ios - swift - read MDM config from UserDefaults

Question

I am trying to read the mdm config from UserDefaults but it keeps crashing.

The code is pretty straight forward:

 let defaults = UserDefaults.standard;
 let serverConfig = defaults.dictionary(forKey: Settings.SETTING_MANAGED_KCONFIGURATIONURL);

Whereas SETTING_MANAGED_KCONFIGURATIONURL is set to: "com.apple.configuration.managed"

Its crashing on the second line.

I am also using the UserDefaults.didChangeNotification Observer.

Here is my crashlog:

Exception Subtype: KERN_PROTECTION_FAILURE at 0x000000016f097e78
VM Region Info: 0x16f097e78 is in 0x16f094000-0x16f098000;  bytes after start: 15992  bytes before end: 391
      REGION TYPE                      START - END             [ VSIZE] PRT/MAX SHRMOD  REGION DETAIL
      MALLOC_TINY            0000000115800000-0000000115900000 [ 1024K] rw-/rwx SM=PRV  
      GAP OF 0x59794000 BYTES
--->  STACK GUARD            000000016f094000-000000016f098000 [   16K] ---/rwx SM=NUL  ... for thread 0
      Stack                  000000016f098000-000000016f194000 [ 1008K] rw-/rwx SM=PRV  thread 0

Termination Signal: Segmentation fault: 11
Termination Reason: Namespace SIGNAL, Code 0xb
Terminating Process: exc handler [560]
Triggered by Thread:  0

