This is an effort to compile a somewhat complete list how PCRs are
actually used on Linux systems these days. It contains data from: the
UEFI PC spec, the shim, the IMA, grub documentation.
I validated these PCRs to some level in the sources.
The grub specific stuff I only added in comments, since I was too lazy
too validate it (also, meh, grub).
It also gives people a hint on which PCR to bind to (and maybe kind of
an explanation of our default choice).
In the past bridge devices used to be created with a generated MAC address
thwarting the inheritance of the first slave's MAC address. This has been
changed by commit [1] some time ago. Reflect that behavioral change in the
documentation.
[1] deb2cfa4c6 ("networkd: do not generate MAC for bridge device.")
The new option --json= works with the 'security' verb and takes in one of three format flags.
These are off which is the default, pretty and short which use JSON format flags for output.
When set to true, it generates a JSON formatted output of the security analysis table. The
format is a JSON array with objects containing the following fields: set which indicates if
the id has been set or not, name which is what is used to refer to the id, json_field
which is the equivalent JSON formatted id name only used for JSON outputs, description which
is an outline of the id state, and exposure which is an unsigned integer in the range 0.0..10.0,
where a higher value corresponds to a higher security threat. The JSON version of the table is
printed on the standard output file.
Example Run:
The unit file testfile.service was created to test the --json= option
maanya-goenka@debian:~/systemd (json-security)$ cat <<EOF >testfile.service
> [Service]
> ExecStart = echo hello
> PrivateNetwork = yes
> PrivateMounts = yes
> PrivateDevices = yes
> EOF
Both the JSON output and the security analysis table below have been truncated to increase readability.
1. Testing for when --json=off
maanya-goenka@debian:~/systemd (json-security)$ sudo build/systemd-analyze security --json=off --root= --offline=true
testfile.service --no-pager
/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/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.
/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.
/home/maanya-goenka/systemd/foo.service:2: Unknown key name 'foo' in section 'Unit', ignoring.
NAME DESCRIPTION EXPOSURE
✓ PrivateNetwork= Service has no access to the host's network
✗ User=/DynamicUser= Service runs as root user 0.4
✗ CapabilityBoundingSet=~CAP_SET(UID|GID|PCAP) Service may change UID/GID identities/capabilities 0.3
✗ CapabilityBoundingSet=~CAP_NET_ADMIN Service has administrator privileges 0.3
→ Overall exposure level for testfile.service: 8.3 EXPOSED 🙁
2. Testing for when --json=pretty
maanya-goenka@debian:~/systemd (json-security)$ sudo build/systemd-analyze security --json=pretty --root= --offline=true
testfile.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/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.
/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.
/home/maanya-goenka/systemd/foo.service:2: Unknown key name 'foo' in section 'Unit', ignoring.
[
{
"set" : true,
"name" : "PrivateNetwork=",
"json-field" : "PrivateNetwork",
"description" : "Service has no access to the host's network",
"exposure" : null
},
{
"set" : false,
"name" : "User=/DynamicUser=",
"json-field" : "UserOrDynamicUser",
"decsription" : "Service runs as root user",
"exposure" : "0.4"
},
{
"set" : false,
"name" : "CapabilityBoundingSet=~CAP_SET(UID|GID|PCAP)",
"json_field" : "CapabilityBoundingSet_CAP_SET_UID_GID_PCAP",
"description" : "Service may change UID/GID identities/capabilities",
"exposure" : "0.3"
},
{
"set" : false,
"name" : "CapabilityBoundingSet=~CAP_NET_ADMIN",
"json_field" : "CapabilityBoundingSet_CAP_NET_ADMIN",
"description" : "Service has administrator privileges",
"exposure" : "0.3"
},
...
]
3. Testing for when --json=short
maanya-goenka@debian:~/systemd (json-security)$ sudo build/systemd-analyze security --json=short --root= --offline=true
testfile.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/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.
/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.
/home/maanya-goenka/systemd/foo.service:2: Unknown key name 'foo' in section 'Unit', ignoring.
[{"set":true,"name":"PrivateNetwork=", "json_field":"PrivateNetwork", "description":"Service has no access to the host's network","exposure":null}, ...]
For most fields, the text shown by `.id` is the value that should be set
in the unit file; however, for RestrictNamespaces, it is not. Changing
this to show the actual text makes it more clear to a user what the
actual change that needs to be made to the unit file is.
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 $? 1
new option
Previously volatile-root was only checked if "/" wasn't backed by a
block device, but the block device isn't necessarily original root block
device (ex: if the rootfs is copied to a ext4 fs backed by zram in the
initramfs), so we always want volatile-root checked.
So shuffle the code around so volatile-root is checked first and
fallback to the automatic logic.
Fix#20557
The `sd_path_lookup(3)` man page states that the returned string shall be
`free(3)`'d but then doesn't do so in the example code.
Also add basic error handling as well.
--threshold option added to work with security verb and with the --offline option so that
users can determine what qualifies as a security threat. The threshold set by the user is
compared with the overall exposure level assigned to a unit file and if the exposure is
higher than the threshold, 'security' will return a non-zero exit status. The default value
of the --threshold option is 100.
Example Run:
1. testcase.service is a unit file created for testing the --threshold option
maanya-goenka@debian:~/systemd (systemd-security)$ 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 $? 0
2. Next, we use the same testcase.service file but add an additional --threshold=60 parameter. We would expect 'security' to exit
with a non-zero status because the overall exposure level (= 96) is higher than the set threshold (= 60).
maanya-goenka@debian:~/systemd (systemd-security)$ 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 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 $? 1
New option --offline which works with the 'security' command and takes in a boolean value. When set to true,
it performs an offline security review of the specified unit file(s). It does not rely on PID 1 to acquire
security information for the files like 'security' when used by itself does. It makes use of the refactored
security_info struct instead (commit #8cd669d3d3cf1b5e8667acc46ba290a9e8a8e529). This means that --offline can be
used with --image and --root as well. When used with --threshold, if a unit's overall exposure level is above
that set by the user, the default value being 100, --offline returns a non-zero exit status.
Example Run:
1. testcase.service is a unit file created for testing the --offline option
maanya-goenka@debian:~/systemd (systemd-security)$ 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
Follow-up for 406041b7de.
Also, this makes
- the settings accept an empty string,
- if the specified value is too large, also use the advertised maximum
value.
- mention the range of the value in the man page.
"max" indicates the hardware advertised maximum queue buffer size
should be used.
The max sizes can be checked by running `ethtool -g <dev>` (Preset maximums).
Since the buffer sizes can't be set to 0 by users, internally we use 0 to
indicate that the hardware advertised maximum should be used.
Previously, when Priority= is unspecified, networkd configured the rule with
the highest (=0) priority. This commit makes networkd distinguish the case
the setting is unspecified and one explicitly specified as Priority=0.
Note.
1) If the priority is unspecified on configure, then kernel dynamically picks
a priority for the rule.
2) The new behavior is consistent with 'ip rule' command.
Replaces #15606.
