Foreign uninstall registry keys can cause errors in Get-IcingaAgentInstallation

[Donien]

Problem

Icinga for Windows uses registry keys for its uninstallation (Icinga agent).

To determine what to uninstall, registry keys under HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\* (and HKLM:\Software\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*) are searched.
Each key found tests for the DisplayName -eq 'Icinga 2'.

Since any program can write keys into this registry path, they can actually cause problems.
I've just had the problem that one program added its key but had no DisplayName attribute.

When comparing DisplayName this portion of the code simply fails/crashes, i.e. Get-IcingaAgentInstallation always fails.

Simplified: Get-ItemProperty 'HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\*' fails

Proposed solution

Before testing DisplayName -eq 'Icinga 2' the code should also test if the attribute DisplayName exists for the given registry key in the first place.

Related part of the code:

icinga-powershell-framework/lib/core/icingaagent/getters/Get-IcingaAgentInstallation.psm1

Lines 3 to 19 in 854ef78

	[string]$architecture = '';
	if ([IntPtr]::Size -eq 4) {
	$architecture = "x86";
	$regPath = 'HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\*';
	} else {
	$architecture = "x86_64";
	$regPath = @('HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\*', 'HKLM:\Software\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*');
	}
	$RegistryData = Get-ItemProperty $regPath;
	$IcingaData = $null;
	foreach ($entry in $RegistryData) {
	if ($entry.DisplayName -eq 'Icinga 2') {
	$IcingaData = $entry;
	break;
	}
	}