commit e63a592135f918583489ab1dbb6861f8f6c93956
author Dominik Laskowski <domlaskowski@google.com> Tue Nov 22 13:59:53 2022 -0500
committer Dominik Laskowski <domlaskowski@google.com> Fri Dec 09 16:18:19 2022 -0500
tree e9ef34386a48e9da47320d3867f293eed071d702
parent 383832ff5b2390f3dcd44592db071d504268787d

SF: Do not deref empty std::optional<PowerMode>

In I3a2eae4efc4a5c6113700a9ca9e9b261e364a878, a display's power mode is
std::nullopt (unknown) until the first setPowerMode. The condition to
power on the display from that state relies on undefined behavior, as
it dereferences std::nullopt. It only works because PowerMode::OFF is
0 and the memory happens to be zeroed.

Bug: 250421145
Test: Boot
Change-Id: I0db8970b37da6eb308043157cd2ac7a9f6764294
Merged-In: I0db8970b37da6eb308043157cd2ac7a9f6764294

services/surfaceflinger/SurfaceFlinger.cpp

diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 4486e33..a701fe3 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -4888,7 +4888,7 @@
         mInterceptor->savePowerModeUpdate(display->getSequenceId(), static_cast<int32_t>(mode));
     }
     const auto refreshRate = display->refreshRateConfigs().getActiveMode()->getFps();
-    if (*currentMode == hal::PowerMode::OFF) {
+    if (!currentMode || *currentMode == hal::PowerMode::OFF) {
         // Turn on the display
         if (display->isInternal() && (!activeDisplay || !activeDisplay->isPoweredOn())) {
             onActiveDisplayChangedLocked(display);