* Add a new access right LANDLOCK_ACCESS_FS_RESOLVE_UNIX, which
controls the lookup operations for named UNIX domain sockets. The
resolution happens during connect() and sendmsg() (depending on
socket type).
* Change access_mask_t from u16 to u32 (see below)
* Hook into the path lookup in unix_find_bsd() in af_unix.c, using a
LSM hook. Make policy decisions based on the new access rights
* Increment the Landlock ABI version.
* Minor test adaptations to keep the tests working.
* Document the design rationale for scoped access rights,
and cross-reference it from the header documentation.
With this access right, access is granted if either of the following
conditions is met:
* The target socket's filesystem path was allow-listed using a
LANDLOCK_RULE_PATH_BENEATH rule, *or*:
* The target socket was created in the same Landlock domain in which
LANDLOCK_ACCESS_FS_RESOLVE_UNIX was restricted.
In case of a denial, connect() and sendmsg() return EACCES, which is
the same error as it is returned if the user does not have the write
bit in the traditional UNIX file system permissions of that file.
The access_mask_t type grows from u16 to u32 to make space for the new
access right. This also doubles the size of struct layer_access_masks
from 32 byte to 64 byte. To avoid memory layout inconsistencies between
architectures (especially m68k), pack and align struct access_masks [2].
Document the (possible future) interaction between scoped flags and
other access rights in struct landlock_ruleset_attr, and summarize the
rationale, as discussed in code review leading up to [3].
This feature was created with substantial discussion and input from
Justin Suess, Tingmao Wang and Mickaël Salaün.
Cc: Tingmao Wang <m@maowtm.org>
Cc: Justin Suess <utilityemal77@gmail.com>
Cc: Kuniyuki Iwashima <kuniyu@google.com>
Suggested-by: Jann Horn <jannh@google.com>
Link[1]: https://github.com/landlock-lsm/linux/issues/36
Link[2]: https://lore.kernel.org/all/20260401.Re1Eesu1Yaij@digikod.net/
Link[3]: https://lore.kernel.org/all/20260205.8531e4005118@gnoack.org/
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20260327164838.38231-5-gnoack3000@gmail.com
[mic: Fix kernel-doc formatting, pack and align access_masks]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
The layer masks data structure tracks the requested but unfulfilled
access rights during an operation's security check. It stores one bit
for each combination of access right and layer index. If the bit is
set, that access right is not granted (yet) in the given layer and we
have to traverse the path further upwards to grant it.
Previously, the layer masks were stored as arrays mapping from access
right indices to layer_mask_t. The layer_mask_t value then indicates
all layers in which the given access right is still (tentatively)
denied.
This patch introduces struct layer_access_masks instead: This struct
contains an array with the access_mask_t of each (tentatively) denied
access right in that layer.
The hypothesis of this patch is that this simplifies the code enough
so that the resulting code will run faster:
* We can use bitwise operations in multiple places where we previously
looped over bits individually with macros. (Should require less
branch speculation and lends itself to better loop unrolling.)
* Code is ~75 lines smaller.
Other noteworthy changes:
* In no_more_access(), call a new helper function may_refer(), which
only solves the asymmetric case. Previously, the code interleaved
the checks for the two symmetric cases in RENAME_EXCHANGE. It feels
that the code is clearer when renames without RENAME_EXCHANGE are
more obviously the normal case.
Tradeoffs:
This change improves performance, at a slight size increase to the
layer masks data structure.
This fixes the size of the data structure at 32 bytes for all types of
access rights. (64, once we introduce a 17th filesystem access right).
For filesystem access rights, at the moment, the data structure has
the same size as before, but once we introduce the 17th filesystem
access right, it will double in size (from 32 to 64 bytes), as
access_mask_t grows from 16 to 32 bit [1].
Link: https://lore.kernel.org/all/20260120.haeCh4li9Vae@digikod.net/ [1]
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260206151154.97915-5-gnoack3000@gmail.com
[mic: Cosmetic fixes, moved struct layer_access_masks definition]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Use the BIT() and BIT_ULL() macros in the new audit code instead of
explicit shifts to improve readability. Use bitmask instead of modulo
operation to simplify code.
Add test_range1_rand15() and test_range2_rand15() KUnit tests to improve
get_id_range() coverage.
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20250512093732.1408485-1-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Most of the time we want to log denied access because they should not
happen and such information helps diagnose issues. However, when
sandboxing processes that we know will try to access denied resources
(e.g. unknown, bogus, or malicious binary), we might want to not log
related access requests that might fill up logs.
By default, denied requests are logged until the task call execve(2).
If the LANDLOCK_RESTRICT_SELF_LOG_SAME_EXEC_OFF flag is set, denied
requests will not be logged for the same executed file.
If the LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON flag is set, denied
requests from after an execve(2) call will be logged.
The rationale is that a program should know its own behavior, but not
necessarily the behavior of other programs.
