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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, 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 85FF7C11F66 for ; Tue, 29 Jun 2021 14:37:04 +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 2430161DB4 for ; Tue, 29 Jun 2021 14:37:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2430161DB4 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]:42544 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lyErH-00058h-8P for qemu-devel@archiver.kernel.org; Tue, 29 Jun 2021 10:37:03 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:57098) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lyEpi-00032Y-1R for qemu-devel@nongnu.org; Tue, 29 Jun 2021 10:35:26 -0400 Received: from us-smtp-delivery-44.mimecast.com ([205.139.111.44]:58719) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lyEpd-0004jb-4q for qemu-devel@nongnu.org; Tue, 29 Jun 2021 10:35:23 -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-568-LI-U_rXINOW77yxMGyQVYA-1; Tue, 29 Jun 2021 10:35:13 -0400 X-MC-Unique: LI-U_rXINOW77yxMGyQVYA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C663B1084F61; Tue, 29 Jun 2021 14:35:12 +0000 (UTC) Received: from bahia.lan (ovpn-113-63.ams2.redhat.com [10.36.113.63]) by smtp.corp.redhat.com (Postfix) with ESMTP id 066E010023B0; Tue, 29 Jun 2021 14:35:07 +0000 (UTC) Date: Tue, 29 Jun 2021 16:35:06 +0200 From: Greg Kurz To: Vivek Goyal Subject: Re: [Virtio-fs] [PATCH v7 2/7] virtiofsd: Fix xattr operations overwriting errno Message-ID: <20210629163506.23c282a8@bahia.lan> In-Reply-To: <20210629132236.GB5231@redhat.com> References: <20210622150852.1507204-1-vgoyal@redhat.com> <20210622150852.1507204-3-vgoyal@redhat.com> <20210629150343.5cf10a26@bahia.lan> <20210629132236.GB5231@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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=205.139.111.44; 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@redhat.com, qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , miklos@szeredi.hu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 29 Jun 2021 09:22:36 -0400 Vivek Goyal wrote: > On Tue, Jun 29, 2021 at 03:03:43PM +0200, Greg Kurz wrote: > > On Mon, 28 Jun 2021 16:31:27 +0100 > > "Dr. David Alan Gilbert" wrote: > >=20 > > > * Vivek Goyal (vgoyal@redhat.com) wrote: > > > > getxattr/setxattr/removexattr/listxattr operations handle regualar > > > > and non-regular files differently. For the case of non-regular file= s > > > > we do fchdir(/proc/self/fd) and the xattr operation and then revert > > > > back to original working directory. After this we are saving errno > > > > and that's buggy because fchdir() will overwrite the errno. > > > >=20 > > > > FCHDIR_NOFAIL(lo->proc_self_fd); > > > > ret =3D getxattr(procname, name, value, size); > > > > FCHDIR_NOFAIL(lo->root.fd); > > > >=20 > > > > if (ret =3D=3D -1) > > > > saverr =3D errno > > > >=20 > > > > In above example, if getxattr() failed, we will still return 0 to c= aller > > > > as errno must have been written by FCHDIR_NOFAIL(lo->root.fd) call. > >=20 > > This assertion doesn't look right. > >=20 > > From the errno(3) manual page: > >=20 > > The value in errno is significant only when the return value of > > the call indicated an error (i.e., -1 from most system calls; -1 > > or NULL from most library functions); a function that succeeds i= s > > allowed to change errno. The value of errno is never set to zer= o > > ^^^^^^^^^^^^^^^^^^^^^^^^^= ^ > > by any system call or library function. >=20 > Ok. So it will not set errno to 0. But it also says "a function that > succeeds is allowed to change errno". So that means a successful > fchdir(fd) can change errno to something else and we lost original > error code returned by getxattr() operation. Even "assert(fchdir_res =3D= =3D 0)" > will not kick in because