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 A6EEFC43331 for ; Fri, 6 Sep 2019 17:14:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8723320842 for ; Fri, 6 Sep 2019 17:14:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389988AbfIFROC (ORCPT ); Fri, 6 Sep 2019 13:14:02 -0400 Received: from mx2.mailbox.org ([80.241.60.215]:62144 "EHLO mx2.mailbox.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731344AbfIFROB (ORCPT ); Fri, 6 Sep 2019 13:14:01 -0400 Received: from smtp1.mailbox.org (smtp1.mailbox.org [IPv6:2001:67c:2050:105:465:1:1:0]) (using TLSv1.2 with cipher ECDHE-RSA-CHACHA20-POLY1305 (256/256 bits)) (No client certificate requested) by mx2.mailbox.org (Postfix) with ESMTPS id 2C196A1701; Fri, 6 Sep 2019 19:13:58 +0200 (CEST) X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp1.mailbox.org ([80.241.60.240]) by spamfilter04.heinlein-hosting.de (spamfilter04.heinlein-hosting.de [80.241.56.122]) (amavisd-new, port 10030) with ESMTP id KTJPQqxl-qfv; Fri, 6 Sep 2019 19:13:54 +0200 (CEST) Date: Sat, 7 Sep 2019 03:13:35 +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: <20190906171335.d7mc3no5tdrcn6r5@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> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ksyy7c2s2dmez4ls" Content-Disposition: inline In-Reply-To: Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: --ksyy7c2s2dmez4ls Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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 load= er, > > > while still being able to run on older kernels. > > >=20 > > > Is it safe to try the open call first, with O_MAYEXEC, and if that fa= ils > > > 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. 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). --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --ksyy7c2s2dmez4ls Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXXKTvAAKCRCdlLljIbnQ Ep42AQDi8f6e24vrdyEbKC1Hri+QQFzpcnoeEUiuXcTSgZHNWgD/eHmpIaIcPrjX g5Pz4p5iuc67RR3OCv44VfaA+oZMjAo= =7221 -----END PGP SIGNATURE----- --ksyy7c2s2dmez4ls--