Fix subfolders in encrypted folders

[daniele-verducci]

How to repro:

• create encrypted folder
• create encrypted subfolder inside the one just created
• app crashes

How to repro 2:

• enter encrypted folder
• enter encrypted subfolder inside the previous one
• app crashes

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• ⛑️ Tests (unit and/or integration) are included or not needed
• 🔙 Backport requests are created or not needed: /backport to stable-xx.x
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[github-actions]

APK file: https://github.com/nextcloud/android/actions/runs/34505348733/artifacts/10163844801
To test this change/fix you can simply download above APK file and install and test it in parallel to your existing Nextcloud app.
(please click on link to get QR code displayed)

[github-actions]

master-IT test failed: https://www.kaminsky.me/nc-dev/android-integrationTests/17608-IT-master-17-26

[github-actions]

📱 QA build

Download	app-qa-debug.apk (76M)
QR code	Open the QR code for this download
Commit	d374ffa
Version	17608
Available until	7 days after this build

The QA build installs alongside a released Nextcloud app, so you can keep
using your existing install while testing.

Downloading the file requires a GitHub account, so open this link on the
device you want to test on, or transfer the APK to it.

[codecov]

Codecov Report

❌ Patch coverage is 7.14286% with 13 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../java/com/nextcloud/utils/e2ee/E2EEKeyInspector.kt	0.00%	12 Missing ⚠️
...va/com/owncloud/android/utils/EncryptionUtilsV2.kt	0.00%	0 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[alperozturk96]

Could you please share the crash-log and explain your approach?

[alperozturk96]

Why we are trying to decrypt the decrypted metadata key here?

[daniele-verducci]

I see, this doesn't make sense. The result is not used, so I believe this call in the previous code was used to throw an exception if the key isn't valid. Is it a correct interpretation?

In that case, maybe I can get directly the key with retrieveTopMostMetadataKey(). It should throw an exception as well.
But then should I verify the key in any way?

[daniele-verducci]

Could you please share the crash-log and explain your approach?

Hey Alper, here's the crashlog:

2026-09-14 12:06:21.801  4737-4737  AndroidRuntime          com.nextcloud.client                 E  FATAL EXCEPTION: main
                                                                                                    Process: com.nextcloud.client, PID: 4737
                                                                                                    java.lang.NullPointerException: Attempt to invoke interface method 'java.util.Iterator java.lang.Iterable.iterator()' on a null object reference
                                                                                                    	at com.nextcloud.utils.e2ee.E2EEKeyInspector.decryptsMetadataV2(E2EEKeyInspector.kt:117)
                                                                                                    	at com.nextcloud.utils.e2ee.E2EEKeyInspector.access$decryptsMetadataV2(E2EEKeyInspector.kt:33)
                                                                                                    	at com.nextcloud.utils.e2ee.E2EEKeyInspector$canDecryptFolderMetadata$2.invokeSuspend(E2EEKeyInspector.kt:105)
                                                                                                    	at com.nextcloud.utils.e2ee.E2EEKeyInspector$canDecryptFolderMetadata$2.invoke(E2EEKeyInspector.kt:8)
                                                                                                    	at com.nextcloud.utils.e2ee.E2EEKeyInspector$canDecryptFolderMetadata$2.invoke(E2EEKeyInspector.kt:4)
                                                                                                    	at kotlinx.coroutines.intrinsics.UndispatchedKt.startUndispatched(Undispatched.kt:66)
                                                                                                    	at kotlinx.coroutines.intrinsics.UndispatchedKt.startUndispatchedOrReturn(Undispatched.kt:43)
                                                                                                    	at kotlinx.coroutines.BuildersKt__Builders_commonKt.withContext(Builders.common.kt:497)
                                                                                                    	at kotlinx.coroutines.BuildersKt.withContext(dex-id-4119e2f2b95ce035797d115b10131393af91e27e:1)
                                                                                                    	at com.nextcloud.utils.e2ee.E2EEKeyInspector.canDecryptFolderMetadata(E2EEKeyInspector.kt:86)
                                                                                                    	at com.nextcloud.utils.e2ee.E2EEActionResolver$checkFolderMetadataKey$2.invokeSuspend(E2EEActionResolver.kt:44)
                                                                                                    	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:34)
                                                                                                    	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100)
                                                                                                    	at kotlinx.coroutines.internal.LimitedDispatcher$Worker.run(LimitedDispatcher.kt:124)
                                                                                                    	at kotlinx.coroutines.scheduling.TaskImpl.run(Tasks.kt:89)
                                                                                                    	at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:586)
                                                                                                    	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:798)
                                                                                                    	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:717)
                                                                                                    	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:704)
                                                                                                    	Suppressed: kotlinx.coroutines.internal.DiagnosticCoroutineContextException: [StandaloneCoroutine{Cancelling}@5e01fcc, Dispatchers.Main.immediate]

This happens when opening a subfolder on an encrypted folder. The crash is caused by the users array being empty/null (the user is used to retrieve the key).
I checked on the web watching the requests and I saw the users array being empty there as well, so I figured out they are using the parent encrypted folder's key.
I then replaced the piece of code that obtains the user array from the current folder with one that retrieves the topmost encrypted folder (that always has the users array populated) and uses its key.

I can say it works, but I'm not sure it's the correct fix. What do you think about it?

[daniele-verducci]

@alperozturk96 Can you check last commit? Could it be a solution?

[github-actions]

blue-Light-Screenshot test failed, but no output was generated. Maybe a preliminary stage failed.

[github-actions]

Codacy

SpotBugs

Category	Base	New
Bad practice	32	32
Correctness	58	58
Dodgy code	186	186
Experimental	1	1
Malicious code vulnerability	2	2
Multithreaded correctness	26	26
Performance	37	37
Security	18	18
Total	360	360

[daniele-verducci]

Completed, but do not merge until the encrypted folder tests are implemented (in a separate PR).

[alperozturk96]

Completed, but do not merge until the encrypted folder tests are implemented (in a separate PR).

You can put this PR in a draft then activate again later :)