[Bug 1972029] Re: dhclient overriding stub-resolv.conf file on Jammy

[Steve Langasek]

The question regarding partner usage of dhclient is in progress
elsewhere and does not block this SRU.

** Changed in: isc-dhcp (Ubuntu Jammy)
       Status: Incomplete => Fix Committed

** Tags added: verification-needed verification-needed-jammy

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Title:
  dhclient overriding stub-resolv.conf file on Jammy

Status in isc-dhcp package in Ubuntu:
  Fix Released
Status in isc-dhcp source package in Jammy:
  Fix Committed
Status in isc-dhcp source package in Kinetic:
  Fix Released

Bug description:
  [Issue]
  On Jammy, the stub-resolv.conf file on /run/systemd/resolve gets overwritten if dhclient is executed.

  While debugging this, I found the reference on LP#1889068 [0] of the
  move of `resolved` hook from dhclient-enter-hooks.d/ to dhclient-exit-
  hooks.d/, and this new hook [2] has no reference of make_resolv_conf()
  being called.

  [Reproducer]
  -
  I used a cloud-image based Jammy installation (uvt-kvm).  Once in:

  $ cat /run/system/resolve/stub-resolv.conf

  And one will see:

  nameserver 127.0.0.53
  options edns0 trust-ad
  search .

  Then:

  $ sudo dhclient
  $ cat /run/system/resolve/stub-resolv.conf

  You'll see the definition of the nameserver(s) in, and the stub IP
  address no longer there.  To revert this, a `systemctl restart
  systemd-resolved` is needed.

  [Impact]

  This is an improper way to keep nameserver(s) in *resolv* files; the
  override of the file should never happen in these circumstances.

  [Extra]
  -
  As a minor test, I copied over the dhclient-enter-hooks.d/resolved file from a Focal installation to a Jammy one, and the problem _does not happen_ when such hook is in place.

  [ . . . ]

  Let me know if further clarification is needed to proceed.  Thank you.

  BR,
  pprincipeza

  [0] https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1889068
  [1] https://paste.ubuntu.com/p/bvqPZXZZ8w/
  [2] https://paste.ubuntu.com/p/YQdG6z4WS7/

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