systemd-analyze: 'security' option to perform offline reviews of the specified unit file(s)

New option --offline which works with the 'security' command and takes in a boolean value. When set to true,
it performs an offline security review of the specified unit file(s). It does not rely on PID 1 to acquire
security information for the files like 'security' when used by itself does. It makes use of the refactored
security_info struct instead (commit #8cd669d3d3cf1b5e8667acc46ba290a9e8a8e529). This means that --offline can be
used with --image and --root as well. When used with --threshold, if a unit's overall exposure level is above
that set by the user, the default value being 100, --offline returns a non-zero exit status.

Example Run:

1. testcase.service is a unit file created for testing the --offline option

maanya-goenka@debian:~/systemd (systemd-security)$ cat<<EOF>testcase.service

> [Service]
> ExecStart = echo hello
> EOF

For the purposes of this demo, the security table outputted below has been cut to show only the first two security settings.

maanya-goenka@debian:~/systemd (systemd-security)$ sudo build/systemd-analyze security --offline=true testcase.service
/usr/lib/systemd/system/plymouth-start.service:15: Unit configured to use KillMode=none. This is unsafe, as it disables systemd's
process lifecycle management for the service. Please update your service to use a safer KillMode=, such as 'mixed' or 'control-group'.
Support for KillMode=none is deprecated and will eventually be removed.
/usr/lib/systemd/system/gdm.service:30: Standard output type syslog is obsolete, automatically updating to journal. Please update your
unit file, and consider removing the setting altogether.
/usr/lib/systemd/system/dbus.socket:5: ListenStream= references a path below legacy directory /var/run/, updating
/var/run/dbus/system_bus_socket → /run/dbus/system_bus_socket; please update the unit file accordingly.

  NAME                                        DESCRIPTION                                                       EXPOSURE
✗ PrivateNetwork=                             Service has access to the host's network                          0.5
✗ User=/DynamicUser=                          Service runs as root user                                         0.4

→ Overall exposure level for testcase.service: 9.6 UNSAFE 😨

maanya-goenka@debian:~/systemd (systemd-security)$ echo $? 0

2. The testcase.service unit file is modified to set PrivateNetwork to "yes". This reduces the exposure level from 9.6 to 9.1.

maanya-goenka@debian:~/systemd (systemd-security)$ nano testcase.service

> [Service]
> ExecStart = echo hello
> PrivateNetwork = yes
> EOF

maanya-goenka@debian:~/systemd (systemd-security)$ sudo build/systemd-analyze security --offline=true testcase.service
/usr/lib/systemd/system/plymouth-start.service:15: Unit configured to use KillMode=none. This is unsafe, as it disables systemd's
process lifecycle management for the service. Please update your service to use a safer KillMode=, such as 'mixed' or 'control-group'.
Support for KillMode=none is deprecated and will eventually be removed.
/usr/lib/systemd/system/gdm.service:30: Standard output type syslog is obsolete, automatically updating to journal. Please update your
unit file, and consider removing the setting altogether.
/usr/lib/systemd/system/dbus.socket:5: ListenStream= references a path below legacy directory /var/run/, updating
/var/run/dbus/system_bus_socket → /run/dbus/system_bus_socket; please update the unit file accordingly.

  NAME                                        DESCRIPTION                                                       EXPOSURE
✓ PrivateNetwork=                             Service has access to the host's network
✗ User=/DynamicUser=                          Service runs as root user                                         0.4

→ Overall exposure level for testcase.service: 9.1 UNSAFE 😨

maanya-goenka@debian:~/systemd (systemd-security)$ echo $? 0

3. Next, we use the same testcase.service unit file but add the additional --threshold=60 option to see how --threshold works with
--offline. Since the overall exposure level is 91 which is greater than the threshold value set by the user (= 60), we can expect
a non-zero exit status.

maanya-goenka@debian:~/systemd (systemd-security)$ sudo build/systemd-analyze security --offline=true --threshold=60 testcase.service
/usr/lib/systemd/system/plymouth-start.service:15: Unit configured to use KillMode=none. This is unsafe, as it disables systemd's
process lifecycle management for the service. Please update your service to use a safer KillMode=, such as 'mixed' or 'control-group'.
Support for KillMode=none is deprecated and will eventually be removed.
/usr/lib/systemd/system/gdm.service:30: Standard output type syslog is obsolete, automatically updating to journal. Please update your
unit file, and consider removing the setting altogether.
/usr/lib/systemd/system/dbus.socket:5: ListenStream= references a path below legacy directory /var/run/, updating
/var/run/dbus/system_bus_socket → /run/dbus/system_bus_socket; please update the unit file accordingly.

  NAME                                        DESCRIPTION                                                       EXPOSURE
✓ PrivateNetwork=                             Service has access to the host's network
✗ User=/DynamicUser=                          Service runs as root user                                         0.4

→ Overall exposure level for testcase.service: 9.1 UNSAFE 😨

maanya-goenka@debian:~/systemd (systemd-security)$ echo $? 1

1 files changed, 12 insertions, 0 deletions

diff --git a/man/systemd-analyze.xml b/man/systemd-analyze.xml
index 48976f52bf..3c276360cd 100644
--- a/man/systemd-analyze.xml
+++ b/man/systemd-analyze.xml
@@ -771,6 +771,18 @@ Service b@0.service not loaded, b.socket cannot be started.
       </varlistentry>
 
       <varlistentry>
+        <term><option>--offline=<replaceable>BOOL</replaceable></option></term>
+
+        <listitem><para>With <command>security</command>, perform an offline security review
+        of the specified unit file(s), i.e. does not have to rely on PID 1 to acquire security
+        information for the files like the <command>security</command> verb when used by itself does.
+        This means that <option>--offline=</option> can be used with <option>--root=</option> and
+        <option>--image=</option> as well. If a unit's overall exposure level is above that set by
+        <option>--threshold=</option> (default value is 100), <option>--offline=</option> will return
+        an error.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
         <term><option>--iterations=<replaceable>NUMBER</replaceable></option></term>
 
         <listitem><para>When used with the <command>calendar</command> command, show the specified number of