isc-dhcp-client adopts server settings despite them not "request"ed
Bug Description
Hi, this is a bug well-known bug in Debian BTS (see #407336, #672232 and #553023), but it
still affects the dhclient/dhclient-scripts. The problem is that the dhclient "accepts"
options provided by the dhcp server even when they're not declared in dhclient.conf
.
For example, I've removed the ntp-servers
servers from my dhclient.conf
, but the
dhclient still set new_ntp_servers
variable and the dhclient-script that deals with
ntp configuration sets it as the ntp server.
To Reproduce
Steps to reproduce the behavior:
- A DHCP server that sends options even if they're not requested
- A dhclient version isc-dhclient-4.4.1 that doesn't request
ntp-servers
indhclient.conf
- Allowing the
debug
script show the following variables set by dhclient:
Thu Feb 14 08:12:04 -02 2019: entering /etc/dhcp/dhclient-enter-hooks.d, dumping variables.
reason='PREINIT'
interface='eth0'
--------------------------
Thu Feb 14 08:12:04 -02 2019: entering /etc/dhcp/dhclient-exit-hooks.d, dumping variables.
reason='PREINIT'
interface='eth0'
--------------------------
Thu Feb 14 08:12:12 -02 2019: entering /etc/dhcp/dhclient-enter-hooks.d, dumping variables.
reason='REBOOT'
interface='eth0'
new_ip_address='192.168.15.11'
new_network_number='192.168.15.0'
new_subnet_mask='255.255.255.0'
new_broadcast_address='192.168.15.255'
new_routers='192.168.15.1'
new_domain_name_servers='192.168.15.11'
new_netbios_name_servers='192.168.15.1'
new_ntp_servers='200.160.7.193'
--------------------------
Thu Feb 14 08:12:12 -02 2019: entering /etc/dhcp/dhclient-exit-hooks.d, dumping variables.
reason='REBOOT'
interface='eth0'
new_ip_address='192.168.15.11'
new_network_number='192.168.15.0'
new_subnet_mask='255.255.255.0'
new_broadcast_address='192.168.15.255'
new_routers='192.168.15.1'
new_domain_name_servers='192.168.15.11'
new_netbios_name_servers='192.168.15.1'
new_ntp_servers='200.160.7.193'
--------------------------
- After that, Debian scripts take care of changing the ntp server to the one provided by the dhcp server.
Expected behavior
I believe that the dhclient shouldn't set variables that weren't requested in dhclient.conf
Environment:
- Raspiberry Pi 3B
- Debian GNU/Linux 10 (buster) AArch64
- isc-dhclient-4.4.1
Additional Information
I've seen that there has been a lot of discussion on the bugs I've pointed out above,
there is a comment about using supersede
, but I think this shouldn't be the preferred
solution since many people don't even touch in configuration files.
Also, the BTS indicates the bug has been forwarded upstream already, but I didn't find it. And since I'm facing this annoying problem every time my rpi3 reboots, I've decided to fill this bug.
I'll also add my dhclient.conf
and the scripts I've talked about bellow.
