How To Do Privilege Elevation on OSX with Objective C

Question

My custom Cocoa-based setup.app on Mac OSX that I made in Objective C needs to install a LaunchDaemon for doing elevated privilege tasks such as an antivirus program that needs to scan the entire hard drive and therefore needs root privileges. How can I make my setup application prompt the customer for their admin login and then install that LaunchDaemon into /Library/LaunchDaemons (and note I don't mean ~/Library/LaunchDaemons)?

The way I'm currently handling it is by using AppleScript with the admin privilege. It prompts for this login and then the AppleScript does the copying into this folder without the OS complaining. However, I assume that's not the proper technique -- that I should be doing this entirely in Objective C somehow?

Note that I can't use SMBlessJob in this case because it is for this reason that I'm creating the Launch Daemon in the first place.

BACKGROUND INFORMATION

I have a special need to create a custom setup.app -- just like the fact that Norton's AV application uses a custom setup.app. This is because the Apple PKG and DMG installers do not permit downloading of very large files (like virus definitions) from a server during install with some kind of friendly feedback. I mean, I can make a PKG file download a file from the server when running a Perl script or Bash script, but then the installer just hangs the progress bar for the amount of minutes it takes to download, not giving any other feedback to the user except that hung progress bar, and so the user thinks the installer is broke, when it's not. That's why I had to make my own custom setup.app, just like Norton did for their AV application.

Answer 1

Normally, SMJobBless would be the technique to do this. It's the one Apple recommends now as of 2016. Here's the readme.txt for Apple's sample project:

https://developer.apple.com/library/mac/samplecode/SMJobBless/Listings/ReadMe_txt.html

However, that's not the only way to do it. Another route would be to have your installer use AppleScript to prompt and run a Bash or Perl script with elevated privileges to install the LaunchDaemon, as well. (That's actually easier than SMJobBless.)

Basically, either technique installs a LaunchDaemon (e.g., "service") into a special folder, and that daemon can be set with elevated privileges, which can then run anything you want -- even command line commands. A super fantastic explanation of LaunchDaemons and LaunchAgents is here:

http://launchd.info/

Now, the problem is how to communicate with it from your application, once installed. They leave that up to you, and there are various techniques. However, they also leave it up to you to secure this so that it's not an attack vector.

A fantastic article on how to do IPC (Inter Process Communication between your application and this service) is here:

http://nshipster.com/inter-process-communication/

One IPC protocol on OSX is Distributed Objects, which is quite smooth from an architecture perspective -- you'll feel more like it's "coding" instead of "sending messages back and forth" like other IPC protocols. I've written a Stack Overflow post on this because the docs are shoddy and the existing examples on the Apple site and others are stale (won't compile on XCode7.1 with OSX 10.10+).

On communication protocol between your application and daemon/service, you can probably get away with key/value, XML, or JSON messages that are encrypted with AES256 with a long password and converted to Base64 encoding, and then use one of the various IPC mechanisms. However, that's another topic entirely.