commit b2f168dd513e980e5ad2641109fdaee95448a8cd
author Mathias Agopian <mathias@google.com> Mon Apr 03 17:14:31 2017 -0700
committer android-build-team Robot <android-build-team-robot@google.com> Tue Jun 20 22:41:13 2017 +0000
tree 9827260541fdbcb505d58be8b86fc02739056a69
parent 24257b4e5b4ab72e7397a4546f9b5a8f03dd340d

fix race condition that can cause a use after free

Backported from 12a0ccd6f7201bac706d903ac3f436c4358fe203.

Bug: 33004354
Test: manual
Change-Id: I9b38ee644b02268c9b995a330db758aa2e568399
(cherry picked from commit 59485525a6047453e6ba16c03989381e2a0d56ec)

libs/gui/BufferQueueProducer.cpp

diff --git a/libs/gui/BufferQueueProducer.cpp b/libs/gui/BufferQueueProducer.cpp
index 05923b5..ce47784 100644
--- a/libs/gui/BufferQueueProducer.cpp
+++ b/libs/gui/BufferQueueProducer.cpp
@@ -921,7 +921,11 @@
 
     // Call back without the main BufferQueue lock held, but with the callback
     // lock held so we can ensure that callbacks occur in order
-    {
+
+    int connectedApi;
+    sp<Fence> lastQueuedFence;
+
+    { // scope for the lock
         Mutex::Autolock lock(mCallbackMutex);
         while (callbackTicket != mCurrentCallbackTicket) {
             mCallbackCondition.wait(mCallbackMutex);
@@ -933,20 +937,24 @@
             frameReplacedListener->onFrameReplaced(item);
         }
 
+        connectedApi = mCore->mConnectedApi;
+        lastQueuedFence = std::move(mLastQueueBufferFence);
+
+        mLastQueueBufferFence = std::move(fence);
+        mLastQueuedCrop = item.mCrop;
+        mLastQueuedTransform = item.mTransform;
+
         ++mCurrentCallbackTicket;
         mCallbackCondition.broadcast();
     }
 
     // Wait without lock held
-    if (mCore->mConnectedApi == NATIVE_WINDOW_API_EGL) {
+    if (connectedApi == NATIVE_WINDOW_API_EGL) {
         // Waiting here allows for two full buffers to be queued but not a
         // third. In the event that frames take varying time, this makes a
         // small trade-off in favor of latency rather than throughput.
-        mLastQueueBufferFence->waitForever("Throttling EGL Production");
+        lastQueuedFence->waitForever("Throttling EGL Production");
     }
-    mLastQueueBufferFence = fence;
-    mLastQueuedCrop = item.mCrop;
-    mLastQueuedTransform = item.mTransform;
 
     return NO_ERROR;
 }