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 32C3EC67872 for ; Thu, 13 Dec 2018 17:44:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F1CB720879 for ; Thu, 13 Dec 2018 17:44:16 +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="cknB3/Rf" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F1CB720879 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 S1729339AbeLMRoM (ORCPT ); Thu, 13 Dec 2018 12:44:12 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:57254 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729208AbeLMRoM (ORCPT ); Thu, 13 Dec 2018 12:44:12 -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=vHGUuj0rnCXK7jCzmngG9EdSGcppwG64C2WaGQxemxQ=; b=cknB3/RfhMcgP/LryCBIdo1cOp Feqy1/knxhUX8eAa3sORC/FcKvArI4TbXYZ1aklrDdcXirP9YOAr5Q7G/r8Lk9KD1D0emIc9+EUH7 +2Ib50F4sxDSQi82OL7/W4CBDLlchqmeWJporWm809fLYmDvK+vu/Jy+bnIFlGrRzYErC5I6fGzqc ZXpkOflllvTR+KUMdZa0myJZ0oKfImIYq4p9/OAv3rewao99cH2xjRuzwNs+2vKYzAmg9CQBEmMJE swKz9k8fF6xjH0MWSZdjGmGr1XllQ+Od0BU4CX+18Bi7bJHjKioedp1AczQ4XEj86G1gj3//Tanr4 B4m+/tCA==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1gXV1s-00082H-FV; Thu, 13 Dec 2018 17:44:08 +0000 Date: Thu, 13 Dec 2018 09:44:08 -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: <20181213174408.GS6830@bombadil.infradead.org> References: <20181212081712.32347-1-mic@digikod.net> <20181213030228.GM6830@bombadil.infradead.org> <374ea88c-edc5-f1a6-3637-748635e1e7df@ssi.gouv.fr> <20181213171310.GR6830@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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 06:36:15PM +0100, Mickaël Salaün wrote: > On 13/12/2018 18:13, Matthew Wilcox wrote: > > On Thu, Dec 13, 2018 at 04:17:29PM +0100, Mickaël Salaün wrote: > >> 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. > > Right, but the interpreter should interpret the script if the open with > O_MAYEXEC succeed (but not otherwise): it may be because the flag is > known by the kernel and the system policy allow this call, or because > the (old) kernel doesn't known about this flag (which is fine and needed > for backward compatibility). The script interpretation must not failed > if the kernel doesn't support O_MAYEXEC, it is then useless for the > interpreter to do any additional check. If that's the way interpreters want to work, then that's fine. They can just call the verify() syscall and ignore the -ENOSYS. Done. Or somebody who cares very, very deeply can change the interpreter to decline to run any scripts if the kernel returns -ENOSYS.