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=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 C6AD1C32750 for ; Sun, 4 Aug 2019 23:56:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 953D12089F for ; Sun, 4 Aug 2019 23:56:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564962975; bh=hacK3bFBwtrAv/U9OhwzLwLEIvnI+bjiQ7pJZVwvUsc=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=u/96UtmswYJXNuW1QnaVImhruu+lF7hpspfOjRS46/kBx4CF3DzUkuPyJeMH4cB2a utTkXh7EGVGLsdjA+Bl4Crb0Cdn/9tpt4C4H/sagHe6jpxkiTmQDveOMQQHbZW83eh JmEB/IglSoD+eeKVfY9DUBKSr5wN/gpophS5D1UU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726834AbfHDX4O (ORCPT ); Sun, 4 Aug 2019 19:56:14 -0400 Received: from mail.kernel.org ([198.145.29.99]:51984 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726821AbfHDX4O (ORCPT ); Sun, 4 Aug 2019 19:56:14 -0400 Received: from mail-wr1-f48.google.com (mail-wr1-f48.google.com [209.85.221.48]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B73182133F for ; Sun, 4 Aug 2019 23:56:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564962973; bh=hacK3bFBwtrAv/U9OhwzLwLEIvnI+bjiQ7pJZVwvUsc=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=HE6lxrmjjgnSG6WMJBYy7hwTcselKZPNXoRvcHYGTFNp3d++lIEJWhIZhGyVTS0ij H5FuIRXvlb9WQVf0AEMhzx6VdSK1wG/sCITYb3PR/VuWOOcW49nSAPUIywi/xC3Yyi uwJfifblUxcnxoOJG8iVwLXlt2VK74AOKZDUbEtI= Received: by mail-wr1-f48.google.com with SMTP id z1so82558327wru.13 for ; Sun, 04 Aug 2019 16:56:12 -0700 (PDT) X-Gm-Message-State: APjAAAWLAF/+rpUma+g2p+lb+rk/2Ac949FTIXBcnZHccfHY/6RjpAdK znzMZX7UfRnaVUnId/7jP9I9mX1BdMmEbJXzRywk5g== X-Google-Smtp-Source: APXvYqxn3tZqaoihIH7prfCxvRtZSNWX//uET+sc6tDLm69XbTAHCOuntBreYunR4c+HxPSsMOCqCHJjQE50/g3L7Sc= X-Received: by 2002:adf:dd0f:: with SMTP id a15mr3574634wrm.265.1564962969300; Sun, 04 Aug 2019 16:56:09 -0700 (PDT) MIME-Version: 1.0 References: <20181212081712.32347-1-mic@digikod.net> <20181212081712.32347-2-mic@digikod.net> <20181212144306.GA19945@quack2.suse.cz> In-Reply-To: <20181212144306.GA19945@quack2.suse.cz> From: Andy Lutomirski Date: Sun, 4 Aug 2019 16:55:58 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH v1 1/5] fs: Add support for an O_MAYEXEC flag on sys_open() To: Jan Kara , Song Liu , Alexei Starovoitov , Daniel Borkmann Cc: =?UTF-8?B?TWlja2HDq2wgU2FsYcO8bg==?= , LKML , Al Viro , James Morris , Jonathan Corbet , Kees Cook , Matthew Garrett , Michael Kerrisk , =?UTF-8?B?TWlja2HDq2wgU2FsYcO8bg==?= , Mimi Zohar , =?UTF-8?Q?Philippe_Tr=C3=A9buchet?= , Shuah Khan , Thibaut Sautereau , Vincent Strubel , Yves-Alexis Perez , Kernel Hardening , Linux API , LSM List , Linux FS Devel , Steve Grubb , Matthew Bobrowski Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On Wed, Dec 12, 2018 at 6:43 AM Jan Kara wrote: > > On Wed 12-12-18 09:17:08, Micka=C3=ABl Sala=C3=BCn wrote: > > When the O_MAYEXEC flag is passed, sys_open() may be subject to > > additional restrictions depending on a security policy implemented by a= n > > 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 ma= y > > be acceptable to allow some script interpreters (e.g. Bash) to interpre= t > > 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/f5cb33= 0d6b684752e403b4e41b39f7004d88e561/1901_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=3DO_= MAYEXEC > > > > Signed-off-by: Micka=C3=ABl Sala=C3=BCn > > Signed-off-by: Thibaut Sautereau > > Signed-off-by: Vincent Strubel > > Reviewed-by: Philippe Tr=C3=A9buchet > > Cc: Al Viro > > Cc: Kees Cook > > Cc: Micka=C3=ABl Sala=C3=BCn > > ... > > > 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, umod= e_t mode, struct open_flags *o > > if (flags & O_APPEND) > > acc_mode |=3D MAY_APPEND; > > > > + /* Check execution permissions on open. */ > > + if (flags & O_MAYEXEC) > > + acc_mode |=3D MAY_OPENEXEC; > > + > > op->acc_mode =3D acc_mode; > > > > op->intent =3D 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