This patch series adds scoping mechanism for abstract UNIX sockets.
Closes: https://github.com/landlock-lsm/linux/issues/7

Problem
=======

Abstract UNIX sockets are used for local inter-process communications
independent of the filesystem. Currently, a sandboxed process can
connect to a socket outside of the sandboxed environment, since Landlock
has no restriction for connecting to an abstract socket address(see more
details in [1,2]). Access to such sockets for a sandboxed process should
be scoped the same way ptrace is limited.

[1] https://lore.kernel.org/all/20231023.ahphah4Wii4v@digikod.net/ (local)
[2] https://lore.kernel.org/all/20231102.MaeWaepav8nu@digikod.net/ (local)

Solution
========

To solve this issue, we extend the user space interface by adding a new
"scoped" field to Landlock ruleset attribute structure. This field can
contains different rights to restrict different functionalities. For
abstract UNIX sockets, we introduce
"LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET" field to specify that a ruleset
will deny any connection from within the sandbox domain to its parent
(i.e. any parent sandbox or non-sandbox processes).

Example
=======

Starting a listening socket with socat(1):
        socat abstract-listen:mysocket -

Starting a sandboxed shell from $HOME with samples/landlock/sandboxer:
        LL_FS_RO=/ LL_FS_RW=. LL_SCOPED="a" ./sandboxer /bin/bash

If we try to connect to the listening socket, the connection gets
refused.
        socat - abstract-connect:mysocket --> fails


Notes of Implementation
=======================

* Using the "scoped" field provides enough compatibility and flexibility
  to extend the scoping mechanism for other IPCs(e.g. signals).

* To access the domain of a socket, we use its credentials of the file's
  FD which point to the credentials of the process that created the
  socket (see more details in [3]). Cases where the process using the
  socket has a different domain than the process created it are covered
  in the "outside_socket" test.

[3]https://lore.kernel.org/all/20240611.Pi8Iph7ootae@digikod.net/ (local)

Previous Versions
=================
v10:https://lore.kernel.org/all/cover.1724125513.git.fahimitahera@gmail.com/ (local)
v9: https://lore.kernel.org/all/cover.1723615689.git.fahimitahera@gmail.com/ (local)
v8: https://lore.kernel.org/all/cover.1722570749.git.fahimitahera@gmail.com/ (local)
v7: https://lore.kernel.org/all/cover.1721269836.git.fahimitahera@gmail.com/ (local)
v6: https://lore.kernel.org/all/Zn32CYZiu7pY+rdI@tahera-OptiPlex-5000/ (local)
and https://lore.kernel.org/all/Zn32KKIJrY7Zi51K@tahera-OptiPlex-5000/ (local)
v5: https://lore.kernel.org/all/ZnSZnhGBiprI6FRk@tahera-OptiPlex-5000/ (local)
v4: https://lore.kernel.org/all/ZnNcE3ph2SWi1qmd@tahera-OptiPlex-5000/ (local)
v3: https://lore.kernel.org/all/ZmJJ7lZdQuQop7e5@tahera-OptiPlex-5000/ (local)
v2: https://lore.kernel.org/all/ZgX5TRTrSDPrJFfF@tahera-OptiPlex-5000/ (local)
v1: https://lore.kernel.org/all/ZgXN5fi6A1YQKiAQ@tahera-OptiPlex-5000/ (local)

Tahera Fahimi (8):
  Landlock: Add abstract UNIX socket restriction
  selftests/landlock: Add test for handling unknown scope
  selftests/landlock: Add abstract UNIX socket restriction tests
  selftests/landlock: Add tests for UNIX sockets with any address
    formats
  selftests/landlock: Test connected vs non-connected datagram UNIX
    socket
  selftests/landlock: Restrict inherited datagram UNIX socket to connect
  sample/landlock: Add support abstract UNIX socket restriction
  Landlock: Document LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET and ABI
    version

 Documentation/userspace-api/landlock.rst      |  45 +-
 include/uapi/linux/landlock.h                 |  28 +
 samples/landlock/sandboxer.c                  |  61 +-
 security/landlock/limits.h                    |   3 +
 security/landlock/ruleset.c                   |   7 +-
 security/landlock/ruleset.h                   |  24 +-
 security/landlock/syscalls.c                  |  17 +-
 security/landlock/task.c                      | 136 +++
 tools/testing/selftests/landlock/base_test.c  |   2 +-
 tools/testing/selftests/landlock/common.h     |  38 +
 tools/testing/selftests/landlock/net_test.c   |  31 +-
 .../landlock/scoped_abstract_unix_test.c      | 993 ++++++++++++++++++
 .../selftests/landlock/scoped_base_variants.h | 154 +++
 .../selftests/landlock/scoped_common.h        |  28 +
 .../scoped_multiple_domain_variants.h         | 154 +++
 .../testing/selftests/landlock/scoped_test.c  |  33 +
 16 files changed, 1709 insertions(+), 45 deletions(-)
 create mode 100644 tools/testing/selftests/landlock/scoped_abstract_unix_test.c
 create mode 100644 tools/testing/selftests/landlock/scoped_base_variants.h
 create mode 100644 tools/testing/selftests/landlock/scoped_common.h
 create mode 100644 tools/testing/selftests/landlock/scoped_multiple_domain_variants.h
 create mode 100644 tools/testing/selftests/landlock/scoped_test.c

-- 
2.34.1