Hi, This seventh patch series do not set __FMODE_EXEC for the sake of simplicity. A notification feature could be added later if needed. The handling of all file types is now well defined and tested: by default, when opening a path, access to a directory is denied (with EISDIR), access to a regular file depends on the sysctl policy, and access to other file types (i.e. fifo, device, socket) is denied if there is any enforced policy. There is new tests covering all these cases (cf. test_file_types() ). As requested by Mimi Zohar, I completed the series with one of her patches for IMA. I also picked Kees Cook's patches to consolidate exec permission checking into do_filp_open()'s flow. # Goal of O_MAYEXEC 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 interpreters 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. 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 magic-links [2], SGX integration [3], bpffs [4] or IPE [5]. # Prerequisite of its use 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 [7]. # Examples The initial idea comes from CLIP OS 4 and the original implementation has been used for more than 12 years: https://github.com/clipos-archive/clipos4_doc Chrome OS has a similar approach: https://chromium.googlesource.com/chromiumos/docs/+/master/security/noexec_shell_scripts.md Userland patches can be found here: https://github.com/clipos-archive/clipos4_portage-overlay/search?q=O_MAYEXEC Actually, there is more than the O_MAYEXEC changes (which matches this search) e.g., to prevent Python interactive execution. There are patches for Bash, Wine, Java (Icedtea), Busybox's ash, Perl and Python. There are also some related patches which do not directly rely on O_MAYEXEC but which restrict the use of browser plugins and extensions, which may be seen as scripts too: https://github.com/clipos-archive/clipos4_portage-overlay/tree/master/www-client 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 See also an overview article: https://lwn.net/Articles/820000/ This patch series can be applied on top of v5.8-rc5 . This can be tested with CONFIG_SYSCTL. I would really appreciate constructive comments on this patch series. Previous version: https://lore.kernel.org/lkml/20200505153156.925111-1-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/ [7] https://lore.kernel.org/lkml/0c70debd-e79e-d514-06c6-4cd1e021fa8b@xxxxxxxxxx/ Regards, Kees Cook (3): exec: Change uselib(2) IS_SREG() failure to EACCES exec: Move S_ISREG() check earlier exec: Move path_noexec() check earlier Mickaël Salaün (3): fs: Introduce O_MAYEXEC flag for openat2(2) fs,doc: Enable to enforce noexec mounts or file exec through O_MAYEXEC selftest/openat2: Add tests for O_MAYEXEC enforcing Mimi Zohar (1): ima: add policy support for the new file open MAY_OPENEXEC flag Documentation/ABI/testing/ima_policy | 2 +- Documentation/admin-guide/sysctl/fs.rst | 49 +++ fs/exec.c | 23 +- fs/fcntl.c | 2 +- fs/namei.c | 36 +- fs/open.c | 12 +- include/linux/fcntl.h | 2 +- include/linux/fs.h | 3 + include/uapi/asm-generic/fcntl.h | 7 + kernel/sysctl.c | 12 +- security/integrity/ima/ima_main.c | 3 +- security/integrity/ima/ima_policy.c | 15 +- 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 | 325 ++++++++++++++++++ 17 files changed, 470 insertions(+), 29 deletions(-) create mode 100644 tools/testing/selftests/openat2/config create mode 100644 tools/testing/selftests/openat2/omayexec_test.c -- 2.27.0
