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=-2.2 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 7F96AC67839 for ; Thu, 13 Dec 2018 17:13:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 460F8208E7 for ; Thu, 13 Dec 2018 17:13:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="ODXbHPL6" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 460F8208E7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-security-module-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727911AbeLMRNR (ORCPT ); Thu, 13 Dec 2018 12:13:17 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:59148 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727511AbeLMRNR (ORCPT ); Thu, 13 Dec 2018 12:13:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=zgLLqs+Me2TbdLlj8B9zK597kfXhai0M2M28sPkMVp0=; b=ODXbHPL6AhflSJ6NiRudG//aZQ 8CNzkuzsbKhKOB4M0bSuN1H7NOGsnFmlJsjEswFW78ArPIt/x2G7zU9NyjklD0zRJtJdZJikmXQCI nklfjvshoZYTWqAJbjPW/0knYJyCkGS2MDb/FYFhgC43DduGkYKF8NmsA5kPnpTqCHW/VR3+ALKeV wJCZDEGHrUYmqFQl5XkAZgxlnCgmR5mAJ7Aw6V8my8s7Ey73AFr8C55C8Fa2GII5pEczwakWLtRpU MEOL6qvHkMnaue2+x3us3Yp9GRFfb2kOf85TibumGbyW0h2d6elojMrBbww6GE5AbmcWHvJUT2JsD XO3Ugwrw==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1gXUXv-0002r0-4G; Thu, 13 Dec 2018 17:13:11 +0000 Date: Thu, 13 Dec 2018 09:13:10 -0800 From: Matthew Wilcox To: =?iso-8859-1?Q?Micka=EBl_Sala=FCn?= Cc: =?iso-8859-1?Q?Micka=EBl_Sala=FCn?= , linux-kernel@vger.kernel.org, Al Viro , James Morris , Jonathan Corbet , Kees Cook , Matthew Garrett , Michael Kerrisk , Mimi Zohar , Philippe =?iso-8859-1?Q?Tr=E9buchet?= , Shuah Khan , 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: [RFC PATCH v1 0/5] Add support for O_MAYEXEC Message-ID: <20181213171310.GR6830@bombadil.infradead.org> References: <20181212081712.32347-1-mic@digikod.net> <20181213030228.GM6830@bombadil.infradead.org> <374ea88c-edc5-f1a6-3637-748635e1e7df@ssi.gouv.fr> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <374ea88c-edc5-f1a6-3637-748635e1e7df@ssi.gouv.fr> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On Thu, Dec 13, 2018 at 04:17:29PM +0100, Mickaël Salaün wrote: > On 13/12/2018 04:02, Matthew Wilcox wrote: > > On Wed, Dec 12, 2018 at 09:17:07AM +0100, Mickaël Salaün wrote: > >> The goal of this patch series is to control script interpretation. A > >> new O_MAYEXEC flag used by sys_open() is added to enable userland script > >> interpreter to delegate to the kernel (and thus the system security > >> policy) the permission to interpret scripts or other files containing > >> what can be seen as commands. > > > > I don't have a problem with the concept, but we're running low on O_ bits. > > Does this have to be done before the process gets a file descriptor, > > or could we have a new syscall? Since we're going to be changing the > > interpreters anyway, it doesn't seem like too much of an imposition to > > ask them to use: > > > > int verify_for_exec(int fd) > > > > instead of adding an O_MAYEXEC. > > Adding a new syscall for this simple use case seems excessive. I think We have somewhat less than 400 syscalls today. We have 20 O_ bits defined. Obviously there's a lower practical limit on syscalls, but in principle we could have up to 2^32 syscalls, and there are only 12 O_ bits remaining. > that the open/openat syscall familly are the right place to do an atomic > open and permission check, the same way the kernel does for other file > access. Moreover, it will be easier to patch upstream interpreters > without the burden of handling a (new) syscall that may not exist on the > running system, whereas unknown open flags are ignored. Ah, but that's the problem. The interpreter can see an -ENOSYS response and handle it appropriately. If the flag is silently ignored, the interpreter has no idea whether it can do a racy check or whether to skip even trying to do the check.