xcb: avoid to use invalid pointers

Pick-to: 6.2 5.15 5.12
Task-number: QTBUG-96399
Change-Id: I33909940b501cb13f78981c43f3aef9fc9d1d52d
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

2 files changed, 14 insertions, 2 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.cpp b/src/plugins/platforms/xcb/qxcbconnection.cpp
index 04718f09db..ac818b984b 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection.cpp
@@ -870,7 +870,13 @@ xcb_timestamp_t QXcbConnection::getTimestamp()
 
 xcb_window_t QXcbConnection::getSelectionOwner(xcb_atom_t atom) const
 {
-    return Q_XCB_REPLY(xcb_get_selection_owner, xcb_connection(), atom)->owner;
+    auto reply = Q_XCB_REPLY(xcb_get_selection_owner, xcb_connection(), atom);
+    if (!reply) {
+        qCDebug(lcQpaXcb) << "failed to query selection owner";
+        return XCB_NONE;
+    }
+
+    return reply->owner;
 }
 
 xcb_window_t QXcbConnection::getQtSelectionOwner()
diff --git a/src/plugins/platforms/xcb/qxcbconnection_basic.cpp b/src/plugins/platforms/xcb/qxcbconnection_basic.cpp
index 6482395f86..c4f24ca0ee 100644
--- a/src/plugins/platforms/xcb/qxcbconnection_basic.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection_basic.cpp
@@ -176,7 +176,13 @@ xcb_atom_t QXcbBasicConnection::internAtom(const char *name)
     if (!name || *name == 0)
         return XCB_NONE;
 
-    return Q_XCB_REPLY(xcb_intern_atom, m_xcbConnection, false, strlen(name), name)->atom;
+    auto reply = Q_XCB_REPLY(xcb_intern_atom, m_xcbConnection, false, strlen(name), name);
+    if (!reply) {
+        qCDebug(lcQpaXcb) << "failed to query intern atom: " << name;
+        return XCB_NONE;
+    }
+
+    return reply->atom;
 }
 
 QByteArray QXcbBasicConnection::atomName(xcb_atom_t atom)