From e4f85f1bd2eb34d9b49da9154a4cc3a1bc284f68 Mon Sep 17 00:00:00 2001
From: Nick Wellnhofer <wellnhofer@aevum.de>
Date: Fri, 7 Apr 2023 11:46:35 +0200
Subject: [PATCH] [CVE-2023-28484] Fix null deref in xmlSchemaFixupComplexType

Fix a null pointer dereference when parsing (invalid) XML schemas.

Thanks to Robby Simpson for the report!

Fixes #491.

Reference:https://github.com/GNOME/libxml2/commit/e4f85f1bd2eb34d9b49da9154a4cc3a1bc284f68
Conflict:NA

---
 result/schemas/issue491_0_0.err |  1 +
 test/schemas/issue491_0.xml     |  1 +
 test/schemas/issue491_0.xsd     | 18 ++++++++++++++++++
 xmlschemas.c                    |  2 +-
 4 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 result/schemas/issue491_0_0.err
 create mode 100644 test/schemas/issue491_0.xml
 create mode 100644 test/schemas/issue491_0.xsd

diff --git a/result/schemas/issue491_0_0.err b/result/schemas/issue491_0_0.err
new file mode 100644
index 0000000..9b2bb96
--- /dev/null
+++ b/result/schemas/issue491_0_0.err
@@ -0,0 +1 @@
+./test/schemas/issue491_0.xsd:8: element complexType: Schemas parser error : complex type 'ChildType': The content type of both, the type and its base type, must either 'mixed' or 'element-only'.
diff --git a/test/schemas/issue491_0.xml b/test/schemas/issue491_0.xml
new file mode 100644
index 0000000..e2b2fc2
--- /dev/null
+++ b/test/schemas/issue491_0.xml
@@ -0,0 +1 @@
+<Child xmlns="http://www.test.com">5</Child>
diff --git a/test/schemas/issue491_0.xsd b/test/schemas/issue491_0.xsd
new file mode 100644
index 0000000..8170264
--- /dev/null
+++ b/test/schemas/issue491_0.xsd
@@ -0,0 +1,18 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="http://www.test.com" targetNamespace="http://www.test.com" elementFormDefault="qualified" attributeFormDefault="unqualified">
+  <xs:complexType name="BaseType">
+    <xs:simpleContent>
+      <xs:extension base="xs:int" />
+    </xs:simpleContent>
+  </xs:complexType>
+  <xs:complexType name="ChildType">
+    <xs:complexContent>
+      <xs:extension base="BaseType">
+        <xs:sequence>
+          <xs:element name="bad" type="xs:int" minOccurs="0" maxOccurs="1"/>
+        </xs:sequence>
+      </xs:extension>
+    </xs:complexContent>
+  </xs:complexType>
+  <xs:element name="Child" type="ChildType" />
+</xs:schema>
diff --git a/xmlschemas.c b/xmlschemas.c
index 4dbee37..7199d23 100644
--- a/xmlschemas.c
+++ b/xmlschemas.c
@@ -18640,7 +18640,7 @@ xmlSchemaFixupComplexType(xmlSchemaParserCtxtPtr pctxt,
 			"allowed to appear inside other model groups",
 			NULL, NULL);
 
-		} else if (! dummySequence) {
+		} else if ((!dummySequence) && (baseType->subtypes != NULL)) {
 		    xmlSchemaTreeItemPtr effectiveContent =
 			(xmlSchemaTreeItemPtr) type->subtypes;
 		    /*
-- 
2.27.0