Because LANDLOCK_RESTRICT_SELF_LOG_SAME_EXEC_OFF is set for a specific
Landlock domain, it makes it possible to selectively mask some access
requests that would be logged by a parent domain, which might be handy
for unprivileged processes to limit logs. However, system
administrators should still use the audit filtering mechanism. There is
intentionally no audit nor sysctl configuration to re-enable these logs.
This is delegated to the user space program.
Increment the Landlock ABI version to reflect this interface change.
Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20250320190717.2287696-18-mic@digikod.net
[mic: Rename variables and fix __maybe_unused]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Add audit support for unix_stream_connect, unix_may_send, task_kill, and
file_send_sigiotask hooks.
The related blockers are:
- scope.abstract_unix_socket
- scope.signal
Audit event sample for abstract unix socket:
type=LANDLOCK_DENY msg=audit(1729738800.268:30): domain=195ba459b blockers=scope.abstract_unix_socket path=00666F6F
Audit event sample for signal:
type=LANDLOCK_DENY msg=audit(1729738800.291:31): domain=195ba459b blockers=scope.signal opid=1 ocomm="systemd"
Refactor and simplify error handling in LSM hooks.
Extend struct landlock_file_security with fown_layer and use it to log
the blocking domain. The struct aligned size is still 16 bytes.
Cc: Günther Noack <gnoack@google.com>
Cc: Tahera Fahimi <fahimitahera@gmail.com>
Link: https://lore.kernel.org/r/20250320190717.2287696-17-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Add audit support to the file_truncate and file_ioctl hooks.
Add a deny_masks_t type and related helpers to store the domain's layer
level per optional access rights (i.e. LANDLOCK_ACCESS_FS_TRUNCATE and
LANDLOCK_ACCESS_FS_IOCTL_DEV) when opening a file, which cannot be
inferred later. In practice, the landlock_file_security aligned blob size is
still 16 bytes because this new one-byte deny_masks field follows the
existing two-bytes allowed_access field and precede the packed
fown_subject.
Implementing deny_masks_t with a bitfield instead of a struct enables a
generic implementation to store and extract layer levels.
Add KUnit tests to check the identification of a layer level from a
deny_masks_t, and the computation of a deny_masks_t from an access right
with its layer level or a layer_mask_t array.
Audit event sample:
type=LANDLOCK_DENY msg=audit(1729738800.349:44): domain=195ba459b blockers=fs.ioctl_dev path="/dev/tty" dev="devtmpfs" ino=9 ioctlcmd=0x5401
Cc: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20250320190717.2287696-15-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Add audit support for path_mkdir, path_mknod, path_symlink, path_unlink,
path_rmdir, path_truncate, path_link, path_rename, and file_open hooks.
The dedicated blockers are:
- 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
- fs.truncate
- fs.ioctl_dev
Audit event sample for a denied link action:
type=LANDLOCK_DENY msg=audit(1729738800.349:44): domain=195ba459b blockers=fs.refer path="/usr/bin" dev="vda2" ino=351
type=LANDLOCK_DENY msg=audit(1729738800.349:44): domain=195ba459b blockers=fs.make_reg,fs.refer path="/usr/local" dev="vda2" ino=365
We could pack blocker names (e.g. "fs:make_reg,refer") but that would
increase complexity for the kernel and log parsers. Moreover, this
could not handle blockers of different classes (e.g. fs and net). Make
it simple and flexible instead.
Add KUnit tests to check the identification from a layer_mask_t array of
the first layer level denying such request.
Cc: Günther Noack <gnoack@google.com>
Depends-on: 058518c209 ("landlock: Align partial refer access checks with final ones")
Depends-on: d617f0d72d ("landlock: Optimize file path walks and prepare for audit support")
Link: https://lore.kernel.org/r/20250320190717.2287696-13-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Add audit support for sb_mount, move_mount, sb_umount, sb_remount, and
sb_pivot_root hooks.
The new related blocker is "fs.change_topology".
Audit event sample:
type=LANDLOCK_DENY msg=audit(1729738800.349:44): domain=195ba459b blockers=fs.change_topology name="/" dev="tmpfs" ino=1
Remove landlock_get_applicable_domain() and get_current_fs_domain()
which are now fully replaced with landlock_get_applicable_subject().
Cc: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20250320190717.2287696-12-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Asynchronously log domain information when it first denies an access.
This minimize the amount of generated logs, which makes it possible to
always log denials for the current execution since they should not
happen. These records are identified with the new AUDIT_LANDLOCK_DOMAIN
type.
The AUDIT_LANDLOCK_DOMAIN message contains:
- the "domain" ID which is described;
- the "status" which can either be "allocated" or "deallocated";
- the "mode" which is for now only "enforcing";
- for the "allocated" status, a minimal set of properties to easily
identify the task that loaded the domain's policy with
landlock_restrict_self(2): "pid", "uid", executable path ("exe"), and
command line ("comm");
- for the "deallocated" state, the number of "denials" accounted to this
domain, which is at least 1.
