[screenlocker] Also grab XInput2 devices

With XInput2 it's possible that multiple pairs of keyboard and pointers
are connected. As the lock screen only grabbed keyboard and pointer using
the core protocol any additional input devices were still reporting
input events to non-lockscreen windows creating the risk of interaction
with the system and accidentially typing a password where it doesn't
belong.

This change ensures that all additional master devices are also grabbed.
Unfortunately there are no xcb bindings for xinput2 (considered
experimental and thus not build on at least all debian based distros)
and because of that the XLib library is used. This brings some problems
as we cannot process the events (for that we would need xcb bindings,
to get the events). To still be able to get any keyboard and mouse events
we grab using the core protocol as it used to be and then ignore the
"Virtual core" devices and don't grab them with XInput2. Input events
from additional devices are grabbed and ignored, but definately no longer
delivered to other windows.

BUG: 341469
FIXED-IN: 5.3.0
REVIEW: 122558

CMakeLists.txt

@@ -79,6 +79,8 @@ if(X11_FOUND)
     message(FATAL_ERROR "\nThe X11 Session Management (SM) development package could not be found.\nPlease install libSM.\n")
   endif(NOT X11_SM_FOUND)
 
+  add_feature_info("XInput" X11_Xinput_FOUND "Required for grabbing XInput2 devices in the screen locker")
+
   find_package(Qt5 ${QT_MIN_VERSION} CONFIG REQUIRED COMPONENTS X11Extras)
 endif()
 

config-X11.h.cmake

@@ -41,4 +41,7 @@
 #cmakedefine HAS_RANDR_1_3 1
 
 /* Define if you have X11 at all */
-#define HAVE_X11 ${X11_FOUND}
+#define HAVE_X11 ${X11_FOUND}
+
+/* Define if you have the XInput extension */
+#cmakedefine X11_Xinput_FOUND 1

ksmserver/screenlocker/CMakeLists.txt

@@ -56,6 +56,10 @@ target_link_libraries(screenlocker_static
    Wayland::Server
 )
 
+if (X11_Xinput_FOUND)
+    target_link_libraries(screenlocker_static ${X11_Xinput_LIB})
+endif()
+
 # Needed to compile on Arm target.
 set_target_properties(screenlocker_static PROPERTIES COMPILE_FLAGS "-fPIC")
 

ksmserver/screenlocker/ksldapp.cpp

@@ -27,6 +27,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "logind.h"
 #include "kscreensaversettings.h"
 #include <config-ksmserver.h>
+#include <config-X11.h>
 #include "waylandserver.h"
 // workspace
 #include <kdisplaymanager.h>
@@ -47,6 +48,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 // X11
 #include <X11/Xlib.h>
 #include <xcb/xcb.h>
+#ifdef X11_Xinput_FOUND
+#include <X11/extensions/XInput2.h>
+#endif
 // other
 #include <unistd.h>
 #include <signal.h>
@@ -108,9 +112,35 @@ void KSldApp::cleanUp()
 static bool s_graceTimeKill = false;
 static bool s_logindExit = false;
 
+static bool hasXInput()
+{
+#ifdef X11_Xinput_FOUND
+    Display *dpy = QX11Info::display();
+    int xi_opcode, event, error;
+    // init XInput extension
+    if (!XQueryExtension(dpy, "XInputExtension", &xi_opcode, &event, &error)) {
+        return false;
+    }
+
+    // verify that the XInput extension is at at least version 2.0
+    int major = 2, minor = 0;
+    int result = XIQueryVersion(dpy, &major, &minor);
+    if (result == BadImplementation) {
+        // Xinput 2.2 returns BadImplementation if checked against 2.0
+        major = 2;
+        minor = 2;
+        return XIQueryVersion(dpy, &major, &minor) == Success;
+    }
+    return result == Success;
+#else
+    return false;
+#endif
+}
+
 void KSldApp::initialize()
 {
     KCrash::setFlags(KCrash::AutoRestart);
+    m_hasXInput2 = hasXInput();
     // Save X screensaver parameters
     XGetScreenSaver(QX11Info::display(), &s_XTimeout, &s_XInterval, &s_XBlanking, &s_XExposures);
     // And disable it. The internal X screensaver is not used at all, but we use its
@@ -351,7 +381,6 @@ static bool grabMouse();
 bool KSldApp::establishGrab()
 {
     XSync(QX11Info::display(), False);
-
     if (!grabKeyboard()) {
         sleep(1);
         if (!grabKeyboard()) {
@@ -367,6 +396,53 @@ bool KSldApp::establishGrab()
         }
     }
 
