From 3bac3ab0b5881df9998c9584c90604be648b79b6 Mon Sep 17 00:00:00 2001
From: Moonchild <moonchild@palemoon.org>
Date: Sun, 16 Feb 2025 19:35:29 +0100
Subject: [PATCH] No issue - avoid potential underflow in StructuredClone.

Prevents potential loop-around if there's bogus internal Map data.
---
 js/src/vm/StructuredClone.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/js/src/vm/StructuredClone.cpp b/js/src/vm/StructuredClone.cpp
index 25e9e93b3b..79f2d23d96 100644
--- a/js/src/vm/StructuredClone.cpp
+++ b/js/src/vm/StructuredClone.cpp
@@ -1700,6 +1700,8 @@ JSStructuredCloneWriter::write(HandleValue v)
                 return false;
 
             if (cls == ESClass::Map) {
+                if (!counts.back())
+                    return false;
                 counts.back()--;
                 RootedValue val(context(), entries.back());
                 entries.popBack();