen fuzz msg)\n",
+          channel->GetName().v1, channel->GetName().v2);
+      channel->mBlockSendRecv = true;
+    }
+    return true;
+  } else if (aMessage.type() == dom::PContent::Msg_SignalFuzzingReady__ID) {
+    MOZ_FUZZING_NYX_PRINT("DEBUG: Ready message detected.\n");
+
+    // TODO: This is specific to PContent fuzzing. If we later want to fuzz
+    // a different process pair, we need additional signals here.
+    OnChildReady();
+
+    // The ready message indicates the right node name for us to work with
+    // and we should only ever receive it once.
+    if (haveTargetNodeName) {
+      MOZ_FUZZING_NYX_PRINT("ERROR: Received ready signal twice?!\n");
+      MOZ_REALLY_CRASH(__LINE__);
+    }
+
+    targetNodeName = channel->GetName();
+    haveTargetNodeName = true;
+
+    // We can also use this message as the base template for other messages
+    if (!this->sampleHeader.initLengthUninitialized(
+            sizeof(IPC::Message::Header))) {
+      MOZ_REALLY_CRASH(__LINE__);
+    }
+
+    memcpy(sampleHeader.begin(), aMessage.header(),
+           sizeof(IPC::Message::Header));
+  } else if (haveTargetNodeName && targetNodeName != channel->GetName()) {
+    // Not our node, no need to observe
+    return true;
+  } else if (Nyx::instance().started()) {
+    // When fuzzing is already started, we shouldn't observe messages anymore.
+    if (!channel->mBlockSendRecv) {
+      MOZ_FUZZING_NYX_PRINTF(
+          "INFO: [NodeChannel::OnMessageReceived] Blocking further "
+          "communication on Port %lu %lu (fuzzing started)\n",
+          channel->GetName().v1, channel->GetName().v2);
+      channel->mBlockSendRecv = true;
+    }
+    return false;
+  }
+
+  Vector<char, 256, InfallibleAllocPolicy> footer;
+
+  if (!footer.initLengthUninitialized(aMessage.event_footer_size())) {
+    MOZ_REALLY_CRASH(__LINE__);
+  }
+
+  if (!aMessage.ReadFooter(footer.begin(), footer.length(), false)) {
+    MOZ_FUZZING_NYX_PRINT("ERROR: ReadFooter() failed?!\n");
+    MOZ_REALLY_CRASH(__LINE__);
+  }
+
+  UniquePtr<Event> event = Event::Deserialize(footer.begin(), footer.length());
+
+  if (!event) {
+    MOZ_FUZZING_NYX_PRINT("ERROR: Failed to deserialize observed message?!\n");
+    MOZ_REALLY_CRASH(__LINE__);
+  }
+
+  if (event->type() == Event::kUserMessage) {
+    if (haveTargetNodeName && !fuzzingStartPending) {
+      bool missingActor = false;
+
+      // Check if we have any entries in our port map that we haven't seen yet
+      // though `OnActorConnected`. That method is called on a background
+      // thread and this call will race with the I/O thread.
+      {
+        MOZ_FUZZING_NYX_DEBUG(
+            "DEBUG: IPCFuzzController::ObserveIPCMessage() Mutex try\n");
+        // Called on the I/O thread and reads `portSeqNos`.
+        //
+        // IMPORTANT: We must give up any locks before entering `StartFuzzing`,
+        // as we will never return. This would cause a deadlock with new actors
+        // being created and `OnActorConnected` being called.
+        MutexAutoLock lock(mMutex);
+
+        MOZ_FUZZING_NYX_DEBUG(
+            "DEBUG: IPCFuzzController::ObserveIPCMessage() Mutex locked\n");
+
+        for (auto iter = portSeqNos.begin(); iter != portSeqNos.end(); ++iter) {
+          auto result = actorIds.find(iter->first);
+          if (result == actorIds.end()) {
+            // Make sure we only wait for actors that belong to us.
