Fix bug #79701: getElementById does not correctly work with duplicate definitions

This is a long standing bug: IDs aren't properly tracked causing either
outdated or plain incorrect results from getElementById.

This PR implements a pragmatic solution in which we still try to use the
ID lookup table to a degree, but only as a performance boost not as a
"single source of truth". Full details are explained in the
getElementById code.

Author: nielsdos

ext/dom/attr.c

@@ -25,6 +25,7 @@
 
 #include "php_dom.h"
 #include "dom_properties.h"
+#include "internal_helpers.h"
 
 /*
 * class DOMAttr extends DOMNode
@@ -106,6 +107,16 @@ zend_result dom_attr_specified_read(dom_object *obj, zval *retval)
 
 /* }}} */
 
+void dom_attr_value_will_change(dom_object *obj, xmlAttrPtr attrp)
+{
+	if (attrp->atype == XML_ATTRIBUTE_ID) {
+		xmlRemoveID(attrp->doc, attrp);
+		attrp->atype = XML_ATTRIBUTE_ID;
+	}
+
+	dom_mark_ids_modified(obj->document);
+}
+
 /* {{{ value	string
 readonly=no
 URL: http://www.w3.org/TR/2003/WD-DOM-Level-3-Core-20030226/DOM3-Core.html#ID-221662474
@@ -122,6 +133,8 @@ zend_result dom_attr_value_write(dom_object *obj, zval *newval)
 {
 	DOM_PROP_NODE(xmlAttrPtr, attrp, obj);
 
+	dom_attr_value_will_change(obj, attrp);
+
 	/* Typed property, this is already a string */
 	ZEND_ASSERT(Z_TYPE_P(newval) == IS_STRING);
 	zend_string *str = Z_STR_P(newval);

ext/dom/document.c

@@ -1028,34 +1028,47 @@ Since: DOM Level 2
 */
 PHP_METHOD(DOMDocument, getElementById)
 {
-	zval *id;
 	xmlDocPtr docp;
-	xmlAttrPtr  attrp;
 	size_t idname_len;
 	dom_object *intern;
 	char *idname;
 
-	id = ZEND_THIS;
-	if (zend_parse_parameters(ZEND_NUM_ARGS(), "s", &idname, &idname_len) == FAILURE) {
-		RETURN_THROWS();
-	}
-
-	DOM_GET_OBJ(docp, id, xmlDocPtr, intern);
+	ZEND_PARSE_PARAMETERS_START(1, 1)
+		Z_PARAM_STRING(idname, idname_len)
+	ZEND_PARSE_PARAMETERS_END();
 
-	attrp = xmlGetID(docp, BAD_CAST idname);
+	DOM_GET_OBJ(docp, ZEND_THIS, xmlDocPtr, intern);
 
-	/* From the moment an ID is created, libxml2's behaviour is to cache that element, even
-	 * if that element is not yet attached to the document. Similarly, only upon destruction of
-	 * the element the ID is actually removed by libxml2. Since libxml2 has such behaviour deeply
-	 * ingrained in the library, and uses the cache for various purposes, it seems like a bad
-	 * idea and lost cause to fight it. Instead, we'll simply walk the tree upwards to check
-	 * if the node is attached to the document. */
-	if (attrp && attrp->parent && php_dom_is_node_connected(attrp->parent)) {
-		DOM_RET_OBJ((xmlNodePtr) attrp->parent, intern);
+	/* If the document has not been manipulated yet, the ID cache will be in sync and we can trust its result.
+	 * This check mainly exists because a lot of times people just query a document without modifying it,
+	 * and we can allow quick access to IDs in that case. */
+	if (!dom_is_document_cache_modified_since_parsing(intern->document)) {
+		const xmlAttr *attrp = xmlGetID(docp, BAD_CAST idname);
+		if (attrp && attrp->parent) {
+			DOM_RET_OBJ(attrp->parent, intern);
+		}
 	} else {
-		RETVAL_NULL();
-	}
+		/* From the moment an ID is created, libxml2's behaviour is to cache that element, even
+		 * if that element is not yet attached to the document. Similarly, only upon destruction of
+		 * the element the ID is actually removed by libxml2. Since libxml2 has such behaviour deeply
+		 * ingrained in the library, and uses the cache for various purposes, it seems like a bad
+		 * idea and lost cause to fight it. */
+
+		const xmlNode *base = (const xmlNode *) docp;
+		const xmlNode *node = base->children;
+		while (node != NULL) {
+			if (node->type == XML_ELEMENT_NODE) {
+				for (const xmlAttr *attr = node->properties; attr != NULL; attr = attr->next) {
+					if (attr->atype == XML_ATTRIBUTE_ID && dom_compare_value(attr, BAD_CAST idname)) {
+						DOM_RET_OBJ((xmlNodePtr) node, intern);
+						return;
+					}
+				}
+			}
 
