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 5AB30C4361B for ; Thu, 10 Dec 2020 13:34:27 +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 726A123119 for ; Thu, 10 Dec 2020 13:34:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 726A123119 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]:58178 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1knM5R-0005L7-Dt for qemu-devel@archiver.kernel.org; Thu, 10 Dec 2020 08:34:25 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:41988) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1knLjS-0002Bw-O7 for qemu-devel@nongnu.org; Thu, 10 Dec 2020 08:11:42 -0500 Received: from indium.canonical.com ([91.189.90.7]:41810) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1knLjM-0007W0-KB for qemu-devel@nongnu.org; Thu, 10 Dec 2020 08:11:42 -0500 Received: from loganberry.canonical.com ([91.189.90.37]) by indium.canonical.com with esmtp (Exim 4.86_2 #2 (Debian)) id 1knLjK-0002nN-9o for ; Thu, 10 Dec 2020 13:11:34 +0000 Received: from loganberry.canonical.com (localhost [127.0.0.1]) by loganberry.canonical.com (Postfix) with ESMTP id 3A72F2E813B for ; Thu, 10 Dec 2020 13:11:34 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Date: Thu, 10 Dec 2020 13:04:50 -0000 From: Fishface60 <1877384@bugs.launchpad.net> To: qemu-devel@nongnu.org X-Launchpad-Notification-Type: bug X-Launchpad-Bug: product=qemu; status=Confirmed; 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: Fishface60 (richard-maw) References: <158886102295.5250.16201751310283363946.malonedeb@chaenomeles.canonical.com> <160760081255.4964.13202614344127315520.malone@gac.canonical.com> Message-Id: Subject: Re: [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: 6a910e59a61953d5f323527ed273b4231c72f97d 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" It might be, I revisited a month back and could no longer trigger the bug, so it's possible unrelated changes or kernel changes have fixed the overlayfs copy-up semantics in cases where it would cause issues with QEMU. If I ever see it again I can resubmit evidence, so it may be better off closed. On Thu, 10 Dec 2020 at 12:01, Thomas Huth <1877384@bugs.launchpad.net> wrot= e: > > Closed by accident, Christian just told me that this is not fixed yet. > Sorry for the inconvenience. > > ** Changed in: qemu > Status: Fix Released =3D> Confirmed > > -- > You received this bug notification because you are subscribed to the bug > report. > https://bugs.launchpad.net/bugs/1877384 > > Title: > 9pfs file create with mapped-xattr can fail on overlayfs > > Status in QEMU: > Confirmed > > 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 co= de 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 directo= ry, 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_DIREC= TORY) =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_N= OFOLLOW, 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 -- = 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: Confirmed 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