From: Kees Cook <keescook@chromium.org>
To: "Mickaël Salaün" <mic@digikod.net>
Cc: linux-kernel@vger.kernel.org, "Aleksa Sarai" <cyphar@cyphar.com>,
"Alexei Starovoitov" <ast@kernel.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Andy Lutomirski" <luto@kernel.org>,
"Christian Brauner" <christian.brauner@ubuntu.com>,
"Christian Heimes" <christian@python.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Deven Bowers" <deven.desai@linux.microsoft.com>,
"Dmitry Vyukov" <dvyukov@google.com>,
"Eric Biggers" <ebiggers@kernel.org>,
"Eric Chiang" <ericchiang@google.com>,
"Florian Weimer" <fweimer@redhat.com>,
"James Morris" <jmorris@namei.org>, "Jan Kara" <jack@suse.cz>,
"Jann Horn" <jannh@google.com>,
"Jonathan Corbet" <corbet@lwn.net>,
"Lakshmi Ramasubramanian" <nramas@linux.microsoft.com>,
"Matthew Garrett" <mjg59@google.com>,
"Matthew Wilcox" <willy@infradead.org>,
"Michael Kerrisk" <mtk.manpages@gmail.com>,
"Mimi Zohar" <zohar@linux.ibm.com>,
"Philippe Trébuchet" <philippe.trebuchet@ssi.gouv.fr>,
"Scott Shell" <scottsh@microsoft.com>,
"Sean Christopherson" <sean.j.christopherson@intel.com>,
"Shuah Khan" <shuah@kernel.org>,
"Steve Dower" <steve.dower@python.org>,
"Steve Grubb" <sgrubb@redhat.com>,
"Tetsuo Handa" <penguin-kernel@I-love.SAKURA.ne.jp>,
"Thibaut Sautereau" <thibaut.sautereau@clip-os.org>,
"Vincent Strubel" <vincent.strubel@ssi.gouv.fr>,
kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org,
linux-fsdevel@vger.kernel.org,
"Thibaut Sautereau" <thibaut.sautereau@ssi.gouv.fr>
Subject: Re: [PATCH v7 4/7] fs: Introduce O_MAYEXEC flag for openat2(2)
Date: Fri, 24 Jul 2020 12:03:01 -0700 [thread overview]
Message-ID: <202007241202.8D07E1F276@keescook> (raw)
In-Reply-To: <20200723171227.446711-5-mic@digikod.net>
On Thu, Jul 23, 2020 at 07:12:24PM +0200, Mickaël Salaün wrote:
> When the O_MAYEXEC flag is passed, openat2(2) may be subject to
> additional restrictions depending on a security policy managed by the
> kernel through a sysctl or implemented by an LSM thanks to the
> inode_permission hook. This new flag is ignored by open(2) and
> openat(2) because of their unspecified flags handling. When used with
> openat2(2), the default behavior is only to forbid to open a directory.
>
> The underlying idea is to be able to restrict scripts interpretation
> according to a policy defined by the system administrator. For this to
> be possible, script interpreters must use the O_MAYEXEC flag
> appropriately. To be fully effective, these interpreters also need to
> handle the other ways to execute code: command line parameters (e.g.,
> option -e for Perl), module loading (e.g., option -m for Python), stdin,
> file sourcing, environment variables, configuration files, etc.
> According to the threat model, it may be acceptable to allow some script
> interpreters (e.g. Bash) to interpret commands from stdin, may it be a
> TTY or a pipe, because it may not be enough to (directly) perform
> syscalls. Further documentation can be found in a following patch.
>
> Even without enforced security policy, userland interpreters can set it
> to enforce the system policy at their level, knowing that it will not
> break anything on running systems which do not care about this feature.
> However, on systems which want this feature enforced, there will be
> knowledgeable people (i.e. sysadmins who enforced O_MAYEXEC
> deliberately) to manage it. A simple security policy implementation,
> configured through a dedicated sysctl, is available in a following
> patch.
