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=-18.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 F134CC49361 for ; Fri, 18 Jun 2021 09:22:41 +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 461BC613CB for ; Fri, 18 Jun 2021 09:22:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 461BC613CB 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]:51604 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1luAi0-0006ZR-6h for qemu-devel@archiver.kernel.org; Fri, 18 Jun 2021 05:22:40 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49638) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1luAhD-0005pJ-8l for qemu-devel@nongnu.org; Fri, 18 Jun 2021 05:21:51 -0400 Received: from us-smtp-delivery-44.mimecast.com ([207.211.30.44]:60643) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1luAhB-0000dR-A7 for qemu-devel@nongnu.org; Fri, 18 Jun 2021 05:21:50 -0400 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-545--1SrqMEXOTeKGyfCc71dOA-1; Fri, 18 Jun 2021 05:21:44 -0400 X-MC-Unique: -1SrqMEXOTeKGyfCc71dOA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0FD591835AC5; Fri, 18 Jun 2021 09:21:43 +0000 (UTC) Received: from bahia.lan (ovpn-112-153.ams2.redhat.com [10.36.112.153]) by smtp.corp.redhat.com (Postfix) with ESMTP id 919E019704; Fri, 18 Jun 2021 09:21:33 +0000 (UTC) Date: Fri, 18 Jun 2021 11:21:31 +0200 From: Greg Kurz To: Miklos Szeredi Subject: Re: [PATCH] virtiofsd: Don't allow file creation with FUSE_OPEN Message-ID: <20210618112131.46ce0b2a@bahia.lan> In-Reply-To: References: <20210617141518.304659-1-groug@kaod.org> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: kaod.org Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Received-SPF: softfail client-ip=207.211.30.44; envelope-from=groug@kaod.org; helo=us-smtp-delivery-44.mimecast.com 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_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_SOFTFAIL=0.665 autolearn=no 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-list , Stefan Hajnoczi , qemu-devel@nongnu.org, Vivek Goyal , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, 18 Jun 2021 10:58:33 +0200 Miklos Szeredi wrote: > On Thu, 17 Jun 2021 at 16:15, Greg Kurz wrote: > > > > A well behaved FUSE client uses FUSE_CREATE to create files. It isn't > > supposed to pass O_CREAT along a FUSE_OPEN request, as documented in > > the "fuse_lowlevel.h" header : > > > > /** > > * Open a file > > * > > * Open flags are available in fi->flags. The following rules > > * apply. > > * > > * - Creation (O_CREAT, O_EXCL, O_NOCTTY) flags will be > > * filtered out / handled by the kernel. > > > > But if it does anyway, virtiofsd crashes with: > > > > *** invalid openat64 call: O_CREAT or O_TMPFILE without mode ***: termi= nated > > > > This is because virtiofsd ends up passing this flag to openat() without > > passing a mode_t 4th argument which is mandatory with O_CREAT, and glib= c > > aborts. > > > > The offending path is: > > > > lo_open() > > lo_do_open() > > lo_inode_open() > > > > Other callers of lo_inode_open() only pass O_RDWR and lo_create() > > passes a valid fd to lo_do_open() which thus doesn't even call > > lo_inode_open() in this case. > > > > Specifying O_CREAT with FUSE_OPEN is a protocol violation. Check this > > in lo_open() and return an error to the client : EINVAL since this is > > already what glibc returns with other illegal flag combinations. > > > > The FUSE filesystem doesn't currently support O_TMPFILE, but the very > > same would happen if O_TMPFILE was passed in a FUSE_OPEN request. Check > > that as well. > > > > Signed-off-by: Greg Kurz > > --- > > tools/virtiofsd/passthrough_ll.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthr= ough_ll.c > > index 49c21fd85570..14f62133131c 100644 > > --- a/tools/virtiofsd/passthrough_ll.c > > +++ b/tools/virtiofsd/passthrough_ll.c > > @@ -2145,6 +2145,12 @@ static void lo_open(fuse_req_t req, fuse_ino_t i= no, struct fuse_file_info *fi) > > return; > > } > > > > + /* File creation is handled by lo_create() */ > > + if (fi->flags & (O_CREAT | O_TMPFILE)) { > > + fuse_reply_err(req, EINVAL); > > + return; > > + } > > + >=20 > Okay. Question comes to mind whether the check should be even more > strict, possibly allowing just a specific set of flags, and erroring > out on everything else? >=20 I've focused on O_CREAT and O_TMPFILE because they cause an explicit abort(= ) in glibc when the code is compiled with -D_FORTIFY_SOURCE=3D2, but yes, maybe it could make sense to check more of them. > AFAICS linux kernel should never pass anything to FUSE_OPEN outside of th= is set: >=20 > O_RDONLY > O_WRONLY > O_RDWR > O_APPEND > O_NDELAY > O_NONBLOCK > __O_SYNC > O_DSYNC > FASYNC > O_DIRECT > O_LARGEFILE > O_NOFOLLOW > O_NOATIME >=20 > A separate question is whether virtiofsd should also be silently > ignoring some of the above flags. >=20 Dunno on the top of my head... BTW, as suggested by Dave, I've submitted a similar patch to upstream libfuse: https://github.com/libfuse/libfuse/pull/615 And I got interesting suggestions: 1) do it in core FUSE, i.e. fuse_lowlevel.c, since this isn't specific to passthrough_ll AFAICT 2) print out an error 3) exit 1 makes a lot of sense. I guess 2 is fine this cannot be used by a buggy guest to flood some log file on the host. 3 doesn't seems to be an acceptable solution, and it wouldn't change much the outcome compared to what we have now. So I will go for 1 and 2. Cheers, -- Greg > Thanks, > Miklos >=20 >=20 >=20 > > err =3D lo_do_open(lo, inode, -1, fi); > > lo_inode_put(lo, &inode); > > if (err) { > > -- > > 2.31.1 > >