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 8F290C11F66 for ; Tue, 29 Jun 2021 13:09:23 +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 3174E60FD8 for ; Tue, 29 Jun 2021 13:09:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3174E60FD8 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]:39062 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lyDUQ-0001Lm-5U for qemu-devel@archiver.kernel.org; Tue, 29 Jun 2021 09:09:22 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60976) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lyDPG-0002be-8Q for qemu-devel@nongnu.org; Tue, 29 Jun 2021 09:04:02 -0400 Received: from us-smtp-delivery-44.mimecast.com ([207.211.30.44]:37792) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lyDPB-0008Dw-7t for qemu-devel@nongnu.org; Tue, 29 Jun 2021 09:03:59 -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-409-96WqqRc-ORGMqrY10BslNg-1; Tue, 29 Jun 2021 09:03:51 -0400 X-MC-Unique: 96WqqRc-ORGMqrY10BslNg-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 3C627C73A5; Tue, 29 Jun 2021 13:03:50 +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 AA11110027A5; Tue, 29 Jun 2021 13:03:45 +0000 (UTC) Date: Tue, 29 Jun 2021 15:03:43 +0200 From: Greg Kurz To: "Dr. David Alan Gilbert" Subject: Re: [Virtio-fs] [PATCH v7 2/7] virtiofsd: Fix xattr operations overwriting errno Message-ID: <20210629150343.5cf10a26@bahia.lan> In-Reply-To: References: <20210622150852.1507204-1-vgoyal@redhat.com> <20210622150852.1507204-3-vgoyal@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=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@redhat.com, qemu-devel@nongnu.org, Vivek Goyal , miklos@szeredi.hu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 28 Jun 2021 16:31:27 +0100 "Dr. David Alan Gilbert" wrote: > * Vivek Goyal (vgoyal@redhat.com) wrote: > > getxattr/setxattr/removexattr/listxattr operations handle regualar > > and non-regular files differently. For the case of non-regular files > > 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 calle= r > > as errno must have been written by FCHDIR_NOFAIL(lo->root.fd) call. This assertion doesn't look right. >From the errno(3) manual page: 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 is allowed to change errno. The value of errno is never set to zero ^^^^^^^^^^^^^^^^^^^^^^^^^^ by any system call or library function. > > Fix all such instances and capture "errno" early and save in "saverr" > > 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 Agreed. With this rationale in the changelog: Reviewed-by: Greg Kurz >=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/passthr= ough_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, fuse_in= o_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, fuse_i= no_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, fuse_in= o_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