Thread 0 name:  Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0   CoreFoundation                  0x00000001926ffee8 __CFStringAppendBytes + 188
1   CoreFoundation                  0x00000001926f2528 __CFStringAppendFormatCore + 10180
2   CoreFoundation                  0x00000001926f2528 __CFStringAppendFormatCore + 10180
3   CoreFoundation                  0x00000001926f35bc _CFStringCreateWithFormatAndArgumentsAux2 + 136
4   CoreFoundation                  0x00000001926f3664 CFStringCreateWithFormat + 44
5   CoreFoundation                  0x00000001926c047c -[CFPrefsSearchListSource copyOSLogDescription] + 116
6   CoreFoundation                  0x0000000192630eb8 -[CFPrefsSearchListSource alreadylocked_copyValueForKey:] + 260
7   CoreFoundation                  0x0000000192630d90 -[CFPrefsSource copyValueForKey:] + 60
8   CoreFoundation                  0x000000019277cae8 __76-[_CFXPreferences copyAppValueForKey:identifier:container:configurationURL:]_block_invoke + 40
9   CoreFoundation                  0x00000001926c0c54 __108-[_CFXPreferences+ 617556 (SearchListAdditions) withSearchListForIdentifier:container:cloudConfigurationURL:perform:]_block_invoke + 272
10  CoreFoundation                  0x00000001926c0698 normalizeQuintuplet + 340
11  CoreFoundation                  0x000000019262ed64 -[_CFXPreferences+ 19812 (SearchListAdditions) withSearchListForIdentifier:container:cloudConfigurationURL:perform:] + 108
12  CoreFoundation                  0x000000019262f5f0 -[_CFXPreferences copyAppValueForKey:identifier:container:configurationURL:] + 148
13  CoreFoundation                  0x000000019277ef30 _CFPreferencesCopyAppValueWithContainerAndConfiguration + 124
14  Foundation                      0x000000019309c8fc -[NSUserDefaults+ 26876 (NSUserDefaults) objectForKey:] + 52
15  MYAPP                       0x0000000100cd3bfc MISettingsManager.checkAndReadMDMSettings() + 424956 (MISettingsManager.swift:303)
16  MYAPP                       0x0000000100cda2b0 specialized closure #1 in static MISettingsManager.instance.getter + 451248 (<compiler-generated>:0)
17  MYAPP                       0x0000000100ccdb5c thunk for @escaping @callee_guaranteed (@in_guaranteed Notification) -> () + 400220 (<compiler-generated>:0)
18  Foundation                      0x00000001930c5ef0 -[__NSObserver _doit:] + 316
19  CoreFoundation                  0x00000001926b421c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 20
20  CoreFoundation                  0x00000001926b41e8 ___CFXRegistrationPost_block_invoke + 64
21  CoreFoundation                  0x00000001926b36dc _CFXRegistrationPost + 392
22  CoreFoundation                  0x00000001926b3388 ___CFXNotificationPost_block_invoke + 96
23  CoreFoundation                  0x000000019262cc54 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1496
24  CoreFoundation                  0x00000001926b2e38 _CFXNotificationPost + 696
25  Foundation                      0x000000019309c1a4 -[NSNotificationCenter postNotificationName:object:userInfo:] + 68
26  MYAPP                       0x0000000100cd2b64 MISettingsManager.setValueForSetting(_:_:) + 420708 (<compiler-generated>:0)
27  MYAPP                       0x0000000100cd4900 MISettingsManager.setSettingsValue(key:value:) + 428288 (MISettingsManager.swift:364)
28  MYAPP                       0x0000000100cd5990 MISettingsManager.validateMDMSettings(url:system:user:) + 432528 (MISettingsManager.swift:411)
29  MYAPP                       0x0000000100cd3fc4 MISettingsManager.checkAndReadMDMSettings() + 425924 (<compiler-generated>:0)
30  MYAPP                       0x0000000100cda2b0 specialized closure #1 in static MISettingsManager.instance.getter + 451248 (<compiler-generated>:0)
31  MYAPP                       0x0000000100ccdb5c thunk for @escaping @callee_guaranteed (@in_guaranteed Notification) -> () + 400220 (<compiler-generated>:0)
32  Foundation                      0x00000001930c5ef0 -[__NSObserver _doit:] + 316
33  CoreFoundation                  0x00000001926b421c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 20
34  CoreFoundation                  0x00000001926b41e8 ___CFXRegistrationPost_block_invoke + 64
35  CoreFoundation                  0x00000001926b36dc _CFXRegistrationPost + 392
36  CoreFoundation                  0x00000001926b3388 ___CFXNotificationPost_block_invoke + 96
37  CoreFoundation                  0x000000019262cc54 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1496
38  CoreFoundation                  0x00000001926b2e38 _CFXNotificationPost + 696
39  Foundation                      0x000000019309c1a4 -[NSNotificationCenter postNotificationName:object:userInfo:] + 68
40  MYAPP                       0x0000000100cd2b64 MISettingsManager.setValueForSetting(_:_:) + 420708 (<compiler-generated>:0)
41  MYAPP                       0x0000000100cd4900 MISettingsManager.setSettingsValue(key:value:) + 428288 (MISettingsManager.swift:364)
42  MYAPP                       0x0000000100cd5990 MISettingsManager.validateMDMSettings(url:system:user:) + 432528 (MISettingsManager.swift:411)
43  MYAPP                       0x0000000100cd3fc4 MISettingsManager.checkAndReadMDMSettings() + 425924 (<compiler-generated>:0)
44  MYAPP                       0x0000000100cda2b0 specialized closure #1 in static MISettingsManager.instance.getter + 451248 (<compiler-generated>:0)
45  MYAPP                       0x0000000100ccdb5c thunk for @escaping @callee_guaranteed (@in_guaranteed Notification) -> () + 400220 (<compiler-generated>:0)
46  Foundation                      0x00000001930c5ef0 -[__NSObserver _doit:] + 316
