Fix GH-12223: Entity reference produces infinite loop in var_dump/print_r

Closes GH-12223.

NEWS

@@ -13,6 +13,8 @@ PHP                                                                        NEWS
   . Fixed bug GH-12170 (Can't use xpath with comments in SimpleXML). (nielsdos)
   . Fixed bug GH-12192 (SimpleXML infinite loop when getName() is called
     within foreach). (nielsdos)
+  . Fixed bug GH-12223 (Entity reference produces infinite loop in
+    var_dump/print_r). (nielsdos)
 
 28 Sep 2023, PHP 8.1.24
 

ext/simplexml/simplexml.c

@@ -1197,6 +1197,12 @@ static HashTable *sxe_get_prop_hash(zend_object *object, int is_debug) /* {{{ */
 				sxe_properties_add(rv, name, namelen, &value);
 			}
 next_iter:
+			if (UNEXPECTED(node->type == XML_ENTITY_DECL)) {
+				/* Entity decls are linked together via the next pointer.
+				 * The only way to get to an entity decl is via an entity reference in the document.
+				 * If we then continue iterating, we'll end up in the DTD. Even worse, if the entities reference each other we'll infinite loop. */
+				break;
+			}
 			if (use_iter) {
 				node = php_sxe_iterator_fetch(sxe, node->next, 0);
 			} else {

ext/simplexml/tests/gh12223.phpt

@@ -0,0 +1,67 @@
+--TEST--
+GH-12223: Entity reference produces infinite loop in var_dump/print_r
+--EXTENSIONS--
+simplexml
+--FILE--
+<?php
+
+$xml = <<<XML
+<?xml version="1.0"?>
+<!DOCTYPE somedoc [
+  <!ENTITY a "something">
+  <!ENTITY b "&a;">
+  <!ENTITY c "&b;">
+]>
+<somedoc>&c;</somedoc>
+XML;
+
+$sxe = simplexml_load_string($xml);
+
+var_dump($sxe);
+print_r($sxe);
+
+?>
+--EXPECT--
+object(SimpleXMLElement)#1 (1) {
+  ["c"]=>
+  object(SimpleXMLElement)#2 (1) {
+    ["c"]=>
+    object(SimpleXMLElement)#3 (1) {
+      ["b"]=>
+      object(SimpleXMLElement)#4 (1) {
+        ["b"]=>
+        object(SimpleXMLElement)#5 (1) {
+          ["a"]=>
+          object(SimpleXMLElement)#6 (1) {
+            ["a"]=>
+            string(9) "something"
+          }
+        }
+      }
+    }
+  }
+}
+SimpleXMLElement Object
+(
+    [c] => SimpleXMLElement Object
+        (
+            [c] => SimpleXMLElement Object
+                (
+                    [b] => SimpleXMLElement Object
+                        (
+                            [b] => SimpleXMLElement Object
+                                (
+                                    [a] => SimpleXMLElement Object
+                                        (
+                                            [a] => something
+                                        )
+
+                                )
+
+                        )
+
+                )
+
+        )
+
+)