+            auto result = portNodeName.find(iter->first);
+            if (result->second == targetNodeName) {
+              missingActor = true;
+              break;
+            }
+          }
+        }
+      }
+
+      if (missingActor) {
+        MOZ_FUZZING_NYX_PRINT(
+            "INFO: Delaying fuzzing start, missing actors...\n");
+      } else if (!childReady) {
+        MOZ_FUZZING_NYX_PRINT(
+            "INFO: Delaying fuzzing start, waiting for child...\n");
+      } else {
+        fuzzingStartPending = true;
+        StartFuzzing(channel, aMessage);
+
+        // In the async case, we return and can already block the relevant
+        // communication.
+        if (targetNodeName == channel->GetName()) {
+          if (!channel->mBlockSendRecv) {
+            MOZ_FUZZING_NYX_PRINTF(
+                "INFO: [NodeChannel::OnMessageReceived] Blocking further "
+                "communication on Port %lu %lu (fuzzing start pending)\n",
+                channel->GetName().v1, channel->GetName().v2);
+            channel->mBlockSendRecv = true;
+          }
+
+          return false;
+        }
+        return true;
+      }
+    }
+
+    // Add/update sequence numbers. We need to make sure to do this after our
+    // call to `StartFuzzing` because once we start fuzzing, the message will
+    // never actually be processed, so we run into a sequence number desync.
+    {
+      // Get the port name associated with this message
+      UserMessageEvent* userMsgEv = static_cast<UserMessageEvent*>(event.get());
+      PortName name = event->port_name();
+
+      // Called on the I/O thread and modifies `portSeqNos`.
+      MutexAutoLock lock(mMutex);
+      portSeqNos.insert_or_assign(
+          name, std::pair<int32_t, uint64_t>(aMessage.seqno(),
+                                             userMsgEv->sequence_num()));
+
+      portNodeName.insert_or_assign(name, channel->GetName());
+    }
+  }
+
+  return true;
+}
+
+bool IPCFuzzController::MakeTargetDecision(
+    uint8_t portIndex, uint8_t portInstanceIndex, uint8_t actorIndex,
+    uint16_t typeOffset, PortName* name, int32_t* seqno, uint64_t* fseqno,
+    int32_t* actorId, uint32_t* type, bool* is_cons, bool update) {
+  // Every possible toplevel actor type has a fixed number that
+  // we assign to it in the constructor of this class. Here, we
+  // use the lower 6 bits to select this toplevel actor type.
+  // This approach has the advantage that the tests will always
+  // select the same toplevel actor type deterministically,
+  // independent of the order they appeared and independent
+  // of the type of fuzzing we are doing.
+  auto portInstances = portNames[portIndex & 0x3f];
+  if (!portInstances.size()) {
+    return false;
+  }
+
+  if (useLastActor) {
+    useLastActor--;
+    *name = lastActorPortName;
+
+    MOZ_FUZZING_NYX_PRINT("DEBUG: MakeTargetDecision: Pinned to last actor.\n");
+
+    // Once we stop pinning to the last actor, we need to decide if we
+    // want to keep the pinning on the port itself. We use one of the
+    // unused upper bits of portIndex for this purpose.
+    if (!useLastActor && (portIndex & (1 << 7))) {
+      MOZ_FUZZING_NYX_PRINT(
+          "DEBUG: MakeTargetDecision: Released pinning on last port.\n");
+      useLastPortName = false;
+    }
+  } else if (useLastPortName) {
+    *name = lastActorPortName;
+    MOZ_FUZZING_NYX_PRINT("DEBUG: MakeTargetDecision: Pinned to last port.\n");
+  } else {
+    *name = portInstances[portInstanceIndex % portInstances.size()];
+  }
+
+  // We should always have at least one actor per port
+  auto result = actorIds.find(*name);
+  if (result == actorIds.end()) {
+    MOZ_FUZZING_NYX_PRINT("ERROR: Couldn't find port in actors map?!\n");
+    return false;
+  }
+
+  // Find a random actor on this port
+  auto actors = result->second;
+  if (actors.empty()) {
+    MOZ_FUZZING_NYX_PRINT(
+        "ERROR: Couldn't find an actor for selected port?!\n");
+    return false;
+  }
+
+  auto seqNos = portSeqNos[*name];
+
+  // Hand out the correct sequence numbers
+  *seqno = seqNos.first - 1;
+  *fseqno = seqNos.second + 1;
+
+  if (update) {
+    portSeqNos.insert_or_assign(*name,
+                                std::pair<int32_t, uint64_t>(*seqno, *fseqno));
+  }
+
+  if (useLastActor) {
+    actorIndex = actors.size() - 1;
+  } else {
+    actorIndex %= actors.size();
+  }
+
+  ActorIdPair ids = actors[actorIndex];
+  *actorId = ids.first;
+
+  // If the actor ID is 0, then we are talking to the toplevel actor
+  // of this port. Hence we must set the ID to MSG_ROUTING_CONTROL.
