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 39C65C00307 for ; Fri, 6 Sep 2019 17:08:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1AB1220578 for ; Fri, 6 Sep 2019 17:08:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2395130AbfIFRIR (ORCPT ); Fri, 6 Sep 2019 13:08:17 -0400 Received: from mx2.mailbox.org ([80.241.60.215]:38946 "EHLO mx2.mailbox.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726012AbfIFRIQ (ORCPT ); Fri, 6 Sep 2019 13:08:16 -0400 Received: from smtp2.mailbox.org (smtp2.mailbox.org [IPv6:2001:67c:2050:105:465:1:2:0]) (using TLSv1.2 with cipher ECDHE-RSA-CHACHA20-POLY1305 (256/256 bits)) (No client certificate requested) by mx2.mailbox.org (Postfix) with ESMTPS id BE83CA10B1; Fri, 6 Sep 2019 19:08:12 +0200 (CEST) X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp2.mailbox.org ([80.241.60.241]) by gerste.heinlein-support.de (gerste.heinlein-support.de [91.198.250.173]) (amavisd-new, port 10030) with ESMTP id LZRQmSkyiH7U; Fri, 6 Sep 2019 19:08:06 +0200 (CEST) Date: Sat, 7 Sep 2019 03:07:39 +1000 From: Aleksa Sarai To: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= Cc: 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: <20190906170739.kk3opr2phidb7ilb@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="6rtmfi5hsevxvupm" Content-Disposition: inline In-Reply-To: <75442f3b-a3d8-12db-579a-2c5983426b4d@ssi.gouv.fr> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org --6rtmfi5hsevxvupm Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2019-09-06, Micka=EBl Sala=FCn wrote: >=20 > 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? >=20 > The kernel ignore unknown open(2) flags, so yes, it is safe even for > older kernel to use O_MAYEXEC. Depends on your definition of "safe" -- a security feature that you will silently not enable on older kernels doesn't sound super safe to me. Unfortunately this is a limitation of open(2) that we cannot change -- which is why the openat2(2) proposal I've been posting gives -EINVAL for unknown O_* flags. There is a way to probe for support (though unpleasant), by creating a test O_MAYEXEC fd and then checking if the flag is present in /proc/self/fdinfo/$n. --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --6rtmfi5hsevxvupm Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXXKSVwAKCRCdlLljIbnQ EqsMAQCcsnT73iJu8qsLaNqcZ8fDsRQoivoCCPz1rmApirVAJwD8Dykhs9u7hP9n 7SbkdjKA/jSU4Chb/m54X97YQPGbcAU= =hMDq -----END PGP SIGNATURE----- --6rtmfi5hsevxvupm--