All autopkgtests for the newly accepted dnsmasq (2.86-1.1ubuntu0.5) for jammy 
have finished running.
The following regressions have been reported in tests triggered by the package:

systemd/249.11-0ubuntu3.11 (ppc64el)


Please visit the excuses page listed below and investigate the failures, 
proceeding afterwards as per the StableReleaseUpdates policy regarding 
autopkgtest regressions [1].

https://people.canonical.com/~ubuntu-archive/proposed-
migration/jammy/update_excuses.html#dnsmasq

[1] https://wiki.ubuntu.com/StableReleaseUpdates#Autopkgtest_Regressions

Thank you!

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https://bugs.launchpad.net/bugs/2045570

Title:
  dnsmasq crash when no servers in resolv.conf

Status in dnsmasq package in Ubuntu:
  Fix Released
Status in dnsmasq source package in Jammy:
  Fix Committed

Bug description:
  [ Impact ]

  dnsmasq "keeps an eye" on /etc/resolv.conf, and reloads it whenever
  the file is updated. When that happens and for some reason there were
  no "nameserver" declarations in the updated file, dnsmasq can crash.

  Here is a log of a reproducer:
  $ dig +short @127.0.0.1 ubuntu.com
  ;; communications error to 127.0.0.1#53: timed out
  ;; communications error to 127.0.0.1#53: connection refused
  ;; communications error to 127.0.0.1#53: connection refused
  ;; no servers could be reached

  We can see the startup, then when resolv.conf is read again and no 
nameservers were found, and the crash:
  Jan 03 13:57:13 j-dnsmasq-2045570 dnsmasq[1507]: started, version 2.86 
cachesize 150
  Jan 03 13:57:13 j-dnsmasq-2045570 dnsmasq[1507]: DNS service limited to local 
subnets
  Jan 03 13:57:13 j-dnsmasq-2045570 dnsmasq[1507]: compile time options: IPv6 
GNU-getopt DBus no-UBus i18n IDN2 DHCP DHCPv6 no-Lua TFTP conntrack ipset auth 
cryptohash DNSSEC loop-detect inotify dumpfile
  Jan 03 13:57:13 j-dnsmasq-2045570 dnsmasq[1507]: reading /etc/resolv.conf
  Jan 03 13:57:13 j-dnsmasq-2045570 dnsmasq[1507]: using nameserver 
10.0.100.1#53
  Jan 03 13:57:13 j-dnsmasq-2045570 dnsmasq[1507]: read /etc/hosts - 7 addresses
  Jan 03 13:57:13 j-dnsmasq-2045570 systemd[1]: Started dnsmasq - A lightweight 
DHCP and caching DNS server.
  Jan 03 13:58:01 j-dnsmasq-2045570 dnsmasq[1507]: no servers found in 
/etc/resolv.conf, will retry
  Jan 03 13:58:22 j-dnsmasq-2045570 systemd[1]: dnsmasq.service: Main process 
exited, code=dumped, status=11/SEGV
  Jan 03 13:58:22 j-dnsmasq-2045570 systemd[1]: dnsmasq.service: Failed with 
result 'core-dump'.

  dnsmasq has provisions for this situation, we can see that in the
  13:58:01 message where it says it will retry, but due to this bug, it
  crashes instead.

  The problem was introduced[1] in version 2.86, and fixed in 2.87, so
  only jammy is affected.

  1. 
https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=patch;h=d290630d31f4517ab26392d00753d1397f9a4114;hp=d2ad5dc073aaacaf22b117f16106282a73586803
  The commit message says:
  """
  This problem was introduced in 2.86.
  """

  And indeed, I wasn't able to crash 2.80 shipped in focal.

  [ Test Plan ]
  It might take a few tries to reproduce the bug, but here is the general 
outline. Also keep in mind that it's important to use a DNS name that isn't 
cached already by a previous query.

  # Create a jammy lxd container

  lxc launch ubuntu-daily:jammy j-dnsmasq-2045570

  # Enter the container

  lxc shell j-dnsmasq-2045570

  # From now on, all commands should be executed in the container.
  # Install dnsmasq, and disable systemd-resolved

  apt update && apt install -y dnsmasq

  # Disable systemd-resolved, and start dnsmasq

  systemctl disable --now systemd-resolved
  systemctl enable --now dnsmasq

  # In one terminal inside the container, watch the dnsmasq logs:

  journalctl -u dnsmasq.service -f

  # In another terminal, remove /etc/resolv.conf and create a new one, empty
  rm /etc/resolv.conf
  echo "nameserver 1.1.1.1" > /etc/resolv.conf

  # restart dnsmasq
  systemctl restart dnsmasq.service

  # Perform a dns query

  dig @127.0.0.1 +short linux.com

  # Comment the namserver directive in resolv.conf
  echo "#nameserver 1.1.1.1" > /etc/resolv.conf

  # Observe in the dnsmasq logs that it notices the change with a
  message like:

  Jan 03 14:14:51 j-dnsmasq-2045570 dnsmasq[2274]: no servers found in
  /etc/resolv.conf, will retry

  # Perform a *different* DNS query

  dig @127.0.0.1 +short ubuntu.com

  # Observe in the dnsmasq logs that it crashes.
  Jan 03 13:58:22 j-dnsmasq-2045570 systemd[1]: dnsmasq.service: Main process 
exited, code=dumped, status=11/SEGV
  Jan 03 13:58:22 j-dnsmasq-2045570 systemd[1]: dnsmasq.service: Failed with 
result 'core-dump'.

  If it doesn't crash right away, repeat these steps a few times, but using a 
different domain name each time:
  - add "nameserver 127.0.0.1" to /etc/resolv.conf
  - observe that dnsmasq notices the change to the file
  - perform a query for some random domain using "dig @127.0.0.1 +short 
<domain-of-your-choosing>"
  - remove "nameserver" from /etc/resolv.conf, observe that dnsmasq noticed the 
change
  - perform a query for another random domain

  The fixed version from proposed will not crash. That last query with
  no "nameserver" lines in resolv.conf won't work, but it won't crash
  the server.

  [ Where problems could occur ]

  This is doing some pointer/memory manipulation that could introduce
  memory leaks or other crashes. In fact, this is exactly what happened
  in the 2.86 release, which, and I quote, "Major rewrite of the DNS
  server and domain handling code. This should be largely transparent,
  but it drastically improves performance and reduces memory foot-
  print"[2]. 2.88 was then released with the fix used in this SRU (the
  commit is also in the 2.87 tag, but the upstream release notes only
  mention it in 2.88).

  2.
  
https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=blob;f=CHANGELOG;h=2ce53a81079810ae43588607f43851dabb5db38d;hb=HEAD#l224

  [ Other Info ]
  Not at this time.

  [ Original description ]

  upstream discussion:
  https://lists.thekelleys.org.uk/pipermail/dnsmasq-
  discuss/2022q3/016563.html

  in my journal, my dns service crash and restart just after:
  Dec 04 17:18:38 dnsmasq[199333]: no servers found in 
/run/NetworkManager/no-stub-resolv.conf, will retry

  oops report: https://errors.ubuntu.com/oops/29cf5e2e-92b1-11ee-9bdf-
  fa163ec44ecd

  ubuntu jammy, dnsmasq-base 2.86-1.1ubuntu0.3

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