Fix GH-14702: DOMDocument::xinclude() crash

The xinclude code from libxml removes the fallback node,
but the fallback node is still reference via $fallback.
The solution is to detach the nodes that are going to be removed in
advance.

Closes GH-14704.

Author: nielsdos

NEWS

@@ -9,6 +9,9 @@ PHP                                                                        NEWS
   . Fixed bug GH-14590 (Memory leak in FPM test gh13563-conf-bool-env.phpt.
     (nielsdos)
 
+- Dom:
+  . Fixed bug GH-14702 (DOMDocument::xinclude() crash). (nielsdos)
+
 - Phar:
   . Fixed bug GH-14603 (null string from zip entry).
     (David Carlier)

ext/dom/document.c

@@ -1566,6 +1566,58 @@ static void php_dom_remove_xinclude_nodes(xmlNodePtr cur) /* {{{ */
 }
 /* }}} */
 
+/* Backported from master branch xml_common.h */
+static zend_always_inline xmlNodePtr php_dom_next_in_tree_order(const xmlNode *nodep, const xmlNode *basep)
+{
+	if (nodep->type == XML_ELEMENT_NODE && nodep->children) {
+		return nodep->children;
+	}
+
+	if (nodep->next) {
+		return nodep->next;
+	} else {
+		/* Go upwards, until we find a parent node with a next sibling, or until we hit the base. */
+		do {
+			nodep = nodep->parent;
+			if (nodep == basep) {
+				return NULL;
+			}
+		} while (nodep->next == NULL);
+		return nodep->next;
+	}
+}
+
+static void dom_xinclude_strip_references(xmlNodePtr basep)
+{
+	php_libxml_node_free_resource(basep);
+
+	xmlNodePtr current = basep->children;
+
+	while (current) {
+		php_libxml_node_free_resource(current);
+		current = php_dom_next_in_tree_order(current, basep);
+	}
+}
+
+/* See GH-14702.
+ * We have to remove userland references to xinclude fallback nodes because libxml2 will make clones of these
+ * and remove the original nodes. If the originals are removed while there are still userland references
+ * this will cause memory corruption. */
+static void dom_xinclude_strip_fallback_references(const xmlNode *basep)
+{
+	xmlNodePtr current = basep->children;
+
+	while (current) {
+		if (current->type == XML_ELEMENT_NODE && current->ns != NULL && current->_private != NULL
+			&& xmlStrEqual(current->name, XINCLUDE_FALLBACK)
+			&& (xmlStrEqual(current->ns->href, XINCLUDE_NS) || xmlStrEqual(current->ns->href, XINCLUDE_OLD_NS))) {
+			dom_xinclude_strip_references(current);
+		}
+
+		current = php_dom_next_in_tree_order(current, basep);
+	}
+}
+
 /* {{{ Substitutues xincludes in a DomDocument */
 PHP_METHOD(DOMDocument, xinclude)
 {
@@ -1588,6 +1640,8 @@ PHP_METHOD(DOMDocument, xinclude)
 
 	DOM_GET_OBJ(docp, id, xmlDocPtr, intern);
 
+	dom_xinclude_strip_fallback_references((const xmlNode *) docp);
+
 	PHP_LIBXML_SANITIZE_GLOBALS(xinclude);
 	err = xmlXIncludeProcessFlags(docp, (int)flags);
 	PHP_LIBXML_RESTORE_GLOBALS(xinclude);

ext/dom/tests/gh14702.phpt

@@ -0,0 +1,66 @@
+--TEST--
+GH-14702 (DOMDocument::xinclude() crash)
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+$doc = new DOMDocument();
+$doc->loadXML(<<<XML
+<?xml version="1.0"?>
+<root>
+  <child/>
+  <include href="foo" xmlns="http://www.w3.org/2001/XInclude">
+    <fallback/>
+  </include>
+  <keep/>
+</root>
+XML);
+$xi = $doc->createElementNS('http://www.w3.org/2001/XInclude', 'xi:include');
+$xi->setAttribute('href', 'nonexistent');
+
+$fallback = $doc->createElementNS('http://www.w3.org/2001/XInclude', 'xi:fallback');
+$xi->appendChild($fallback);
+$child1 = $fallback->appendChild($doc->createElement('fallback-child1'));
+$child2 = $fallback->appendChild($doc->createElement('fallback-child2'));
+
+$xpath = new DOMXPath($doc);
+$toReplace = $xpath->query('//child')->item(0);
+$toReplace->parentNode->replaceChild($xi, $toReplace);
+
+$keep = $doc->documentElement->lastElementChild;
+
+var_dump(@$doc->xinclude());
+echo $doc->saveXML();
+
+var_dump($child1, $child2, $fallback, $keep->nodeName);
+
+$keep->textContent = 'still works';
+echo $doc->saveXML();
+?>
+--EXPECT--
+int(2)
+<?xml version="1.0"?>
+<root>
+  <fallback-child1/><fallback-child2/>
+  
+  <keep/>
+</root>
+object(DOMElement)#4 (1) {
+  ["schemaTypeInfo"]=>
+  NULL
+}
+object(DOMElement)#5 (1) {
+  ["schemaTypeInfo"]=>
+  NULL
+}
+object(DOMElement)#3 (1) {
+  ["schemaTypeInfo"]=>
+  NULL
+}
+string(4) "keep"
+<?xml version="1.0"?>
+<root>
+  <fallback-child1/><fallback-child2/>
+  
+  <keep>still works</keep>
+</root>