+			node = php_dom_next_in_tree_order(node, base);
+		}
+	}
 }
 /* }}} end dom_document_get_element_by_id */
 

ext/dom/element.c

@@ -183,15 +183,15 @@ zend_result dom_element_id_read(dom_object *obj, zval *retval)
 	return dom_element_reflected_attribute_read(obj, retval, "id");
 }
 
-static void php_set_attribute_id(xmlAttrPtr attrp, bool is_id);
+static void php_set_attribute_id(xmlAttrPtr attrp, bool is_id, php_libxml_ref_obj *document);
 
 zend_result dom_element_id_write(dom_object *obj, zval *newval)
 {
 	xmlAttrPtr attr = dom_element_reflected_attribute_write(obj, newval, "id");
 	if (!attr) {
 		return FAILURE;
 	}
-	php_set_attribute_id(attr, true);
+	php_set_attribute_id(attr, true, obj->document);
 	return SUCCESS;
 }
 /* }}} */
@@ -352,6 +352,16 @@ static xmlNodePtr dom_create_attribute(xmlNodePtr nodep, const char *name, const
 	}
 }
 
+static void dom_check_register_attribute_id(xmlAttrPtr attr, php_libxml_ref_obj *document)
+{
+	dom_mark_ids_modified(document);
+
+	if (attr->atype != XML_ATTRIBUTE_ID && attr->doc->type == XML_HTML_DOCUMENT_NODE && attr->ns == NULL && xmlStrEqual(attr->name, BAD_CAST "id")) {
+		/* To respect XML's ID behaviour, we only do this registration for HTML documents. */
+		attr->atype = XML_ATTRIBUTE_ID;
+	}
+}
+
 /* {{{ URL: http://www.w3.org/TR/2003/WD-DOM-Level-3-Core-20030226/DOM3-Core.html#core-ID-F68F082
 Modern spec URL: https://dom.spec.whatwg.org/#dom-element-setattribute
 Since:
@@ -360,7 +370,6 @@ PHP_METHOD(DOMElement, setAttribute)
 {
 	zval *id;
 	xmlNode *nodep;
-	xmlNodePtr attr = NULL;
 	int name_valid;
 	size_t name_len, value_len;
 	dom_object *intern;
@@ -394,23 +403,26 @@ PHP_METHOD(DOMElement, setAttribute)
 		}
 
 		/* Can't use xmlSetNsProp unconditionally here because that doesn't take into account the qualified name matching... */
-		attr = (xmlNodePtr) php_dom_get_attribute_node(nodep, BAD_CAST name, name_len);
+		xmlAttrPtr attr = php_dom_get_attribute_node(nodep, BAD_CAST name, name_len);
 		if (attr != NULL) {
-			dom_remove_all_children(attr);
+			dom_attr_value_will_change(intern, attr);
+			dom_remove_all_children((xmlNodePtr) attr);
 			xmlNodePtr node = xmlNewDocText(attr->doc, BAD_CAST value);
-			xmlAddChild(attr, node);
+			xmlAddChild((xmlNodePtr) attr, node);
 		} else {
-			attr = (xmlNodePtr) xmlSetNsProp(nodep, NULL, name_processed, BAD_CAST value);
+			attr = xmlSetNsProp(nodep, NULL, name_processed, BAD_CAST value);
+			dom_check_register_attribute_id(attr, intern->document);
 		}
 
 		if (name_processed != BAD_CAST name) {
 			efree(name_processed);
 		}
 	} else {
-		attr = dom_get_attribute_or_nsdecl(intern, nodep, BAD_CAST name, name_len);
+		xmlNodePtr attr = dom_get_attribute_or_nsdecl(intern, nodep, BAD_CAST name, name_len);
 		if (attr != NULL) {
 			switch (attr->type) {
 				case XML_ATTRIBUTE_NODE:
+					dom_attr_value_will_change(intern, (xmlAttrPtr) attr);
 					node_list_unlink(attr->children);
 					break;
 				case XML_NAMESPACE_DECL:
@@ -693,7 +705,10 @@ static void dom_element_set_attribute_node_common(INTERNAL_FUNCTION_PARAMETERS,
 
 	xmlAddChild(nodep, (xmlNodePtr) attrp);
 	if (!modern) {
+		dom_mark_ids_modified(intern->document);
 		php_dom_reconcile_attribute_namespace_after_insertion(attrp);
+	} else {
+		dom_check_register_attribute_id(attrp, intern->document);
 	}
 
