OverlayFS: Wrong mnt_id and path reported in /proc

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apport-collect 1479468

and then change the status of the bug to 'Confirmed'.

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This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

I posted these patches to the kernel team ML. I've tested the above reproducer script and it does indeed fix the issue, and in addition I've ran the unionmount-testsuite 'sudo ./run --ov' on the new kernel and no regressions were noticed (all test passing).

Great! Thanks a lot Chris.

--Saied

On Thu, Jul 30, 2015 at 7:43 AM, Chris J Arges <email address hidden>
wrote:

> I posted these patches to the kernel team ML. I've tested the above
> reproducer script and it does indeed fix the issue, and in addition I've
> ran the unionmount-testsuite 'sudo ./run --ov' on the new kernel and no
> regressions were noticed (all test passing).
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1479468
>
> Title:
> OverlayFS: Wrong mnt_id and path reported in /proc
>
> Status in linux package in Ubuntu:
> Triaged
> Status in linux source package in Vivid:
> Triaged
>
> Bug description:
> SRU Justification:
>
> [Impact]
>
> I am running Ubuntu Vivid (3.19.0-22-generic #22-Ubuntu SMP Tue Jun 16
> 17:15:15 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux). There are two
> issues in OverlayFS as follows:
>
> 1. /proc/<pid>/fdinfo/<fd> reports wrong mnt_id (non-existent in
> /proc/<pid>/mountinfo)
>
> 2. /proc/<pid>/fd/<fd> shows incorrect path for the symlink target
>
> [Fix]
>
> These problems can be easily reproduced with the shell script below.
> Fortunately, both problems have been fixed in the upstream's master
> branch of the kernel via the following commits:
>
> torvalds 4.0: 155e35d4d VFS: Introduce inode-getting helpers for
> layered/unioned fs environments (this is already in ubuntu-vivid)
>
> torvalds 4.0: df1a085af VFS: Add a fallthrough flag for marking
> virtual dentries
> torvalds 4.2-rc2: f25801ee4 overlay: Call ovl_drop_write() earlier
> in ovl_dentry_open()
> torvalds 4.2-rc2: 4bacc9c92 overlayfs: Make f_path always point to
> the overlay and f_inode to the underlay
> torvalds 4.2-rc2: 9391dd00d fix a braino in ovl_d_select_inode()
>
> (The commit df1a085af may technically not be needed but it prevents a
> conflict when applying 4bacc9c92.)
>
> [Test Case]
>
> Simple script to reproduce the problem:
>
> #!/bin/bash
>
> set -eu
>
> ERROR=0
>
> setup() {
> setup_mount
> start_python > /dev/null 2>&1 &
> BASH_PID=$!
> PYTHON_PID=$(ps -C python | awk '/python/ { print $1 }')
> sleep 1
> }
>
> setup_mount() {
> mkdir overlay_test
> cd overlay_test
> mkdir a b c z
> sudo mount -t overlay -o lowerdir=a,upperdir=b,workdir=c overlayfs z
> }
>
> start_python() {
> python << EOF
> import time
> fd = open("z/file", "w")
> time.sleep(10)
> EOF
> }
>
> check_path() {
> WD=$(pwd)
> if ! ls -l /proc/$PYTHON_PID/fd | grep -qw "$WD/z/file"; then
> ERROR=1
> echo "ERROR! expected $WD/z/file"
> set -x
> ls -l /proc/$PYTHON_PID/fd
> set +x
> fi
> }
>
> check_mnt_id() {
> FDINFO_MNT_ID=$(awk '/mnt_id:/ { print $2 }' /proc/$PYTHON_PID/fdinfo/3)
> MOUNTINFO_MNT_ID=$(awk '/overlayfs/ { print $1 }' /proc/self/mountinfo)
> if [[ $FDINFO_MNT_ID -ne $MOUNTINFO_MNT_ID ]]; then
> ERROR=1
> echo "ERROR! mnt_id $FDINFO_MNT_ID not in /proc/self/mountinfo"
> set -x
> cat /proc/$PYTHON_PID/fdinfo/3
> cat /proc/self/mountinfo
> set +x
> fi
> }
>
> f...

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-vivid' to 'verification-done-vivid'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

Installed from -proposed (see below) and verified that it fixes the OverlayFS mnt_id and symlink target path issues.

Selected version '3.19.0-27.29' (Ubuntu:15.04/vivid-proposed [amd64]) for 'linux-image-3.19.0-27-generic'

tags:changed: verification-done-vivid

This bug was fixed in the package linux - 3.19.0-28.30

---------------
linux (3.19.0-28.30) vivid; urgency=low

  [ Luis Henriques ]

  * Release Tracking Bug
    - LP: #1490606

  [ Gary Wang ]

  * SAUCE: i915_bpo: drm/i915: set CDCLK if DPLL0 enabled during resuming
    from S3
    - LP: #1490035

  [ Timo Aaltonen ]

  * Revert "SAUCE: i915_bpo: drm/i915/skl: DDI-E and DDI-A shares 4 lanes."
    - LP: #1490038

linux (3.19.0-27.29) vivid; urgency=low

  [ Brad Figg ]

  * Release Tracking Bug
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  [ Arun Siluvery ]

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  * SAUCE: i915_bpo: drm/i915/gen9: Add
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    - LP: #1484486
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Bug #1507463 has been filed for the 3.13 kernel in Ubuntu Trusty, which is also affected and has not yet been patched.

Status changed to 'Confirmed' because the bug affects multiple users.