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From: Andy Lutomirski <luto@kernel.org>
To: Jan Kara <jack@suse.cz>, Song Liu <songliubraving@fb.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>
Cc: "Mickaël Salaün" <mic@digikod.net>,
	LKML <linux-kernel@vger.kernel.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"James Morris" <jmorris@namei.org>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Kees Cook" <keescook@chromium.org>,
	"Matthew Garrett" <mjg59@google.com>,
	"Michael Kerrisk" <mtk.manpages@gmail.com>,
	"Mickaël Salaün" <mickael.salaun@ssi.gouv.fr>,
	"Mimi Zohar" <zohar@linux.ibm.com>,
	"Philippe Trébuchet" <philippe.trebuchet@ssi.gouv.fr>,
	"Shuah Khan" <shuah@kernel.org>,
	"Thibaut Sautereau" <thibaut.sautereau@ssi.gouv.fr>,
	"Vincent Strubel" <vincent.strubel@ssi.gouv.fr>,
	"Yves-Alexis Perez" <yves-alexis.perez@ssi.gouv.fr>,
	"Kernel Hardening" <kernel-hardening@lists.openwall.com>,
	"Linux API" <linux-api@vger.kernel.org>,
	"LSM List" <linux-security-module@vger.kernel.org>,
	"Linux FS Devel" <linux-fsdevel@vger.kernel.org>,
	"Steve Grubb" <sgrubb@redhat.com>,
	"Matthew Bobrowski" <mbobrowski@mbobrowski.org>
Subject: Re: [RFC PATCH v1 1/5] fs: Add support for an O_MAYEXEC flag on sys_open()
Date: Sun, 4 Aug 2019 16:55:58 -0700
Message-ID: <CALCETrVeZ0eufFXwfhtaG_j+AdvbzEWE0M3wjXMWVEO7pj+xkw@mail.gmail.com> (raw)
In-Reply-To: <20181212144306.GA19945@quack2.suse.cz>

On Wed, Dec 12, 2018 at 6:43 AM Jan Kara <jack@suse.cz> wrote:
>
> On Wed 12-12-18 09:17:08, Mickaël Salaün wrote:
> > When the O_MAYEXEC flag is passed, sys_open() may be subject to
> > additional restrictions depending on a security policy implemented by an
> > LSM through the inode_permission hook.
> >
> > 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 (for which the kernel can't help):
> > command line parameters (e.g., option -e for Perl), module loading
> > (e.g., option -m for Python), stdin, file sourcing, environment
> > variables, configuration files...  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.
> >
> > A simple security policy implementation is available in a following
> > patch for Yama.
> >
> > This is an updated subset of the patch initially written by Vincent
> > Strubel for CLIP OS:
> > https://github.com/clipos-archive/src_platform_clip-patches/blob/f5cb330d6b684752e403b4e41b39f7004d88e561/1901_open_mayexec.patch
> > This patch has been used for more than 10 years with customized script
> > interpreters.  Some examples can be found here:
> > https://github.com/clipos-archive/clipos4_portage-overlay/search?q=O_MAYEXEC
> >
> > Signed-off-by: Mickaël Salaün <mic@digikod.net>
> > Signed-off-by: Thibaut Sautereau <thibaut.sautereau@ssi.gouv.fr>
> > Signed-off-by: Vincent Strubel <vincent.strubel@ssi.gouv.fr>
> > Reviewed-by: Philippe Trébuchet <philippe.trebuchet@ssi.gouv.fr>
> > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: Mickaël Salaün <mickael.salaun@ssi.gouv.fr>
>
> ...
>
> > diff --git a/fs/open.c b/fs/open.c
> > index 0285ce7dbd51..75479b79a58f 100644
> > --- a/fs/open.c
> > +++ b/fs/open.c
> > @@ -974,6 +974,10 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o
> >       if (flags & O_APPEND)
> >               acc_mode |= MAY_APPEND;
> >
> > +     /* Check execution permissions on open. */
> > +     if (flags & O_MAYEXEC)
> > +             acc_mode |= MAY_OPENEXEC;
> > +
> >       op->acc_mode = acc_mode;
> >
> >       op->intent = flags & O_PATH ? 0 : LOOKUP_OPEN;
>
> I don't feel experienced enough in security to tell whether we want this
> functionality or not. But if we do this, shouldn't we also set FMODE_EXEC
> on the resulting struct file? That way also security_file_open() can be
> used to arbitrate such executable opens and in particular
> fanotify permission event FAN_OPEN_EXEC will get properly generated which I
> guess is desirable (support for it is sitting in my tree waiting for the
> merge window) - adding some audit people involved in FAN_OPEN_EXEC to
> CC. Just an idea...
>