47  CoreFoundation                  0x00000001926b421c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 20
48  CoreFoundation                  0x00000001926b41e8 ___CFXRegistrationPost_block_invoke + 64
49  CoreFoundation                  0x00000001926b36dc _CFXRegistrationPost + 392
50  CoreFoundation                  0x00000001926b3388 ___CFXNotificationPost_block_invoke + 96
51  CoreFoundation                  0x000000019262cc54 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1496
52  CoreFoundation                  0x00000001926b2e38 _CFXNotificationPost + 696
53  Foundation                      0x000000019309c1a4 -[NSNotificationCenter postNotificationName:object:userInfo:] + 68
54  MYAPP                       0x0000000100cd2b64 MISettingsManager.setValueForSetting(_:_:) + 420708 (<compiler-generated>:0)
55  MYAPP                       0x0000000100cd4900 MISettingsManager.setSettingsValue(key:value:) + 428288 (MISettingsManager.swift:364)
56  MYAPP                       0x0000000100cd5990 MISettingsManager.validateMDMSettings(url:system:user:) + 432528 (MISettingsManager.swift:411)
57  MYAPP                       0x0000000100cd3fc4 MISettingsManager.checkAndReadMDMSettings() + 425924 (<compiler-generated>:0)
58  MYAPP                       0x0000000100cda2b0 specialized closure #1 in static MISettingsManager.instance.getter + 451248 (<compiler-generated>:0)
59  MYAPP                       0x0000000100ccdb5c thunk for @escaping @callee_guaranteed (@in_guaranteed Notification) -> () + 400220 (<compiler-generated>:0)
60  Foundation                      0x00000001930c5ef0 -[__NSObserver _doit:] + 316
61  CoreFoundation                  0x00000001926b421c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 20
62  CoreFoundation                  0x00000001926b41e8 ___CFXRegistrationPost_block_invoke + 64
63  CoreFoundation                  0x00000001926b36dc _CFXRegistrationPost + 392
64  CoreFoundation                  0x00000001926b3388 ___CFXNotificationPost_block_invoke + 96
65  CoreFoundation                  0x000000019262cc54 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1496
66  CoreFoundation                  0x00000001926b2e38 _CFXNotificationPost + 696
67  Foundation                      0x000000019309c1a4 -[NSNotificationCenter postNotificationName:object:userInfo:] + 68
68  MYAPP                       0x0000000100cd2b64 MISettingsManager.setValueForSetting(_:_:) + 420708 (<compiler-generated>:0)
69  MYAPP                       0x0000000100cd4900 MISettingsManager.setSettingsValue(key:value:) + 428288 (MISettingsManager.swift:364)
70  MYAPP                       0x0000000100cd5990 MISettingsManager.validateMDMSettings(url:system:user:) + 432528 (MISettingsManager.swift:411)
71  MYAPP                       0x0000000100cd3fc4 MISettingsManager.checkAndReadMDMSettings() + 425924 (<compiler-generated>:0)
72  MYAPP                       0x0000000100cda2b0 specialized closure #1 in static MISettingsManager.instance.getter + 451248 (<compiler-generated>:0)
73  MYAPP                       0x0000000100ccdb5c thunk for @escaping @callee_guaranteed (@in_guaranteed Notification) -> () + 400220 (<compiler-generated>:0)
74  Foundation                      0x00000001930c5ef0 -[__NSObserver _doit:] + 316
75  CoreFoundation                  0x00000001926b421c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 20
76  CoreFoundation                  0x00000001926b41e8 ___CFXRegistrationPost_block_invoke + 64
77  CoreFoundation                  0x00000001926b36dc _CFXRegistrationPost + 392
78  CoreFoundation                  0x00000001926b3388 ___CFXNotificationPost_block_invoke + 96
79  CoreFoundation                  0x000000019262cc54 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1496
80  CoreFoundation                  0x00000001926b2e38 _CFXNotificationPost + 696
81  Foundation                      0x000000019309c1a4 -[NSNotificationCenter postNotificationName:object:userInfo:] + 68
82  MYAPP                       0x0000000100cd2b64 MISettingsManager.setValueForSetting(_:_:) + 420708 (<compiler-generated>:0)
83  MYAPP                       0x0000000100cd4900 MISettingsManager.setSettingsValue(key:value:) + 428288 (MISettingsManager.swift:364)
84  MYAPP                       0x0000000100cd5990 MISettingsManager.validateMDMSettings(url:system:user:) + 432528 (MISettingsManager.swift:411)
85  MYAPP                       0x0000000100cd3fc4 MISettingsManager.checkAndReadMDMSettings() + 425924 (<compiler-generated>:0)
86  MYAPP                       0x0000000100cda2b0 specialized closure #1 in static MISettingsManager.instance.getter + 451248 (<compiler-generated>:0)
87  MYAPP                       0x0000000100ccdb5c thunk for @escaping @callee_guaranteed (@in_guaranteed Notification) -> () + 400220 (<compiler-generated>:0)
88  Foundation                      0x00000001930c5ef0 -[__NSObserver _doit:] + 316
89  CoreFoundation                  0x00000001926b421c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 20
90  CoreFoundation                  0x00000001926b41e8 ___CFXRegistrationPost_block_invoke + 64
91  CoreFoundation                  0x00000001926b36dc _CFXRegistrationPost + 392
92  CoreFoundation                  0x00000001926b3388 ___CFXNotificationPost_block_invoke + 96
93  CoreFoundation                  0x000000019262cc54 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1496
94  CoreFoundation                  0x00000001926b2e38 _CFXNotificationPost + 696
95  Foundation                      0x000000019309c1a4 -[NSNotificationCenter postNotificationName:object:userInfo:] + 68
[...]

