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

[Aki Tuomi]

> On 11 April 2019 11:02 Laura Smith via dovecot <dovecot at dovecot.org> wrote:
> 
>  
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Thursday, April 11, 2019 12:55 AM, John Fawcett via dovecot <dovecot at dovecot.org> wrote:
> 
> > On 11/04/2019 00:51, Laura Smith via dovecot wrote:
> >
> > > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > > On Wednesday, April 10, 2019 11:48 PM, John Fawcett via dovecot dovecot at dovecot.org wrote:
> > >
> > > > 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
> > >
> > > John,
> > > Here's the definitive answer to your question (and anyone else thinking of pointing the finger at apparmor):
> > > foo:/home/foo # sudo systemctl stop apparmor
> > > foo:/home/foo # doveadm -v -o mail_fsync=never backup -R -u foobar at example.com imapc:
> > > dsync(foobar at example.com): Error: imapc(foobar.example.com:993): dns_lookup(foobar.example.com) failed: DNS lookup timed out
> > > dsync(foobar at example.com): Error: Failed to initialize user: imapc: Login to foobar.example.com failed: Disconnected from server
> > > So. Can we move on from the "blame apparmor" ? ;-)
> >
> > Laura
> >
> > I'd suggest doing the test with a restart of dovecot in between stopping
> > apparmor and running the doveadm command. Check your logs to see if
> > there is no longer any message generated about not being able to execv
> > /usr/lib/dovecot/dns-client.
> >
> > foo:/home/foo # sudo systemctl stop apparmor
> > foo:/home/foo # sudo systemctl restart dovecot
> > foo:/home/foo # doveadm -v -o mail_fsync=never backup -R -u foobar at example.com imapc:
> >
> > John
> 
> 
> Same again....
> 
> failed: read(/var/run/dovecot/dns-client) failed: read(size=512) failed: Connection reset by peer

And your logs probably indicate that same Fatal error that the service cannot be started?

Wonder if this is caused by systemd? Can you try also

systemctl stop dovecot
dovecot -F

then try socat and see if it works?

Aki