[Dnsmasq-discuss] dnsmasq stuck at reading socket

[Juhyung Park]

Wow, that's one hell of a dumb mistake.
Thanks a lot!

Would have pulled a lot of hair out if I were to keep debugging this alone..

Sorry for the false alarm.

On Sun, Oct 17, 2021 at 5:29 AM Simon Kelley <simon at thekelleys.org.uk> wrote:
>
>
>
> On 16/10/2021 21:18, Juhyung Park wrote:
> > On Sun, Oct 17, 2021 at 5:06 AM Simon Kelley <simon at thekelleys.org.uk> wrote:
> >>
> >> Are you running dnsmasq in debug mode?
> >>
> >
> > Nope, the only argument passed to dnsmasq executable is --no-daemon.
> > The rest is set up via /etc/dnsmasq.conf, which is provided in the
> > earlier email.
> >
>
>    -d, --no-daemon
>        Debug mode: don't fork to the  background,  don't  write  a  pid
>        file,  don't  change  user id, generate a complete cache dump on
>        receipt on SIGUSR1, log to stderr as well as syslog, don't  fork
>        new  processes  to  handle TCP queries. Note that this option is
>        for use in debugging only, to stop dnsmasq daemonising  in  pro‐
>        duction, use --keep-in-foreground.
>
>
> So is something opens a TCP connection to dnsmasq then fails to close it
> again, exactly the behaviour you're seeing is expected. The last
> sentence tells you what to do instead.
>
>
> Cheers,
>
> Simon.
>
>
>
> > Thanks.
> >
> >> 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.
> >>>
> >>> _______________________________________________
> >>> Dnsmasq-discuss mailing list
> >>> Dnsmasq-discuss at lists.thekelleys.org.uk
> >>> https://lists.thekelleys.org.uk/cgi-bin/mailman/listinfo/dnsmasq-discuss
> >>>
> >>
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> >