isc-dhcp-server using wrong env variable for INTERFACES

[Rafael David Tinoco]

[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).

[Seth Arnold (seth-arnold)]

see also https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1774342

Thanks

[Łukasz Zemczak (sil2100)]

Hello Rafael, or anyone else affected,

Accepted isc-dhcp into groovy-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/isc-dhcp/4.4.1-2.1ubuntu10 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, what testing has been performed on the package and change the tag from verification-needed-groovy to verification-done-groovy. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-groovy. In either case, without details of your testing we will not be able to proceed.

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

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Łukasz Zemczak (sil2100)]

Hello Rafael, or anyone else affected,

Accepted isc-dhcp into focal-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/isc-dhcp/4.4.1-2.1ubuntu5.20.04.1 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, what testing has been performed on the package and change the tag from verification-needed-focal to verification-done-focal. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-focal. In either case, without details of your testing we will not be able to proceed.

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

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Łukasz Zemczak (sil2100)]

Hello Rafael, or anyone else affected,

Accepted isc-dhcp into bionic-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/isc-dhcp/4.3.5-3ubuntu7.2 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, what testing has been performed on the package and change the tag from verification-needed-bionic to verification-done-bionic. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-bionic. In either case, without details of your testing we will not be able to proceed.

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

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Ubuntu SRU Bot (ubuntu-sru-bot)]

All autopkgtests for the newly accepted isc-dhcp (4.3.5-3ubuntu7.2) for bionic have finished running.
The following regressions have been reported in tests triggered by the package:

chrony/3.2-4ubuntu4.5 (armhf)

Please visit the excuses page listed below and investigate the failures, proceeding afterwards as per the StableReleaseUpdates policy regarding autopkgtest regressions [1].

https://people.canonical.com/~ubuntu-archive/proposed-migration/bionic/update_excuses.html#isc-dhcp

[1] https://wiki.ubuntu.com/StableReleaseUpdates#Autopkgtest_Regressions

Thank you!

[Utkarsh Gupta (utkarsh)]

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/

[Utkarsh Gupta (utkarsh)]

Hello,

I just did the verification and the upgrade seems to be working as intended for me. I went ahead and added the verficiation-done tag (and the release-specific tags as well!).

[Launchpad Janitor (janitor)]

This bug was fixed in the package isc-dhcp - 4.4.1-2.1ubuntu10

---------------
isc-dhcp (4.4.1-2.1ubuntu10) groovy; urgency=medium

  * Fix env variable for INTERFACES (LP: #1894172)
    - d/isc-dhcp-server.isc-dhcp-server{,6}.service: Replace $INTERFACES
      variable with $INTERFACEv4 and $INTERFACESv6, respectively, for
      respective services file.

 -- Utkarsh Gupta <email address hidden> Wed, 10 Mar 2021 20:04:04 +0530

[Brian Murray (brian-murray)]

The verification of the Stable Release Update for isc-dhcp has completed successfully and the package is now being 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.

[Launchpad Janitor (janitor)]

This bug was fixed in the package isc-dhcp - 4.4.1-2.1ubuntu5.20.04.1

---------------
isc-dhcp (4.4.1-2.1ubuntu5.20.04.1) focal; urgency=medium

  * Fix env variable for INTERFACES (LP: #1894172)
    - d/isc-dhcp-server.isc-dhcp-server{,6}.service: Replace $INTERFACES
      variable with $INTERFACEv4 and $INTERFACESv6, respectively, for
      respective services file.

 -- Utkarsh Gupta <email address hidden> Tue, 09 Mar 2021 20:49:45 +0530

[Launchpad Janitor (janitor)]

This bug was fixed in the package isc-dhcp - 4.3.5-3ubuntu7.2

---------------
isc-dhcp (4.3.5-3ubuntu7.2) bionic; urgency=medium

  * Fix env variable for INTERFACES (LP: #1894172)
    - d/isc-dhcp-server.isc-dhcp-server{,6}.service: Replace $INTERFACES
      variable with $INTERFACEv4 and $INTERFACESv6, respectively, for
      respective services file.

 -- Utkarsh Gupta <email address hidden> Wed, 10 Mar 2021 19:57:51 +0530