+  if (!*actorId) {
+    *actorId = MSG_ROUTING_CONTROL;
+  }
+
+  if (!this->GetRandomIPCMessageType(ids.second, typeOffset, type)) {
+    MOZ_FUZZING_NYX_PRINT("ERROR: GetRandomIPCMessageType failed?!\n");
+    return false;
+  }
+
+  *is_cons = false;
+  if (constructorTypes.find(*type) != constructorTypes.end()) {
+    *is_cons = true;
+  }
+
+#ifdef FUZZ_DEBUG
+  MOZ_FUZZING_NYX_PRINTF(
+      "DEBUG: MakeTargetDecision: Protocol: %s msgType: %s\n",
+      ProtocolIdToName(ids.second), IPC::StringFromIPCMessageType(*type));
+#endif
+
+  return true;
+}
+
+void IPCFuzzController::OnMessageTaskStart() { messageStartCount++; }
+
+void IPCFuzzController::OnMessageTaskStop() { messageStopCount++; }
+
+void IPCFuzzController::OnPreFuzzMessageTaskRun() { messageTaskCount++; }
+void IPCFuzzController::OnPreFuzzMessageTaskStop() { messageTaskCount--; }
+
+void IPCFuzzController::OnDropPeer(const char* reason = nullptr,
+                                   const char* file = nullptr, int line = 0) {
+  if (!XRE_IsParentProcess()) {
+    return;
+  }
+
+  if (!Nyx::instance().started()) {
+    // It's possible to close a connection to some peer before we have even
+    // started fuzzing. We ignore these events until we are actually fuzzing.
+    return;
+  }
+
+  MOZ_FUZZING_NYX_PRINT(
+      "ERROR: ======== END OF ITERATION (DROP_PEER) ========\n");
+#ifdef FUZZ_DEBUG
+  MOZ_FUZZING_NYX_PRINTF("DEBUG: ======== %s:%d ========\n", file, line);
+#endif
+  Nyx::instance().handle_event("MOZ_IPC_DROP_PEER", file, line, reason);
+
+  if (Nyx::instance().is_replay()) {
+    // In replay mode, let's ignore drop peer to avoid races with it.
+    return;
+  }
+
+  Nyx::instance().release(IPCFuzzController::instance().getMessageStopCount());
+}
+
+void IPCFuzzController::StartFuzzing(mozilla::ipc::NodeChannel* channel,
+                                     IPC::Message& aMessage) {
+  nodeChannel = channel;
+
+  RefPtr<IPCFuzzLoop> runnable = new IPCFuzzLoop();
+
+#if MOZ_FUZZ_IPC_SYNC_INJECT
+  runnable->Run();
+#else
+  nsCOMPtr<nsIThread> newThread;
+  nsresult rv =
+      NS_NewNamedThread("IPCFuzzLoop", getter_AddRefs(newThread), runnable);
+
+  if (NS_FAILED(rv)) {
+    MOZ_FUZZING_NYX_PRINT("ERROR: [StartFuzzing] NS_NewNamedThread failed?!\n");
+    MOZ_REALLY_CRASH(__LINE__);
+  }
+#endif
+}
+
+IPCFuzzController::IPCFuzzLoop::IPCFuzzLoop()
+    : mozilla::Runnable("IPCFuzzLoop") {}
+
+NS_IMETHODIMP IPCFuzzController::IPCFuzzLoop::Run() {
+  MOZ_FUZZING_NYX_DEBUG("DEBUG: BEGIN IPCFuzzLoop::Run()\n");
+
+  const size_t maxMsgSize = 2048;
+  const size_t controlLen = 16;
+
+  Vector<char, 256, InfallibleAllocPolicy> buffer;
+
+  RefPtr<NodeController> controller = NodeController::GetSingleton();
+
+  // TODO: The following code is full of data races. We need synchronization
+  // on the `IPCFuzzController` instance, because the I/O thread can call into
+  // this class via ObserveIPCMessages. The problem is that any such call
+  // must either be observed to update the sequence numbers, or the packet
+  // must be dropped already.
