From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 38B76C00307 for ; Fri, 6 Sep 2019 22:06:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1B2942081B for ; Fri, 6 Sep 2019 22:06:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392141AbfIFWGP (ORCPT ); Fri, 6 Sep 2019 18:06:15 -0400 Received: from mx2.mailbox.org ([80.241.60.215]:29954 "EHLO mx2.mailbox.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2392106AbfIFWGP (ORCPT ); Fri, 6 Sep 2019 18:06:15 -0400 Received: from smtp2.mailbox.org (smtp2.mailbox.org [80.241.60.241]) (using TLSv1.2 with cipher ECDHE-RSA-CHACHA20-POLY1305 (256/256 bits)) (No client certificate requested) by mx2.mailbox.org (Postfix) with ESMTPS id E1EB1A107B; Sat, 7 Sep 2019 00:06:10 +0200 (CEST) X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp2.mailbox.org ([80.241.60.241]) by spamfilter03.heinlein-hosting.de (spamfilter03.heinlein-hosting.de [80.241.56.117]) (amavisd-new, port 10030) with ESMTP id A7H_cRDXqsD8; Sat, 7 Sep 2019 00:06:06 +0200 (CEST) Date: Sat, 7 Sep 2019 08:05:46 +1000 From: Aleksa Sarai To: Jeff Layton Cc: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= , Florian Weimer , =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= , linux-kernel@vger.kernel.org, Alexei Starovoitov , Al Viro , Andy Lutomirski , Christian Heimes , Daniel Borkmann , Eric Chiang , James Morris , Jan Kara , Jann Horn , Jonathan Corbet , Kees Cook , Matthew Garrett , Matthew Wilcox , Michael Kerrisk , Mimi Zohar , Philippe =?utf-8?Q?Tr=C3=A9buchet?= , Scott Shell , Sean Christopherson , Shuah Khan , Song Liu , Steve Dower , Steve Grubb , Thibaut Sautereau , Vincent Strubel , Yves-Alexis Perez , 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() Message-ID: <20190906220546.gkqxzm4y3ynevvtz@yavin.dot.cyphar.com> References: <20190906152455.22757-1-mic@digikod.net> <20190906152455.22757-2-mic@digikod.net> <87ef0te7v3.fsf@oldenburg2.str.redhat.com> <75442f3b-a3d8-12db-579a-2c5983426b4d@ssi.gouv.fr> <20190906171335.d7mc3no5tdrcn6r5@yavin.dot.cyphar.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="hzjxi4l2tpqisjxr" Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org --hzjxi4l2tpqisjxr Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2019-09-06, Jeff Layton wrote: > On Sat, 2019-09-07 at 03:13 +1000, Aleksa Sarai wrote: > > On 2019-09-06, Jeff Layton wrote: > > > On Fri, 2019-09-06 at 18:06 +0200, Micka=EBl Sala=FCn 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. > > > > >=20 > > > > > Is it safe to try the open call first, with O_MAYEXEC, and if tha= t fails > > > > > with EINVAL, try again without O_MAYEXEC? > > > >=20 > > > > The kernel ignore unknown open(2) flags, so yes, it is safe even for > > > > older kernel to use O_MAYEXEC. > > > >=20 > > >=20 > > > 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. > >=20 > > 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. > >=20 > > 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. > >=20 > > > Maybe this should be a new flag that is only usable in the new openat= 2() > > > 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. > >=20 > > 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). > >=20 >=20 > 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? >=20 > That seems like something reasonable to do with a brand new API, and > might be very helpful for preventing certain classes of attacks. In that case, maybe openat2(2) should default to not allowing any upgrades by default? The reason I pitched UPGRADE_NOEXEC is because UPGRADE_NO{READ,WRITE} are the existing @how->upgrade_mask flags. However, I just noticed something else about this series -- if you do O_PATH|O_MAYEXEC the new flag gets ignored. Given that you can do fexecve(2) on an O_PATH (and O_PATHs have some other benefits), is this something that we'd want to have? --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --hzjxi4l2tpqisjxr Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXXLYNwAKCRCdlLljIbnQ EgL6APsE8ukJjBgDXqsWSAB5qojHX/kiDFpH8SNcQ7ll9qDWoQEA1azjUmwZIuag abVp9S1zKQWqQobR05kRty8P5rp3swE= =ubv+ -----END PGP SIGNATURE----- --hzjxi4l2tpqisjxr--