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[Bug 1527902] Re: 3.13.0-71: IPv6 UDP DNS packets are not received


Good news, everyone!  TL;DR:

Pali, I've (finally) managed to reproduce and fix this bug (IPv6 UDP
DNS), with your recommendation of the program 'jdns'.  For reference,
here's my reproduction procedure, on a fresh install of Precise server
(a slight variation on a method Pali developed):

sudo apt-get install dnsmasq
echo listen-address=::1 | sudo tee /etc/dnsmasq.d/ipv6
echo nameserver ::1 | sudo resolvconf -a lo.inet6
sudo /etc/init.d/dnsmasq restart
# fetch and build https://github.com/psi-im/iris/tree/master/src/jdns
./jdns -d -6 uni AAAA google.com ::1 

    ... kernel versions >= 3.13.0-69.112~precise1 fail with "[1] Error:

Ian, thanks very much for the pointer!  Your mention of Debian bug
808293 led to this pending patch, which does fix this bug (and hopefully
your tftp bug also):  https://patchwork.ozlabs.org/patch/561746/ ("udp:
properly support MSG_PEEK with truncated buffers")

Here's an amd64 test kernel which is 3.13.0-69.112~precise1 + a simple
backport of that patch.   Pali, this passes the 'jdns' test.  Can you
confirm that it resolves your original issue too?  Ian, does it also fix
your tftp problem?


** Changed in: linux (Ubuntu)
     Assignee: Joseph Salisbury (jsalisbury) => Kamal Mostafa (kamalmostafa)

** Changed in: linux-lts-trusty (Ubuntu)
     Assignee: Joseph Salisbury (jsalisbury) => Kamal Mostafa (kamalmostafa)

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  3.13.0-71: IPv6 UDP DNS packets are not received

Status in linux package in Ubuntu:
  In Progress
Status in linux-lts-trusty package in Ubuntu:
  In Progress

Bug description:
  After upgrading linux kernel from version 3.13.0-68 to 3.13.0-71 then
  Kopete (IM messenger) stopped working, cannot connect to any jabber

  I started debugging this problem and found out that, problem resolve
  when I boot back 3.13.0-68 kernel version (without touching any system
  files or packages). When I boot 3.13.0-71 Kopete always does not

  Next I debugged that problem on 3.13.0-71 is just when
  /etc/resolv.conf contains only IPv6 addresses of DNS servers.

  Problem is comes down to dns resolver (jabber in Kopete has its own
  for SRV records) and syscall recvfrom() (on IPv6 socket) always return
  error -EAGAIN without any data returned. But wireshark see that DNS
  response was recevied.

  So it looks like that after 3.13.0-68 kernel was included some change
  which broke receiving UDP packets via IPv6 socket. IPv4 is OK.

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