+  if (!IPCFuzzController::instance().haveTargetNodeName) {
+    MOZ_FUZZING_NYX_PRINT("ERROR: I don't have the target NodeName?!\n");
+    MOZ_REALLY_CRASH(__LINE__);
+  }
+
+  {
+    MOZ_FUZZING_NYX_DEBUG("DEBUG: IPCFuzzLoop::Run() Mutex try\n");
+    // Called on the I/O thread and modifies `portSeqNos` and `actorIds`.
+    MutexAutoLock lock(IPCFuzzController::instance().mMutex);
+    MOZ_FUZZING_NYX_DEBUG("DEBUG: IPCFuzzLoop::Run() Mutex locked\n");
+
+    // The wait/delay logic in ObserveIPCMessage should ensure that we haven't
+    // seen any packets on ports for which we haven't received actor information
+    // yet, if those ports belong to our channel. However, we might also have
+    // seen ports not belonging to our channel, which we have to remove now.
+    for (auto iter = IPCFuzzController::instance().portSeqNos.begin();
+         iter != IPCFuzzController::instance().portSeqNos.end();) {
+      auto result = IPCFuzzController::instance().actorIds.find(iter->first);
+      if (result == IPCFuzzController::instance().actorIds.end()) {
+        auto portNameResult =
+            IPCFuzzController::instance().portNodeName.find(iter->first);
+        if (portNameResult->second ==
+            IPCFuzzController::instance().targetNodeName) {
+          MOZ_FUZZING_NYX_PRINT(
+              "ERROR: We should not have port map entries without a "
+              "corresponding "
+              "entry in our actors map\n");
+          MOZ_REALLY_CRASH(__LINE__);
+        } else {
+          iter = IPCFuzzController::instance().portSeqNos.erase(iter);
+        }
+      } else {
+        ++iter;
+      }
+    }
+
+    // TODO: Technically, at this point we only know that PContent (or whatever
+    // toplevel protocol we decided to synchronize on), is present. It might
+    // be possible that others aren't created yet and we are racing on this.
+    //
+    // Note: The delay logic mentioned above makes this less likely. Only actors
+    // which are created on-demand and which have not been referenced yet at all
+    // would be affected by such a race.
+    for (auto iter = IPCFuzzController::instance().actorIds.begin();
+         iter != IPCFuzzController::instance().actorIds.end(); ++iter) {
+      bool isValidTarget = false;
+      Maybe<PortStatus> status;
+      PortRef ref = controller->GetPort(iter->first);
+      if (ref.is_valid()) {
+        status = controller->GetStatus(ref);
+        if (status) {
+          isValidTarget = status->peer_node_name ==
+                          IPCFuzzController::instance().targetNodeName;
+        }
+      }
+
+      auto result = IPCFuzzController::instance().portSeqNos.find(iter->first);
+      if (result == IPCFuzzController::instance().portSeqNos.end()) {
+        if (isValidTarget) {
+          MOZ_FUZZING_NYX_PRINTF(
+              "INFO: Using Port %lu %lu for protocol %s (*)\n", iter->first.v1,
+              iter->first.v2, ProtocolIdToName(iter->second[0].second));
+
+          // Normally the start sequence numbers would be -1 and 1, but our map
+          // does not record the next numbers, but the "last seen" state. So we
+          // have to adjust these so the next calculated sequence number pair
+          // matches the start sequence numbers.
