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Daniel Hilst
4bf66d7c0b
makedhcp wrote the interface list into /etc/default/isc-dhcp-server as
INTERFACES="..."
which is no longer always the variable the daemon is started with. The
systemd unit sources that file and expands exactly one variable onto dhcpd's
command line, and which one changed with the package:
14.04 4.2.4-7ubuntu12 sysvinit only $INTERFACES
16.04 4.3.3-5ubuntu12 unit $INTERFACES
18.04 4.3.5-3ubuntu7 unit $INTERFACES
20.04 4.4.1-2.1ubuntu5 unit $INTERFACES
22.04 4.4.1-2.3ubuntu2 unit $INTERFACESv4
24.04 4.4.3-P1-4ubuntu2 unit $INTERFACESv4
26.04 4.4.3-P1-4ubuntu2 unit $INTERFACESv4
with the matching v6 unit reading $INTERFACES before the change and
$INTERFACESv6 after it. Note the boundary is not an upstream ISC release:
20.04 and 22.04 both ship upstream 4.4.1 and are told apart only by the
Debian revision, so it has to be decided on the whole package version.
The sysvinit script does copy INTERFACES into INTERFACESv4 when the latter is
empty, but the unit is what starts the daemon on any of these releases and it
has no such bridge. So from 22.04 on, the unit ran
exec dhcpd -user dhcpd -group dhcpd -f -4 ... -cf $CONFIG_FILE $INTERFACESv4
against a variable xCAT never set. An unset variable expands to nothing, so
dhcpd was launched with no interface argument at all. It does not fail for
that: it binds every interface it can find and only warns about the ones with
no subnet declaration. site.dhcpinterfaces and servicenode.dhcpinterfaces
were therefore silently inert -- the provisioning NIC was served because
makedhcp had also emitted a subnet stanza for it, not because anything
honoured the setting, and any other interface on that subnet was served
alongside it.
The line match compounded it. m/^$dhcpd_key/ is not anchored on the
assignment, and INTERFACES is a prefix of both variables the package ships.
Since 18.04 the postinst seeds only INTERFACESv4="" and INTERFACESv6="" --
no INTERFACES line exists to match -- so the rewrite claimed those two lines
instead and overwrote both, discarding whatever debconf or the administrator
had put there and leaving a file with two INTERFACES assignments and nothing
either unit reads.
Pick the variables through a dispatcher keyed on the installed
isc-dhcp-server version, so both behaviours are served rather than one being
traded for the other, and anchor the match on the '=' so a key cannot claim a
line it is merely a prefix of. When the version cannot be established the
dispatcher writes every spelling, since an unset variable is the outcome that
leaves dhcpd bound to everything. Duplicate assignments left behind by the
old writer are collapsed to one, which repairs a file already damaged on an
upgraded management node.
The EL and SLES paths keep their single DHCPDARGS / DHCPD_INTERFACE /
DHCPD6_INTERFACE key and are unchanged.