[PATCH v2 0/4] Landlock: Signal Scoping Support

[Tahera Fahimi <fahimitahera@gmail.com>]

This patch series adds scoping mechanism for signals.
Closes: https://github.com/landlock-lsm/linux/issues/8

Problem
=======

A sandboxed process is currently not restricted from sending signals
(e.g. SIGKILL) to processes outside the sandbox since Landlock has
no restriction on signals(see more details in [1]).

A simple way to apply this restriction would be to scope signals the
same way abstract unix sockets are restricted.

[1]https://lore.kernel.org/all/20231023.ahphah4Wii4v@digikod.net/

Solution
========

To solve this issue, we extend the "scoped" field in the Landlock
ruleset attribute structure by introducing "LANDLOCK_SCOPED_SIGNAL"
field to specify that a ruleset will deny sending any signals from
within the sandbox domain to its parent(i.e. any parent sandbox or
non-sandbox processes).

Example
=======

Create a sansboxed shell and pass the character "s" to LL_SCOPED:
LL_FD_RO=/ LL_FS_RW=. LL_SCOPED="s" ./sandboxer /bin/bash
Try to send a signal(like SIGTRAP) to a process ID <PID> through:
kill -SIGTRAP <PID>
The sandboxed process should not be able to send the signal.

Tahera Fahimi (4):
  Landlock: Add signal control
  selftest/Landlock: Signal restriction tests
  sample/Landlock: Support signal scoping restriction
  Landlock: Document LANDLOCK_SCOPED_SIGNAL

 Documentation/userspace-api/landlock.rst      |  27 +-
 include/uapi/linux/landlock.h                 |   3 +
 samples/landlock/sandboxer.c                  |  13 +-
 security/landlock/limits.h                    |   2 +-
 security/landlock/task.c                      |  43 +++
 tools/testing/selftests/landlock/base_test.c  |   2 +-
 .../selftests/landlock/scoped_signal_test.c   | 303 ++++++++++++++++++
 7 files changed, 376 insertions(+), 17 deletions(-)
 create mode 100644 tools/testing/selftests/landlock/scoped_signal_test.c

-- 
2.34.1