================================ Landlock: system-wide management

:Author: Mickaël Salaün :Date: January 2026

Landlock can leverage the audit framework to log events.

User space documentation can be found here: Documentation/userspace-api/landlock.rst.

Audit

Denied access requests are logged by default for a sandboxed program if audit is enabled. This default behavior can be changed with the sys_landlock_restrict_self() flags (cf. Documentation/userspace-api/landlock.rst). Landlock logs can also be masked thanks to audit rules. Landlock can generate 2 audit record types.

Record types

AUDIT_LANDLOCK_ACCESS This record type identifies a denied access request to a kernel resource. The domain field indicates the ID of the domain that blocked the request. The blockers field indicates the cause(s) of this denial (separated by a comma), and the following fields identify the kernel object (similar to SELinux). There may be more than one of this record type per audit event.

Example with a file link request generating two records in the same event::

    domain=195ba459b blockers=fs.refer path="/usr/bin" dev="vda2" ino=351
    domain=195ba459b blockers=fs.make_reg,fs.refer path="/usr/local" dev="vda2" ino=365


The ``blockers`` field uses dot-separated prefixes to indicate the type of
restriction that caused the denial:

**fs.*** - Filesystem access rights (ABI 1+):
    - fs.execute, fs.write_file, fs.read_file, fs.read_dir
    - fs.remove_dir, fs.remove_file
    - fs.make_char, fs.make_dir, fs.make_reg, fs.make_sock
    - fs.make_fifo, fs.make_block, fs.make_sym
    - fs.refer (ABI 2+)
    - fs.truncate (ABI 3+)
    - fs.ioctl_dev (ABI 5+)

**net.*** - Network access rights (ABI 4+):
    - net.bind_tcp - TCP port binding was denied
    - net.connect_tcp - TCP connection was denied

**scope.*** - IPC scoping restrictions (ABI 6+):
    - scope.abstract_unix_socket - Abstract UNIX socket connection denied
    - scope.signal - Signal sending denied

Multiple blockers can appear in a single event (comma-separated) when
multiple access rights are missing. For example, creating a regular file
in a directory that lacks both ``make_reg`` and ``refer`` rights would show
``blockers=fs.make_reg,fs.refer``.

The object identification fields (path, dev, ino for filesystem; opid,
ocomm for signals) depend on the type of access being blocked and provide
context about what resource was involved in the denial.

AUDIT_LANDLOCK_DOMAIN This record type describes the status of a Landlock domain. The status field can be either allocated or deallocated.

The ``allocated`` status is part of the same audit event and follows
the first logged ``AUDIT_LANDLOCK_ACCESS`` record of a domain.  It identifies
Landlock domain information at the time of the sys_landlock_restrict_self()
call with the following fields:

- the ``domain`` ID
- the enforcement ``mode``
- the domain creator's ``pid``
- the domain creator's ``uid``
- the domain creator's executable path (``exe``)
- the domain creator's command line (``comm``)

Example::

    domain=195ba459b status=allocated mode=enforcing pid=300 uid=0 exe="/root/sandboxer" comm="sandboxer"

The ``deallocated`` status is an event on its own and it identifies a
Landlock domain release.  After such event, it is guarantee that the
related domain ID will never be reused during the lifetime of the system.
The ``domain`` field indicates the ID of the domain which is released, and
the ``denials`` field indicates the total number of denied access request,
which might not have been logged according to the audit rules and
sys_landlock_restrict_self()'s flags.

Example::

    domain=195ba459b status=deallocated denials=3

Event samples

Here are two examples of log events (see serial numbers).

In this example a sandboxed program (kill) tries to send a signal to the init process, which is denied because of the signal scoping restriction (LL_SCOPED=s)::

$ LL_FS_RO=/ LL_FS_RW=/ LL_SCOPED=s LL_FORCE_LOG=1 ./sandboxer kill 1

This command generates two events, each identified with a unique serial number following a timestamp (msg=audit(1729738800.268:30)). The first event (serial 30) contains 4 records. The first record (type=LANDLOCK_ACCESS) shows an access denied by the domain 1a6fdc66f. The cause of this denial is signal scoping restriction (blockers=scope.signal). The process that would have receive this signal is the init process (opid=1 ocomm="systemd").

