From b8841f8ebe03fd9dec42cd95be2c032fe80abc87 Mon Sep 17 00:00:00 2001
From: Andy Tamilo <andytamilo@gmail.com>
Date: Fri, 26 Jul 2024 10:49:03 +0300
Subject: [PATCH] Fix race condition on ObjCNetworkMonitor::network_monitor_

There is a race condition on reading
`ObjCNetworkMonitor::_network_monitor` field.
The `ObjCNetworkMonitor::OnPathUpdate()` checks its nullability
on the org.webrtc.RTCDispatcherNetworkMonitor thread BEFORE the
`ObjCNetworkMonitor::Start()` assigns it on the network_monitor thread.
In addition, this field is neither atomic nor protected by mutex so its
last assigned value is not guaranteed to be visible to
another [reading] thread.

Bug: webrtc:355238623
Change-Id: I1a05215111cc873b7d4931824e18f281aebfb91f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/357880
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Reviewed-by: Peter Hanspers <peterhanspers@webrtc.org>
Reviewed-by: Jonas Oreland <jonaso@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42778}
---
 AUTHORS                                     | 1 +
 sdk/objc/native/src/objc_network_monitor.mm | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/AUTHORS b/AUTHORS
index 7b16d7c38a..48214c53a6 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -20,6 +20,7 @@ Alex Henrie <alexhenrie24@gmail.com>
 Andrew MacDonald <andrew@webrtc.org>
 Andrey Efremov <yoklmnprst@ya.ru>
 Andrew Johnson <ajohnson@draster.com>
+Andy Tamilo <andytamilo@gmail.com>
 Anil Kumar <an1kumar@gmail.com>
 Anton Barkov <anton.barkov@macpaw.com>
 Ben Strong <bstrong@gmail.com>
diff --git a/sdk/objc/native/src/objc_network_monitor.mm b/sdk/objc/native/src/objc_network_monitor.mm
index 535548c64c..1a1f445e1d 100644
--- a/sdk/objc/native/src/objc_network_monitor.mm
+++ b/sdk/objc/native/src/objc_network_monitor.mm
@@ -84,9 +84,9 @@ rtc::NetworkMonitorInterface::InterfaceInfo ObjCNetworkMonitor::GetInterfaceInfo
 
 void ObjCNetworkMonitor::OnPathUpdate(
     std::map<std::string, rtc::AdapterType, rtc::AbslStringViewCmp> adapter_type_by_name) {
-  RTC_DCHECK(network_monitor_ != nil);
   thread_->PostTask(SafeTask(safety_flag_, [this, adapter_type_by_name] {
     RTC_DCHECK_RUN_ON(thread_);
+    RTC_DCHECK(network_monitor_ != nil);
     adapter_type_by_name_ = adapter_type_by_name;
     InvokeNetworksChangedCallback();
   }));