[Bug] connectivity_plus iOS Crash: swift::fatalError in NWPathMonitor (race condition)

[manuel-goester-n41]

Description

Firebase Crashlytics reported a fatal crash on iOS originating from connectivity_plus.

The stack trace indicates a memory corruption issue (swift::fatalError / swift_deallocPartialClassInstance) occurring within NWPathMonitor. This appears to be caused by a race condition where network updates are processed on a concurrent background queue while the monitor is being deallocated.

Stack Trace

Crashed: com.apple.root.utility-qos
0  libsystem_kernel.dylib         0x7198 __pthread_kill + 8
1  libsystem_pthread.dylib        0xd5f8 pthread_kill + 208
2  libsystem_c.dylib              0x1c4b8 abort + 124
3  libswiftCore.dylib             0x2f2998 swift::fatalError(unsigned int, char const*, ...) + 130
4  libswiftCore.dylib             0x2f29b4 swift::warningv(unsigned int, char const*, char*) + 26
5  libswiftCore.dylib             0x2f72ec swift_deallocPartialClassInstance + 170
6  libswiftCore.dylib             0x2f7184 _swift_release_dealloc + 28
7  libswiftCore.dylib             0x2f8060 bool swift::RefCounts<swift::RefCountBitsT<(swift::RefCountInlinedness)1>>::doDecrementSlow<(swift::PerformDeinit)1>(swift::RefCountBitsT<(swift::RefCountInlinedness)1>, unsigned int) + 184
8  libswiftNetwork.dylib          0x32794 assignWithTake for NWPath + 64
9  libswiftNetwork.dylib          0x32f28 outlined assign with take of NWPath + 52
10 libswiftNetwork.dylib          0x30400 closure #1 in NWPathMonitor.init(_:) + 144
11 libswiftNetwork.dylib          0x307a8 partial apply for closure #1 in NWPathMonitor.init(requiredInterfaceType:) + 16
12 libswiftNetwork.dylib          0x166a8 thunk for @escaping @callee_guaranteed (@guaranteed OS_nw_path) -> () + 44
13 Network                        0x7d1918 __nw_path_necp_update_evaluator_block_invoke + 448
14 libdispatch.dylib              0x637a8 _dispatch_call_block_and_release + 24
15 libdispatch.dylib              0x64780 _dispatch_client_callout + 16
16 libdispatch.dylib              0x48d88 _dispatch_root_queue_drain + 616
17 libdispatch.dylib              0x49430 _dispatch_worker_thread2 + 160
18 libsystem_pthread.dylib        0x1b94 _pthread_wqthread + 224
19 libsystem_pthread.dylib        0x1720 start_wqthread + 8

Environment

• Plugin: connectivity_plus
• OS Version: iOS 16.7.12
• Device: iPhone 8

Fix

A fix has been proposed in PR #3752 which moves the NWPathMonitor to a serial queue.