[Bug 1894172] Re: isc-dhcp-server using wrong env variable for INTERFACES

[Utkarsh Gupta]

Hey,

The above regression was a false-positive; there were several retries,
all of them passed (cf:
https://autopkgtest.ubuntu.com/packages/c/chrony/bionic/armhf).

So this should be good to go (regression-wise)! \o/

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https://bugs.launchpad.net/bugs/1894172

Title:
  isc-dhcp-server using wrong env variable for INTERFACES

Status in isc-dhcp package in Ubuntu:
  Fix Released
Status in isc-dhcp source package in Bionic:
  Fix Committed
Status in isc-dhcp source package in Focal:
  Fix Committed
Status in isc-dhcp source package in Groovy:
  Fix Committed

Bug description:
  [Impact]

  When checking isc-dhcp-server unit file it was seen that isc-dhcp-
  server is being started by:

  ConditionPathExists=/etc/default/isc-dhcp-server
  ConditionPathExists=|/etc/ltsp/dhcpd.conf
  ConditionPathExists=|/etc/dhcp/dhcpd.conf

  [Service]
  EnvironmentFile=/etc/default/isc-dhcp-server
  RuntimeDirectory=dhcp-server
  # The leases files need to be root:dhcpd even when dropping privileges
  ExecStart=/bin/sh -ec '\
      CONFIG_FILE=/etc/dhcp/dhcpd.conf; \
      if [ -f /etc/ltsp/dhcpd.conf ]; then CONFIG_FILE=/etc/ltsp/dhcpd.conf; fi; \
      [ -e /var/lib/dhcp/dhcpd.leases ] || touch /var/lib/dhcp/dhcpd.leases; \
      chown root:dhcpd /var/lib/dhcp /var/lib/dhcp/dhcpd.leases; \
      chmod 775 /var/lib/dhcp ; chmod 664 /var/lib/dhcp/dhcpd.leases; \
      exec dhcpd -user dhcpd -group dhcpd -f -4 -pf /run/dhcp-server/dhcpd.pid -cf $CONFIG_FILE $INTERFACES'

  But the /etc/default/isc-dhcp-server file sets $INTERFACESv4 and
  $INTERFACESv6.

  This causes the service to listen on all interfaces, which is what the
  user might not want. In case the user wants to use *only* IPv6 and not
  IPv4, this could maybe lead to problems as what the user intended to
  do could be really different from what the outcome turns out to be
  (because of this bug).

  The previous upload(er) forgot to mention (and split) the INTERFACES
  variable to v4 and v6 and as a result, it has been this way for so
  long.

  The SRU would split the variables into respective names, thereby
  making sure that what /etc/default/isc-dhcp-serve sets, is available
  in the respective service file.

  [Test Plan]

  To reproduce this bug, simply do the following:

  $ lxc launch ubuntu-daily:focal isc-dhcp-lp1894172-focal

  $ lxc shell isc-dhcp-lp1894172-focal

  # apt update && apt install isc-dhcp-server -y

  # grep "INTERFACES" /etc/default/isc-dhcp-server
  INTERFACESv4=""
  INTERFACESv6=""

  grep "INTERFACES" /lib/systemd/system/isc-dhcp-server.service
      exec dhcpd -user dhcpd -group dhcpd -f -4 -pf /run/dhcp-server/dhcpd.pid -cf $CONFIG_FILE $INTERFACES'

  # grep "INTERFACES" /lib/systemd/system/isc-dhcp-server6.service
      exec dhcpd -user dhcpd -group dhcpd -f -6 -pf /run/dhcp-server/dhcpd6.pid -cf $CONFIG_FILE $INTERFACES'

  With this, it is clearly visible that even though /lib/systemd/system
  /isc-dhcp-server{,6}.service file uses the INTERFACES variable but the
  /etc/default/isc-dhcp-server defines 2 different variables,
  INTERFACESv4 and INTERFACESv6.

  After the SRU is performed, the respective services files should use
  INTERFACESv4 and INTERFACESv6 variable, instead of just INTERFACES.

  To ensure smooth upgrade of this package, we'd check if the user
  hasn't manually set a INTERFACESv{4,6} variable to workaround this
  bug. If they have, then we simply check and make sure, we use the
  correct variable.

  [Where problems could occur]

  The problem could occur if the user has manually set some different
  workaround for this bug and so the usual upgrade could break some of
  their old configuration(s).

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