From: Jeff Layton <jlayton@kernel.org>
To: Aleksa Sarai <cyphar@cyphar.com>
Cc: "Mickaël Salaün" <mickael.salaun@ssi.gouv.fr>,
"Florian Weimer" <fweimer@redhat.com>,
"Mickaël Salaün" <mic@digikod.net>,
linux-kernel@vger.kernel.org,
"Alexei Starovoitov" <ast@kernel.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Andy Lutomirski" <luto@kernel.org>,
"Christian Heimes" <christian@python.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Eric Chiang" <ericchiang@google.com>,
"James Morris" <jmorris@namei.org>, "Jan Kara" <jack@suse.cz>,
"Jann Horn" <jannh@google.com>,
"Jonathan Corbet" <corbet@lwn.net>,
"Kees Cook" <keescook@chromium.org>,
"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>,
"Song Liu" <songliubraving@fb.com>,
"Steve Dower" <steve.dower@python.org>,
"Steve Grubb" <sgrubb@redhat.com>,
"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@lists.openwall.com, linux-api@vger.kernel.org,
linux-security-module@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2 1/5] fs: Add support for an O_MAYEXEC flag on sys_open()
Date: Fri, 06 Sep 2019 15:43:33 -0400 [thread overview]
Message-ID: <e1ac9428e6b768ac3145aafbe19b24dd6cf410b9.camel@kernel.org> (raw)
In-Reply-To: <20190906171335.d7mc3no5tdrcn6r5@yavin.dot.cyphar.com>
On Sat, 2019-09-07 at 03:13 +1000, Aleksa Sarai wrote:
> On 2019-09-06, Jeff Layton <jlayton@kernel.org> wrote:
> > On Fri, 2019-09-06 at 18:06 +0200, Mickaël Salaün wrote:
> > > On 06/09/2019 17:56, Florian Weimer wrote:
> > > > Let's assume I want to add support for this to the glibc dynamic loader,
> > > > while still being able to run on older kernels.
> > > >
> > > > Is it safe to try the open call first, with O_MAYEXEC, and if that fails
> > > > with EINVAL, try again without O_MAYEXEC?
> > >
> > > The kernel ignore unknown open(2) flags, so yes, it is safe even for
> > > older kernel to use O_MAYEXEC.
> > >
> >
> > Well...maybe. What about existing programs that are sending down bogus
> > open flags? Once you turn this on, they may break...or provide a way to
> > circumvent the protections this gives.
>
> It should be noted that this has been a valid concern for every new O_*
> flag introduced (and yet we still introduced new flags, despite the
> concern) -- though to be fair, O_TMPFILE actually does have a
> work-around with the O_DIRECTORY mask setup.
>
> The openat2() set adds O_EMPTYPATH -- though in fairness it's also
> backwards compatible because empty path strings have always given ENOENT
> (or EINVAL?) while O_EMPTYPATH is a no-op non-empty strings.
>
> > Maybe this should be a new flag that is only usable in the new openat2()
> > syscall that's still under discussion? That syscall will enforce that
> > all flags are recognized. You presumably wouldn't need the sysctl if you
> > went that route too.
>
> I'm also interested in whether we could add an UPGRADE_NOEXEC flag to
> how->upgrade_mask for the openat2(2) patchset (I reserved a flag bit for
> it, since I'd heard about this work through the grape-vine).
>
I rather like the idea of having openat2 fds be non-executable by
default, and having userland request it specifically via O_MAYEXEC (or
some similar openat2 flag) if it's needed. Then you could add an
UPGRADE_EXEC flag instead?
That seems like something reasonable to do with a brand new API, and
might be very helpful for preventing certain classes of attacks.
--
Jeff Layton <jlayton@kernel.org>
next prev parent reply other threads:[~2019-09-06 19:43 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-06 15:24 [PATCH v2 0/5] Add support for O_MAYEXEC Mickaël Salaün
2019-09-06 15:24 ` [PATCH v2 1/5] fs: Add support for an O_MAYEXEC flag on sys_open() Mickaël Salaün
2019-09-06 15:56 ` Florian Weimer
2019-09-06 16:06 ` Mickaël Salaün
2019-09-06 16:48 ` Jeff Layton
2019-09-06 17:13 ` Aleksa Sarai
2019-09-06 19:43 ` Jeff Layton [this message]
2019-09-06 20:06 ` Andy Lutomirski
2019-09-06 20:51 ` Jeff Layton
2019-09-06 21:27 ` Andy Lutomirski
2019-09-06 22:12 ` Aleksa Sarai
2019-09-09 9:33 ` Mickaël Salaün
2019-09-06 22:05 ` Aleksa Sarai
2019-09-06 22:18 ` Aleksa Sarai
2019-09-06 17:14 ` Mickaël Salaün
2019-09-06 18:38 ` Jeff Layton
2019-09-06 18:41 ` Andy Lutomirski
2019-09-09 9:18 ` Mickaël Salaün
2019-09-09 15:49 ` Andy Lutomirski
2019-09-06 18:44 ` Florian Weimer
2019-09-06 19:03 ` James Morris
2019-09-09 9:25 ` Mickaël Salaün
2019-09-09 10:12 ` James Morris
2019-09-09 10:54 ` Mickaël Salaün
2019-09-09 12:28 ` Aleksa Sarai
2019-09-09 12:33 ` Mickaël Salaün
2019-09-09 11:54 ` Aleksa Sarai
2019-09-09 12:28 ` Mickaël Salaün
2019-09-06 17:07 ` Aleksa Sarai
2019-09-06 17:20 ` Christian Brauner
2019-09-06 17:24 ` Mickaël Salaün
2019-09-06 17:40 ` Tycho Andersen
2019-09-06 18:27 ` Florian Weimer
2019-09-06 18:46 ` Tycho Andersen
2019-09-06 15:24 ` [PATCH v2 2/5] fs: Add a MAY_EXECMOUNT flag to infer the noexec mount propertie Mickaël Salaün
2019-09-06 15:24 ` [PATCH v2 3/5] fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC Mickaël Salaün
2019-09-06 15:24 ` [PATCH v2 4/5] selftest/exec: Add tests for O_MAYEXEC enforcing Mickaël Salaün
2019-09-06 15:24 ` [PATCH v2 5/5] doc: Add documentation for the fs.open_mayexec_enforce sysctl Mickaël Salaün
2019-09-06 18:50 ` [PATCH v2 0/5] Add support for O_MAYEXEC Steve Grubb
2019-09-06 18:57 ` Florian Weimer
2019-09-06 19:07 ` Steve Grubb
2019-09-06 19:26 ` Andy Lutomirski
2019-09-06 22:44 ` Aleksa Sarai
2019-09-09 9:09 ` Mickaël Salaün
2019-09-09 0:16 ` James Morris
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