Date: Tue, 29 Oct 2019 18:14:58 +0100 From: Mickaël Salaün <mic@...ikod.net> To: linux-kernel@...r.kernel.org Cc: Mickaël Salaün <mic@...ikod.net>, Alexei Starovoitov <ast@...nel.org>, Andy Lutomirski <luto@...capital.net>, Casey Schaufler <casey@...aufler-ca.com>, Daniel Borkmann <daniel@...earbox.net>, David Drysdale <drysdale@...gle.com>, Florent Revest <revest@...omium.org>, James Morris <jmorris@...ei.org>, Jann Horn <jann@...jh.net>, John Johansen <john.johansen@...onical.com>, Jonathan Corbet <corbet@....net>, Kees Cook <keescook@...omium.org>, KP Singh <kpsingh@...omium.org>, Michael Kerrisk <mtk.manpages@...il.com>, Mickaël Salaün <mickael.salaun@....gouv.fr>, Paul Moore <paul@...l-moore.com>, Sargun Dhillon <sargun@...gun.me>, "Serge E . Hallyn" <serge@...lyn.com>, Shuah Khan <shuah@...nel.org>, Stephen Smalley <sds@...ho.nsa.gov>, Tejun Heo <tj@...nel.org>, Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>, Tycho Andersen <tycho@...ho.ws>, Will Drewry <wad@...omium.org>, bpf@...r.kernel.org, kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org, linux-security-module@...r.kernel.org Subject: [PATCH bpf-next v11 0/7] Landlock LSM Hi, This eleventh series is a major rework of the previous series  to make the patches smaller while still putting in place the foundations of Landlock and implementing a useful feature. The whole file-system support (i.e. inode map and program triggers) has been removed (but is still planed in the future). This series rewrite the previous static ptrace restrictions with a programmatic one thanks to eBPF. To be more independent from seccomp, Landlock is now a full LSM using task's credentials thanks to the LSM stacking infrastructure. The only part of seccomp still used is the syscall, which makes sense and which is a quite simple interface. The clear definition of Landlock domains (sets of eBPF programs) can be used for other use-cases than sandboxing e.g., to implement a system-wide security signaling framework as described by KRSI . In addition to improvements and bug fixes, I split the patches as much as possible to ease the review process. As discussed at LSS NA  (with Kees Cook, James Morris, KP Singh and Florent Revest) and at Kernel Recipes (with Alexei Starovoitov), I planned to shrink the code of Landlock to a bare minimum to enable incremental feature integration. The idea was to create a "memory protection" hook and the appropriate eBPF program type. After some experimentations, I concluded that it is not easy to implement a simple interface to control actions such as mmap(2) or mprotect(2). I then focused on an old stable feature of Landlock: ptrace protection. But instead of keeping the static security policy, which make sense in a sandboxing scenario, I extended Landlock with a ptrace hook and the appropriate eBPF program type. The ptrace enforcement is not mandatory anymore but this new hook could be used (and extended with new helpers) for a security signaling mechanism such as KRSI. I hope the KRSI developments could take advantage of this new Landlock version. This is the first step of the roadmap discussed at LPC . While the intended final goal is to allow unprivileged users to use Landlock, this series allows only a process with global CAP_SYS_ADMIN to load and enforce a rule. This may help to get feedback and avoid unexpected behaviors. This series can be applied on top of bpf-next, commit e93d99180abd ("selftests/bpf: Restore $(OUTPUT)/test_stub.o rule"). This can be tested with CONFIG_BPF_SYSCALL, CONFIG_SECCOMP_FILTER and CONFIG_SECURITY_LANDLOCK. This patch series can be found in a Git repository here: https://github.com/landlock-lsm/linux/commits/landlock-v11 I would really appreciate constructive comments on the design and the code. # Landlock LSM Landlock is a stackable LSM  intended to be used as a low-level framework to build custom access-control/audit systems or safe endpoint security agents. There is currently one Landlock hook dedicated to check ptrace(2). This hook accepts a dedicated eBPF program, called a Landlock program, which can currently compare its position in the hierarchy of similar programs tied to other processes. This enables to enforce programmatic scoped ptrace restrictions. The final goal of this new Linux Security Module (LSM) called Landlock is to allow any process, including unprivileged ones, to create powerful security sandboxes comparable to XNU Sandbox, FreeBSD Capsicum or OpenBSD Pledge (which could be implemented with Landlock). This kind of sandbox is expected to help mitigate the security impact of bugs or unexpected/malicious behaviors in user-space applications. The use of seccomp and Landlock is more suitable with the help of a user-space library (e.g. libseccomp) that could help to specify a high-level language to express a security policy instead of raw eBPF programs. Moreover, thanks to the LLVM front-end, it is quite easy to write an eBPF program with a subset of the C language. The documentation patch contains some kernel documentation, explanations on how to use Landlock and a FAQ. The compiled documentation and some talks can be found here: https://landlock.io # Frequently asked questions ## Why is seccomp-bpf not enough? A seccomp filter can access only raw syscall arguments (i.e. the register values) which means that it is not possible to filter according to the value pointed to by an argument, such as a file pathname. As an embryonic Landlock version demonstrated (i.e. seccomp-object), filtering at the syscall level is complicated (e.g. need to take care of race conditions). This is mainly because the access control checkpoints of the kernel are not at this