[Dnsmasq-discuss] dnsmasq stuck at reading socket

Simon Kelley simon at thekelleys.org.uk
Sat Oct 16 19:53:46 UTC 2021


Are you running dnsmasq in debug mode?

Simon.


On 16/10/2021 15:17, Juhyung Park wrote:
> Hi.
> 
> I'm trying to debug an issue with dnsmasq that gets completely
> unresponsive after a few days of uptime.
> 
> We have dnsmasq setup to serve as a DHCP server to local, wired
> network (192.168.10.0/24) and as a DNS resolver to local and WireGuard
> VPN network (192.168.240.0/24).
> 
> After the dnsmasq daemon runs for a few days, it gets completely
> unresponsive. DHCP isn't renewed, DNS resolver doesn't work, etc.
> 
> Using strace, I'm able to see that it's blocked from reading a socket:
> # strace -f -p 342291
> strace: Process 342291 attached
> read(13, ^Cstrace: Process 342291 detached
>  <detached ...>
> 
> dnsmasq.conf:
> bogus-priv
> cache-size=5000
> domain-needed
> no-negcache
> no-resolv
> no-poll
> no-hosts
> log-facility=/dev/kmsg
> 
> # DHCP
> dhcp-range=192.168.10.2,192.168.10.254,255.255.255.0
> dhcp-no-override
> dhcp-authoritative
> dhcp-lease-max=253
> dhcp-option=6,192.168.10.1
> 
> server=164.124.101.2
> 
> /proc/?/fd:
> /proc/342291/fd# ll
> total 0
> dr-x------ 2 root root  0 Oct 16 22:30 ./
> dr-xr-xr-x 9 root root  0 Oct 16 18:53 ../
> lr-x------ 1 root root 64 Oct 16 22:30 0 -> 'pipe:[3988]'
> l-wx------ 1 root root 64 Oct 16 22:30 1 -> /dev/null
> lr-x------ 1 root root 64 Oct 16 22:30 10 -> 'pipe:[526396]'
> l-wx------ 1 root root 64 Oct 16 22:30 11 -> 'pipe:[526396]'
> l-wx------ 1 root root 64 Oct 16 22:30 12 -> /dev/kmsg
> lrwx------ 1 root root 64 Oct 16 22:30 13 -> 'socket:[2740642]'
> l-wx------ 1 root root 64 Oct 16 22:30 2 -> /dev/null
> lrwx------ 1 root root 64 Oct 16 22:30 3 -> /var/lib/misc/dnsmasq.leases
> lrwx------ 1 root root 64 Oct 16 22:30 4 -> 'socket:[526385]'
> lrwx------ 1 root root 64 Oct 16 22:30 5 -> 'socket:[526386]'
> lrwx------ 1 root root 64 Oct 16 22:30 6 -> 'socket:[526388]'
> lrwx------ 1 root root 64 Oct 16 22:30 7 -> 'socket:[526389]'
> lrwx------ 1 root root 64 Oct 16 22:30 8 -> 'socket:[526390]'
> lrwx------ 1 root root 64 Oct 16 22:30 9 -> 'socket:[526391]'
> 
> lsof:
> # lsof -i -a -p 342291
> COMMAND    PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
> dnsmasq 342291 root    4u  IPv4  526385      0t0  UDP *:bootps
> dnsmasq 342291 root    6u  IPv4  526388      0t0  UDP *:domain
> dnsmasq 342291 root    7u  IPv4  526389      0t0  TCP *:domain (LISTEN)
> dnsmasq 342291 root    8u  IPv6  526390      0t0  UDP *:domain
> dnsmasq 342291 root    9u  IPv6  526391      0t0  TCP *:domain (LISTEN)
> dnsmasq 342291 root   13u  IPv4 2740642      0t0  TCP
> 192.168.240.1:domain->192.168.240.103:63169 (ESTABLISHED)
> 
> It seems that a WireGuard client DNS socket (fd 13) is forever
> blocked. Since I'm not sure as to whether this is WireGuard's or
> dnsmasq's issue, I figured I'd try contacting dnsmasq mailing list
> first.
> 
> dnsmasq is version 2.85, but we've tried older versions as well.
> 
> Any suggestions?
> 
> Thanks.
> 
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