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=-8.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 1F132C433B4 for ; Thu, 6 May 2021 16:22:02 +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 B39A561078 for ; Thu, 6 May 2021 16:22:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B39A561078 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:46890 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1leglE-0004iB-P1 for qemu-devel@archiver.kernel.org; Thu, 06 May 2021 12:22:00 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:58600) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1legSU-0001nr-DM for qemu-devel@nongnu.org; Thu, 06 May 2021 12:02:46 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:23770) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1legSR-0002Qy-Mv for qemu-devel@nongnu.org; Thu, 06 May 2021 12:02:38 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620316955; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=sTNEbKcnXCambpACrV1BNqfYIWb/tXEnzCtPppiYR8s=; b=A7RQYqNp+ejEzwm+fcFhzeMpUEGpxxxActxe1GxblpJJrZHkZOyeeUXmTgQ8yQ2IWOvSzX nELFkCHN8mlgThE1rDY4FaTm+ajmudO6/T25kXxzN82ziNxzQUMl1KGnb/K/ZUDQUmi3/T zFLaGlzIiAGnClkb2LPE/D3fkbP8ltc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-491-Y0F5BMiqN7KjUw3oG7x6mg-1; Thu, 06 May 2021 12:02:33 -0400 X-MC-Unique: Y0F5BMiqN7KjUw3oG7x6mg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2E11218B9ED7; Thu, 6 May 2021 16:02:31 +0000 (UTC) Received: from horse.redhat.com (ovpn-114-166.rdu2.redhat.com [10.10.114.166]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0FEA760871; Thu, 6 May 2021 16:02:24 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id 8C59B22054F; Thu, 6 May 2021 12:02:23 -0400 (EDT) Date: Thu, 6 May 2021 12:02:23 -0400 From: Vivek Goyal To: Stefan Hajnoczi Subject: Re: [PATCH v3 26/26] virtiofsd: Ask qemu to drop CAP_FSETID if client asked for it Message-ID: <20210506160223.GA277745@redhat.com> References: <20210428110100.27757-1-dgilbert@redhat.com> <20210428110100.27757-27-dgilbert@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vgoyal@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=vgoyal@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.69, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, 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: virtio-fs@redhat.com, groug@kaod.org, "Dr. David Alan Gilbert \(git\)" , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, May 06, 2021 at 04:37:04PM +0100, Stefan Hajnoczi wrote: > On Wed, Apr 28, 2021 at 12:01:00PM +0100, Dr. David Alan Gilbert (git) wrote: > > From: Vivek Goyal > > > > If qemu guest asked to drop CAP_FSETID upon write, send that info > > to qemu in SLAVE_FS_IO message so that qemu can drop capability > > before WRITE. This is to make sure that any setuid bit is killed > > on fd (if there is one set). > > > > Signed-off-by: Vivek Goyal > > I'm not sure if the QEMU FSETID patches make sense. QEMU shouldn't be > running with FSETID because QEMU is untrusted. FSETGID would allow QEMU > to create setgid files, thereby potentially allowing an attacker to gain > any GID. Sure, its not recommended to run QEMU as root, but we don't block that either and I do regularly test with qemu running as root. > > I think it's better not to implement QEMU FSETID functionality at all > and to handle it another way. One way could be that virtiofsd tries to clear setuid bit after I/O has finished. But that will be non-atomic operation and it is filled with perils as it requires virtiofsd to know what all kernel will do if this write has been done with CAP_FSETID dropped. > In the worst case I/O requests should just > fail, it seems like a rare case anyway: Is there a way for virtiofsd to know if qemu is running with CAP_FSETID or not. If there is one, it might be reasonable to error out. If we don't know, then we can't fail all the operations. > I/O to a setuid/setgid file with > a memory buffer that is not mapped in virtiofsd. With DAX it is easily triggerable. User has to append to a setuid file in virtiofs and this path will trigger. I am fine with not supporting this patch but will also need a reaosonable alternative solution. Vivek