+          IPCFuzzController::instance().portSeqNos.insert_or_assign(
+              iter->first, std::pair<int32_t, uint64_t>(0, 0));
+
+          IPCFuzzController::instance().AddToplevelActor(
+              iter->first, iter->second[0].second);
+
+        } else {
+          MOZ_FUZZING_NYX_PRINTF(
+              "INFO: Removing Port %lu %lu for protocol %s (*)\n",
+              iter->first.v1, iter->first.v2,
+              ProtocolIdToName(iter->second[0].second));
+
+          // This toplevel actor does not belong to us, but we haven't added
+          // it to `portSeqNos`, so we don't have to remove it.
+        }
+      } else {
+        if (isValidTarget) {
+          MOZ_FUZZING_NYX_PRINTF("INFO: Using Port %lu %lu for protocol %s\n",
+                                 iter->first.v1, iter->first.v2,
+                                 ProtocolIdToName(iter->second[0].second));
+
+          IPCFuzzController::instance().AddToplevelActor(
+              iter->first, iter->second[0].second);
+        } else {
+          MOZ_FUZZING_NYX_PRINTF(
+              "INFO: Removing Port %lu %lu for protocol %s\n", iter->first.v1,
+              iter->first.v2, ProtocolIdToName(iter->second[0].second));
+
+          // This toplevel actor does not belong to us, so remove it.
+          IPCFuzzController::instance().portSeqNos.erase(result);
+        }
+      }
+    }
+  }
+
+  IPCFuzzController::instance().runnableDone = false;
+
+  SyncRunnable::DispatchToThread(
+      GetMainThreadEventTarget(),
+      NS_NewRunnableFunction("IPCFuzzController::StartFuzzing", [&]() -> void {
+        MOZ_FUZZING_NYX_PRINT("INFO: Main thread runnable start.\n");
+        NS_ProcessPendingEvents(NS_GetCurrentThread());
+        MOZ_FUZZING_NYX_PRINT("INFO: Main thread runnable done.\n");
+      }));
+
+  MOZ_FUZZING_NYX_PRINT("INFO: Performing snapshot...\n");
+  Nyx::instance().start();
+
+  uint32_t expected_messages = 0;
+
+  IPCFuzzController::instance().useLastActor = 0;
+  IPCFuzzController::instance().useLastPortName = false;
+
+  for (int i = 0; i < 16; ++i) {
+    if (!buffer.initLengthUninitialized(maxMsgSize)) {
+      MOZ_REALLY_CRASH(__LINE__);
+    }
+
+    // Grab enough data to potentially fill our everything except the footer.
+    uint32_t bufsize =
+        Nyx::instance().get_data((uint8_t*)buffer.begin(), buffer.length());
+
+    if (bufsize == 0xFFFFFFFF) {
+      // Done constructing
+      MOZ_FUZZING_NYX_DEBUG("Iteration complete: Out of data.\n");
+      break;
+    }
+
+    // Payload must be int aligned
+    bufsize -= bufsize % 4;
+
+    // Need at least a header and the control bytes.
