From 1774cca47c587e070b2cbdad951d9590777a4e99 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A9ter=20G=C3=A1l?= <pgal.usz@partner.samsung.com>
Date: Mon, 25 May 2020 16:36:54 +0200
Subject: [PATCH] Fix array length check in lastIndexOf (#3789)

When lastIndexOf is executed the array length can change and in
case of fast arrays the length should be re-checked.

JerryScript-DCO-1.0-Signed-off-by: Peter Gal pgal.usz@partner.samsung.com
---
 .../ecma-builtin-array-prototype.c            |  4 ++-
 tests/jerry/regression-test-issue-3779.js     | 32 +++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 tests/jerry/regression-test-issue-3779.js

diff --git a/jerry-core/ecma/builtin-objects/ecma-builtin-array-prototype.c b/jerry-core/ecma/builtin-objects/ecma-builtin-array-prototype.c
index 7dbbdeef8..383aeb74a 100644
--- a/jerry-core/ecma/builtin-objects/ecma-builtin-array-prototype.c
+++ b/jerry-core/ecma/builtin-objects/ecma-builtin-array-prototype.c
@@ -1775,9 +1775,11 @@ ecma_builtin_array_prototype_object_last_index_of (const ecma_value_t args[], /*
   if (ecma_op_object_is_fast_array (obj_p))
   {
     ecma_extended_object_t *ext_obj_p = (ecma_extended_object_t *) obj_p;
+    // It is possible that the length changed due to the callback performed above.
+    uint32_t array_length = ext_obj_p->u.array.length;
 
     if (ext_obj_p->u.array.u.hole_count < ECMA_FAST_ARRAY_HOLE_ONE
-        && len != 0)
+        && array_length > 0)
     {
       ecma_value_t *buffer_p = ECMA_GET_NON_NULL_POINTER (ecma_value_t, obj_p->u1.property_list_cp);
 
diff --git a/tests/jerry/regression-test-issue-3779.js b/tests/jerry/regression-test-issue-3779.js
new file mode 100644
index 000000000..c97db4b33
--- /dev/null
+++ b/tests/jerry/regression-test-issue-3779.js
@@ -0,0 +1,32 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+var array = [1, 2, 3];
+var idx_50 = array.lastIndexOf(50, {
+    valueOf: function() {
+        // Trigger removing elements from fast array.
+        array.length = 0;
+    }
+})
+
+assert (idx_50 === -1);
+
+var idx_51 = array.lastIndexOf(51, {
+    valueOf: function() {
+        array.push(51)
+        return 10;
+    }
+})
+
+assert (idx_51 === -1);