From 7a4f84f311ebd29857cef880c753a732dd723877 Mon Sep 17 00:00:00 2001
From: Boris Zbarsky <bzbarsky@apple.com>
Date: Mon, 1 Aug 2022 18:37:11 -0400
Subject: [PATCH] Don't touch member variables from async dispatch. (#21456)

We were null-checking members, then calling them from an async block,
by which point they might be null.

Fixes https://github.com/project-chip/connectedhomeip/issues/21453
---
 src/darwin/Framework/CHIP/MTRBaseDevice.mm | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/darwin/Framework/CHIP/MTRBaseDevice.mm b/src/darwin/Framework/CHIP/MTRBaseDevice.mm
index c1a54ac7b6983d..05a0eb023a0c74 100644
--- a/src/darwin/Framework/CHIP/MTRBaseDevice.mm
+++ b/src/darwin/Framework/CHIP/MTRBaseDevice.mm
@@ -1384,16 +1384,20 @@ - (instancetype)initWithPath:(const ConcreteEventPath &)path
 {
     __block NSArray * attributeReports = mAttributeReports;
     mAttributeReports = nil;
+    __block auto attributeCallback = mAttributeReportCallback;
+
     __block NSArray * eventReports = mEventReports;
     mEventReports = nil;
-    if (mAttributeReportCallback && attributeReports.count) {
+    __block auto eventCallback = mEventReportCallback;
+
+    if (attributeCallback != nil && attributeReports.count) {
         dispatch_async(mQueue, ^{
-            mAttributeReportCallback(attributeReports);
+            attributeCallback(attributeReports);
         });
     }
-    if (mEventReportCallback && eventReports.count) {
+    if (eventCallback != nil && eventReports.count) {
         dispatch_async(mQueue, ^{
-            mEventReportCallback(eventReports);
+            eventCallback(eventReports);
         });
     }
 }