path: root/src/platformsupport/input
diff options
authorJungi Byun <>2021-12-21 14:37:36 +0900
committerTor Arne Vestbø <>2022-01-26 01:01:31 +0000
commit574b625914bf6913d44d0c33ed16a7432abeecba (patch)
treecc755ea9e536923107155e42a46b37016b23e92c /src/platformsupport/input
parent2e29a427ca2127ff7aff23049c65881d3c55bb40 (diff)
evdev: Prevent race condition in touch events processing
Unlike other input devices, touch devices are managed by corresponding handler threads which are not the main thread. InputEvent that is inherited by TouchEvent has a constant pointer member for device, but in touch events case, handler threads may destroy the device which is pointed by events while processing these events in main thread, and this may cause critical potential issues such as crash. In order to prevent this race condition, move device of QEvdevTouchScreenHandler into main thread and delete this device later if QGuiApplication instance exists when handler thread quits, and check event's device is valid when processing touch events. Change-Id: I02583238d97d768abcc544ee882160eda3178282 Reviewed-by: Elvis Lee <> Reviewed-by: Shawn Rutledge <>
Diffstat (limited to 'src/platformsupport/input')
1 files changed, 38 insertions, 1 deletions
diff --git a/src/platformsupport/input/evdevtouch/qevdevtouchhandler.cpp b/src/platformsupport/input/evdevtouch/qevdevtouchhandler.cpp
index 95265b3378..a3f6a470be 100644
--- a/src/platformsupport/input/evdevtouch/qevdevtouchhandler.cpp
+++ b/src/platformsupport/input/evdevtouch/qevdevtouchhandler.cpp
@@ -474,9 +474,46 @@ void QEvdevTouchScreenHandler::registerPointingDevice()
+/*! \internal
+ QEvdevTouchScreenHandler::unregisterPointingDevice can be called by several cases.
+ First of all, the case that an application is terminated, and destroy all input devices
+ immediately to unregister in this case.
+ Secondly, the case that removing a device without touch events for the device while the
+ application is still running. In this case, the destructor of QEvdevTouchScreenHandler from
+ the connection with QDeviceDiscovery::deviceRemoved in QEvdevTouchManager calls this method.
+ And this method moves a device into the main thread and then deletes it later but there is no
+ touch events for the device so that the device would be deleted in appropriate time.
+ Finally, this case is similar as the second one but with touch events, that is, a device is
+ removed while touch events are given to the device and the application is still running.
+ In this case, this method is called by readData with ENODEV error and the destructor of
+ QEvdevTouchScreenHandler. So in order to prevent accessing the device which is already nullptr,
+ check the nullity of a device first. And as same as the second case, move the device into the
+ main thread and then delete it later. But in this case, cannot guarantee which event is
+ handled first since the list or queue where posting QDeferredDeleteEvent and appending touch
+ events are different.
+ If touch events are handled first, there is no problem because the device which is used for
+ these events is registered. However if QDeferredDeleteEvent for deleting the device is
+ handled first, this may cause a crash due to using unregistered device when processing touch
+ events later. In order to prevent processing such touch events, check a device which is used
+ for touch events is registered when processing touch events.
+ see QGuiApplicationPrivate::processTouchEvent().
+ */
void QEvdevTouchScreenHandler::unregisterPointingDevice()
- delete m_device;
+ if (!m_device)
+ return;
+ if (QGuiApplication::instance()) {
+ m_device->moveToThread(QGuiApplication::instance()->thread());
+ m_device->deleteLater();
+ } else {
+ delete m_device;
+ }
m_device = nullptr;