Any help would be nice. Thanks!

[UPDATE]

I changed my code slightly to see what is really returned. It's still crashing but on at a different spot. Which doesn't makes sense since I haven't changed the logic. The first 5 lines are just for testing purpose and can be ignored. But I also added the PushNotification as mentioned here. Unfortunately there wasn't an explanation on why to add this.

let defaults = UserDefaults.standard;

let server = defaults.object(forKey: Settings.SETTING_MANAGED_KCONFIGURATIONURL);
print("[MISettingsManager] checkAndReadMDMSettings - server: \(server ?? "NULL")");
if let server = server as! [String:Any]? {
   print("[MISettingsManager] readManagedDefaultValues - \(server.description)");
}

let serverConfig = defaults.dictionary(forKey: Settings.SETTING_MANAGED_KCONFIGURATIONURL);
if(nil == serverConfig) {
   return;
}
print("[MISettingsManager] readManagedDefaultValues - \(serverConfig!.description)");

let url: String? = serverConfig![Settings.SETTING_SERVER_SERVICEURL] as? String;
if (!(url ?? "").isEmpty) {
   self.setSettingsValue(key: Settings.SETTING_SERVER_SERVICEURL, value: url);
}

setSettingsValue is written like this. Its also where its crashing. Null value check is done before this.

self.setValueForSetting(key!, value!);

This is the new crashlog:

Exception Type:  EXC_BAD_ACCESS (SIGSEGV)
Exception Subtype: KERN_PROTECTION_FAILURE at 0x000000016eeb3b10
VM Region Info: 0x16eeb3b10 is in 0x16eeb0000-0x16eeb4000;  bytes after start: 15120  bytes before end: 1263
      REGION TYPE                      START - END             [ VSIZE] PRT/MAX SHRMOD  REGION DETAIL
      mapped file            0000000104bf0000-0000000104d48000 [ 1376K] r--/rw- SM=COW  
      GAP OF 0x6a168000 BYTES
--->  STACK GUARD            000000016eeb0000-000000016eeb4000 [   16K] ---/rwx SM=NUL  ... for thread 0
      Stack                  000000016eeb4000-000000016efb0000 [ 1008K] rw-/rwx SM=PRV  thread 0

Termination Signal: Segmentation fault: 11
Termination Reason: Namespace SIGNAL, Code 0xb
Terminating Process: exc handler [607]
Triggered by Thread:  0

