Regression: Router Discovery broken after ifup lan

Description

Following commit: https://github.com/openwrt/odhcpd/commit/c6dae8e6b2a82dca6e2e00e17b0bc968a504d7fc#diff-25d902c24283ab8cfbac54dfa101ad31

introduces an issue in odhcpd after 'ifup lan' resulting in the fact that Router Discovery is broken until odhcpd is restarted. Periodic Router Advertisement's are still send out.

Following description describes the reproduction on a TP-Link 1750:

Made use of rdisc6 as part of ndsic6 package (apt install ndisc6) to trigger a Router Solicitation from a host toward the gateway. host# rdisc6 -1 eth0

REPRODUCTION CONFIG

Used following config on a TP-Link 1750: Config introduces second bridge 'lan2' as the test bridge next to the existing 'lan' bridge that is used to control the gateway. Run odhcpd on top of lan2 to handle Router Solicitation/Advertisement

root@OpenWrt:~# cat /etc/config/network 

config interface 'loopback'
    option ifname 'lo'
    option proto 'static'
    option ipaddr '127.0.0.1'
    option netmask '255.0.0.0'

config globals 'globals'
    option ula_prefix 'fd34:c595:be3b::/48'

config interface 'lan'
    option type 'bridge'
    option ifname 'eth1.1'
    option proto 'static'
    option ipaddr '192.168.1.1'
    option netmask '255.255.255.0'
    option ip6assign '60'

config interface 'wan'
    option ifname 'eth0.2'
    option proto 'dhcp'

config interface 'wan6'
    option ifname 'eth0.2'
    option proto 'dhcpv6'

config switch
    option name 'switch0'
    option reset '1'
    option enable_vlan '1'

config switch_vlan
    option device 'switch0'
    option vlan '1'
    option ports '2 3 0t'

config switch_vlan
    option device 'switch0'
    option vlan '2'
    option ports '1 6t'

config switch_vlan
    option device 'switch0'
    option vlan '3'
    option ports '4 5 0t'

config interface 'lan2'
    option type 'bridge'
    option ifname 'eth1.3'
    option proto 'static'
    option netmask '255.255.255.0'
    option ipaddr '192.168.2.1'
    option ip6assign '60'

root@OpenWrt:~# 

root@OpenWrt:~# cat /etc/config/dhcp 

config dnsmasq
    option domainneeded '1'
    option boguspriv '1'
    option filterwin2k '0'
    option localise_queries '1'
    option rebind_protection '1'
    option rebind_localhost '1'
    option local '/lan/'
    option domain 'lan'
    option expandhosts '1'
    option nonegcache '0'
    option authoritative '1'
    option readethers '1'
    option leasefile '/tmp/dhcp.leases'
    option resolvfile '/tmp/resolv.conf.auto'
    option nonwildcard '1'
    option localservice '1'

config dhcp 'lan'
    option interface 'lan'
    option start '100'
    option limit '150'
    option leasetime '12h'
    option dhcpv6 'server'
    option ra 'server'

config dhcp 'lan2'
    option interface 'lan2'
    option start '100'
    option limit '150'
    option leasetime '12h'
    option dhcpv6 'server'
    option ra 'server'

config dhcp 'wan'
    option interface 'wan'
    option ignore '1'

config odhcpd 'odhcpd'
    option maindhcp '0'
    option leasefile '/tmp/hosts/odhcpd'
    option leasetrigger '/usr/sbin/odhcpd-update'
    option loglevel '7'

root@OpenWrt:~#

STEPS TO REPRODUCE

STEP 1:

Apply this config, reboot and connect a test host to switch port 3 or 4

STEP 2:

Make sure that Router Solicitation works at this point on lan2

root@testuser-Latitude-E5410:/usr/localdisk/openwrt/bin/targets/ar71xx/generic# rdisc6 -1 eth0
Soliciting ff02::2 (ff02::2) on eth0...

Hop limit                 :           64 (      0x40)
Stateful address conf.    :          Yes
Stateful other conf.      :          Yes
Mobile home agent         :           No
Router preference         :       medium
Neighbor discovery proxy  :           No
Router lifetime           :            0 (0x00000000) seconds
Reachable time            :  unspecified (0x00000000)
Retransmit time           :  unspecified (0x00000000)
 Source link-layer address: EC:08:6B:27:45:A0
 MTU                      :         1500 bytes (valid)
 Prefix                   : fd34:c595:be3b:10::/64
  On-link                 :          Yes
  Autonomous address conf.:          Yes
  Valid time              :     infinite (0xffffffff)
  Pref. time              :     infinite (0xffffffff)
 Route                    : fd34:c595:be3b::/48
  Route preference        :       medium
  Route lifetime          :         1800 (0x00000708) seconds
 Recursive DNS server     : fd34:c595:be3b:10::1
  DNS server lifetime     :         1800 (0x00000708) seconds
root@testuser-Latitude-E5410:/usr/localdisk/openwrt/bin/targets/ar71xx/generic#

STEP 3:

execute ifup lan2 on target

┌──[aertsk@cplx1015]──[/home/users/aertsk/Downloads]──────────                                                                             ──────[13:40:29]──[0.19]──────
$ ssh root@192.168.1.1

BusyBox v1.31.0 () built-in shell (ash)

  _______                     ________        __
 |       |.-----.-----.-----.|  |  |  |.----.|  |_
 |   -   ||  _  |  -__|     ||  |  |  ||   _||   _|
 |_______||   __|_____|__|__||________||__|  |____|
          |__| W I R E L E S S   F R E E D O M
 -----------------------------------------------------
 OpenWrt SNAPSHOT, r10444-5c094ff660
 -----------------------------------------------------
=== WARNING! =====================================
There is no root password defined on this device!
Use the "passwd" command to set up a new password
in order to prevent unauthorized SSH logins.
--------------------------------------------------
root@OpenWrt:~# 
root@OpenWrt:~# 
root@OpenWrt:~# ifup lan2
root@OpenWrt:~#

STEP 4:

Trigger another Router Solicitation toward the gateway which should fail at this point

root@testuser-Latitude-E5410:/usr/localdisk/openwrt/bin/targets/ar71xx/generic# rdisc6 -1 eth0
Soliciting ff02::2 (ff02::2) on eth0...
Timed out.
Timed out.
Timed out.
No response.
root@testuser-Latitude-E5410:/usr/localdisk/openwrt/bin/targets/ar71xx/generic#

Internally the Recv-Q on the raw socket starts to increase until odhcpd is restarted manually.

root@OpenWrt:~# netstat -lnp | grep odhcpd
udp        0      0 :::547                  :::*                                2508/odhcpd
udp        0      0 :::547                  :::*                                2508/odhcpd
raw     3968      0 ::%2143929572:58        ::%4381825:*            58          2508/odhcpd
raw        0      0 ::%2143929572:58        ::%4381825:*            58          2508/odhcpd
root@OpenWrt:~#

RECOVER THE GATEWAY:

root@OpenWrt:~# /etc/init.d/odhcpd restart

openwrt / odhcpd