I would really like to land this patch.  I'm fiddling with making
bpffs handle permissions intelligently, and the lack of a way to say
"hey, I want to open this bpf program so that I can run it" is
annoying.

--Andy

  parent reply index

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-12  8:17 [RFC PATCH v1 0/5] Add support for O_MAYEXEC Mickaël Salaün
2018-12-12  8:17 ` [RFC PATCH v1 1/5] fs: Add support for an O_MAYEXEC flag on sys_open() Mickaël Salaün
2018-12-12 14:43   ` Jan Kara
2018-12-12 17:09     ` Mickaël Salaün
2018-12-12 20:42     ` Mimi Zohar
2018-12-13  9:47     ` Matthew Bobrowski
2018-12-13 14:23       ` Mickaël Salaün
2019-04-15 18:47     ` Steve Grubb
2019-04-16 11:49       ` Florian Weimer
2019-04-16 15:34         ` Steve Grubb
2019-04-17 10:01           ` Florian Weimer
2019-04-17 15:04             ` Mickaël Salaün
2019-04-17 14:55       ` Mickaël Salaün
2019-08-04 23:55     ` Andy Lutomirski [this message]
2019-08-06 16:40       ` Mickaël Salaün
2018-12-12  8:17 ` [RFC PATCH v1 2/5] fs: Add a MAY_EXECMOUNT flag to infer the noexec mount propertie Mickaël Salaün
2018-12-12  8:17 ` [RFC PATCH v1 3/5] Yama: Enforces noexec mounts or file executability through O_MAYEXEC Mickaël Salaün
2018-12-12 14:28   ` Mickaël Salaün
2018-12-12 17:09   ` Jann Horn
2018-12-13 14:49     ` Mickaël Salaün
2019-01-03 11:17       ` Jann Horn
2019-01-08 13:29         ` Mickaël Salaün
2019-01-08 23:30           ` Kees Cook
2019-01-09 13:41             ` Mickaël Salaün
2018-12-12  8:17 ` [RFC PATCH v1 4/5] selftest/yama: Add tests for O_MAYEXEC enforcing Mickaël Salaün
2018-12-12  8:17 ` [RFC PATCH v1 5/5] doc: Add documentation for Yama's open_mayexec_enforce Mickaël Salaün
2018-12-12 16:29 ` [RFC PATCH v1 0/5] Add support for O_MAYEXEC Jordan Glover
2018-12-12 17:01   ` Mickaël Salaün
2018-12-12 19:51 ` James Morris
2018-12-12 20:13   ` Florian Weimer
2018-12-12 23:40     ` James Morris
2018-12-13  5:13       ` Florian Weimer
2018-12-13 14:57         ` Mickaël Salaün
2018-12-13  3:02 ` Matthew Wilcox
2018-12-13  5:22   ` Florian Weimer
2018-12-13 11:04   ` Mimi Zohar
2018-12-13 11:26     ` Florian Weimer
2018-12-13 12:16       ` Mimi Zohar
2018-12-13 12:16     ` Matthew Wilcox
2018-12-13 15:17   ` Mickaël Salaün
2018-12-13 17:13     ` Matthew Wilcox
2018-12-13 17:36       ` Mickaël Salaün
2018-12-13 17:44         ` Matthew Wilcox

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