I think this looks good now. Andrew, since you're already carrying my exec clean-ups (repeated here in patch 1-3), can you pick the rest of this series too? Thanks! -Kees On Thu, Jul 23, 2020 at 07:12:20PM +0200, Mickaël Salaün wrote: > 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 > -- Kees Cook
