failed: read(/var/run/dovecot/dns-client)

[John Fawcett]

On 11/04/2019 00:18, Laura Smith via dovecot wrote:
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Wednesday, April 10, 2019 10:24 PM, Aki Tuomi <aki.tuomi at open-xchange.com> wrote:
>
>>> On 10 April 2019 23:56 Laura Smith via dovecot < dovecot at dovecot.org> wrote:
>>>
>>> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
>>> On Wednesday, April 10, 2019 9:14 PM, Aki Tuomi < aki.tuomi at open-xchange.com> wrote:
>>>
>>>>> On 10 April 2019 23:13 Laura Smith via dovecot dovecot at dovecot.org wrote:
>>>>> Sent with ProtonMail Secure Email.
>>>>> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
>>>>> On Wednesday, April 10, 2019 8:20 PM, Aki Tuomi aki.tuomi at open-xchange.com wrote:
>>>>>>> On 10 April 2019 22:13 Laura Smith via dovecot dovecot at dovecot.org wrote:
>>>>>>> On Wednesday, April 10, 2019 7:57 PM, Aki Tuomi aki.tuomi at open-xchange.com wrote:
>>>>>>>>> On 10 April 2019 21:26 Laura Smith via dovecot dovecot at dovecot.org wrote:
>>>>>>>>> ==========================================================================
>>>>>>>>> dsync( foobar at example.com): Error: imapc(foobar.example.com:993): dns_lookup(foobar.example.com) failed: read(/var/run/dovecot/dns-client) failed: read(size=512) failed: Connection reset by peer
>>>>>>>> This is dovecot's internal dns-client, and something goes wrong when talking to the service.
>>>>>>>>> dsync( foobar at example.com): Error: Failed to initialize user: imapc: Login to foobar.example.com failed: Disconnected from server
>>>>>>>> This is btw dsync service, not imap service.
>>>>>>>>> ===
>>>>>>>>> Initially I thought "oh no, not another AppArmor block".
>>>>>>>>> But then surely the second message would not appear if the DNS lookup was not successful ?
>>>>>>>>> Also "dig foobar.example.com" works fine.
>>>>>>>>> How should I be troubleshooting this ? And if it is still likely to be AppArmor, what is calling it ? "doveadm" itself or something else ? What does "/var/run/dovecot/dns-client" do and why doesn't dovecot use standard OS calls like everyone else ?
>>>>>>>> Because the "standard OS call" is blocking and we would prefer it to not block everything else.
>>>>>>>>> So many questions !
>>>>>>>> Aki
>>>>>>> Thanks for your reply, but both those message are generated from a simple :
>>>>>>> doveadm -v -o mail_fsync=never backup -R -u foobar at example.com imapc:
>>>>>>> So I don't know what you mean about dsync service failing ? Surely the DNS lookup succeeded if the 'dsync service' failed due to remote disconnect ?
>>>>>>> I'm still none the wiser as to where to start looking for troubleshoting ?
>>>>>> Did you check dovecot logs? Maybe there is something useful?
>>>>>> Aki
>>>>> Only the same old cryptic message about dns-client ?
>>>>> master: Fatal: execv(/usr/lib/dovecot/dns-client) failed: Permission denied
>>>> Something prevents executing the dns-client binary.
>>>>> master: Error: service(dns_client): command startup failed, throttling for 16 secs
>>>>> dns_client: Fatal: master: service(dns_client): child 14293 returned error 84 (exec() failed)
>>>> Aki
>>> Yes but is it being called by doveadm directly or by some other dovecot program ? If I'm going to have to go down the AppArmor route, then I would prefer if you told me what was calling it instead of me having to un-necessarily spend time doing straces !
>>>
>>> Also, should I be able to call dns-client directly myself ? (or is there a way to do so to enable testing ?
>> It is started by dovecot's master process when you connect to dns-client unix socket. You can try
>>
>> socat stdio unix-connect:/var/run/dovecot/dns-client
>>
>> I thought apparmor tells when something is blocked into kernel log? have you checked dmesg?
>>
>> Apologies for your frustration. 
>> ---
> Yeah nothing in dmesg.  I'm still hunting around to find some log somewhere but so far silence.
>
> "socat stdio unix-connect:/var/run/dovecot/dns-client" runs but returns nothing. Is that expected ?
>
> When you say "dovecot's master process", so  doveadm sync talks to the master process ?  So in terms of apparmor I would therefore be looking at /usr/sbin/dovecot ?  If that's the case, the relevant apparmor permisssions are already provided :
>   /{,var/}run/dovecot/ rw,
>   /{,var/}run/dovecot/** rw,

Laura

Do the above apparmor settings give permission to dovecot to execute
/usr/lib/dovecot/dns-client, assuming that the user under which dovecot
is running already has file system permissions to do that?

John