+#ifdef X11_Xinput_FOUND
+    if (m_hasXInput2) {
+        // get all devices
+        Display *dpy = QX11Info::display();
+        int numMasters;
+        XIDeviceInfo *masters = XIQueryDevice(dpy, XIAllMasterDevices, &numMasters);
+        bool success = true;
+        for (int i = 0; i < numMasters; ++i) {
+            // ignoring core pointer and core keyboard as we already grabbed them
+            if (qstrcmp(masters[i].name, "Virtual core pointer") == 0) {
+                continue;
+            }
+            if (qstrcmp(masters[i].name, "Virtual core keyboard") == 0) {
+                continue;
+            }
+            XIEventMask mask;
+            uchar bitmask[] = { 0, 0 };
+            mask.deviceid = masters[i].deviceid;
+            mask.mask = bitmask;
+            mask.mask_len = sizeof(bitmask);
+            XISetMask(bitmask, XI_ButtonPress);
+            XISetMask(bitmask, XI_ButtonRelease);
+            XISetMask(bitmask, XI_Motion);
+            XISetMask(bitmask, XI_Enter);
+            XISetMask(bitmask, XI_Leave);
+            const int result = XIGrabDevice(dpy, masters[i].deviceid, QX11Info::appRootWindow(),
+                                            XCB_TIME_CURRENT_TIME, XCB_CURSOR_NONE, XIGrabModeAsync,
+                                            XIGrabModeAsync, True, &mask);
+            if (result != XIGrabSuccess) {
+                success = false;
+                break;
+            }
+        }
+        if (!success) {
+            // ungrab all devices again
+            for (int i = 0; i < numMasters; ++i) {
+                XIUngrabDevice(dpy, masters[i].deviceid, XCB_TIME_CURRENT_TIME);
+            }
+            xcb_connection_t *c = QX11Info::connection();
+            xcb_ungrab_keyboard(c, XCB_CURRENT_TIME);
+            xcb_ungrab_pointer(c, XCB_CURRENT_TIME);
+        }
+        XIFreeDeviceInfo(masters);
+        return success;
+    }
+#endif
+
     return true;
 }
 
@@ -397,6 +473,19 @@ void KSldApp::doUnlock()
     xcb_ungrab_keyboard(c, XCB_CURRENT_TIME);
     xcb_ungrab_pointer(c, XCB_CURRENT_TIME);
     xcb_flush(c);
+#ifdef X11_Xinput_FOUND
+    if (m_hasXInput2) {
+        // get all devices
+        Display *dpy = QX11Info::display();
+        int numMasters;
+        XIDeviceInfo *masters = XIQueryDevice(dpy, XIAllMasterDevices, &numMasters);
+        // ungrab all devices again
+        for (int i = 0; i < numMasters; ++i) {
+            XIUngrabDevice(dpy, masters[i].deviceid, XCB_TIME_CURRENT_TIME);
+        }
+        XIFreeDeviceInfo(masters);
+    }
+#endif
     hideLockWindow();
     // delete the window again, to get rid of event filter
     delete m_lockWindow;

ksmserver/screenlocker/ksldapp.h

@@ -132,6 +132,7 @@ private Q_SLOTS:
     int m_inhibitCounter;
     LogindIntegration *m_logind;
     GlobalAccel *m_globalAccel = nullptr;
+    bool m_hasXInput2 = false;
 
     // for auto tests
     friend KSldTest;