Documentation/admin-guide/LSM/landlock.rst

.. SPDX-License-Identifier: GPL-2.0
.. Copyright © 2025 Microsoft Corporation
.. Copyright © 2026 Cloudflare, Inc.

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

:Author: Mickaël Salaün
:Date: August 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), or suppressed on a per-object
basis by using ``LANDLOCK_ADD_RULE_QUIET`` (ABI 10+).  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+)
        - fs.resolve_unix (ABI 9+)

    **net.*** - Network access rights (ABI 4+):
        - net.bind_tcp - TCP port binding was denied
        - net.connect_tcp - TCP connection was denied
        - net.bind_udp - UDP port binding was denied
        - net.connect_send_udp - UDP connection and send 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, or
  ``LANDLOCK_ADD_RULE_QUIET`` (ABI 10+) if we can fix the sandboxed
  programs,
- or with audit rules (see :manpage:`auditctl(8)`).

Tracepoints
===========

Landlock also provides tracepoints as an alternative to audit for
debugging and observability.  Tracepoints fire unconditionally,
independent of audit configuration, ``audit_enabled``, and domain log
flags.  This makes them suitable for always-on monitoring with eBPF or
for ad-hoc debugging with ``trace-pipe``.

See Documentation/trace/events-landlock.rst for the complete event
reference: the full event list, how to enable events and read their
output, the field formats, the ``check_rule`` interpretation guide,
worked event samples, ftrace filtering, and eBPF access.

.. _landlock_observability:

When to use tracing vs audit
-----------------------------

Audit and tracing both help diagnose Landlock policy issues:

**Audit** records denied accesses with the blockers, domain, and object
identification (path, port).  Audit is the standard Linux mechanism for
security events, with a stable record format that is well established
and already supported by log management systems, SIEM platforms, and EDR
solutions.  Audit is always active when the kernel is built with audit
support, filtered by the Landlock log flags to reduce noise in
production, and designed for long-term security monitoring and
compliance.

**Tracing** provides deeper introspection for policy debugging.  In
addition to denied accesses, trace events cover the complete lifecycle
of Landlock objects (rulesets, domains) and intermediate rule matching
during access checks.  Trace events are disabled by default (zero
overhead) and fire unconditionally.  eBPF
programs attached to trace events can access the full kernel context
(ruleset rules, domain hierarchy, process credentials) via BTF, enabling
richer analysis than the flat fields in audit records.  For example, an
eBPF-based live monitoring tool can correlate creation, rule-addition,
and denial events to build a real-time view of all active Landlock
domains and their policies.  However, BTF-based access depends on
internal kernel struct layouts which have no stability guarantee.  CO-RE
(Compile Once, Run Everywhere) provides best-effort field relocation.
The ftrace printk format is also not a stable ABI, but is
self-describing via the per-event ``format`` file, allowing tools to
adapt dynamically.

Observability guarantees and limitations
-----------------------------------------

Both audit records and trace events are emitted for every denied access,
with these exceptions:

- **Landlock log flags** (audit only): ``LANDLOCK_RESTRICT_SELF_LOG_SAME_EXEC_OFF``,
  ``LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON``, and
  ``LANDLOCK_RESTRICT_SELF_LOG_SUBDOMAINS_OFF`` control which denials
  generate audit records.  Trace events fire regardless of these flags.

- **NOAUDIT hooks**: Some LSM hooks suppress logging for speculative
  permission probes (e.g., reading ``/proc/<pid>/status`` uses
  ``PTRACE_MODE_NOAUDIT``).  When NOAUDIT is set, neither audit records
  nor trace events are emitted, and the denial is not counted in
  ``denials``.  The denial is still enforced.  This avoids performance
  overhead and noise from speculative probes that test permissions
  without performing an actual access.

- **Audit rate limiting**: The audit subsystem may silently drop records
  when the audit queue is full.  Trace events are not rate-limited.

- **Tracepoint disabled**: When a trace event is disabled (the default
  state), the tracepoint is a no-op with zero overhead.

When both audit and tracing are active, every denial emits a trace event,
and a denial that the domain's log policy selects additionally produces an
audit record (subject to the Landlock log flags).  The ``denials`` count in
``free_domain`` events is incremented for every denial regardless of the
log flags, so it can exceed the number of audit records (which the log
flags and audit-side rate-limiting or exclude rules may suppress).

.. _landlock_observability_security:

Observability security considerations
---------------------------------------

Both audit records and trace events expose information about all
Landlock-sandboxed processes on the system, including filesystem paths
being accessed, network ports, and process identities.  System
administrators must ensure that access to audit logs (controlled by the
audit subsystem configuration) and to trace events (requiring
``CAP_SYS_ADMIN`` or ``CAP_BPF`` + ``CAP_PERFMON``) is restricted to
trusted users.

eBPF programs attached to Landlock trace events have access to the full
kernel context of each event (ruleset rules, domain hierarchy, process
credentials) via BTF, exposing sensitive state about every sandboxed
process.  Restrict this access to trusted users, as for the audit logs.

Audit logs and kernel trace events require elevated privileges and are
system-wide; they are not designed for per-sandbox unprivileged
monitoring.

Additional documentation
========================

* `Linux Audit Documentation`_
* Documentation/userspace-api/landlock.rst
* Documentation/trace/events-landlock.rst
* Documentation/security/landlock.rst
* https://landlock.io

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