From 0fc1f9a2edda6c08fb0857e780b49102420a4179 Mon Sep 17 00:00:00 2001
From: Andrew Paseltiner <apaseltiner@gmail.com>
Date: Tue, 24 Nov 2015 16:40:25 -0500
Subject: [PATCH] Add overflow check to `arc::Weak::upgrade`

Closes #30031.
---
 src/liballoc/arc.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/liballoc/arc.rs b/src/liballoc/arc.rs
index dba9b71c61cd4..45a47ae075e72 100644
--- a/src/liballoc/arc.rs
+++ b/src/liballoc/arc.rs
@@ -637,6 +637,11 @@ impl<T: ?Sized> Weak<T> {
                 return None
             }
 
+            // See comments in `Arc::clone` for why we do this (for `mem::forget`).
+            if n > MAX_REFCOUNT {
+                unsafe { abort(); }
+            }
+
             // Relaxed is valid for the same reason it is on Arc's Clone impl
             let old = inner.strong.compare_and_swap(n, n + 1, Relaxed);
             if old == n {