Rework IP range filtering for clarity, add 172.16/12

Signed-off-by: Clinton Wolfe <clintoncwolfe@gmail.com>

lib/inspec/resources/interfaces.rb

@@ -24,32 +24,33 @@ module Inspec::Resources
       .install_filter_methods_on_resource(self, :scan_interfaces)
 
     def ipv4_address
+      require "ipaddr"
+
       # Loop over interface names
       # Select those that are up and have an ipv4 address
       interfaces = names.map { |n| inspec.interface(n) }.select do |i|
         i.ipv4_address? && i.up?
       end
 
-      all_addrs = interfaces.map(&:ipv4_addresses).flatten
+      addrs = interfaces.map(&:ipv4_addresses).flatten.map { |a| IPAddr.new(a) }
 
       # Look for progressively "better" IP addresses
+      [
+        # Loopback and private IP ranges
+        IPAddr.new("127.0.0.0/8"),
+        IPAddr.new("192.168.0.0/16"),
+        IPAddr.new("172.16.0.0/12"),
+        IPAddr.new("10.0.0.0/8"),
+      ].each do |private_range|
+        filtered_addrs = addrs.reject { |a| private_range.include?(a) }
+        if filtered_addrs.empty?
+          # Everything we had was a private or loopback IP. Return the "best" thing we were left with.
+          return addrs.first.to_s
+        end
 
-      # Reject anything that looks loopback-ish
-      non_loopback_addrs = all_addrs.reject { |a| a =~ /^127/ }
-      return all_addrs.first if non_loopback_addrs.empty?
-
-      # OK, we have something that isn't loopbackish.
-      # Try to filter out management networks.
-      non_management_addrs = non_loopback_addrs.reject { |a| a =~ /^10\./ }
-      return non_loopback_addrs.first if non_management_addrs.empty?
-
-      # OK, we have something that isn't management.
-      # Check for local networks.
-      non_local_addrs = non_management_addrs.reject { |a| a =~ /^192\.168/ }
-      return non_management_addrs.first if non_local_addrs.empty?
-
-      # Whatever is left is the best guess
-      non_local_addrs.first
+        addrs = filtered_addrs
+      end
+      addrs.first.to_s
     end
 
     private