fchdir() succeeded. >=20 > IOW, with current code we can still lose original error code as experienc= ed > while executing getxattr()/setxattr()/listxattr(). So it makese sense > to fix it. >=20 Sure ! I wasn't challenging the fix, but rather the "still return 0 to call= er" wording :) Cheers, -- Greg > Vivek >=20 > > > > Fix all such instances and capture "errno" early and save in "saver= r" > > > > variable. > > > >=20 > > > > Signed-off-by: Vivek Goyal > > >=20 > > > I think the existing code is actually safe; I don't think fchdir > > > will/should set errno unless there's an error, and we're explictly > > > asserting there isn't one. > > >=20 > > > However, I do prefer doing this save since we already have the save > > > variables and it makes the chance of screwing it up from any other > > > forgotten syscall less likely, so > > >=20 > >=20 > > Agreed. With this rationale in the changelog: > >=20 > > Reviewed-by: Greg Kurz > >=20 > > >=20 > > > Reviewed-by: Dr. David Alan Gilbert > > >=20 > > > > --- > > > > tools/virtiofsd/passthrough_ll.c | 16 ++++++++++------ > > > > 1 file changed, 10 insertions(+), 6 deletions(-) > > > >=20 > > > > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/pas= sthrough_ll.c > > > > index 49c21fd855..ec91b3c133 100644 > > > > --- a/tools/virtiofsd/passthrough_ll.c > > > > +++ b/tools/virtiofsd/passthrough_ll.c > > > > @@ -2791,15 +2791,17 @@ static void lo_getxattr(fuse_req_t req, fus= e_ino_t ino, const char *in_name, > > > > goto out_err; > > > > } > > > > ret =3D fgetxattr(fd, name, value, size); > > > > + saverr =3D ret =3D=3D -1 ? errno : 0; > > > > } else { > > > > /* fchdir should not fail here */ > > > > FCHDIR_NOFAIL(lo->proc_self_fd); > > > > ret =3D getxattr(procname, name, value, size); > > > > + saverr =3D ret =3D=3D -1 ? errno : 0; > > > > FCHDIR_NOFAIL(lo->root.fd); > > > > } > > > > =20 > > > > if (ret =3D=3D -1) { > > > > - goto out_err; > > > > + goto out; > > > > } > > > > if (size) { > > > > saverr =3D 0; > > > > @@ -2864,15 +2866,17 @@ static void lo_listxattr(fuse_req_t req, fu= se_ino_t ino, size_t size) > > > > goto out_err; > > > > } > > > > ret =3D flistxattr(fd, value, size); > > > > + saverr =3D ret =3D=3D -1 ? errno : 0; > > > > } else { > > > > /* fchdir should not fail here */ > > > > FCHDIR_NOFAIL(lo->proc_self_fd); > > > > ret =3D listxattr(procname, value, size); > > > > + saverr =3D ret =3D=3D -1 ? errno : 0; > > > > FCHDIR_NOFAIL(lo->root.fd); > > > > } > > > > =20 > > > > if (ret =3D=3D -1) { > > > > - goto out_err; > > > > + goto out; > > > > } > > > > if (size) { > > > > saverr =3D 0; > > > > @@ -2998,15 +3002,15 @@ static void lo_setxattr(fuse_req_t req, fus= e_ino_t ino, const char *in_name, > > > > goto out; > > > > } > > > > ret =3D fsetxattr(fd, name, value, size, flags); > > > > + saverr =3D ret =3D=3D -1 ? errno : 0; > > > > } else { > > > > /* fchdir should not fail here */ > > > > FCHDIR_NOFAIL(lo->proc_self_fd); > > > > ret =3D setxattr(procname, name, value, size, flags); > > > > + saverr =3D ret =3D=3D -1 ? errno : 0; > > > > FCHDIR_NOFAIL(lo->root.fd); > > > > } > > > > =20 > > > > - saverr =3D ret =3D=3D -1 ? errno : 0; > > > > - > > > > out: > > > > if (fd >=3D 0) { > > > > close(fd); > > > > @@ -3064,15 +3068,15 @@ static void lo_removexattr(fuse_req_t req, = fuse_ino_t ino, const char *in_name) > > > > goto out; > > > > } > > > > ret =3D fremovexattr(fd, name); > > > > + saverr =3D ret =3D=3D -1 ? errno : 0; > > > > } else { > > > > /* fchdir should not fail here */ > > > > FCHDIR_NOFAIL(lo->proc_self_fd); > > > > ret =3D removexattr(procname, name); > > > > + saverr =3D ret =3D=3D -1 ? errno : 0; > > > > FCHDIR_NOFAIL(lo->root.fd); > > > > } > > > > =20 > > > > - saverr =3D ret =3D=3D -1 ? errno : 0; > > > > - > > > > out: > > > > if (fd >=3D 0) { > > > > close(fd); > > > > --=20 > > > > 2.25.4 > > > >=20 > >=20 >=20