[PATCH v3 0/6] Landlock: Signal Scoping Support

Tahera Fahimi
2024-08-15T18:29:42Z

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.

Previous Versions
=================
v2:https://lore.kernel.org/all/cover.1722966592.git.fahimitahera@gmail.com/
v1:https://lore.kernel.org/all/cover.1720203255.git.fahimitahera@gmail.com/

Tahera Fahimi (6):
Landlock: Add signal control
Landlock: Adding file_send_sigiotask signal scoping support
selftest/Landlock: Signal restriction tests
selftest/Landlock: pthread_kill(3) tests
sample/Landlock: Support signal scoping restriction
Landlock: Document LANDLOCK_SCOPED_SIGNAL

Documentation/userspace-api/landlock.rst | 25 +-
include/uapi/linux/landlock.h | 3 +
samples/landlock/sandboxer.c | 16 +-
security/landlock/fs.c | 18 +
security/landlock/fs.h | 6 +
security/landlock/limits.h | 2 +-
security/landlock/task.c | 54 +++
.../selftests/landlock/scoped_signal_test.c | 331 ++++++++++++++++++
8 files changed, 443 insertions(+), 12 deletions(-)
create mode 100644 tools/testing/selftests/landlock/scoped_signal_test.c

--
2.34.1