Hi, The goal of this patch series is to enable to control script execution with interpreters help. A new O_MAYEXEC flag, usable through openat2(2), is added to enable userspace script interpreter to delegate to the kernel (and thus the system security policy) the permission to interpret/execute scripts or other files containing what can be seen as commands. This fourth patch series switch back from RESOLVE_MAYEXEC to O_MAYEXEC which is more appropriate. However, this new flag is only taken into account by openat2(2), but not open(2) nor openat(2). A simple system-wide security policy can be enforced by the system administrator through a sysctl configuration consistent with the mount points or the file access rights. The documentation patch explains the prerequisites. Furthermore, the security policy can also be delegated to an LSM, either a MAC system or an integrity system. For instance, the new kernel MAY_OPENEXEC flag closes a major IMA measurement/appraisal interpreter integrity gap by bringing the ability to check the use of scripts [1]. Other uses are expected, such as for openat2(2) [2], SGX integration [3], bpffs [4] or IPE [5]. Userspace needs to adapt to take advantage of this new feature. For example, the PEP 578 [6] (Runtime Audit Hooks) enables Python 3.8 to be extended with policy enforcement points related to code interpretation, which can be used to align with the PowerShell audit features. Additional Python security improvements (e.g. a limited interpreter withou -c, stdin piping of code) are on their way. The initial idea come from CLIP OS 4 and the original implementation has been used for more than 11 years: https://github.com/clipos-archive/clipos4_doc An introduction to O_MAYEXEC was given at the Linux Security Summit Europe 2018 - Linux Kernel Security Contributions by ANSSI: https://www.youtube.com/watch?v=chNjCRtPKQY&t=17m15s The "write xor execute" principle was explained at Kernel Recipes 2018 - CLIP OS: a defense-in-depth OS: https://www.youtube.com/watch?v=PjRE0uBtkHU&t=11m14s This patch series can be applied on top of v5.7-rc3. This can be tested with CONFIG_SYSCTL. I would really appreciate constructive comments on this patch series. Previous version: https://lore.kernel.org/lkml/20200428175129.634352-1-mic@xxxxxxxxxxx/ [1] https://lore.kernel.org/lkml/1544647356.4028.105.camel@xxxxxxxxxxxxx/ [2] https://lore.kernel.org/lkml/20190904201933.10736-6-cyphar@xxxxxxxxxx/ [3] https://lore.kernel.org/lkml/CALCETrVovr8XNZSroey7pHF46O=kj_c5D9K8h=z2T_cNrpvMig@xxxxxxxxxxxxxx/ [4] https://lore.kernel.org/lkml/CALCETrVeZ0eufFXwfhtaG_j+AdvbzEWE0M3wjXMWVEO7pj+xkw@xxxxxxxxxxxxxx/ [5] https://lore.kernel.org/lkml/20200406221439.1469862-12-deven.desai@xxxxxxxxxxxxxxxxxxx/ [6] https://www.python.org/dev/peps/pep-0578/ Regards, Mickaël Salaün (5): fs: Add support for an O_MAYEXEC flag on openat2(2) fs: Add a MAY_EXECMOUNT flag to infer the noexec mount property fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC selftest/openat2: Add tests for O_MAYEXEC enforcing doc: Add documentation for the fs.open_mayexec_enforce sysctl Documentation/admin-guide/sysctl/fs.rst | 44 +++ fs/fcntl.c | 2 +- fs/namei.c | 74 +++- fs/open.c | 8 + include/linux/fcntl.h | 2 +- include/linux/fs.h | 7 + include/uapi/asm-generic/fcntl.h | 7 + kernel/sysctl.c | 7 + tools/testing/selftests/kselftest_harness.h | 3 + tools/testing/selftests/openat2/Makefile | 3 +- tools/testing/selftests/openat2/config | 1 + tools/testing/selftests/openat2/helpers.h | 1 + .../testing/selftests/openat2/omayexec_test.c | 330 ++++++++++++++++++ 13 files changed, 485 insertions(+), 4 deletions(-) create mode 100644 tools/testing/selftests/openat2/config create mode 100644 tools/testing/selftests/openat2/omayexec_test.c -- 2.26.2
