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Subject[RFC PATCH v14 00/10] Landlock LSM
Date
Hi,

This new version of Landlock is a major revamp of the previous series
[1], hence the RFC tag. The three main changes are the replacement of
eBPF with a dedicated safe management of access rules, the replacement
of the use of seccomp(2) with a dedicated syscall, and the management of
filesystem access-control (back from the v10).

As discussed in [2], eBPF may be too powerful and dangerous to be put in
the hand of unprivileged and potentially malicious processes, especially
because of side-channel attacks against access-controls or other parts
of the kernel.

Thanks to this new implementation (1540 SLOC), designed from the ground
to be used by unprivileged processes, this series enables a process to
sandbox itself without requiring CAP_SYS_ADMIN, but only the
no_new_privs constraint (like seccomp). Not relying on eBPF also
enables to improve performances, especially for stacked security
policies thanks to mergeable rulesets.

The compiled documentation is available here:
https://landlock.io/linux-doc/landlock-v14/security/landlock/index.html

This series can be applied on top of v5.6-rc3. This can be tested with
CONFIG_SECURITY_LANDLOCK and CONFIG_SAMPLE_LANDLOCK. This patch series
can be found in a Git repository here:
https://github.com/landlock-lsm/linux/commits/landlock-v14
I would really appreciate constructive comments on the design and the code.


# Landlock LSM

The goal of Landlock is to enable to restrict ambient rights (e.g.
global filesystem access) for a set of processes. Because Landlock is a
stackable LSM [3], it makes possible to create safe security sandboxes
as new security layers in addition to the existing system-wide
access-controls. This kind of sandbox is expected to help mitigate the
security impact of bugs or unexpected/malicious behaviors in user-space
applications. Landlock empower any process, including unprivileged ones,
to securely restrict themselves.

Landlock is inspired by seccomp-bpf but instead of filtering syscalls
and their raw arguments, a Landlock rule can restrict the use of kernel
objects like file hierarchies, according to the kernel semantic.
Landlock also takes inspiration from other OS sandbox mechanisms: XNU
Sandbox, FreeBSD Capsicum or OpenBSD Pledge/Unveil.


# Current limitations

## Path walk

Landlock need to use dentries to identify a file hierarchy, which is
needed for composable and unprivileged access-controls. This means that
path resolution/walking (handled with inode_permission()) is not
supported, yet. This could be filled with a future extension first of
the LSM framework. The Landlock userspace ABI can handle such change
with new option (e.g. to the struct landlock_ruleset).

## UnionFS

An UnionFS super-block use a set of upper and lower directories. An
access request to a file in one of these hierarchy trigger a call to
ovl_path_real() which generate another access request according to the
matching hierarchy. Because such super-block is not aware of its current
mount point, OverlayFS can't create a dedicated mnt_parent for each of
the upper and lower directories mount clones. It is then not currently
possible to track the source of such indirect access-request, and then
not possible to identify a unified OverlayFS hierarchy.

## Syscall

Because it is only tested on x86_64, the syscall is only wired up for
this architecture. The whole x86 family (and probably all the others)
will be supported in the next patch series.


## Memory limits

There is currently no limit on the memory usage. Any idea to leverage
an existing mechanism (e.g. rlimit)?


# Changes since v13

* Revamp of the LSM: remove the need for eBPF and seccomp(2).
* Implement a full filesystem access-control.
* Take care of the backward compatibility issues, especially for
this security features.