>
> O_MAYEXEC should not be confused with the O_EXEC flag which is intended
> for execute-only, which obviously doesn't work for scripts. However, a
> similar behavior could be implemented in userland with O_PATH:
> https://lore.kernel.org/lkml/1e2f6913-42f2-3578-28ed-567f6a4bdda1@digikod.net/
>
> The implementation of O_MAYEXEC almost duplicates what execve(2) and
> uselib(2) are already doing: setting MAY_OPENEXEC in acc_mode (which can
> then be checked as MAY_EXEC, if enforced).
>
> This is an updated subset of the patch initially written by Vincent
> Strubel for CLIP OS 4:
> https://github.com/clipos-archive/src_platform_clip-patches/blob/f5cb330d6b684752e403b4e41b39f7004d88e561/1901_open_mayexec.patch
> This patch has been used for more than 12 years with customized script
> interpreters. Some examples (with the original O_MAYEXEC) can be found
> here:
> https://github.com/clipos-archive/clipos4_portage-overlay/search?q=O_MAYEXEC
>
> Co-developed-by: Vincent Strubel <vincent.strubel@ssi.gouv.fr>
> Signed-off-by: Vincent Strubel <vincent.strubel@ssi.gouv.fr>
Acked-by: Kees Cook <keescook@chromium.org>
--
Kees Cook
next prev parent reply other threads:[~2020-07-24 19:03 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-23 17:12 [PATCH v7 0/7] Add support for O_MAYEXEC Mickaël Salaün
2020-07-23 17:12 ` [PATCH v7 1/7] exec: Change uselib(2) IS_SREG() failure to EACCES Mickaël Salaün
2020-08-11 18:59 ` Eric W. Biederman
2020-08-11 19:14 ` Eric W. Biederman
2020-07-23 17:12 ` [PATCH v7 2/7] exec: Move S_ISREG() check earlier Mickaël Salaün
2020-08-11 19:27 ` Eric W. Biederman
2020-07-23 17:12 ` [PATCH v7 3/7] exec: Move path_noexec() " Mickaël Salaün
2020-08-11 19:36 ` Eric W. Biederman
2020-08-13 15:31 ` Mickaël Salaün
2020-07-23 17:12 ` [PATCH v7 4/7] fs: Introduce O_MAYEXEC flag for openat2(2) Mickaël Salaün
2020-07-24 19:03 ` Kees Cook [this message]
2020-07-27 4:21 ` Al Viro
2020-07-27 5:27 ` Florian Weimer
2020-07-27 19:46 ` Mickaël Salaün
2020-08-11 19:51 ` Eric W. Biederman
2020-08-13 14:36 ` Mickaël Salaün
2020-07-23 17:12 ` [PATCH v7 5/7] fs,doc: Enable to enforce noexec mounts or file exec through O_MAYEXEC Mickaël Salaün
2020-07-24 19:03 ` Kees Cook
2020-08-11 19:58 ` Eric W. Biederman
2020-08-13 14:49 ` Mickaël Salaün
2020-07-23 17:12 ` [PATCH v7 6/7] selftest/openat2: Add tests for O_MAYEXEC enforcing Mickaël Salaün
2020-07-24 19:03 ` Kees Cook
2020-07-23 17:12 ` [PATCH v7 7/7] ima: add policy support for the new file open MAY_OPENEXEC flag Mickaël Salaün
2020-07-24 19:04 ` Kees Cook
2020-07-24 11:20 ` [PATCH v7 0/7] Add support for O_MAYEXEC Thibaut Sautereau
2020-07-24 19:06 ` Kees Cook
2020-07-25 11:15 ` Christian Brauner
2020-08-10 20:11 ` Mickaël Salaün
2020-08-10 20:21 ` Al Viro
2020-08-10 22:09 ` David Laight
2020-08-10 22:28 ` Al Viro
2020-08-10 22:47 ` Mickaël Salaün
2020-08-11 8:09 ` David Laight
2020-08-11 8:50 ` Mickaël Salaün
2020-08-10 22:43 ` Mickaël Salaün
2020-08-10 23:03 ` Jann Horn
2020-08-11 8:48 ` Mickaël Salaün
2020-08-11 13:56 ` Mimi Zohar
2020-08-11 14:02 ` Matthew Wilcox
2020-08-11 14:30 ` Mimi Zohar
2020-08-11 17:18 ` Deven Bowers
2020-08-10 23:05 ` Al Viro
2020-08-11 8:49 ` Mickaël Salaün
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