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=-0.5 required=3.0 tests=DKIM_ADSP_CUSTOM_MED, FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 6B1D1C433DF for ; Mon, 18 May 2020 13:27:22 +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 3FE5C2065F for ; Mon, 18 May 2020 13:27:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3FE5C2065F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:57126 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jafnd-0000CF-GF for qemu-devel@archiver.kernel.org; Mon, 18 May 2020 09:27:21 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60640) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jafme-0007UQ-Md for qemu-devel@nongnu.org; Mon, 18 May 2020 09:26:20 -0400 Received: from indium.canonical.com ([91.189.90.7]:53854) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jafmJ-0000EG-9U for qemu-devel@nongnu.org; Mon, 18 May 2020 09:26:20 -0400 Received: from loganberry.canonical.com ([91.189.90.37]) by indium.canonical.com with esmtp (Exim 4.86_2 #2 (Debian)) id 1jafmE-00070p-Of for ; Mon, 18 May 2020 13:25:54 +0000 Received: from loganberry.canonical.com (localhost [127.0.0.1]) by loganberry.canonical.com (Postfix) with ESMTP id 090E92E8131 for ; Mon, 18 May 2020 13:25:53 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Date: Mon, 18 May 2020 13:15:50 -0000 From: Fishface60 To: qemu-devel@nongnu.org X-Launchpad-Notification-Type: bug X-Launchpad-Bug: product=qemu; status=New; 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 X-Launchpad-Bug-Reporter: Fishface60 (richard-maw) X-Launchpad-Bug-Modifier: Fishface60 (richard-maw) References: <158886102295.5250.16201751310283363946.malonedeb@chaenomeles.canonical.com> <158962979567.22424.13386143965250658312.malone@wampee.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="0385b538081bc4718df6fb844a3afc89729c94ce"; Instance="production-secrets-lazr.conf" X-Launchpad-Hash: a410e005585f44944ce3e680dcd2e5357e1c3bc1 Received-SPF: none client-ip=91.189.90.7; envelope-from=bounces@canonical.com; helo=indium.canonical.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/18 09:25:56 X-ACL-Warn: Detected OS = Linux 3.11 and newer X-Spam_score_int: -55 X-Spam_score: -5.6 X-Spam_bar: ----- X-Spam_report: (-5.6 / 5.0 requ) BAYES_00=-1.9, DKIM_ADSP_CUSTOM_MED=0.001, FORGED_GMAIL_RCVD=1, FREEMAIL_FORGED_FROMDOMAIN=0.001, FREEMAIL_FROM=0.001, HEADER_FROM_DIFFERENT_DOMAINS=0.249, RCVD_IN_DNSWL_HI=-5, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN 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" Swamped with other work at the moment, but this hasn't been forgotten. I might be able to take a look at it next week. On Sat, 16 May 2020 at 12:55, Christian Schoenebeck <1877384@bugs.launchpad.net> wrote: > > Yes, that compile error with QEMU + recent kernel headers is a bit > annoying, and AFAICS it is not fixed in Debian yet. > > Would you mind writing a test case for this bug that you fixed, to > prevent this accidentally being broken in future again? > > Please note that 9pfs is currently only been taken care of by 2 people, > and both only on a side channel. The 9pfs code base is complex and error > prone to edge cases like this one, so active assistance would be very > much appreciated! > > If you might consider writing a test case, I would give you quick, easy > and short instructions how to compile the 9pfs test cases, and which > source files to touch. There is no guest OS installation required for > the test cases. > > Thanks! > > -- > 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: > New > > 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: New 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