SurfaceFlinger: fix a potential race condition in stealReceiveChannel

Add a mutex to prevent a potential race condition.

Bug: 232541124
Test: See bug for details
Change-Id: Ia338f124c786bf12d6adba10a67b9048fe9c34a5

2 files changed, 7 insertions, 1 deletions

diff --git a/services/surfaceflinger/Scheduler/EventThread.cpp b/services/surfaceflinger/Scheduler/EventThread.cpp
index cbea77e8fb..639ba5a3f1 100644
--- a/services/surfaceflinger/Scheduler/EventThread.cpp
+++ b/services/surfaceflinger/Scheduler/EventThread.cpp
@@ -177,6 +177,11 @@ void EventThreadConnection::onFirstRef() {
 }
 
 binder::Status EventThreadConnection::stealReceiveChannel(gui::BitTube* outChannel) {
+    std::scoped_lock lock(mLock);
+    if (mChannel.initCheck() != NO_ERROR) {
+        return binder::Status::fromStatusT(NAME_NOT_FOUND);
+    }
+
     outChannel->setReceiveFd(mChannel.moveReceiveFd());
     outChannel->setSendFd(base::unique_fd(dup(mChannel.getSendFd())));
     return binder::Status::ok();
diff --git a/services/surfaceflinger/Scheduler/EventThread.h b/services/surfaceflinger/Scheduler/EventThread.h
index c406478c17..adb96fd462 100644
--- a/services/surfaceflinger/Scheduler/EventThread.h
+++ b/services/surfaceflinger/Scheduler/EventThread.h
@@ -112,7 +112,8 @@ public:
 private:
     virtual void onFirstRef();
     EventThread* const mEventThread;
-    gui::BitTube mChannel;
+    std::mutex mLock;
+    gui::BitTube mChannel GUARDED_BY(mLock);
 
     std::vector<DisplayEventReceiver::Event> mPendingEvents;
 };