systemd-analyze: add new 'security' option to allow user to choose custom requirements

A new option --security-policy= is added to work with the 'security' verb in order to enable
users to create and pass in a JSON file consisting of user defined requirements
against which to compare the specified unit file(s). These requirements then serve
as the measure of security threats for the file instead of the initial hard coded set of
requirements that the 'security' verb of systemd-analyze relied on.

Example Run:

A snapshot of the user defined testfile.json file is shown below instead of the complete file
for readability purposes.

{
"PrivateDevices":
    {"description_good": "Service has no access to hardware devices",
    "description_bad": "Service potentially has access to hardware devices",
    "weight": 1000,
    "range": 1
    },
"PrivateMounts":
    {"description_good": "Service cannot install system mounts",
    "description_bad": "Service may install system mounts",
    "weight": 1000,
    "range": 1
    },
"PrivateNetwork":
    {"description_good": "Service has no access to the host's network",
    "description_bad": "Service has access to the host's network",
    "weight": 2500,
    "range": 1
    },
"PrivateTmp":
    {"description_good": "Service has no access to other software's temporary files",
    "description_bad": "Service has access to other software's temporary files",
    "weight": 1000,
    "range": 1
    },
"PrivateUsers":
    {"description_good": "Service does not have access to other users",
    "description_bad": "Service has access to other users",
    "weight": 1000,
    "range": 1
    }
}

1. I created the jsontest.service file in order to test the --security-policy= option as follows:

maanya-goenka@debian:~/systemd (custom-security)$ cat<<EOF>jsontest.service
> [Service]
> ExecStart = echo hello
> PrivateNetwork = yes
> PrivateDevices = yes
> PrivateMounts = yes
> EOF

The security analysis table outputted below has been truncated to include only the first few lines for readability.

maanya-goenka@debian:~/systemd (custom-security)$ sudo build/systemd-analyze security --root= --offline=true
--security-policy=src/analyze/testfile.json jsontest.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
✓ PrivateNetwork                                               Service has no access to the host's network
✗ UserOrDynamicUser                                            Service runs as root user
✗ CapabilityBoundingSet_CAP_SET_UID_GID_PCAP                   Service may change UID/GID identities/capabilities
✓ PrivateMounts                                                Service cannot install system mounts
✓ PrivateDevices                                               Service has no access to hardware devices

→ Overall exposure level for jsontest.service: 8.3 EXPOSED 🙁

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

2. In order to ensure that the JSON data was actually being correctly parsed, I made some changes to the JSON
file, specifically to the id "PrivateNetwork" as follows:

Before:
--------

"PrivateNetwork":
    {"description_good": "Service has no access to the host's network",
    "description_bad": "Service has access to the host's network",
    "weight": 2500,
    "range": 1
    }

After:
--------

"PrivateNetwork":
    {"description_good": "Service runs without access to host network",
    "description_bad": "Service has access to the host's network",
    "weight": 6000,
    "range": 1
    }

As expected, the new description for the description_good field of the Private Network id was updated in
the analysis table outputted below and the overall exposure level of the unit file decreased because
the weight assigned to 'Private Network' (which is set to yes) increased from 2500 to 6000.

maanya-goenka@debian:~/systemd (custom-security)$ sudo build/systemd-analyze security --root= --offline=true
--security-policy=src/analyze/testfile.json jsontest.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
✓ PrivateNetwork                                               Service runs without access to the host's network
✗ UserOrDynamicUser                                            Service runs as root user
✗ CapabilityBoundingSet_CAP_SET_UID_GID_PCAP                   Service may change UID/GID identities/capabilities
✓ PrivateMounts                                                Service cannot install system mounts
✓ PrivateDevices                                               Service has no access to hardware devices

→ Overall exposure level for jsontest.service: 7.8 EXPOSED 🙁

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

3. When paired with security's --threshold= option, systemd-analyze exits with a non-zero error status indicating
that the overall exposure level for the unit file (=78) is greater than the set threshold (=70). The same
jsontest.service file is used for the demo run below:

maanya-goenka@debian:~/systemd (custom-security)$ sudo build/systemd-analyze security --root= --offline=true
--security-policy=src/analyze/testfile.json --threshold=70 jsontest.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
✓ PrivateNetwork                                               Service runs without access to host network
✗ UserOrDynamicUser                                            Service runs as root user
✗ CapabilityBoundingSet_CAP_SET_UID_GID_PCAP                   Service may change UID/GID identities/capabilities
✓ PrivateMounts                                                Service cannot install system mounts
✓ PrivateDevices                                               Service has no access to hardware devices

→ Overall exposure level for jsontest.service: 7.8 EXPOSED 🙁

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

new option

2 files changed, 2 insertions, 1 deletions

diff --git a/shell-completion/bash/systemd-analyze b/shell-completion/bash/systemd-analyze
index 6f33d53cfc..07d069a6d7 100644
--- a/shell-completion/bash/systemd-analyze
+++ b/shell-completion/bash/systemd-analyze
@@ -144,7 +144,7 @@ _systemd_analyze() {
 
     elif __contains_word "$verb" ${VERBS[SECURITY]}; then
         if [[ $cur = -* ]]; then
-            comps='--help --version --no-pager --system --user -H --host -M --machine --offline --threshold'
+            comps='--help --version --no-pager --system --user -H --host -M --machine --offline --threshold --security-policy'
         else
             if __contains_word "--user" ${COMP_WORDS[*]}; then
                 mode=--user
diff --git a/shell-completion/zsh/_systemd-analyze b/shell-completion/zsh/_systemd-analyze
index f91357cb61..3b77c3b938 100644
--- a/shell-completion/zsh/_systemd-analyze
+++ b/shell-completion/zsh/_systemd-analyze
@@ -92,6 +92,7 @@ _arguments \
     '--recursive-errors=[When verifying a unit, control dependency verification]:MODE' \
     '--offline=[Perform a security review of the specified unit file(s)]:BOOL' \
     '--threshold=[Set a value to compare the overall security exposure level with]: NUMBER' \
+    '--security-policy=[Allow user to use customized requirements to compare unit file(s) against]: PATH' \
     '--no-pager[Do not pipe output into a pager]' \
     '--man=[Do (not) check for existence of man pages]:boolean:(1 0)' \
     '--order[When generating graph for dot, show only order]' \