Landlock: system-wide management¶

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

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.

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 auditctl(8)).