Thread 0 name:  Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0   CoreFoundation                  0x00000001927711c4 CFBasicHashCreateCopy + 4
1   CoreFoundation                  0x00000001926a1664 CFDictionaryCreateMutableCopy + 180
2   CoreFoundation                  0x00000001926308a4 -[_CFXNotificationNameWildcardObjectRegistration find:matching:] + 308
3   CoreFoundation                  0x000000019262cbdc -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1376
4   CoreFoundation                  0x00000001926b2e38 _CFXNotificationPost + 696
5   Foundation                      0x000000019309c1a4 -[NSNotificationCenter postNotificationName:object:userInfo:] + 68
6   MYAPP                       0x0000000100eb693c MISettingsManager.setValueForSetting(_:_:) + 420156 (<compiler-generated>:0)
7   MYAPP                       0x0000000100eb8920 MISettingsManager.setSettingsValue(key:value:) + 428320 (MISettingsManager.swift:375)
8   MYAPP                       0x0000000100eb99b0 MISettingsManager.validateMDMSettings(url:system:user:) + 432560 (MISettingsManager.swift:422)
9   MYAPP                       0x0000000100eb7fe4 MISettingsManager.checkAndReadMDMSettings() + 425956 (<compiler-generated>:0)
10  MYAPP                       0x0000000100ebe2d0 specialized closure #1 in static MISettingsManager.instance.getter + 451280 (<compiler-generated>:0)
11  MYAPP                       0x0000000100eb1b24 thunk for @escaping @callee_guaranteed (@in_guaranteed Notification) -> () + 400164 (<compiler-generated>:0)
12  Foundation                      0x00000001930c5ef0 -[__NSObserver _doit:] + 316
13  CoreFoundation                  0x00000001926b421c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 20
14  CoreFoundation                  0x00000001926b41e8 ___CFXRegistrationPost_block_invoke + 64
15  CoreFoundation                  0x00000001926b36dc _CFXRegistrationPost + 392
16  CoreFoundation                  0x00000001926b3388 ___CFXNotificationPost_block_invoke + 96
17  CoreFoundation                  0x000000019262cc54 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1496
18  CoreFoundation                  0x00000001926b2e38 _CFXNotificationPost + 696
19  Foundation                      0x000000019309c1a4 -[NSNotificationCenter postNotificationName:object:userInfo:] + 68
20  MYAPP                       0x0000000100eb693c MISettingsManager.setValueForSetting(_:_:) + 420156 (<compiler-generated>:0)
21  MYAPP                       0x0000000100eb8920 MISettingsManager.setSettingsValue(key:value:) + 428320 (MISettingsManager.swift:375)
22  MYAPP                       0x0000000100eb99b0 MISettingsManager.validateMDMSettings(url:system:user:) + 432560 (MISettingsManager.swift:422)
23  MYAPP                       0x0000000100eb7fe4 MISettingsManager.checkAndReadMDMSettings() + 425956 (<compiler-generated>:0)
24  MYAPP                       0x0000000100ebe2d0 specialized closure #1 in static MISettingsManager.instance.getter + 451280 (<compiler-generated>:0)
25  MYAPP                       0x0000000100eb1b24 thunk for @escaping @callee_guaranteed (@in_guaranteed Notification) -> () + 400164 (<compiler-generated>:0)
26  Foundation                      0x00000001930c5ef0 -[__NSObserver _doit:] + 316

```

Is the preferences value a string or a dictionary?. You are trying to fetch a dictionary but you said that the value is a string and the crash log indicates that iOS is fetching a string. — Paulw11, May 18 '20 at 20:46
It should be a dictionary. I also tried using `defaults.object(forKey:...)` but its also crashing. I followed the answer [here](https://stackoverflow.com/a/43124181) and [here](https://stackoverflow.com/questions/29231487/ios-8-mdm-managed-app-configuration-doesnt-work) — robidd, May 19 '20 at 05:44

score 0 · Answer 1 · answered Nov 12 '21 at 17:26

Infinite loop. You are writing to UserDefaults in the same method that fires as a result of the observer that fires whenever UserDefaults is modified.

Fix: don't write to UserDefaults as a side-effect of a method that is the target of an observer that fires whenever UserDefaults is written to.

ios - swift - read MDM config from UserDefaults

1 Answers1