+    if (bufsize < sizeof(IPC::Message::Header) + controlLen) {
+      MOZ_FUZZING_NYX_DEBUG("INFO: Not enough data to craft IPC message.\n");
+      continue;
+    }
+
+    buffer.shrinkTo(bufsize);
+
+    const uint8_t* controlData = (uint8_t*)buffer.begin();
+
+    char* ipcMsgData = buffer.begin() + controlLen;
+    size_t ipcMsgLen = buffer.length() - controlLen;
+
+    // Copy the header of the original message
+    memcpy(ipcMsgData, IPCFuzzController::instance().sampleHeader.begin(),
+           sizeof(IPC::Message::Header));
+
+    IPC::Message::Header* ipchdr = (IPC::Message::Header*)ipcMsgData;
+
+    ipchdr->payload_size = ipcMsgLen - sizeof(IPC::Message::Header);
+
+    PortName new_port_name;
+    int32_t new_seqno;
+    uint64_t new_fseqno;
+
+    int32_t actorId;
+    uint32_t msgType;
+    bool isConstructor;
+    // Control Data Layout (16 byte)
+    // Byte  0 - Port Index (selects out of the valid ports seen)
+    // Byte  1 - Actor Index (selects one of the actors for that port)
+    // Byte  2 - Type Offset (select valid type for the specified actor)
+    // Byte  3 -  ^- continued
+    // Byte  4 - Sync Bit
+    // Byte  5 - Optionally select a particular instance of the selected
+    //           port type. Some toplevel protocols can have multiple
+    //           instances running at the same time.
+
+    uint8_t portIndex = controlData[0];
+    uint8_t actorIndex = controlData[1];
+    uint16_t typeOffset = *(uint16_t*)(&controlData[2]);
+    bool isSync = controlData[4] > 127;
+    uint8_t portInstanceIndex = controlData[5];
+
+    if (!IPCFuzzController::instance().MakeTargetDecision(
+            portIndex, portInstanceIndex, actorIndex, typeOffset,
+            &new_port_name, &new_seqno, &new_fseqno, &actorId, &msgType,
+            &isConstructor)) {
+      MOZ_FUZZING_NYX_DEBUG("DEBUG: MakeTargetDecision returned false.\n");
+      continue;
+    }
+
+    if (Nyx::instance().is_replay()) {
+      MOZ_FUZZING_NYX_PRINT("INFO: Replaying IPC packet with payload:\n");
+      for (uint32_t i = 0; i < ipcMsgLen - sizeof(IPC::Message::Header); ++i) {
+        if (i % 16 == 0) {
+          MOZ_FUZZING_NYX_PRINT("\n  ");
+        }
+
+        MOZ_FUZZING_NYX_PRINTF(
+            "0x%02X ",
+            (unsigned char)(ipcMsgData[sizeof(IPC::Message::Header) + i]));
+      }
+      MOZ_FUZZING_NYX_PRINT("\n");
+    }
+
+    UniquePtr<IPC::Message> msg(new IPC::Message(ipcMsgData, ipcMsgLen));
+
+    if (isConstructor) {
+      MOZ_FUZZING_NYX_DEBUG("DEBUG: Sending constructor message...\n");
+      msg->header()->flags.SetConstructor();
+    }
+
+    if (!isConstructor && isSync) {
+      MOZ_FUZZING_NYX_DEBUG("INFO: Sending sync message...\n");
+      msg->header()->flags.SetSync();
+    }
+
+    msg->set_seqno(new_seqno);
+    msg->set_routing_id(actorId);
+
+    // TODO: There is no setter for this.
+    msg->header()->type = msgType;
+
+    // Create the footer
+    auto messageEvent = MakeUnique<UserMessageEvent>(0);
+    messageEvent->set_port_name(new_port_name);
+    messageEvent->set_sequence_num(new_fseqno);
+
+    Vector<char, 256, InfallibleAllocPolicy> footerBuffer;
+    (void)footerBuffer.initLengthUninitialized(
+        messageEvent->GetSerializedSize());
+    messageEvent->Serialize(footerBuffer.begin());
+
+    msg->WriteFooter(footerBuffer.begin(), footerBuffer.length());
+    msg->set_event_footer_size(footerBuffer.length());
+
+    // This marks the message as a fuzzing message. Without this, it will
+    // be ignored by MessageTask and also not even scheduled by NodeChannel
+    // in asynchronous mode. We use this to ignore any IPC activity that
+    // happens just while we are fuzzing.
