Overview

Plan B is a remediation program for managed Macs. It is meant to be run to re-install other management software.

Features

• Secure download of disk images from an Internet-facing server.
• Installation of package files contained on the disk images.
• Validation of server certificate against explicitly trusted certificate authorities only.
• Support for client certificate authentication to ensure only trusted clients can access the server.
• URL construction to download packages based on a client’s configuration in a plist.
• Extensive logging of presented certificate details for auditing and MITM detection.
• No external dependencies; the compiled program is tiny and can be easily deployed.

Usage

First, create a Web server which will host disk images containing a single .pkg package file on each .dmg disk image file.

There is a shell script included in this directory to generate a public-key infrastructure, if one is not already in place. There are also many excellent guides and programs, like easy-rsa, available online.

If the server has enabled client certificate authentication, first install the client certificate and private key to system keychain. You may first need to convert them to PKCS#12 format with something like, openssl pkcs12 -export -in client.crt -inkey client.key -certfile ca.pem -out client.p12. Otherwise, the program will perform server certificate validation only.

Compiling Plan B requires a modern version of Xcode, available from Apple’s Developer site.

• Download the source code with git clone https://github.com/google/macops-planb

• Change directory into the repo cd macops-planb

• Install required CocoaPods with pod install

• Open the Xcode project with open planb.xcworkspace

• Edit main.m and change kBaseURL to the URL of the server and folder containing disk images. By default, the program will use https://mac.internal.megacorp.com/pkgs/

• Edit main.m and change the packages array to match the names of disk image names and their contained packages’ receipt names. By default, the program will construct pkg1/package1-stable.dmg and forget the receipt for package com.megacorp.package1 prior to re-installation, and so on.

• Edit main.m and change the kMachineInfo to match a machine information plist, which may contain a ConfigurationTrack value, for example. This value is used to construct the disk image suffix, like package1-stable.dmg, package1-testing.dmg or package1-unstable.dmg. This is useful if you have machines on multiple configuration tracks.

• Edit roots.pem and change the contents to include a single or multiple PEM-encoded certificate authority certificates you wish to trust for server validation. By default, the program will use GeoTrust Global CA, the authority used to sign Google’s intermediate CA, however you should use the CA which has signed the server’s certificate or the server’s intermediate certificate.

• Compile the program with xcodebuild -workspace planb.xcworkspace -scheme planb -configuration Release. It will appear in ./Build/Products/Release/planb

The planb binary must be run as root in order to install packages. It will run on its own without any external dependencies.

Deployment

It is recommended to create a simple script to determine the health of the machine, for example by checking the last successful run date of the primary management software, and running Plan B if the condition is not met. This script can then be started periodically as a system launch daemon.

Have a look at the planb_check shell script and the com.megacorp.planb.plist launch daemon property list for an example.

In our environment, we have a wrapper tool for Puppet, which verifies the configuration run was successful and updates the timestamp on a file. We track this in planb_check and base the decision to kick off planb from it.