This requires each domain to save these task properties at creation
time in the new struct landlock_details. A reference to the PID is kept
for the lifetime of the domain to avoid race conditions when
investigating the related task. The executable path is resolved and
stored to not keep a reference to the filesystem and block related
actions. All these metadata are stored for the lifetime of the related
domain and should then be minimal. The required memory is not accounted
to the task calling landlock_restrict_self(2) contrary to most other
Landlock allocations (see related comment).
The AUDIT_LANDLOCK_DOMAIN record follows the first AUDIT_LANDLOCK_ACCESS
record for the same domain, which is always followed by AUDIT_SYSCALL
and AUDIT_PROCTITLE. This is in line with the audit logic to first
record the cause of an event, and then add context with other types of
record.
Audit event sample for a first denial:
type=LANDLOCK_ACCESS msg=audit(1732186800.349:44): domain=195ba459b blockers=ptrace opid=1 ocomm="systemd"
type=LANDLOCK_DOMAIN msg=audit(1732186800.349:44): domain=195ba459b status=allocated mode=enforcing pid=300 uid=0 exe="/root/sandboxer" comm="sandboxer"
type=SYSCALL msg=audit(1732186800.349:44): arch=c000003e syscall=101 success=no [...] pid=300 auid=0
Audit event sample for a following denial:
type=LANDLOCK_ACCESS msg=audit(1732186800.372:45): domain=195ba459b blockers=ptrace opid=1 ocomm="systemd"
type=SYSCALL msg=audit(1732186800.372:45): arch=c000003e syscall=101 success=no [...] pid=300 auid=0
Log domain deletion with the "deallocated" state when a domain was
previously logged. This makes it possible for log parsers to free
potential resources when a domain ID will never show again.
The number of denied access requests is useful to easily check how many
access requests a domain blocked and potentially if some of them are
missing in logs because of audit rate limiting, audit rules, or Landlock
log configuration flags (see following commit).
Audit event sample for a deletion of a domain that denied something:
type=LANDLOCK_DOMAIN msg=audit(1732186800.393:46): domain=195ba459b status=deallocated denials=2
Cc: Günther Noack <gnoack@google.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20250320190717.2287696-11-mic@digikod.net
[mic: Update comment and GFP flag for landlock_log_drop_domain()]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Add a new AUDIT_LANDLOCK_ACCESS record type dedicated to an access
request denied by a Landlock domain. AUDIT_LANDLOCK_ACCESS indicates
that something unexpected happened.
For now, only denied access are logged, which means that any
AUDIT_LANDLOCK_ACCESS record is always followed by a SYSCALL record with
"success=no". However, log parsers should check this syscall property
because this is the only sign that a request was denied. Indeed, we
could have "success=yes" if Landlock would support a "permissive" mode.
We could also add a new field to AUDIT_LANDLOCK_DOMAIN for this mode
(see following commit).
By default, the only logged access requests are those coming from the
same executed program that enforced the Landlock restriction on itself.
In other words, no audit record are created for a task after it called
execve(2). This is required to avoid log spam because programs may only
be aware of their own restrictions, but not the inherited ones.
Following commits will allow to conditionally generate
AUDIT_LANDLOCK_ACCESS records according to dedicated
landlock_restrict_self(2)'s flags.
The AUDIT_LANDLOCK_ACCESS message contains:
- the "domain" ID restricting the action on an object,
- the "blockers" that are missing to allow the requested access,
- a set of fields identifying the related object (e.g. task identified
with "opid" and "ocomm").
The blockers are implicit restrictions (e.g. ptrace), or explicit access
rights (e.g. filesystem), or explicit scopes (e.g. signal). This field
contains a list of at least one element, each separated with a comma.
The initial blocker is "ptrace", which describe all implicit Landlock
restrictions related to ptrace (e.g. deny tracing of tasks outside a
sandbox).
Add audit support to ptrace_access_check and ptrace_traceme hooks. For
the ptrace_access_check case, we log the current/parent domain and the
child task. For the ptrace_traceme case, we log the parent domain and
the current/child task. Indeed, the requester and the target are the
current task, but the action would be performed by the parent task.
Audit event sample:
type=LANDLOCK_ACCESS msg=audit(1729738800.349:44): domain=195ba459b blockers=ptrace opid=1 ocomm="systemd"
type=SYSCALL msg=audit(1729738800.349:44): arch=c000003e syscall=101 success=no [...] pid=300 auid=0
A following commit adds user documentation.
Add KUnit tests to check reading of domain ID relative to layer level.
The quick return for non-landlocked tasks is moved from task_ptrace() to
each LSM hooks.
It is not useful to inline the audit_enabled check because other
computation are performed by landlock_log_denial().
Use scoped guards for RCU read-side critical sections.
Cc: Günther Noack <gnoack@google.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20250320190717.2287696-10-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