 	/* Returns old property if removed otherwise NULL */
@@ -958,8 +973,11 @@ static void dom_set_attribute_ns_modern(dom_object *intern, xmlNodePtr elemp, ze
 	if (errorcode == 0) {
 		php_dom_libxml_ns_mapper *ns_mapper = php_dom_get_ns_mapper(intern);
 		xmlNsPtr ns = php_dom_libxml_ns_mapper_get_ns_raw_prefix_string(ns_mapper, prefix, xmlStrlen(prefix), uri);
-		if (UNEXPECTED(xmlSetNsProp(elemp, ns, localname, BAD_CAST value) == NULL)) {
+		xmlAttrPtr attr = xmlSetNsProp(elemp, ns, localname, BAD_CAST value);
+		if (UNEXPECTED(attr == NULL)) {
 			php_dom_throw_error(INVALID_STATE_ERR, /* strict */ true);
+		} else {
+			dom_check_register_attribute_id(attr, intern->document);
 		}
 	} else {
 		php_dom_throw_error(errorcode, /* strict */ true);
@@ -993,6 +1011,7 @@ PHP_METHOD(DOMElement, setAttributeNS)
 	if (php_dom_follow_spec_intern(intern)) {
 		dom_set_attribute_ns_modern(intern, elemp, uri, name, value);
 	} else {
+		dom_mark_ids_modified(intern->document);
 		dom_set_attribute_ns_legacy(intern, elemp, uri ? ZSTR_VAL(uri) : NULL, uri ? ZSTR_LEN(uri) : 0, ZSTR_VAL(name), ZSTR_LEN(name), value);
 	}
 }
@@ -1270,20 +1289,16 @@ PHP_METHOD(DOMElement, hasAttributeNS)
 }
 /* }}} end dom_element_has_attribute_ns */
 
-static void php_set_attribute_id(xmlAttrPtr attrp, bool is_id) /* {{{ */
+static void php_set_attribute_id(xmlAttrPtr attrp, bool is_id, php_libxml_ref_obj *document) /* {{{ */
 {
-	if (is_id == 1 && attrp->atype != XML_ATTRIBUTE_ID) {
-		xmlChar *id_val;
-
-		id_val = xmlNodeListGetString(attrp->doc, attrp->children, 1);
-		if (id_val != NULL) {
-			xmlAddID(NULL, attrp->doc, id_val, attrp);
-			xmlFree(id_val);
-		}
-	} else if (is_id == 0 && attrp->atype == XML_ATTRIBUTE_ID) {
+	if (is_id && attrp->atype != XML_ATTRIBUTE_ID) {
+		attrp->atype = XML_ATTRIBUTE_ID;
+	} else if (!is_id && attrp->atype == XML_ATTRIBUTE_ID) {
 		xmlRemoveID(attrp->doc, attrp);
 		attrp->atype = 0;
 	}
+
+	dom_mark_ids_modified(document);
 }
 /* }}} */
 
@@ -1311,7 +1326,7 @@ PHP_METHOD(DOMElement, setIdAttribute)
 	if (attrp == NULL || attrp->type == XML_ATTRIBUTE_DECL) {
 		php_dom_throw_error(NOT_FOUND_ERR, dom_get_strict_error(intern->document));
 	} else {
-		php_set_attribute_id(attrp, is_id);
+		php_set_attribute_id(attrp, is_id, intern->document);
 	}
 }
 /* }}} end dom_element_set_id_attribute */
@@ -1340,7 +1355,7 @@ PHP_METHOD(DOMElement, setIdAttributeNS)
 	if (attrp == NULL || attrp->type == XML_ATTRIBUTE_DECL) {
 		php_dom_throw_error(NOT_FOUND_ERR, dom_get_strict_error(intern->document));
 	} else {
-		php_set_attribute_id(attrp, is_id);
+		php_set_attribute_id(attrp, is_id, intern->document);
 	}
 }
 /* }}} end dom_element_set_id_attribute_ns */
@@ -1367,7 +1382,7 @@ static void dom_element_set_id_attribute_node(INTERNAL_FUNCTION_PARAMETERS, zend
 	if (attrp->parent != nodep) {
 		php_dom_throw_error(NOT_FOUND_ERR, dom_get_strict_error(intern->document));
 	} else {
-		php_set_attribute_id(attrp, is_id);
+		php_set_attribute_id(attrp, is_id, intern->document);
 	}
 }
 

ext/dom/internal_helpers.h

@@ -63,4 +63,31 @@ DOM_DEF_GET_CE_FUNC(domimplementation)
 