dhclient.conf
# Configuration file for /sbin/dhclient.
#
# This is a sample configuration file for dhclient. See dhclient.conf's
# man page for more information about the syntax of this file
# and a more comprehensive list of the parameters understood by
# dhclient.
#
# Normally, if the DHCP server provides reasonable information and does
# not leave anything out (like the domain name, for example), then
# few changes must be made to this file, if any.
#
option rfc3442-classless-static-routes code 121 = array of unsigned integer 8;
send host-name = gethostname();
request subnet-mask, broadcast-address, time-offset, routers,
domain-name, domain-name-servers, domain-search, host-name,
dhcp6.name-servers, dhcp6.domain-search, dhcp6.fqdn,
netbios-name-servers, netbios-scope, interface-mtu,
rfc3442-classless-static-routes;
#send dhcp-client-identifier 1:0:a0:24:ab:fb:9c;
#send dhcp-lease-time 3600;
#supersede domain-name "fugue.com home.vix.com";
#prepend domain-name-servers 127.0.0.1;
#require subnet-mask, domain-name-servers;
#timeout 60;
#retry 60;
#reboot 10;
#select-timeout 5;
#initial-interval 2;
#script "/sbin/dhclient-script";
#media "-link0 -link1 -link2", "link0 link1";
#reject 192.33.137.209;
#alias {
# interface "eth0";
# fixed-address 192.5.5.213;
# option subnet-mask 255.255.255.255;
#}
#lease {
# interface "eth0";
# fixed-address 192.33.137.200;
# medium "link0 link1";
# option host-name "andare.swiftmedia.com";
# option subnet-mask 255.255.255.0;
# option broadcast-address 192.33.137.255;
# option routers 192.33.137.250;
# option domain-name-servers 127.0.0.1;
# renew 2 2000/1/12 00:00:01;
# rebind 2 2000/1/12 00:00:01;
# expire 2 2000/1/12 00:00:01;
#}
debug
#
# The purpose of this script is just to show the variables that are
# available to all the scripts in this directory. All these scripts are
# called from dhclient-script, which exports all the variables shown
# before. If you want to debug a problem with your DHCP setup you can
# enable this script and take a look at /tmp/dhclient-script.debug.
# To enable this script set the following variable to "yes"
RUN="yes"
if [ "$RUN" = "yes" ]; then
echo "$(date): entering ${1%/*}, dumping variables." \
>> /tmp/dhclient-script.debug
# loop over the 4 possible prefixes: (empty), cur_, new_, old_
for prefix in '' 'cur_' 'new_' 'old_'; do
# loop over the DHCP variables passed to dhclient-script
for basevar in reason interface medium alias_ip_address \
ip_address host_name network_number subnet_mask \
broadcast_address routers static_routes \
rfc3442_classless_static_routes \
domain_name domain_search domain_name_servers \
netbios_name_servers netbios_scope \
ntp_servers \
ip6_address ip6_prefix ip6_prefixlen \
dhcp6_domain_search dhcp6_name_servers ; do
var="${prefix}${basevar}"
eval "content=\$$var"
# show only variables with values set
if [ -n "${content}" ]; then
echo "$var='${content}'" >> /tmp/dhclient-script.debug
fi
done
done
echo '--------------------------' >> /tmp/dhclient-script.debug
fi
dhclient-exit-hooks.d/ntp
NTP_CONF=/etc/ntp.conf
NTP_DHCP_CONF=/run/ntp.conf.dhcp
ntp_server_restart() {
invoke-rc.d ntp try-restart
}
ntp_servers_setup_remove() {
if [ ! -e $NTP_DHCP_CONF ]; then
return
fi
rm -f $NTP_DHCP_CONF
ntp_server_restart
}
ntp_servers_setup_add() {
if [ -e $NTP_DHCP_CONF ] && [ "$new_ntp_servers" = "$old_ntp_servers" ]; then
return
fi
if [ -z "$new_ntp_servers" ]; then
ntp_servers_setup_remove
return
fi
tmp=$(mktemp "$NTP_DHCP_CONF.XXXXXX") || return
chmod --reference=$NTP_CONF $tmp
chown --reference=$NTP_CONF $tmp
(
echo "# This file was copied from $NTP_CONF with the server options changed"
echo "# to reflect the information sent by the DHCP server. Any changes made"
echo "# here will be lost at the next DHCP event. Edit $NTP_CONF instead."
echo
echo "# NTP server entries received from DHCP server"
for server in $new_ntp_servers; do
echo "server $server iburst"
done
echo
sed '/^[[:space:]]*\(server\|peer\|pool\)[[:space:]]/d' $NTP_CONF
) >>$tmp
mv $tmp $NTP_DHCP_CONF
ntp_server_restart
}
ntp_servers_setup() {
case $reason in
BOUND|RENEW|REBIND|REBOOT)
ntp_servers_setup_add
;;
EXPIRE|FAIL|RELEASE|STOP)
ntp_servers_setup_remove
;;
esac
}
ntp_servers_setup