Fix use after free because of data clobbering by user error handler

Fixes oss-fuzz #41692

Author: dstogov

Zend/tests/falsetoarray_002.phpt

@@ -0,0 +1,15 @@
+--TEST--
+Autovivification of false to array with data clobbering by error handler
+--FILE--
+<?php
+set_error_handler(function($code, $msg) {
+    echo "Err: $msg\n";
+    $GLOBALS['a']='';
+});
+$a=[!'a'];
+$a[0][$d]='b';
+var_dump($a);
+?>
+--EXPECT--
+Err: Automatic conversion of false to array is deprecated
+string(0) ""

Zend/zend_execute.c

@@ -2508,13 +2508,24 @@ static zend_always_inline void zend_fetch_dimension_address(zval *result, zval *
 			if (type != BP_VAR_W && UNEXPECTED(Z_TYPE_P(container) == IS_UNDEF)) {
 				ZVAL_UNDEFINED_OP1();
 			}
-			if (Z_TYPE_P(container) == IS_FALSE) {
-				zend_false_to_array_deprecated();
-			}
 			if (type != BP_VAR_UNSET) {
-				array_init(container);
+				HashTable *ht = zend_new_array(0);
+				zend_uchar old_type = Z_TYPE_P(container);
+
+				ZVAL_ARR(container, ht);
+				if (UNEXPECTED(old_type == IS_FALSE)) {
+					GC_ADDREF(ht);
+					zend_false_to_array_deprecated();
+					if (UNEXPECTED(GC_DELREF(ht) == 0)) {
+						zend_array_destroy(ht);
+						goto return_null;
+					}
+				}
 				goto fetch_from_array;
 			} else {
+				if (UNEXPECTED(Z_TYPE_P(container) == IS_FALSE)) {
+					zend_false_to_array_deprecated();
+				}
 return_null:
 				/* for read-mode only */
 				if (ZEND_CONST_COND(dim_type == IS_CV, dim != NULL) && UNEXPECTED(Z_TYPE_P(dim) == IS_UNDEF)) {

Zend/zend_vm_def.h

@@ -1217,13 +1217,23 @@ ZEND_VM_C_LABEL(assign_dim_op_new_array):
 			}
 			zend_binary_assign_op_obj_dim(container, dim OPLINE_CC EXECUTE_DATA_CC);
 		} else if (EXPECTED(Z_TYPE_P(container) <= IS_FALSE)) {
+			HashTable *ht;
+			zend_uchar old_type;
+
 			if (OP1_TYPE == IS_CV && UNEXPECTED(Z_TYPE_INFO_P(container) == IS_UNDEF)) {
 				ZVAL_UNDEFINED_OP1();
 			}
-			if (Z_TYPE_P(container) == IS_FALSE) {
+			ht = zend_new_array(8);
+			old_type = Z_TYPE_P(container);
+			ZVAL_ARR(container, ht);
+			if (UNEXPECTED(old_type == IS_FALSE)) {
+				GC_ADDREF(ht);
 				zend_false_to_array_deprecated();
+				if (UNEXPECTED(GC_DELREF(ht) == 0)) {
+					zend_array_destroy(ht);
+					ZEND_VM_C_GOTO(assign_dim_op_ret_null);
+				}
 			}
-			ZVAL_ARR(container, zend_new_array(8));
 			ZEND_VM_C_GOTO(assign_dim_op_new_array);
 		} else {
 			dim = GET_OP2_ZVAL_PTR(BP_VAR_R);
@@ -2626,18 +2636,25 @@ ZEND_VM_C_LABEL(try_assign_dim_array):
 				FREE_OP_DATA();
 			}
 		} else if (EXPECTED(Z_TYPE_P(object_ptr) <= IS_FALSE)) {
-			if (Z_TYPE_P(object_ptr) == IS_FALSE) {
-				zend_false_to_array_deprecated();
-			}
-
 			if (Z_ISREF_P(orig_object_ptr)
 			 && ZEND_REF_HAS_TYPE_SOURCES(Z_REF_P(orig_object_ptr))
 			 && !zend_verify_ref_array_assignable(Z_REF_P(orig_object_ptr))) {
 				dim = GET_OP2_ZVAL_PTR(BP_VAR_R);
 				FREE_OP_DATA();
 				UNDEF_RESULT();
 			} else {
-				ZVAL_ARR(object_ptr, zend_new_array(8));
+				HashTable *ht = zend_new_array(8);
+				zend_uchar old_type = Z_TYPE_P(object_ptr);
+
+				ZVAL_ARR(object_ptr, ht);
+				if (UNEXPECTED(old_type == IS_FALSE)) {
+					GC_ADDREF(ht);
+					zend_false_to_array_deprecated();
+					if (UNEXPECTED(GC_DELREF(ht) == 0)) {
+						zend_array_destroy(ht);
+						ZEND_VM_C_GOTO(assign_dim_error);
+					}
+				}
 				ZEND_VM_C_GOTO(try_assign_dim_array);
 			}
 		} else {