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=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 B3D37C4167B for ; Thu, 10 Dec 2020 09:06:52 +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 1DEF52343B for ; Thu, 10 Dec 2020 09:06:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1DEF52343B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=bugs.launchpad.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:48548 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1knHuV-0007Kh-44 for qemu-devel@archiver.kernel.org; Thu, 10 Dec 2020 04:06:51 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:41576) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1knHpK-00027L-D0 for qemu-devel@nongnu.org; Thu, 10 Dec 2020 04:01:30 -0500 Received: from indium.canonical.com ([91.189.90.7]:60062) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1knHpA-0000iF-0I for qemu-devel@nongnu.org; Thu, 10 Dec 2020 04:01:30 -0500 Received: from loganberry.canonical.com ([91.189.90.37]) by indium.canonical.com with esmtp (Exim 4.86_2 #2 (Debian)) id 1knHp7-0004i4-Ku for ; Thu, 10 Dec 2020 09:01:17 +0000 Received: from loganberry.canonical.com (localhost [127.0.0.1]) by loganberry.canonical.com (Postfix) with ESMTP id 9D1812E8047 for ; Thu, 10 Dec 2020 09:01:17 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Date: Thu, 10 Dec 2020 08:55:16 -0000 From: Thomas Huth <1877384@bugs.launchpad.net> To: qemu-devel@nongnu.org X-Launchpad-Notification-Type: bug X-Launchpad-Bug: product=qemu; status=Fix Released; importance=Undecided; assignee=None; X-Launchpad-Bug-Information-Type: Public X-Launchpad-Bug-Private: no X-Launchpad-Bug-Security-Vulnerability: no X-Launchpad-Bug-Commenters: richard-maw schoenebeck th-huth X-Launchpad-Bug-Reporter: Fishface60 (richard-maw) X-Launchpad-Bug-Modifier: Thomas Huth (th-huth) References: <158886102295.5250.16201751310283363946.malonedeb@chaenomeles.canonical.com> Message-Id: <160759051615.11526.14189244857812791663.malone@wampee.canonical.com> Subject: [Bug 1877384] Re: 9pfs file create with mapped-xattr can fail on overlayfs X-Launchpad-Message-Rationale: Subscriber (QEMU) @qemu-devel-ml X-Launchpad-Message-For: qemu-devel-ml Precedence: bulk X-Generated-By: Launchpad (canonical.com); Revision="4853cb86c14c5a9e513816c8a61121c639b30835"; Instance="production" X-Launchpad-Hash: eef4e33119723cf99c37f1d1861f2a79fec1c1a1 Received-SPF: none client-ip=91.189.90.7; envelope-from=bounces@canonical.com; helo=indium.canonical.com X-Spam_score_int: -65 X-Spam_score: -6.6 X-Spam_bar: ------ X-Spam_report: (-6.6 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.25, RCVD_IN_DNSWL_HI=-5, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Bug 1877384 <1877384@bugs.launchpad.net> Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Fixed in commit d76f4f97eb2772bf85fe286097183d0c7db19ae8 ** Changed in: qemu Status: New =3D> Fix Released -- = You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1877384 Title: 9pfs file create with mapped-xattr can fail on overlayfs Status in QEMU: Fix Released Bug description: QEMU Version: 3.1.0 as packaged in debian buster, but the code appears to= do the same in master. qemu command-line: qemu-system-x86_64 -m 1G -nographic -nic "user,model= =3Dvirtio-net-pci,tftp=3D$(pwd),net=3D10.0.2.0/24,host=3D10.0.2.2" -fsdev l= ocal,id=3Dfs,path=3D$thisdir/..,security_model=3Dmapped-xattr -device virti= o-9p-pci,fsdev=3Dfs,mount_tag=3Dfs -drive "file=3D$rootdisk,if=3Dvirtio,for= mat=3Draw" -kernel "$kernel" -initrd "$initrd" -append "$append" = I'm using CI that runs in a Docker container and runs a qemu VM with code= and results shared via virtio 9p. The 9p fsdev is configured with security_model=3Dmapped-xattr When the test code attempts to create a log file in an existing directory= , open with O_CREAT fails with -ENOENT. The relevant strace excerpt is: 28791 openat(11, ".", O_RDONLY|O_NOFOLLOW|O_PATH|O_DIRECTORY) =3D 20 28791 openat(20, "src", O_RDONLY|O_NOCTTY|O_NONBLOCK|O_NOFOLLOW|O_DIRECTO= RY) =3D 21 28791 fcntl(21, F_SETFL, O_RDONLY|O_DIRECTORY) =3D 0 28791 close(20) =3D 0 28791 openat(21, "client.log", O_WRONLY|O_CREAT|O_NOCTTY|O_NONBLOCK|O_NOF= OLLOW, 0600) =3D 20 28791 fcntl(20, F_SETFL, O_WRONLY|O_CREAT|O_NONBLOCK|O_NOFOLLOW) =3D 0 28791 lsetxattr("/proc/self/fd/21/client.log", "user.virtfs.uid", "\0\0\0= ", 4, 0) =3D -1 ENOENT (No such file or directory) My hypothesis for what's going wrong is since the Docker container's overlayfs copies-up on writes, when it opens the file it's created a new version of the `src` directory containing a `client.log`, but this new src directory isn't accessible by file descriptor 20 and the lsetxattr call is instead attempting to set attributes on the path in the old `src` directory. Looking at the code, a fix would be to change `hw/9pfs/9p-local.c` and change `local_open2` to instead of calling `local_set_xattrat` to set the xattrs by directory file descriptor and file name, to have a version of local_set_xattrat` which uses `fsetxattr` to set the virtfs attributes instead of the `fsetxattrat_nofollow` helper. This reliably happened for me in CI, but I don't have access to the CI host or the time to strip the test down to make a minimal test case, and had difficulty reproducing the error on other machines. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1877384/+subscriptions