Previous version:
https://lore.kernel.org/lkml/20191104172146.30797-1-mic@digikod.net/

[1] https://lore.kernel.org/lkml/20191104172146.30797-1-mic@digikod.net/
[2] https://lore.kernel.org/lkml/a6b61f33-82dc-0c1c-7a6c-1926343ef63e@digikod.net/
[3] https://lore.kernel.org/lkml/50db058a-7dde-441b-a7f9-f6837fe8b69f@schaufler-ca.com/

Regards,

Mickaël Salaün (10):
landlock: Add object and rule management
landlock: Add ruleset and domain management
landlock: Set up the security framework and manage credentials
landlock: Add ptrace restrictions
fs,landlock: Support filesystem access-control
landlock: Add syscall implementation
arch: Wire up landlock() syscall
selftests/landlock: Add initial tests
samples/landlock: Add a sandbox manager example
landlock: Add user and kernel documentation

Documentation/security/index.rst | 1 +
Documentation/security/landlock/index.rst | 18 +
Documentation/security/landlock/kernel.rst | 44 ++
Documentation/security/landlock/user.rst | 233 +++++++
MAINTAINERS | 12 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
fs/super.c | 2 +
include/linux/landlock.h | 22 +
include/linux/syscalls.h | 3 +
include/uapi/asm-generic/unistd.h | 4 +-
include/uapi/linux/landlock.h | 315 +++++++++
samples/Kconfig | 7 +
samples/Makefile | 1 +
samples/landlock/.gitignore | 1 +
samples/landlock/Makefile | 15 +
samples/landlock/sandboxer.c | 226 +++++++
security/Kconfig | 11 +-
security/Makefile | 2 +
security/landlock/Kconfig | 16 +
security/landlock/Makefile | 4 +
security/landlock/cred.c | 47 ++
security/landlock/cred.h | 55 ++
security/landlock/fs.c | 591 +++++++++++++++++
security/landlock/fs.h | 42 ++
security/landlock/object.c | 341 ++++++++++
security/landlock/object.h | 134 ++++
security/landlock/ptrace.c | 118 ++++
security/landlock/ptrace.h | 14 +
security/landlock/ruleset.c | 463 +++++++++++++
security/landlock/ruleset.h | 106 +++
security/landlock/setup.c | 38 ++
security/landlock/setup.h | 20 +
security/landlock/syscall.c | 470 +++++++++++++
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/landlock/.gitignore | 3 +
tools/testing/selftests/landlock/Makefile | 13 +
tools/testing/selftests/landlock/config | 4 +
tools/testing/selftests/landlock/test.h | 40 ++
tools/testing/selftests/landlock/test_base.c | 80 +++
tools/testing/selftests/landlock/test_fs.c | 624 ++++++++++++++++++
.../testing/selftests/landlock/test_ptrace.c | 293 ++++++++
41 files changed, 4429 insertions(+), 6 deletions(-)
create mode 100644 Documentation/security/landlock/index.rst
create mode 100644 Documentation/security/landlock/kernel.rst
create mode 100644 Documentation/security/landlock/user.rst
create mode 100644 include/linux/landlock.h
create mode 100644 include/uapi/linux/landlock.h
create mode 100644 samples/landlock/.gitignore
create mode 100644 samples/landlock/Makefile
create mode 100644 samples/landlock/sandboxer.c
create mode 100644 security/landlock/Kconfig
create mode 100644 security/landlock/Makefile
create mode 100644 security/landlock/cred.c
create mode 100644 security/landlock/cred.h
create mode 100644 security/landlock/fs.c
create mode 100644 security/landlock/fs.h
create mode 100644 security/landlock/object.c
create mode 100644 security/landlock/object.h
create mode 100644 security/landlock/ptrace.c
create mode 100644 security/landlock/ptrace.h
create mode 100644 security/landlock/ruleset.c
create mode 100644 security/landlock/ruleset.h
create mode 100644 security/landlock/setup.c
create mode 100644 security/landlock/setup.h
create mode 100644 security/landlock/syscall.c
create mode 100644 tools/testing/selftests/landlock/.gitignore
create mode 100644 tools/testing/selftests/landlock/Makefile
create mode 100644 tools/testing/selftests/landlock/config
create mode 100644 tools/testing/selftests/landlock/test.h
create mode 100644 tools/testing/selftests/landlock/test_base.c
create mode 100644 tools/testing/selftests/landlock/test_fs.c
create mode 100644 tools/testing/selftests/landlock/test_ptrace.c

--
2.25.0

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