Fix use-after-free of name in var-var with malicious error handler

Fixes oss-fuzz #54325
Closes phpGH-12732

Author: iluuu1994

NEWS

@@ -2,6 +2,10 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 8.2.14
 
+- Core:
+  . Fixed oss-fuzz #54325 (Use-after-free of name in var-var with malicious
+    error handler). (ilutov)
+
 - DOM:
   . Fixed bug GH-12616 (DOM: Removing XMLNS namespace node results in invalid
     default: prefix). (nielsdos)

Zend/tests/oss_fuzz_54325.phpt

@@ -0,0 +1,19 @@
+--TEST--
+oss-fuzz #54325: Fix use-after-free of name in var-var with malicious error handler
+--FILE--
+<?php
+set_error_handler(function ($errno, $errstr) {
+    var_dump($errstr);
+    global $x;
+    $x = new stdClass;
+});
+
+// Needs to be non-interned string
+$x = strrev('foo');
+$$x++;
+var_dump($x);
+?>
+--EXPECT--
+string(23) "Undefined variable $oof"
+object(stdClass)#2 (0) {
+}

Zend/zend_vm_def.h

@@ -1748,13 +1748,20 @@ ZEND_VM_C_LABEL(fetch_this):
 		} else if (type == BP_VAR_IS || type == BP_VAR_UNSET) {
 			retval = &EG(uninitialized_zval);
 		} else {
+			if (OP1_TYPE == IS_CV) {
+				/* Keep name alive in case an error handler tries to free it. */
+				zend_string_addref(name);
+			}
 			zend_error(E_WARNING, "Undefined %svariable $%s",
 				(opline->extended_value & ZEND_FETCH_GLOBAL ? "global " : ""), ZSTR_VAL(name));
 			if (type == BP_VAR_RW && !EG(exception)) {
 				retval = zend_hash_update(target_symbol_table, name, &EG(uninitialized_zval));
 			} else {
 				retval = &EG(uninitialized_zval);
 			}
+			if (OP1_TYPE == IS_CV) {
+				zend_string_release(name);
+			}
 		}
 	/* GLOBAL or $$name variable may be an INDIRECT pointer to CV */
 	} else if (Z_TYPE_P(retval) == IS_INDIRECT) {