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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 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 16CC3C433E0 for ; Wed, 27 Jan 2021 15:36:39 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 75912207D2 for ; Wed, 27 Jan 2021 15:36:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 75912207D2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kaod.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:50712 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l4ms1-0000lP-Fh for qemu-devel@archiver.kernel.org; Wed, 27 Jan 2021 10:36:37 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:38206) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l4mqx-0008Ju-Rw for qemu-devel@nongnu.org; Wed, 27 Jan 2021 10:35:31 -0500 Received: from 2.mo51.mail-out.ovh.net ([178.33.255.19]:60226) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l4mqv-0000ET-Le for qemu-devel@nongnu.org; Wed, 27 Jan 2021 10:35:31 -0500 Received: from mxplan5.mail.ovh.net (unknown [10.109.143.158]) by mo51.mail-out.ovh.net (Postfix) with ESMTPS id 734B625F19F; Wed, 27 Jan 2021 16:35:26 +0100 (CET) Received: from kaod.org (37.59.142.95) by DAG8EX1.mxp5.local (172.16.2.71) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2106.2; Wed, 27 Jan 2021 16:35:25 +0100 Authentication-Results: garm.ovh; auth=pass (GARM-95G001022afe38-3914-4839-8a53-eacdb7afdae6, E0AEAA2FFBCC539F7495E66DC8DC75F2C85CA1F9) smtp.auth=groug@kaod.org X-OVh-ClientIp: 78.197.208.248 Date: Wed, 27 Jan 2021 16:35:24 +0100 From: Greg Kurz To: Miklos Szeredi Subject: Re: [Virtio-fs] [PATCH v2] virtiofsd: prevent opening of special files (CVE-2020-35517) Message-ID: <20210127163524.4e34596d@bahia.lan> In-Reply-To: References: <20210126103502.260758-1-stefanha@redhat.com> <20210126181604.1a4c69c6@bahia.lan> <20210127112023.0e97f909@bahia.lan> <20210127144909.22dd778e@bahia.lan> <20210127160920.062e47f0@bahia.lan> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [37.59.142.95] X-ClientProxiedBy: DAG5EX1.mxp5.local (172.16.2.41) To DAG8EX1.mxp5.local (172.16.2.71) X-Ovh-Tracer-GUID: 02286c32-f5ff-42dd-83f6-70d7953d8b82 X-Ovh-Tracer-Id: 9817284240177797423 X-VR-SPAMSTATE: OK X-VR-SPAMSCORE: -100 X-VR-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgeduledrvdekgdejjecutefuodetggdotefrodftvfcurfhrohhfihhlvgemucfqggfjpdevjffgvefmvefgnecuuegrihhlohhuthemucehtddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenucfjughrpeffhffvuffkjghfofggtgfgihesthejredtredtvdenucfhrhhomhepifhrvghgucfmuhhriicuoehgrhhouhhgsehkrghougdrohhrgheqnecuggftrfgrthhtvghrnhepfedutdeijeejveehkeeileetgfelteekteehtedtieefffevhffflefftdefleejnecukfhppedtrddtrddtrddtpdefjedrheelrddugedvrdelheenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmhhouggvpehsmhhtphdqohhuthdphhgvlhhopehmgihplhgrnhehrdhmrghilhdrohhvhhdrnhgvthdpihhnvghtpedtrddtrddtrddtpdhmrghilhhfrhhomhepghhrohhugheskhgrohgurdhorhhgpdhrtghpthhtohepvhhgohihrghlsehrvgguhhgrthdrtghomh Received-SPF: pass client-ip=178.33.255.19; envelope-from=groug@kaod.org; helo=2.mo51.mail-out.ovh.net X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniel Berrange , QEMU Developers , P J P , virtio-fs-list , Alex Xu , Stefan Hajnoczi , Laszlo Ersek , Vivek Goyal Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 27 Jan 2021 16:22:49 +0100 Miklos Szeredi wrote: > On Wed, Jan 27, 2021 at 4:09 PM Greg Kurz wrote: > > > > On Wed, 27 Jan 2021 15:09:50 +0100 > > Miklos Szeredi wrote: > > > The semantics of O_CREATE are that it can fail neither because the > > > file exists nor because it doesn't. This doesn't matter if the > > > exported tree is not modified outside of a single guest, because of > > > locking provided by the guest kernel. > > > > > > > Wrong. O_CREAT can legitimately fail with ENOENT if one element > > Let me make my statement more precise: > > O_CREAT cannot fail with ENOENT if parent directory exists throughout > the operation. > True, but I still don't see what guarantees guest userspace that the parent directory doesn't go away... I must have missed something. Please elaborate. > I'm sure this property is used all over the place in userspace code, > and hence should be supported in strict coherence (cache=none) mode. > > For relaxed coherence (cache=auto) I'm not quite sure. NFS is usually > the reference, we'd need to look into what guarantees it provides wrt. > O_CREAT and remote racing unlink. > > Thanks, > Miklos >