From ca6d005dceb293729be56c96c26c2a7ae19877ef Mon Sep 17 00:00:00 2001
From: Magdalena Stojek <magdalena.stojek@qt.io>
Date: Tue, 04 Aug 2026 14:26:05 +0200
Subject: [PATCH] QDom: Guard against null nodes returned by factory functions

Since the default InvalidDataPolicy changed to ReturnNullNode, the
QDomDocumentPrivate factory functions return nullptr when the input
contains data that is invalid per XML 1.0. QDomBuilder::characters(),
QDomBuilder::skippedEntity() and QDomBuilder::comment() used the
returned node without checking, causing a crash.

Check for nullptr and return false, as startElement() and
processingInstruction() already do.

Pick-to: 6.8 6.5 5.15
Fixes: QTBUG-148791
Change-Id: Id46c8438e648008d7edad50ae411d682ec5152f6
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 8b5670485050cbedffe92c9ca48537f89dc896bd)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit ec02738a2f8edea9b578c4ed914f575d47d54b61)
---

diff --git a/src/xml/dom/qdomhelpers.cpp b/src/xml/dom/qdomhelpers.cpp
index 6b73f1b..d3213ab 100644
--- a/src/xml/dom/qdomhelpers.cpp
+++ b/src/xml/dom/qdomhelpers.cpp
@@ -151,6 +151,8 @@
     } else {
         n.reset(doc->createTextNode(characters));
     }
+    if (!n)
+        return false;
     n->setLocation(int(reader->lineNumber()), int(reader->columnNumber()));
     node->appendChild(n.get());
 
@@ -172,6 +174,8 @@
 bool QDomBuilder::skippedEntity(const QString &name)
 {
     QDomNodePrivate *n = doc->createEntityReference(name);
+    if (!n)
+        return false;
     n->setLocation(int(reader->lineNumber()), int(reader->columnNumber()));
     node->appendChild(n);
     return true;
@@ -200,6 +204,8 @@
 {
     QDomNodePrivate *n;
     n = doc->createComment(characters);
+    if (!n)
+        return false;
     n->setLocation(int(reader->lineNumber()), int(reader->columnNumber()));
     node->appendChild(n);
     return true;
diff --git a/tests/auto/xml/dom/qdom/tst_qdom.cpp b/tests/auto/xml/dom/qdom/tst_qdom.cpp
index 0c68221..ad81148 100644
--- a/tests/auto/xml/dom/qdom/tst_qdom.cpp
+++ b/tests/auto/xml/dom/qdom/tst_qdom.cpp
@@ -105,6 +105,8 @@
     void germanUmlautToFile() const;
     void setInvalidDataPolicy() const;
     void crashInSetContent() const;
+    void invalidCharDataInSetContent() const;
+    void invalidCharDataInSetContent_data() const;
     void doubleNamespaceDeclarations() const;
     void setContentQXmlReaderOverload() const;
     void toStringWithoutNewlines() const;
@@ -2336,6 +2338,60 @@
     QVERIFY(docImport.setContent(QLatin1String("<?xml version=\"1.0\"?><e/>")));
 }
 
+void tst_QDom::invalidCharDataInSetContent_data() const
+{
+    QTest::addColumn<QByteArray>("input");
+    QTest::addColumn<bool>("parsed");
+    QTest::addColumn<QString>("document");
+
+    QTest::newRow("control")
+            << "<r><before/><a>TextNode</a><after/></r>"_ba << true
+            << u"<r><before/><a>TextNode</a><after/></r>"_s;
+    QTest::newRow("text-with-nul")
+            << "<r><before/><a>te\0xt</a><after/></r>"_ba << false
+            << u"<r><before/><a>te</a></r>"_s;
+    QTest::newRow("cdata")
+            << "<r><before/><![CDATA[da\0ta]]><after/></r>"_ba << false
+            << u"<r><before/></r>"_s;
+    QTest::newRow("comment")
+            << "<r><before/><!-- co\0m --><after/></r>"_ba << false
+            << u"<r><before/></r>"_s;
+    QTest::newRow("pi-data")
+            << "<r><before/><?pi da\0ta?><after/></r>"_ba << false
+            << u"<r><before/></r>"_s;
+    QTest::newRow("start-element")
+            << "<r><before/><a\0b/><after/></r>"_ba << false
+            << u"<r><before/></r>"_s;
+    QTest::newRow("nul-at-end")
+            << "<r><before/><before2/></r>\0"_ba << false
+            << u"<r><before/><before2/></r>"_s;
+}
+
+void tst_QDom::invalidCharDataInSetContent() const
+{
+    QFETCH(const QByteArray, input);
+    QFETCH(const bool, parsed);
+    QFETCH(const QString, document);
+
+    const auto policy = QDomImplementation::invalidDataPolicy();
+    const auto restoreInvalidDataPolicy = qScopeGuard([policy] {
+        QDomImplementation::setInvalidDataPolicy(policy);
+    });
+    QDomImplementation::setInvalidDataPolicy(QDomImplementation::ReturnNullNode);
+
+    QDomDocument doc;
+    const QDomDocument::ParseResult result =
+            doc.setContent(input, QDomDocument::ParseOption::UseNamespaceProcessing);
+
+    QCOMPARE(bool(result), parsed);
+    if (!parsed) {
+        QVERIFY(!result.errorMessage.isEmpty());
+        QCOMPARE(result.errorLine, qsizetype(1));
+        QVERIFY(result.errorColumn > 0);
+    }
+    QCOMPARE(doc.toString(-1), document);
+}
+
 void tst_QDom::doubleNamespaceDeclarations() const
 {
     QDomDocument doc;