commit 067def0585f4b290f48e79d8f43c5fea9a934a83
author Ady Abraham <adyabr@google.com> Mon Jun 06 15:16:06 2022 -0700
committer Ady Abraham <adyabr@google.com> Tue Jun 07 00:18:34 2022 +0000
tree 5759c0a3c26e508cdaca83c185fea6e8ea44d7d0
parent 4648ad64f28236871476286f329c3dcb7c4e0f24

RESTRICT AUTOMERGE 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

services/surfaceflinger/Scheduler/EventThread.cpp

diff --git a/services/surfaceflinger/Scheduler/EventThread.cpp b/services/surfaceflinger/Scheduler/EventThread.cpp
index 845bf50..c116dae 100644
--- a/services/surfaceflinger/Scheduler/EventThread.cpp
+++ b/services/surfaceflinger/Scheduler/EventThread.cpp
@@ -138,6 +138,11 @@
 }
 
 status_t EventThreadConnection::stealReceiveChannel(gui::BitTube* outChannel) {
+    std::scoped_lock lock(mLock);
+    if (mChannel.initCheck() != NO_ERROR) {
+        return NAME_NOT_FOUND;
+    }
+
     outChannel->setReceiveFd(mChannel.moveReceiveFd());
     outChannel->setSendFd(base::unique_fd(dup(mChannel.getSendFd())));
     return NO_ERROR;

services/surfaceflinger/Scheduler/EventThread.h

diff --git a/services/surfaceflinger/Scheduler/EventThread.h b/services/surfaceflinger/Scheduler/EventThread.h
index 49f624c..df7fb7d 100644
--- a/services/surfaceflinger/Scheduler/EventThread.h
+++ b/services/surfaceflinger/Scheduler/EventThread.h
@@ -92,7 +92,8 @@
 private:
     virtual void onFirstRef();
     EventThread* const mEventThread;
-    gui::BitTube mChannel;
+    std::mutex mLock;
+    gui::BitTube mChannel GUARDED_BY(mLock);
 };
 
 class EventThread {