Hi,
This new patch series brings improvements, fix some bugs but mainly simplify the code.
The object, rule and ruleset management are simplified at the expense of a less aggressive memory freeing (contributed by Jann Horn [1]). There is now less use of RCU for an improved readability. Access checks that can be reached by file-descriptor-based syscalls are removed for now (truncate, getattr, lock, chmod, chown, chgrp, ioctl). This will be handle in a future evolution of Landlock, but right now the goal is to lighten the code to ease review. The SLOC count for security/landlock/ was 1542 with the previous patch series while the current series shrinks it to 1273.
The other main improvement is the addition of rule layer levels to ensure that a nested sandbox cannot bypass the access restrictions set by its parents.
The syscall is now wired for all architectures and the tests passed for x86_32 and x86_64.
The compiled documentation is available here: https://landlock.io/linux-doc/landlock-v15/security/landlock/index.html
This series can be applied on top of v5.6-rc7. 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-v15 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 [2], 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 empowers 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. The same limitation also apply to readlink(2). This could be filled with a future extension first of the LSM framework. The Landlock userspace ABI can handle such change with new options (e.g. to the struct landlock_ruleset).
## UnionFS
An UnionFS super-block use a set of upper and lower directories. 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.
## Memory limits
There is currently no limit on the memory usage. Any idea to leverage an existing mechanism (e.g. rlimit)?
# Changes since v14
* Simplify the object, rule and ruleset management at the expense of a less aggressive memory freeing. * Remove access checks that may be required for FD-only requests: truncate, getattr, lock, chmod, chown, chgrp, ioctl. * Add the notion of rule layer level to ensure that a nested sandbox cannot bypass the access restrictions set by its parent. * Wire up the syscall for all architectures. * Clean up the code and add more documentation. * Some improvements and bug fixes.
# 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 security features, following a best-effort approach.
Previous version: https://lore.kernel.org/lkml/20200224160215.4136-1-mic@digikod.net/
[1] https://lore.kernel.org/lkml/CAG48ez21bEn0wL1bbmTiiu8j9jP5iEWtHOwz4tURUJ+ki0... [2] https://lore.kernel.org/lkml/50db058a-7dde-441b-a7f9-f6837fe8b69f@schaufler-...
Regards,
Mickaël Salaün (10): landlock: Add object 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 | 69 + Documentation/security/landlock/user.rst | 227 +++ MAINTAINERS | 12 + arch/alpha/kernel/syscalls/syscall.tbl | 1 + arch/arm/tools/syscall.tbl | 1 + arch/arm64/include/asm/unistd.h | 2 +- arch/arm64/include/asm/unistd32.h | 2 + arch/ia64/kernel/syscalls/syscall.tbl | 1 + arch/m68k/kernel/syscalls/syscall.tbl | 1 + arch/microblaze/kernel/syscalls/syscall.tbl | 1 + arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + arch/mips/kernel/syscalls/syscall_n64.tbl | 1 + arch/mips/kernel/syscalls/syscall_o32.tbl | 1 + arch/parisc/kernel/syscalls/syscall.tbl | 1 + arch/powerpc/kernel/syscalls/syscall.tbl | 1 + arch/s390/kernel/syscalls/syscall.tbl | 1 + arch/sh/kernel/syscalls/syscall.tbl | 1 + arch/sparc/kernel/syscalls/syscall.tbl | 1 + arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/xtensa/kernel/syscalls/syscall.tbl | 1 + fs/super.c | 2 + include/linux/fs.h | 5 + include/linux/landlock.h | 22 + include/linux/syscalls.h | 3 + include/uapi/asm-generic/unistd.h | 4 +- include/uapi/linux/landlock.h | 311 ++++ kernel/sys_ni.c | 3 + samples/Kconfig | 7 + samples/Makefile | 1 + samples/landlock/.gitignore | 1 + samples/landlock/Makefile | 15 + samples/landlock/sandboxer.c | 217 +++ security/Kconfig | 11 +- security/Makefile | 2 + security/landlock/Kconfig | 18 + security/landlock/Makefile | 4 + security/landlock/common.h | 20 + security/landlock/cred.c | 46 + security/landlock/cred.h | 55 + security/landlock/fs.c | 561 ++++++++ security/landlock/fs.h | 42 + security/landlock/object.c | 66 + security/landlock/object.h | 92 ++ security/landlock/ptrace.c | 120 ++ security/landlock/ptrace.h | 14 + security/landlock/ruleset.c | 352 +++++ security/landlock/ruleset.h | 182 +++ security/landlock/setup.c | 39 + security/landlock/setup.h | 18 + security/landlock/syscall.c | 521 +++++++ tools/testing/selftests/Makefile | 1 + tools/testing/selftests/landlock/.gitignore | 4 + tools/testing/selftests/landlock/Makefile | 26 + tools/testing/selftests/landlock/common.h | 42 + tools/testing/selftests/landlock/config | 5 + tools/testing/selftests/landlock/test_base.c | 113 ++ tools/testing/selftests/landlock/test_fs.c | 1249 +++++++++++++++++ .../testing/selftests/landlock/test_ptrace.c | 294 ++++ tools/testing/selftests/landlock/true.c | 5 + 62 files changed, 4833 insertions(+), 7 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/common.h 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/common.h create mode 100644 tools/testing/selftests/landlock/config 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 create mode 100644 tools/testing/selftests/landlock/true.c