The second record (type=LANDLOCK_DOMAIN) describes (status=allocated) domain 1a6fdc66f. This domain was created by process 286 executing the /root/sandboxer program launched by the root user.

The third record (type=SYSCALL) describes the syscall, its provided arguments, its result (success=no exit=-1), and the process that called it.

The fourth record (type=PROCTITLE) shows the command's name as an hexadecimal value. This can be translated with python -c 'print(bytes.fromhex("6B696C6C0031"))'.

Finally, the last record (type=LANDLOCK_DOMAIN) is also the only one from the second event (serial 31). It is not tied to a direct user space action but an asynchronous one to free resources tied to a Landlock domain (status=deallocated). This can be useful to know that the following logs will not concern the domain 1a6fdc66f anymore. This record also summarize the number of requests this domain denied (denials=1), whether they were logged or not.

.. code-block::

type=LANDLOCK_ACCESS msg=audit(1729738800.268:30): domain=1a6fdc66f blockers=scope.signal opid=1 ocomm="systemd" type=LANDLOCK_DOMAIN msg=audit(1729738800.268:30): domain=1a6fdc66f status=allocated mode=enforcing pid=286 uid=0 exe="/root/sandboxer" comm="sandboxer" type=SYSCALL msg=audit(1729738800.268:30): arch=c000003e syscall=62 success=no exit=-1 [..] ppid=272 pid=286 auid=0 uid=0 gid=0 [...] comm="kill" [...] type=PROCTITLE msg=audit(1729738800.268:30): proctitle=6B696C6C0031 type=LANDLOCK_DOMAIN msg=audit(1729738800.324:31): domain=1a6fdc66f status=deallocated denials=1

Here is another example showcasing filesystem access control::

$ LL_FS_RO=/ LL_FS_RW=/tmp LL_FORCE_LOG=1 ./sandboxer sh -c "echo > /etc/passwd"

The related audit logs contains 8 records from 3 different events (serials 33, 34 and 35) created by the same domain 1a6fdc679::

type=LANDLOCK_ACCESS msg=audit(1729738800.221:33): domain=1a6fdc679 blockers=fs.write_file path="/dev/tty" dev="devtmpfs" ino=9 type=LANDLOCK_DOMAIN msg=audit(1729738800.221:33): domain=1a6fdc679 status=allocated mode=enforcing pid=289 uid=0 exe="/root/sandboxer" comm="sandboxer" type=SYSCALL msg=audit(1729738800.221:33): arch=c000003e syscall=257 success=no exit=-13 [...] ppid=272 pid=289 auid=0 uid=0 gid=0 [...] comm="sh" [...] type=PROCTITLE msg=audit(1729738800.221:33): proctitle=7368002D63006563686F203E202F6574632F706173737764 type=LANDLOCK_ACCESS msg=audit(1729738800.221:34): domain=1a6fdc679 blockers=fs.write_file path="/etc/passwd" dev="vda2" ino=143821 type=SYSCALL msg=audit(1729738800.221:34): arch=c000003e syscall=257 success=no exit=-13 [...] ppid=272 pid=289 auid=0 uid=0 gid=0 [...] comm="sh" [...] type=PROCTITLE msg=audit(1729738800.221:34): proctitle=7368002D63006563686F203E202F6574632F706173737764 type=LANDLOCK_DOMAIN msg=audit(1729738800.261:35): domain=1a6fdc679 status=deallocated denials=2

Event filtering

If you get spammed with audit logs related to Landlock, this is either an attack attempt or a bug in the security policy. We can put in place some filters to limit noise with two complementary ways:

with sys_landlock_restrict_self()'s flags if we can fix the sandboxed programs,
or with audit rules (see :manpage:auditctl(8)).

Additional documentation

Linux Audit Documentation_
Documentation/userspace-api/landlock.rst
Documentation/security/landlock.rst
https://landlock.io

.. Links .. _Linux Audit Documentation: https://github.com/linux-audit/audit-documentation/wiki