[nsd-users] NSD still shows permission errors on Debian 10 Buster

[Simon Deziel]

On 2020-05-27 11:48 a.m., Anand Buddhdev wrote:
> On 27/05/2020 16:37, Simon Deziel via nsd-users wrote:
> 
> Hi Simon,
> 
>> As you saw, you need to add "ReadWritePaths=/var/log/" to the systemd
>> unit so that nsd can create the file.
>>
>> When you do so, on first startup, nsd changes UID from root -> nsd and
>> then creates /var/log/nsd.log:
>>
>> root at d10-nsd:~# ls -l /var/log/nsd.log
>> -rw-r--r-- 1 nsd nsd 151 May 27 14:15 /var/log/nsd.log
>>
>> On subsequent starts, nsd checks if it can append to the log while still
>> running as root. I believe this is a bug as this check should happen
> 
> Are you certain of this? I have never seen any errors on my NSD systems.

I reproduced it all in a Debian Buster VM before posting. Are you using
the same systemd unit as Debian Buster's [*] ?

>> after the switch from root->nsd. You can workaround it by using the big
>> hammer that is CAP_DAC_OVERRIDE [*] or add this with `systemctl edit
>> nsd`:
>>
>> [Service]
>> ExecStartPre=-/bin/chown --quiet root:root /var/log/nsd.log
> 
> All of this seems to be band-aid upon band-aid of unnecessary hacks.

That's a band-aid indeed. IMHO the proper fix is to be consistent in
handling the file. So either open it as root and not chown it or always
touch it after setuid().

>> As for the failed unlinking of the pidfile, this is harmless and should
>> not be logged as a warning. It may already be fixed in newer releases as
>> it was done with Unbound already.
> 
> PID files are so passé! They are irrelevant on systems where daemons are
> run under supervisors. I would highly recommend setting "pidfile" to ""
> in nsd.conf. This prevents creation of a PID file. Systemd already knows
> the PID of the NSD process, and can signal it directly.

Would it make sense to simply ignore the pidfile directive when running
through systemd?


*:
https://salsa.debian.org/dns-team/nsd/-/blob/nsd_debian/4.1.26-1/debian/nsd.service