[SRU] resolvconf is racy, which leads to broken resolv.conf in parallel calls

The attachment "debdiff.patch" seems to be a debdiff. The ubuntu-sponsors team has been subscribed to the bug report so that they can review and hopefully sponsor the debdiff. If the attachment isn't a patch, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are member of the ~ubuntu-sponsors, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issue please contact him.]

@Alfonso

What's the use case for calling 'netplan apply' in this scenario? Is NM the configured as the netplan renderer?

Is there ever a case where "systemd-networkd-resolvconf-update.service" can call resolvconf even though NM is the renderer from the start (i.e. there's no transition from networkd to NM)?

I've always contended that mixing two network management services on the same device was asking for trouble...

I assume this is primarily an issue for UC16, since in UC18 we no longer use resolvconf at all, and have targeted the bug accordingly. Do you want to prepare a corresponding debdiff for xenial, and adjust the bug description to include a complete SRU template per https://wiki.ubuntu.com/StableReleaseUpdates#SRU_Bug_Template ?

This bug was fixed in the package resolvconf - 1.79ubuntu13

---------------
resolvconf (1.79ubuntu13) disco; urgency=medium

  * bin/resolvconf: use flock so resolvconf can be called in parallel
    safely (LP: #1825194).

 -- Alfonso Sanchez-Beato (email Canonical) <email address hidden> Wed, 17 Apr 2019 16:53:53 +0200

Unsubscribing the Sponsors Team because there is no SRU bug template yet.

Patch for xenial.

@vorlon, @tsimonq2, patch for xenial attached, and description changed for SRU. Sponsors teamm re-subscribed.

uploaded to the SRU queue.

(please note that the changelog had to be adjusted; the current version of resolvconf in xenial-updates is 1.78ubuntu6.)

Review question: what ensures that /run/resolvconf exists before flock is called? I only see an "mkdir -p" inside the block, not outside it. flock doesn't seem to create parent directories automatically in my test, and I don't see a tmpfiles.d entry.

Thanks Robie, that's a very good point and something I didn't notice while sponsoring. Alfonso, do you want to adjust the patch to address this? (That will also give us a chance to reupload the SRU and remove the misapplied diff cruft.)

Will this also need addressing in the development release?

On Wed, May 01, 2019 at 05:25:22PM -0000, Robie Basak wrote:
> Will this also need addressing in the development release?

It looks like it to me.

An upload of resolvconf to xenial-proposed has been rejected from the upload queue for the following reason: "Needs adjustment; see https://bugs.launchpad.net/ubuntu/+source/resolvconf/+bug/1825194/comments/11".

Thanks Robie, good catch. Please find attached the new patch for xenial: I have moved a bit below the call to flock to ensure the dir was created - the lines now out of the lock do not change any files so that should not be a problem.

Hello Alfonso, or anyone else affected,

Accepted resolvconf into xenial-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/resolvconf/1.78ubuntu7 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-xenial to verification-done-xenial. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-xenial. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

Unsubscribing ~ubuntu-sponsors.

Are you planning on fixing Bionic, Cosmic or Disco?

On Wed, May 15, 2019 at 12:22:20PM -0000, Robie Basak wrote:
> Unsubscribing ~ubuntu-sponsors.

> Are you planning on fixing Bionic, Cosmic or Disco?

Per
https://bugs.launchpad.net/ubuntu/+source/resolvconf/+bug/1825194/comments/4,
I believe this is "uninteresting" to fix for releases other than xenial;
xenial needs it because UC16 is netplan+resolvconf and may have both
networkd and NetworkManager backends on some devices, UC18 does not use
resolvconf, and Ubuntu 18.04 classic is unlikely to have users making use of
resolvconf+netplan (since resolvconf is only present by default on upgrade
for users who have their network configured using ifupdown).

On Wed, May 15, 2019 at 12:42:24PM -0000, Steve Langasek wrote:
> Per
> https://bugs.launchpad.net/ubuntu/+source/resolvconf/+bug/1825194/comments/4,
> I believe this is "uninteresting" to fix for releases other than xenial;
> xenial needs it because UC16 is netplan+resolvconf and may have both
> networkd and NetworkManager backends on some devices, UC18 does not use
> resolvconf, and Ubuntu 18.04 classic is unlikely to have users making use of
> resolvconf+netplan (since resolvconf is only present by default on upgrade
> for users who have their network configured using ifupdown).

Ah sorry. I remember reading that when I looked at that last time, but
missed that today. Fair enough.

I have tested on xenial, the problem is solved with the change.

ubuntu@xenial:~$ apt policy resolvconf
resolvconf:
  Installed: 1.78ubuntu7
  Candidate: 1.78ubuntu7
  Version table:
 *** 1.78ubuntu7 500
        500 http://archive.ubuntu.com/ubuntu xenial-proposed/main amd64 Packages
        100 /var/lib/dpkg/status
     1.78ubuntu6 500
        500 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
     1.78ubuntu2 500
        500 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages
ubuntu@xenial:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.6 LTS
Release: 16.04

This bug was fixed in the package resolvconf - 1.78ubuntu7

---------------
resolvconf (1.78ubuntu7) xenial; urgency=medium

  * bin/resolvconf: use flock so resolvconf can be called in parallel
    safely (LP: #1825194).

 -- Alfonso Sanchez-Beato (email Canonical) <email address hidden> Mon, 06 May 2019 10:39:40 +0200

The verification of the Stable Release Update for resolvconf has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.