+    msg->SetFuzzMsg();
+
+#ifdef FUZZ_DEBUG
+    MOZ_FUZZING_NYX_PRINTF(
+        "DEBUG: OnEventMessage iteration %d, EVS: %u Payload: %u.\n", i,
+        ipchdr->event_footer_size, ipchdr->payload_size);
+#endif
+
+#ifdef FUZZ_DEBUG
+    MOZ_FUZZING_NYX_PRINTF("DEBUG: OnEventMessage: Port %lu %lu. Actor %d\n",
+                           new_port_name.v1, new_port_name.v2, actorId);
+    MOZ_FUZZING_NYX_PRINTF(
+        "DEBUG: OnEventMessage: Flags: %u TxID: %d Handles: %u\n",
+        msg->header()->flags, msg->header()->txid, msg->header()->num_handles);
+#endif
+
+    // The number of messages we expect to see stopped.
+    expected_messages++;
+
+#if MOZ_FUZZ_IPC_SYNC_INJECT
+    // For synchronous injection, we just call OnMessageReceived directly.
+    IPCFuzzController::instance().nodeChannel->OnMessageReceived(
+        std::move(msg));
+#else
+    // For asynchronous injection, we have to post to the I/O thread instead.
+    XRE_GetIOMessageLoop()->PostTask(NS_NewRunnableFunction(
+        "NodeChannel::OnMessageReceived",
+        [msg = std::move(msg),
+         nodeChannel =
+             RefPtr{IPCFuzzController::instance().nodeChannel}]() mutable {
+          nodeChannel->OnMessageReceived(std::move(msg));
+        }));
+#endif
+
+#ifdef MOZ_FUZZ_IPC_SYNC_AFTER_EACH_MSG
+    MOZ_FUZZING_NYX_DEBUG("DEBUG: Synchronizing after message...\n");
+    IPCFuzzController::instance().SynchronizeOnMessageExecution(
+        expected_messages);
+#else
+
+    if (isConstructor) {
+      MOZ_FUZZING_NYX_DEBUG(
+          "DEBUG: Synchronizing due to constructor message...\n");
+      IPCFuzzController::instance().SynchronizeOnMessageExecution(
+          expected_messages);
+    }
+#endif
+  }
+
+  MOZ_FUZZING_NYX_DEBUG("DEBUG: Synchronizing due to end of iteration...\n");
+  IPCFuzzController::instance().SynchronizeOnMessageExecution(
+      expected_messages);
+
+  MOZ_FUZZING_NYX_DEBUG(
+      "DEBUG: ======== END OF ITERATION (RELEASE) ========\n");
+
+  Nyx::instance().release(IPCFuzzController::instance().getMessageStopCount());
+
+  // Never reached.
+  return NS_OK;
+}
+
+void IPCFuzzController::SynchronizeOnMessageExecution(
+    uint32_t expected_messages) {
+  // This synchronization will work in both the sync and async case.
+  // For the async case, it is important to wait for the exact stop count
+  // because the message task is not even started potentially when we
+  // read this loop.
+  int hang_timeout = 10 * 1000;
+  while (IPCFuzzController::instance().getMessageStopCount() !=
+         expected_messages) {
+#ifdef FUZZ_DEBUG
+    uint32_t count_stopped =
+        IPCFuzzController::instance().getMessageStopCount();
+    uint32_t count_live = IPCFuzzController::instance().getMessageStartCount();
+    MOZ_FUZZING_NYX_PRINTF(
+        "DEBUG: Post Constructor: %d stopped messages (%d live, %d "
+        "expected)!\n",
+        count_stopped, count_live, expected_messages);
+#endif
+    PR_Sleep(PR_MillisecondsToInterval(50));
+    hang_timeout -= 50;
+
+    if (hang_timeout <= 0) {
+      Nyx::instance().handle_event("MOZ_TIMEOUT", nullptr, 0, nullptr);
+      MOZ_FUZZING_NYX_PRINT(
+          "ERROR: ======== END OF ITERATION (TIMEOUT) ========\n");
+      Nyx::instance().release(
+          IPCFuzzController::instance().getMessageStopCount());
+    }
+  }
+}
+
+}  // namespace fuzzing
+}  // namespace mozilla