* 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>

LANDLOCK_RESTRICT_SELF_TSYNC does not allow
LANDLOCK_RESTRICT_SELF_LOG_SUBDOMAINS_OFF with ruleset_fd=-1, preventing
a multithreaded process from atomically propagating subdomain log muting
to all threads without creating a domain layer.  Relax the fd=-1
condition to accept TSYNC alongside LOG_SUBDOMAINS_OFF, and update the
documentation accordingly.

Add flag validation tests for all TSYNC combinations with ruleset_fd=-1,
and audit tests verifying both transition directions: muting via TSYNC
(logged to not logged) and override via TSYNC (not logged to logged).

Cc: Günther Noack <gnoack@google.com>
Cc: stable@vger.kernel.org
Fixes: 42fc7e6543f6 ("landlock: Multithreading support for landlock_restrict_self()")
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260407164107.2012589-2-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

- Move ABI requirement next to each access right to prepare adding more
  access rights;
- Mention the possibility to remove the random component of a socket's
  ephemeral port choice within the netns-wide ephemeral port range,
  since it allows choosing the "random" ephemeral port.

Signed-off-by: Matthieu Buffet <matthieu@buffet.re>
Link: https://lore.kernel.org/r/20251212163704.142301-2-matthieu@buffet.re
Signed-off-by: Mickaël Salaün <mic@digikod.net>

Introduce the LANDLOCK_RESTRICT_SELF_TSYNC flag.  With this flag, a
given Landlock ruleset is applied to all threads of the calling
process, instead of only the current one.

Without this flag, multithreaded userspace programs currently resort
to using the nptl(7)/libpsx hack for multithreaded policy enforcement,
which is also used by libcap and for setuid(2).  Using this
userspace-based scheme, the threads of a process enforce the same
Landlock policy, but the resulting Landlock domains are still
separate.  The domains being separate causes multiple problems:

* When using Landlock's "scoped" access rights, the domain identity is
  used to determine whether an operation is permitted.  As a result,
  when using LANLDOCK_SCOPE_SIGNAL, signaling between sibling threads
  stops working.  This is a problem for programming languages and
  frameworks which are inherently multithreaded (e.g. Go).

* In audit logging, the domains of separate threads in a process will
  get logged with different domain IDs, even when they are based on
  the same ruleset FD, which might confuse users.

Cc: Andrew G. Morgan <morgan@kernel.org>
Cc: John Johansen <john.johansen@canonical.com>
Cc: Paul Moore <paul@paul-moore.com>
Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20251127115136.3064948-2-gnoack@google.com
[mic: Fix restrict_self_flags test, clean up Makefile, allign comments,
reduce local variable scope, add missing includes]
Closes: https://github.com/landlock-lsm/linux/issues/2
Signed-off-by: Mickaël Salaün <mic@digikod.net>

Move the description of the LANDLOCK_ACCESS_FS_IOCTL_DEV access right
together with the file access rights.

This group of access rights applies to files (in this case device
files), and they can be added to file or directory inodes using
landlock_add_rule(2).  The check for that works the same for all file
access rights, including LANDLOCK_ACCESS_FS_IOCTL_DEV.

Invoking ioctl(2) on directory FDs can not currently be restricted
with Landlock.  Having it grouped separately in the documentation is a
remnant from earlier revisions of the LANDLOCK_ACCESS_FS_IOCTL_DEV
patch set.

Link: https://lore.kernel.org/all/20260108.Thaex5ruach2@digikod.net/
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260111175203.6545-2-gnoack3000@gmail.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>

Fix and improve documentation related to landlock_restrict_self(2)'s
flags.  Update the LANDLOCK_RESTRICT_SELF_LOG_SAME_EXEC_OFF
documentation according to the current semantic.

Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20250416154716.1799902-3-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

Fix, deduplicate, and improve rendering of landlock_restrict_self(2)'s
flags documentation.

The flags are now rendered like the syscall's parameters and
description.

Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20250416154716.1799902-2-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

Move and fix the flags documentation, and improve formatting.

It makes more sense and it eases maintenance to document syscall flags
in landlock.h, where they are defined.  This is already the case for
landlock_restrict_self(2)'s flags.

The flags are now rendered like the syscall's parameters and
description.

Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20250416154716.1799902-1-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

Add LANDLOCK_RESTRICT_SELF_LOG_SUBDOMAINS_OFF for the case of sandboxer
tools, init systems, or runtime containers launching programs sandboxing
themselves in an inconsistent way.  Setting this flag should only
depends on runtime configuration (i.e. not hardcoded).

We don't create a new ruleset's option because this should not be part
of the security policy: only the task that enforces the policy (not the
one that create it) knows if itself or its children may request denied
actions.

This is the first and only flag that can be set without actually
restricting the caller (i.e. without providing a ruleset).

Extend struct landlock_cred_security with a u8 log_subdomains_off.
struct landlock_file_security is still 16 bytes.

Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Closes: https://github.com/landlock-lsm/linux/issues/3
Link: https://lore.kernel.org/r/20250320190717.2287696-19-mic@digikod.net
[mic: Fix comment]
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>