 #endif
 
+static zend_always_inline size_t dom_minimum_modification_nr_since_parsing(php_libxml_ref_obj *doc_ptr)
+{
+	/* For old-style DOM, we need a "new DOMDocument" + a load, so the minimum modification nr is 2.
+	 * For new-style DOM, we need only to call a named constructor, so the minimum modification nr is 1. */
+	return doc_ptr->class_type == PHP_LIBXML_CLASS_MODERN ? 1 : 2;
+}
+
+static zend_always_inline void dom_mark_document_cache_as_modified_since_parsing(php_libxml_ref_obj *doc_ptr)
+{
+	if (doc_ptr) {
+		doc_ptr->cache_tag.modification_nr = MAX(dom_minimum_modification_nr_since_parsing(doc_ptr) + 1,
+												 doc_ptr->cache_tag.modification_nr);
+	}
+}
+
+/* Marks the ID cache as potentially stale */
+static zend_always_inline void dom_mark_ids_modified(php_libxml_ref_obj *doc_ptr)
+{
+	/* Although this is currently a wrapper function, it's best to abstract the actual implementation away. */
+	dom_mark_document_cache_as_modified_since_parsing(doc_ptr);
+}
+
+static zend_always_inline bool dom_is_document_cache_modified_since_parsing(php_libxml_ref_obj *doc_ptr)
+{
+	return !doc_ptr || doc_ptr->cache_tag.modification_nr > dom_minimum_modification_nr_since_parsing(doc_ptr);
+}
+
 #endif

ext/dom/node.c

@@ -185,6 +185,7 @@ zend_result dom_node_node_value_write(dom_object *obj, zval *newval)
 	/* Access to Element node is implemented as a convenience method */
 	switch (nodep->type) {
 		case XML_ATTRIBUTE_NODE:
+			dom_attr_value_will_change(obj, (xmlAttrPtr) nodep);
 			if (php_dom_follow_spec_intern(obj)) {
 				dom_remove_all_children(nodep);
 				xmlAddChild(nodep, xmlNewTextLen(BAD_CAST ZSTR_VAL(str), ZSTR_LEN(str)));

ext/dom/php_dom.h

@@ -174,6 +174,7 @@ xmlDocPtr php_dom_create_html_doc(void);
 xmlEntityPtr dom_entity_reference_fetch_and_sync_declaration(xmlNodePtr reference);
 void dom_set_xml_class(php_libxml_ref_obj *document);
 bool dom_compare_value(const xmlAttr *attr, const xmlChar *value);
+void dom_attr_value_will_change(dom_object *obj, xmlAttrPtr attrp);
 
 typedef enum {
 	DOM_LOAD_STRING = 0,

ext/dom/tests/bug79701/id_property.phpt

@@ -0,0 +1,53 @@
+--TEST--
+Bug #79701 (getElementById does not correctly work with duplicate definitions) - id property variation
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+$dom = Dom\XMLDocument::createFromString(<<<XML
+<root>
+    <test1/>
+    <test2/>
+</root>
+XML);
+
+$test1 = $dom->documentElement->firstElementChild;
+$test2 = $test1->nextElementSibling;
+
+echo "--- After parsing ---\n";
+var_dump($dom->getElementById("x")?->nodeName);
+
+echo "--- After setting test2 ---\n";
+$test2->id = "x";
+var_dump($dom->getElementById("x")?->nodeName);
+echo "--- After setting test1 ---\n";
+$test1->id = "x";
+var_dump($dom->getElementById("x")?->nodeName);
+echo "--- After resetting test1 ---\n";
+$test1->id = "y";
+var_dump($dom->getElementById("x")?->nodeName);
+echo "--- After resetting test2 ---\n";
+$test2->id = "y";
+var_dump($dom->getElementById("x")?->nodeName);
+echo "--- After resetting test1 ---\n";
+$test1->id = "x";
+var_dump($dom->getElementById("x")?->nodeName);
+echo "--- After calling setIdAttribute with false on test1 ---\n";
+$test1->setIdAttribute("id", false);
+var_dump($dom->getElementById("x")?->nodeName);
+?>
+--EXPECT--
+--- After parsing ---
+NULL
+--- After setting test2 ---
+string(5) "test2"
+--- After setting test1 ---
+string(5) "test1"
+--- After resetting test1 ---
+string(5) "test2"
+--- After resetting test2 ---
+NULL
+--- After resetting test1 ---
+string(5) "test1"
+--- After calling setIdAttribute with false on test1 ---
+NULL

ext/dom/tests/bug79701/node.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Bug #79701 (getElementById does not correctly work with duplicate definitions) - attribute node variation
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+$dom = Dom\HTMLDocument::createEmpty();
+$element = $dom->createElement('foo');
+$dom->append($element);
+$attr = $dom->createAttribute('id');
+$attr->value = 'test';
+var_dump($dom->getElementById('test')?->nodeName);
+$element->setAttributeNode($attr);
+var_dump($dom->getElementById('test')?->nodeName);
+?>
+--EXPECT--
+NULL
+string(3) "FOO"