sandbox

~/Library/Keychains is…a file?

No, it’s actually not a file, it’s a directory. At least it’s supposed to be. But, multiple reports from multiple lab maintainers had been coming in that included error messages from applications which were trying and failing to access the user’s keychain store. I started troubleshooting by repairing the keychain with /Applications/Utilities/Keychain Access.app, but that did nothing aside from provide more of the same error messages. I suspected keychain corruption or possibly mucked up permissions, so I opened Terminal to take a look. ~/Library/Keychains was a file!

It took me a while to figure this one out, and now that I know what it was, I’m admittedly a little embarrassed. This is one for #macadminshame. For the machines I maintain directly, I manage the user environment with Local MCX. That’s not a technology that my lab maintainers are comfortable with; they’d much rather login using a special account, make their changes, and then rest comfortably knowing that those changes would be present for everyone who logged into their lab machines. I get that – we all have better things to do than learn about complex technologies that we’ll use less than 3 times annually. So I wrote a logout hook for them that ran when this special account logged out. The script empties the trash, clears caches and logs; generally cleans up the home directory for that account. Once cleaned, it bundles that home directory up in an installer package which I then import into Munki and deploy to the rest of their lab machines for them.

Of all the cleanup tasks that I had been doing, one very important one had slipped right by; ~/Library/Containers/. If you happen to update your Non_localized.lproj, English.lproj, .lproj directory like this (which isn’t recommended), please be sure to purge the contents of ~/Library/Containers.

I didn’t bother trying to figure out which container was touching ~/Library/Keychains because once I realized my error, I knew everything in there needed to go anyway. Moral of the story: Profiles/MCX is the way to go, but if you can’t, make sure you’re not putting anything in /System/Library/User\ Template/.lproj/Library/Containers/.

Also, if you find yourself already in this scenario (hopefully I’m the only one who will), you can fix existing home directories by deleting ~/Library/Keychains (as long as it’s a file, not a directory!) before the user’s next login.

 

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Sandboxing vs. LocalMCX

This is a (albeit late) follow up post to a conversation started over on MacEnterprise as well as the MunkiDev list.

If you use LocalMCX to manage machines, this post by Greg Neagle is probably very familiar to you. In it, Greg outlines some of the changes that came with dscl in Mountain Lion and how those changes affect Local MCX management. Basically, the changes were such that you could no longer use dscl or Workgroup Manager to create or modify MCX settings and groups in your custom (non-“Default”) node.

It turns out, we can still use those tools to edit and manage our custom nodes. The problem isn’t a rewrite of dscl to specifically reject custom local MCX nodes, as many of us suspected. It’s sandboxing.

So what changed? Mountain Lion is all about Sandboxing (which is a very good thing). Apple’s goal with its App Sandbox is to split applications into collections of binaries so that each of those binaries can be assigned only the permissions and resources that it needs to do its job. When Apple sandboxed opendirectoryd, they rightly gave it read/write access to /var/db/dslocal/nodes/Default and nothing else. This is actually very good news for us because sandbox permissions can be modified, meaning we can get Workgroup Manager to edit users/groups/etc directly in our custom node. Here’s how:

  1. Open /System/Library/Sandbox/Profiles/com.apple.opendirectoryd.sbin your favorite text editor
  2. Find the line referring to /var/db/dslocal/nodes/Default, should be line 43 (notice how this is under the allow file-write* container?)
  3. Insert a new line after that one with the following contents, making adjustments where needed for your local MCX path:
    #"^(/private)?/var/db/dslocal/nodes/MCX(/|$)"
    
  4. Reload the daemon, effectively forcing sandboxd to reload the permissions:
    killall opendirectoryd

Keep in mind, this only solves the problem of getting our favorite MCX editing tools back in our hands without the need to copy records back and forth between nodes, so it really wouldn’t make sense to push this out to all of your OS X client machines.

That’s it. You should now be able to use Workgroup Manager again to edit your local MCX settings, in place.