WireGuard Configurations Gone After iOS 15 Upgrade

Miguel Arroz miguel.arroz at gmail.com
Thu Sep 23 02:54:00 UTC 2021


  (Now without HTML…)

  I never wrote code touching the Keychain on iOS, but did on macOS using the iOS behaviour (kSecUseDataProtectionKeychain set to true).

  There are two things in that class that I would look into:

  - Line 40: items[kSecAttrAccessGroup] = FileManager.appGroupId

  If I understand correctly, this ends up being "group.$(APP_ID_IOS)”. I’m a bit surprised this doesn’t need the Team ID before “group”, as it definitely needs that in macOS.

  - The openReference() function, because it’s not setting the same kSecAttrAccessGroup parameter when reading. The documentation mentions what happens when it’s not set (https://developer.apple.com/documentation/security/ksecattraccessgroup), I wonder if that changed (intentionally or due to a bug in iOS 15):

> If you don’t explicitly set a group, keychain services defaults to the app’s first access group, which is either the first keychain access group, or the app ID when the app has no keychain groups.

  None of these explain why the tunnel keeps working after upgrading to iOS 15 (if the on-demand flag is set), as I would expect the Network Extension to hit the same problem, as it goes through the same Keychain code. But maybe the behaviour is slightly different than when it’s running through the app for some reason. It could explain why re-building the tunnels would work from then on (although then I would expect the extension to *not* be able to read them). So all this may be just a red herring.

  Hope it helps somehow.


Miguel Arroz

> On Sep 22, 2021, at 6:34 PM, Jason A. Donenfeld <Jason at zx2c4.com> wrote:
> Hey folks,
> Small update: I've managed to update a fresh 14 device to 15 using the
> latest build, and things are broken still.
> On the plus side:
> - The new build no longer deletes VPN profiles when the corresponding
> keychain references are unresolvable, so if there's any chance of
> recovery in a next build, it won't ruin those chances.
> - Now that I can reproduce it, I can hammer away at trying to fix this directly.
> On the minus side:
> - The fact that a keychain reference goes stale during an update from
> 14 to 15 sounds solidly like an Apple bug, rather than any sort of API
> misuse.
> - I'm skeptical that there'll be a workaround, and if there is, it
> will probably be pretty ugly.
> If anyone knows the SecItem APIs well, the file in question is:
> https://git.zx2c4.com/wireguard-apple/tree/Sources/Shared/Keychain.swift
> So, I guess I'll jump into this in full force now. Here we go...
> Jason

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