Checkmk Werk 14827: Re-work agent plugin for monitoring SSH daemon configuration

ID: 14827 Title: Re-work agent plugin for monitoring SSH daemon configuration Component: Checks & agents Level: 1 Class: Bug fix Version: 2.2.0i1 The agent plugin for monitoring the SSH daemon configuration (<tt>mk_sshd_config</tt>) has been re-worked. The previous version of the plugin used the contents of <tt>/etc/ssh/sshd_config</tt> to monitor the daemon configuration. This is problematic in multiple ways: LI: Include directives, such as <tt>Include /etc/ssh/sshd_config.d/*.conf</tt>, are not taken into account, resulting in potentially wrong monitoring results. LI: Match directives are evaluated incorrectly, leading to monitoring results such as "PasswordAuthentication: noyes". LI: Defaults are not taken into account properly. For example, under Ubuntu, the default is that password authentication is enabled if not explictly configured differently. The re-worked version of the agent plugin reports the effective daemon configuration queried via <tt>sshd -T</tt>. This evaluates include directives and takes into daemon defaults, but does explicitly not evaluate Match directives. Hence, as an example, even if Checkmk reports that password authentication is off, this does not garantuee that no user can ssh into the system using a password. This werk is marked as incompatible for two reasons: LI: The behavioural changes listed above. LI: <tt>sshd -T</tt> will likely require root permissions to execute successfully. Hence, the new version of the plugin will likely not work on systems where the agent is executed as non-root.