[PATCH v5 24/24] landlock: Add audit documentation

Mickaël Salaün
2025-01-31T16:32:33Z

Because audit is dedicated to the system administrator, create a new
entry in Documentation/admin-guide/LSM .

Extend other Landlock documentation's pages with this new one.

Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20250131163059.1139617-25-mic@digikod.net
---

Changes since v4:
- New patch.
---
Documentation/admin-guide/LSM/index.rst | 1 +
Documentation/admin-guide/LSM/landlock.rst | 157 +++++++++++++++++++++
Documentation/security/landlock.rst | 7 +
Documentation/userspace-api/landlock.rst | 7 +
MAINTAINERS | 1 +
5 files changed, 173 insertions(+)
create mode 100644 Documentation/admin-guide/LSM/landlock.rst

diff --git a/Documentation/admin-guide/LSM/index.rst b/Documentation/admin-guide/LSM/index.rst
index ce63be6d64ad..b44ef68f6e4d 100644
--- a/Documentation/admin-guide/LSM/index.rst
+++ b/Documentation/admin-guide/LSM/index.rst
@@ -48,3 +48,4 @@ subdirectories.
Yama
SafeSetID
ipe
+ landlock
diff --git a/Documentation/admin-guide/LSM/landlock.rst b/Documentation/admin-guide/LSM/landlock.rst
new file mode 100644
index 000000000000..d69245ee236a
--- /dev/null
+++ b/Documentation/admin-guide/LSM/landlock.rst
@@ -0,0 +1,157 @@
+.. SPDX-License-Identifier: GPL-2.0
+.. Copyright © 2025 Microsoft Corporation
+
+================================
+Landlock: system-wide management
+================================
+
+:Author: Mickaël Salaün
+:Date: January 2025
+
+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 if `audit` is enabled. Programs
+may opt-out with the ``LANDLOCK_RESTRICT_SELF_QUIET`` flag (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 which 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
+
+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 scopping 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
diff --git a/Documentation/security/landlock.rst b/Documentation/security/landlock.rst
index 59ecdb1c0d4d..fe04c1b4d9d8 100644
--- a/Documentation/security/landlock.rst
+++ b/Documentation/security/landlock.rst
@@ -124,6 +124,13 @@ makes the reasoning much easier and helps avoid pitfalls.
.. kernel-doc:: security/landlock/ruleset.h
:identifiers:

+Additional documentation
+========================
+
+* Documentation/userspace-api/landlock.rst
+* Documentation/admin-guide/LSM/landlock.rst
+* https://landlock.io
+
.. Links
.. _tools/testing/selftests/landlock/:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/landlock/
diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
index a7c1ebef2c79..4009179665c9 100644
--- a/Documentation/userspace-api/landlock.rst
+++ b/Documentation/userspace-api/landlock.rst
@@ -683,9 +683,16 @@ fine-grained restrictions). Moreover, their complexity can lead to security
issues, especially when untrusted processes can manipulate them (cf.
`Controlling access to user namespaces <https://lwn.net/Articles/673597/>`_).

+How to disable Landlock audit records?
+--------------------------------------
+
+You might want to put in place filters as explained here:
+Documentation/admin-guide/LSM/landlock.rst
+
Additional documentation
========================

+* Documentation/admin-guide/LSM/landlock.rst
* Documentation/security/landlock.rst
* https://landlock.io

diff --git a/MAINTAINERS b/MAINTAINERS
index d1086e53a317..70712e823d4c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13066,6 +13066,7 @@ L: linux-security-module@vger.kernel.org
S: Supported
W: https://landlock.io
T: git https://git.kernel.org/pub/scm/linux/kernel/git/mic/linux.git
+F: Documentation/admin-guide/LSM/landlock.rst
F: Documentation/security/landlock.rst
F: Documentation/userspace-api/landlock.rst
F: fs/ioctl.c
--
2.48.1