[RFC,v3,00/19] Support socket access-control

Hello! This is v3 RFC patch dedicated to socket protocols restriction.

It is based on the landlock's mic-next branch on top of v6.11-rc1 kernel
version.

Objective
=========
Extend Landlock with a mechanism to restrict any set of protocols in
a sandboxed process.

Closes: https://github.com/landlock-lsm/linux/issues/6

Motivation
==========
Landlock implements the `LANDLOCK_RULE_NET_PORT` rule type, which provides
fine-grained control of actions for a specific protocol. Any action or
protocol that is not supported by this rule can not be controlled. As a
result, protocols for which fine-grained control is not supported can be
used in a sandboxed system and lead to vulnerabilities or unexpected
behavior.

Controlling the protocols used will allow to use only those that are
necessary for the system and/or which have fine-grained Landlock control
through others types of rules (e.g. TCP bind/connect control with
`LANDLOCK_RULE_NET_PORT`, UNIX bind control with
`LANDLOCK_RULE_PATH_BENEATH`).

Consider following examples:
* Server may want to use only TCP sockets for which there is fine-grained
  control of bind(2) and connect(2) actions [1].
* System that does not need a network or that may want to disable network
  for security reasons (e.g. [2]) can achieve this by restricting the use
  of all possible protocols.

[1] https://lore.kernel.org/all/ZJvy2SViorgc+cZI@google.com/
[2] https://cr.yp.to/unix/disablenetwork.html

Implementation
==============
This patchset adds control over the protocols used by implementing a
restriction of socket creation. This is possible thanks to the new type
of rule - `LANDLOCK_RULE_SOCKET`, that allows to restrict actions on
sockets, and a new access right - `LANDLOCK_ACCESS_SOCKET_CREATE`, that
corresponds to creating user space sockets. The key in this rule is a pair
of address family and socket type (Cf. socket(2)).

The right to create a socket is checked in the LSM hook, which is called
in the __sock_create method. The following user space operations are
subject to this check: socket(2), socketpair(2), io_uring(7).

In the case of connection-based socket types,
`LANDLOCK_ACCESS_SOCKET_CREATE` does not restrict the actions that result
in creation of sockets used for messaging between already existing
endpoints (e.g. accept(2), setsockopt(2) with option
`SCTP_SOCKOPT_PEELOFF`).

Current limitations
===================
`SCTP_SOCKOPT_PEELOFF` should not be restricted (see test
socket_creation.sctp_peeloff).

SCTP socket can be connected to a multiple endpoints (one-to-many
relation). Calling setsockopt(2) on such socket with option
`SCTP_SOCKOPT_PEELOFF` detaches one of existing connections to a separate
UDP socket. This detach is currently restrictable.

Code coverage
=============
Code coverage(gcov) report with the launch of all the landlock selftests:
* security/landlock:
lines......: 93.5% (794 of 849 lines)
functions..: 95.5% (106 of 111 functions)

* security/landlock/socket.c:
lines......: 100.0% (33 of 33 lines)
functions..: 100.0% (4 of 4 functions)

General changes v2->v3
======================
* Implementation
  * Accepts (AF_INET, SOCK_PACKET) as an alias for (AF_PACKET, SOCK_PACKET).
  * Adds check to not restrict kernel sockets.
  * Fixes UB in pack_socket_key().
  * Refactors documentation.
* Tests
  * Extends variants of `protocol` fixture with every protocol that can be
    used to create user space sockets.
  * Adds 5 new tests:
    * 3 tests to check socketpair(2), accept(2) and sctp_peeloff
      restriction.
    * 1 test to check restriction of kernel sockets.
    * 1 test to check AF_PACKET aliases.
* Documentation
  * Updates Documentation/userspace-api/landlock.rst.
* Commits
  * Rebases on mic-next.
  * Refactors commits.

Previous versions
=================
v2: https://lore.kernel.org/all/20240524093015.2402952-1-ivanov.mikhail1@huawei-partners.com/
v1: https://lore.kernel.org/all/20240408093927.1759381-1-ivanov.mikhail1@huawei-partners.com/

Mikhail Ivanov (19):
  landlock: Support socket access-control
  landlock: Add hook on socket creation
  selftests/landlock: Test basic socket restriction
  selftests/landlock: Test adding a rule with each supported access
  selftests/landlock: Test adding a rule for each unknown access
  selftests/landlock: Test adding a rule for unhandled access
  selftests/landlock: Test adding a rule for empty access
  selftests/landlock: Test overlapped restriction
  selftests/landlock: Test creating a ruleset with unknown access
  selftests/landlock: Test adding a rule with family and type outside
    the range
  selftests/landlock: Test unsupported protocol restriction
  selftests/landlock: Test that kernel space sockets are not restricted
  selftests/landlock: Test packet protocol alias
  selftests/landlock: Test socketpair(2) restriction
  selftests/landlock: Test SCTP peeloff restriction
  selftests/landlock: Test that accept(2) is not restricted
  samples/landlock: Replace atoi() with strtoull() in
    populate_ruleset_net()
  samples/landlock: Support socket protocol restrictions
  landlock: Document socket rule type support

 Documentation/userspace-api/landlock.rst      |   46 +-
 include/uapi/linux/landlock.h                 |   61 +-
 samples/landlock/sandboxer.c                  |  135 ++-
 security/landlock/Makefile                    |    2 +-
 security/landlock/limits.h                    |    4 +
 security/landlock/ruleset.c                   |   33 +-
 security/landlock/ruleset.h                   |   45 +-
 security/landlock/setup.c                     |    2 +
 security/landlock/socket.c                    |  137 +++
 security/landlock/socket.h                    |   19 +
 security/landlock/syscalls.c                  |   66 +-
 tools/testing/selftests/landlock/base_test.c  |    2 +-
 tools/testing/selftests/landlock/common.h     |   13 +
 tools/testing/selftests/landlock/config       |   47 +
 tools/testing/selftests/landlock/net_test.c   |   11 -
 .../testing/selftests/landlock/socket_test.c  | 1013 +++++++++++++++++
 16 files changed, 1593 insertions(+), 43 deletions(-)
 create mode 100644 security/landlock/socket.c
 create mode 100644 security/landlock/socket.h
 create mode 100644 tools/testing/selftests/landlock/socket_test.c


base-commit: 8400291e289ee6b2bf9779ff1c83a291501f017b