high-level but more underneath, at the LSM-hook level. The LSM hooks are designed to handle this kind of checks. Landlock abstracts this approach to leverage the ability of unprivileged users to limit themselves. Cf. section "What it isn't?" in Documentation/userspace-api/seccomp_filter.rst ## Why use the seccomp(2) syscall? Landlock use the same semantic as seccomp to apply access rule restrictions. It add a new layer of security for the current process which is inherited by its children. It makes sense to use an unique access-restricting syscall (that should be allowed by seccomp filters) which can only drop privileges. Moreover, a Landlock rule could come from outside a process (e.g. passed through a UNIX socket). It is then useful to differentiate the creation/load of Landlock eBPF programs via bpf(2), from rule enforcement via seccomp(2). ## Why a new LSM? Are SELinux, AppArmor, Smack and Tomoyo not good enough? The current access control LSMs are fine for their purpose which is to give the *root* the ability to enforce a security policy for the *system*. What is missing is a way to enforce a security policy for any application by its developer and *unprivileged user* as seccomp can do for raw syscall filtering. Differences from other (access control) LSMs: * not only dedicated to administrators (i.e. no_new_priv); * limited kernel attack surface (e.g. policy parsing); * constrained policy rules (no DoS: deterministic execution time); * do not leak more information than the loader process can legitimately have access to (minimize metadata inference). # Changes since v10 * remove all the file system related features: program types, inode map and expected_attach_triggers * replace the static ptrace security policy with a new and simpler ptrace program (attached) type and a task_landlock_ptrace_ancestor() eBPF helper * do not rely on seccomp internal structure but use stacked credentials insdead * extend ptrace tests * add more documentation * split and rename files/patches * miscellaneous fixes Previous changes can be found in the previous cover-letter .  https://email@example.com/  https://firstname.lastname@example.org/  https://lwn.net/Articles/798157/  https://lore.kernel.org/lkml/5828776A.email@example.com/  https://firstname.lastname@example.org/ Regards, Mickaël Salaün (7): bpf,landlock: Define an eBPF program type for Landlock hooks landlock: Add the management of domains landlock,seccomp: Load Landlock programs per process hierarchy landlock: Add ptrace LSM hooks bpf,landlock: Add task_landlock_ptrace_ancestor() helper bpf,landlock: Add tests for the Landlock ptrace program type landlock: Add user and kernel documentation for Landlock Documentation/security/index.rst | 1 + Documentation/security/landlock/index.rst | 22 ++ Documentation/security/landlock/kernel.rst | 139 +++++++++ Documentation/security/landlock/user.rst | 142 ++++++++++ MAINTAINERS | 9 + include/linux/bpf.h | 3 + include/linux/bpf_types.h | 3 + include/linux/landlock.h | 25 ++ include/linux/lsm_hooks.h | 1 + include/uapi/linux/bpf.h | 23 +- include/uapi/linux/landlock.h | 39 +++ include/uapi/linux/seccomp.h | 1 + kernel/bpf/syscall.c | 9 + kernel/bpf/verifier.c | 11 + kernel/seccomp.c | 4 + scripts/bpf_helpers_doc.py | 1 + security/Kconfig | 1 + security/Makefile | 2 + security/landlock/Kconfig | 19 ++ security/landlock/Makefile | 6 + security/landlock/bpf_ptrace.c | 98 +++++++ security/landlock/bpf_ptrace.h | 17 ++ security/landlock/bpf_run.c | 62 ++++ security/landlock/bpf_run.h | 25 ++ security/landlock/bpf_verify.c | 87 ++++++ security/landlock/common.h | 84 ++++++ security/landlock/domain_manage.c | 265 ++++++++++++++++++ security/landlock/domain_manage.h | 23 ++ security/landlock/domain_syscall.c | 87 ++++++ security/landlock/hooks_cred.c | 47 ++++ security/landlock/hooks_cred.h | 14 + security/landlock/hooks_ptrace.c | 114 ++++++++ security/landlock/hooks_ptrace.h | 19 ++ security/landlock/init.c | 32 +++ security/security.c | 15 + tools/include/uapi/linux/bpf.h | 23 +- tools/include/uapi/linux/landlock.h | 22 ++ tools/lib/bpf/libbpf_probes.c | 3 + tools/testing/selftests/bpf/config | 3 + tools/testing/selftests/bpf/test_verifier.c | 1 + .../testing/selftests/bpf/verifier/landlock.c | 56 ++++ tools/testing/selftests/landlock/.gitignore | 5 + tools/testing/selftests/landlock/Makefile | 27 ++ tools/testing/selftests/landlock/config | 5 + tools/testing/selftests/landlock/test.h | 48 ++++ tools/testing/selftests/landlock/test_base.c | 24 ++ .../testing/selftests/landlock/test_ptrace.c | 210 ++++++++++++++ 47 files changed, 1875 insertions(+), 2 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 security/landlock/Kconfig create mode 100644 security/landlock/Makefile create mode 100644 security/landlock/bpf_ptrace.c create mode 100644 security/landlock/bpf_ptrace.h create mode 100644 security/landlock/bpf_run.c create mode 100644 security/landlock/bpf_run.h create mode 100644 security/landlock/bpf_verify.c create mode 100644 security/landlock/common.h create mode 100644 security/landlock/domain_manage.c create mode 100644 security/landlock/domain_manage.h create mode 100644 security/landlock/domain_syscall.c create mode 100644 security/landlock/hooks_cred.c create mode 100644 security/landlock/hooks_cred.h create mode 100644 security/landlock/hooks_ptrace.c create mode 100644 security/landlock/hooks_ptrace.h create mode 100644 security/landlock/init.c create mode 100644 tools/include/uapi/linux/landlock.h create mode 100644 tools/testing/selftests/bpf/verifier/landlock.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_ptrace.c -- 2.23.0
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