Guard var_export() against native stack overflow (GH-24605)

ext/standard/tests/general_functions/gh24605_var_export_stack_guard.phpt

@@ -0,0 +1,57 @@
+--TEST--
+GH-24605: var_export() checks native stack limit for arrays and objects
+--SKIPIF--
+<?php
+if (ini_get('zend.max_allowed_stack_size') === false) {
+    die('skip No stack limit support');
+}
+if (getenv('SKIP_ASAN')) {
+    die('skip ASAN needs different stack limit setting');
+}
+?>
+--INI--
+zend.max_allowed_stack_size=256K
+--FILE--
+<?php
+function test_export(string $name, mixed $value): void {
+    try {
+        var_export($value, true);
+        echo "$name: NOT GUARDED\n";
+    } catch (Error $e) {
+        echo $name, ': ', str_contains($e->getMessage(), 'Maximum call stack size')
+            ? "guarded\n"
+            : "unexpected error\n";
+    }
+}
+
+$data = 0;
+for ($i = 0; $i < 3000; $i++) {
+    $data = [$data];
+}
+test_export('array', $data);
+
+// Detach the nested arrays without recursively destroying them.
+while (is_array($data)) {
+    $data = $data[0];
+}
+
+class StackNode { public ?StackNode $next = null; }
+$first = new StackNode();
+$node = $first;
+for ($i = 0; $i < 3000; $i++) {
+    $node->next = new StackNode();
+    $node = $node->next;
+}
+test_export('object', $first);
+
+// Break the chain iteratively to avoid teardown recursion.
+$node = $first;
+while ($node !== null) {
+    $next = $node->next;
+    $node->next = null;
+    $node = $next;
+}
+?>
+--EXPECT--
+array: guarded
+object: guarded

ext/standard/var.c

@@ -542,6 +542,13 @@ PHPAPI zend_result php_var_export_ex(zval *struc, int level, smart_str *buf) /*
 	zend_string *key;
 	zval *val;
 
+#ifdef ZEND_CHECK_STACK_LIMIT
+	if (UNEXPECTED(zend_call_stack_overflowed(EG(stack_limit)))) {
+		zend_call_stack_size_error();
+		return FAILURE;
+	}
+#endif
+
 again:
 	switch (Z_TYPE_P(struc)) {
 		case IS_FALSE:
@@ -672,10 +679,15 @@ PHPAPI zend_result php_var_export_ex(zval *struc, int level, smart_str *buf) /*
 								return FAILURE;
 							}
 						}
-						php_object_element_export(val, index, key, level, buf);
+						zend_result result = php_object_element_export(val, index, key, level, buf);
 						if (val == &tmp) {
 							zval_ptr_dtor(val);
 						}
+						if (UNEXPECTED(result == FAILURE)) {
+							ZEND_GUARD_OR_GC_UNPROTECT_RECURSION(guard, EXPORT, zobj);
+							zend_release_properties(myht);
+							return FAILURE;
+						}
 					} ZEND_HASH_FOREACH_END();
 				}
 				zend_release_properties(myht);