[SR-6143] Crash from static UUID._unconditionallyBridgeFromObjectiveC(_:)

[swift-ci]

Previous ID	SR-6143
Radar	https://bugreport.apple.com/web/?problemID=38213021
Original Reporter	rexmas (JIRA User)
Type	Bug
Status	Reopened
Resolution

Attachment: Download

Environment

iOS 13.x.x

Xcode 11.4

Swift 5

Additional Detail from JIRA

Votes	6
Component/s	Foundation
Labels	Bug, RunTimeCrash
Assignee	None
Priority	Medium

md5: 315dfe10afb0709dfc204bfedd91b325

Issue Description:

We're getting a random crash, affecting a very significant number of our users. Unfortunately we have not been able to reproduce the crash.

The crash occurs while trying to update a header in our networking stack. We update UUID for the applications session, using an NSUUID. At the point where we read the NSUUID for the session (which is in ObjC) we get an implicit call to

UUID._unconditionallyBridgeFromObjectiveC(_:)

to cast to UUID. This UUID is converted to a string to assign to the header it. This is where it crashes.

We are on Swift 3.2 and the crash only happens on iOS 11.x.x.

The Session object is Optional so the NSUUID that is read and cast is an Optional type, NSUUID?, via optional chaining.

I looked at the source on master https://github.com/apple/swift-corelibs-foundation/blob/f550ea64a4736222b5d32d7a95e1669d31d238b9/Foundation/UUID.swift#L153 and it appears to be implicitly unwrapping an optional type (haven't checked if this is different than swift 3.2). Is it possibly crashing because the value may be nil?

Relevant callstack

Crashed: com.apple.main-thread
EXC_BREAKPOINT 0x0000000106f035f4
0 libswiftFoundation.dylib 0x106f035f4 static UUID._unconditionallyBridgeFromObjectiveC(_:) + 60920
1 Remind101 0x104bb0c38 specialized RDHTTPHeaderable.setSessionUUIDGeneric() -> () (AFHTTPRequestSerializer+Headers.swift:78)
2 Remind101 0x104bb1114 @objc AFHTTPRequestSerializer.setSessionUUID() -> () (AFHTTPRequestSerializer+Headers.swift:131)
3 Remind101 0x1048b7db4 -[RDAPICommunicator setSessionUuid] (RDAPICommunicator.m:121)
4 CoreFoundation 0x18277212c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 20
5 CoreFoundation 0x1827716cc _CFXRegistrationPost + 420
6 CoreFoundation 0x182771430 ___CFXNotificationPost_block_invoke + 60
7 CoreFoundation 0x1827ee9f4 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1408
8 CoreFoundation 0x1826a83e0 _CFXNotificationPost + 380
9 Foundation 0x1830c8498 -[NSNotificationCenter postNotificationName:object:userInfo:] + 68
10 Remind101 0x1048bf4a4 +[RDSession beginNewSession] (RDSession.m:85)
11 Remind101 0x104977944 -[RDAppDelegate applicationDidBecomeActive:] (RDAppDelegate.m:297)

{{}}

[belkadan]

The unconditional unwrap there shouldn't matter—the unconditionallyBridge… function shouldn't even be called unless you're in the non-optional branch of the chain. Is it possible for you to share your project, or a toy project where this reproduces?

[swift-ci]

Comment by Mathäus Zingerle (JIRA)

We are having the same problem. Only occurred 3 times for 1 user so far though.

Crashed: com.apple.main-thread
0  libswiftFoundation.dylib       0x104c1be18 static UUID._unconditionallyBridgeFromObjectiveC(_:) + 60624
...
20 libdyld.dylib                  0x183b5856c start + 4

Happened on an iPad Pro (9.7 inch) with iOS 11.2.6.
We are on Xcode 9.2.

[belkadan]

@swift-ci create

[swift-ci]

Comment by Ben Pious (JIRA)

Does your UUID come from ASIdentifierManager.advertisingIdentifier by any chance? It's misannotated as nonnull. Not sure if that should be a Radar or if it should be an issue here.

[swift-ci]

Comment by Mathäus Zingerle (JIRA)

It actually does, yes. That's how we call it:

ASIdentifierManager.shared().advertisingIdentifier.uuidString

You are correct.

var advertisingIdentifier: UUID { get }

vs.

If the value is nil, wait and get the value again later. This happens, for example, after the device has been restarted but before the user has unlocked the device.

I'll create a Radar. That really should be fixed.

[swift-ci]

Comment by Rex Fenley (JIRA)

For the record, this wasn't the case for us. We don't use advertisingIdentifier anywhere in our codebase.

[swift-ci]

Comment by Fabian Ehrentraud (JIRA)

i have also created a radar: https://bugreport.apple.com/web/?problemID=38213021

[swift-ci]

Comment by Fabian Ehrentraud (JIRA)

as recommended by @belkadan, we should use an objc wrapper function with correct nullability: https://forums.swift.org/t/is-it-safe-to-cast-a-nonnull-objc-type-to-a-swift-optional/10658/2?u=fabb

[keith]

I've duped the radar about this publicly so it's easier for others to dup as well http://www.openradar.me/46397907

Note another case where you get hit by this is if you run a XCTest bundle on a simulator that isn't booted.

[belkadan]

The original Radar has been specifically connected to a nil advertising identifier. You probably should not dup it for any other case.

I'm going to close this JIRA since Swift/Foundation is behaving as best it can.

[swift-ci]

Comment by Rex Fenley (JIRA)

@belkadan fwiw I did not report this in association with using an advertising identifier. However, haven't seen this crash in quite a while either so I assumed it got fixed somewhere along the way.

[swift-ci]

Comment by wentaozone (JIRA)

My colleague recently ran into this problem on iOS 13 phones

struct APPInfoHelper {
    static func deviceId()->String{
        var idfa = ASIdentifierManager.shared().advertisingIdentifier.uuidString;
        if idfa == "" {
            idfa = "unknown"
        }
        return idfa
    }
}

[swift-ci]

Comment by Brodie Sellar (JIRA)

Hello,

We got one crash on iOS 13 today. From what I understand, there is some case where advertisingIdentifer can be nil and this make Swift crash.

Any idea when advertisingIdentifier can be nil ? I want to be able to reproduce this to test the following solution (from this [post|http://example.com|https://forums.swift.org/t/is-it-safe-to-cast-a-nonnull-objc-type-to-a-swift-optional/10658/4]):

extension ASIdentifierManager {
    public var safeAdvertisingIdentifier: UUID? {
        return self.perform(#selector(getter: ASIdentifierManager.advertisingIdentifier))?.takeUnretainedValue() as? UUID
    }
}

Exception:

Crashed: com.apple.main-thread
0 libswiftFoundation.dylib 0x1ee2394e0 static UUID.unconditionallyBridgeFromObjectiveC(🙂 + 108

[swift-ci]

Comment by wentaozone (JIRA)

Brodie (JIRA User) Thank you for your reply:

I'm going to use objc today, but the implementation you provided is more elegant, thank you very much.

I am not sure clear repetition steps, now may be the appearance of this path, the App into background back to the front desk is trigger unlock (and fail to unlock), at this time in applicationWillEnterForeground get advertisingIdentifier.uuidString prone to.

By the way, are you an engineer from Swift Team?

[swift-ci]

Comment by Claus Jørgensen (JIRA)

This haven't been fixed in iOS 14.0 or 14.1 either.