[dnsdist] dnsdist using loopback address as source address for queries

[Remi Gacogne]

Hi Adam,

On 10/29/21 12:10, Adam Bishop via dnsdist wrote:
> On 13 Sep 2021, at 13:47, Adam Bishop <adam.bishop at jisc.ac.uk> wrote:
>> On 13 Sep 2021, at 13:31, Remi Gacogne via dnsdist <dnsdist at mailman.powerdns.com> wrote:
>>> That's very weird, I don't have any clue to what might be happening. Would you mind sharing the whole configuration? In particular, do you set the source interface? I would also be very interested in seeing a strace of the process while the issue is happening.
>>
>> Sure, I can attach strace the next time I catch it in the act. It's occurring infrequently, but reliably so might take me a few days. Source interface is not explicitly set, as the host is single homed.
> 
> Took a while to recur, but I attached trace. Nothing immediately jumps out at me, there's no errors returned by the socket.
> 
> Command used was: strace -v -s 1024 -Ff -p 1351 2>&1 | grep -v epoll_wait | grep -v nanosleep
> 
> I've left the instance in the broken state, so if there's additional testing that would be useful, please let me know.

I'll look at the trace more closely in a bit but would you mind getting 
the output of "lsof -n -p <pid of dnsdist>" while the issue is still 
happening? A full backtrace with gdb might also be good to have, you 
would first need to attach to the running process with 'gdb -p <pid of 
dnsdist' then issue the 'thread apply all bt full' command. You can then 
close gdb and let dnsdit running (or not).

Thanks!
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