[Pkg-utopia-maintainers] Bug#898038: caused by host

[Andrej Shadura]

On Mon, 7 May 2018 09:52:49 +0800 Trent Lloyd <trent at lloyd.id.au> wrote:
> I have been tracking this issue in Ubuntu at: 
> https://bugs.launchpad.net/bugs/1752411
> 
> The root cause of this issue is a bug in 'host', in certain 
> circumstances the host command hangs and never returns. I can reproduce 
> this reliably.
> The main case I have found is when an interface is up, but the link is 
> still down and a default route is installed in the state 'linkdown'.  
> This only happens if that is the route used to send packets to a 
> nameserver listed in resolv.conf
> 
> I haven't yet managed to debug what causes host to fail internally and 
> never timeout in this case, but a workaround is to modify 
> avahi-daemon-check-dns.sh to launch host under the 'timeout' command 
> with a 5 second timeout to ensure it doesn't block forever.
> 
> The real issue in host needs to be fixed, though, I have a machine that 
> reproduces this issue reliably if anyone is experience in bind9-host 
> debugging and I can reproduce it on demand.

I’d say the host never timing out is slightly a different issue, yet
another place where this may fail. So there are two issues at the same
time here:

1) avahi-daemon-check-dns.sh shouldn’t call potentially blocking host
when it’s guaranteed to block (e.g. no connectivity)

2) host should probably time out in a reasonable amount of time (e.g.
max. 2 seconds)

My patch fixes the first part, by preventing the host calls when the
nameserver is not reachable (the script mistakenly thinks
2001:1234:5678::10 is a nameserver at localhost since it matches the
"::1" pattern, and attempts to talk to it).

-- 
Cheers,
  Andrej