Date: Mon, 10 Aug 2020 22:11:53 +0200 From: Mickaël Salaün <mic@...ikod.net> To: Kees Cook <keescook@...omium.org>, Andrew Morton <akpm@...ux-foundation.org> Cc: linux-kernel@...r.kernel.org, Aleksa Sarai <cyphar@...har.com>, Alexei Starovoitov <ast@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, Andy Lutomirski <luto@...nel.org>, Christian Brauner <christian.brauner@...ntu.com>, Christian Heimes <christian@...hon.org>, Daniel Borkmann <daniel@...earbox.net>, Deven Bowers <deven.desai@...ux.microsoft.com>, Dmitry Vyukov <dvyukov@...gle.com>, Eric Biggers <ebiggers@...nel.org>, Eric Chiang <ericchiang@...gle.com>, Florian Weimer <fweimer@...hat.com>, James Morris <jmorris@...ei.org>, Jan Kara <jack@...e.cz>, Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>, Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>, Matthew Garrett <mjg59@...gle.com>, Matthew Wilcox <willy@...radead.org>, Michael Kerrisk <mtk.manpages@...il.com>, Mimi Zohar <zohar@...ux.ibm.com>, Philippe Trébuchet <philippe.trebuchet@....gouv.fr>, Scott Shell <scottsh@...rosoft.com>, Sean Christopherson <sean.j.christopherson@...el.com>, Shuah Khan <shuah@...nel.org>, Steve Dower <steve.dower@...hon.org>, Steve Grubb <sgrubb@...hat.com>, Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>, Thibaut Sautereau <thibaut.sautereau@...p-os.org>, Vincent Strubel <vincent.strubel@....gouv.fr>, kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org, linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org, linux-fsdevel@...r.kernel.org Subject: Re: [PATCH v7 0/7] Add support for O_MAYEXEC It seems that there is no more complains nor questions. Do you want me to send another series to fix the order of the S-o-b in patch 7? On 24/07/2020 21:06, Kees Cook wrote: > 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 . >> Other uses are expected, such as for magic-links , SGX integration >> , bpffs  or IPE . >> >> >> # Prerequisite of its use >> >> Userspace needs to adapt to take advantage of this new feature. For >> example, the PEP 578  (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 . >> >> >> # 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://email@example.com/ >> >> >>  https://firstname.lastname@example.org/ >>  https://email@example.com/ >>  https://lore.kernel.org/lkml/CALCETrVovr8XNZSroey7pHF46O=kj_c5D9K8h=z2T_cNrpvMig@mail.gmail.com/ >>  https://lore.kernel.org/lkml/CALCETrVeZ0eufFXwfhtaG_j+AdvbzEWE0M3wjXMWVEO7pjfirstname.lastname@example.org/ >>  https://email@example.com/ >>  https://www.python.org/dev/peps/pep-0578/ >>  https://firstname.lastname@example.org/ >> >> 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 >> >
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