[Bug 1849658] Re: resolved fallback to TCP fails for truncated UDP replies

[Launchpad Bug Tracker]

This bug was fixed in the package systemd - 243-3ubuntu1

---------------
systemd (243-3ubuntu1) focal; urgency=medium

  [ Dan Streetman ]
  * Fix resolved fallback to TCP (LP: #1849658)
    Author: Dan Streetman
    File: debian/patches/resolved-set-stream-type-during-DnsStream-creation.patch
    https://git.launchpad.net/~ubuntu-core-dev/ubuntu/+source/systemd/commit/?id=f1ee30b13c9d2d34968b09ce620f3bc24a1a78c7
  * Separate stderr and stdout of /etc/dhcp/dhclient-enter-hooks.d/resolved
    (LP: #1849608)
    Author: Dan Streetman
    File: debian/extra/dhclient-enter-resolved-hook
    https://git.launchpad.net/~ubuntu-core-dev/ubuntu/+source/systemd/commit/?id=fec4d6d026488a1d32ad9dceef18d9ea9c8acbda

  [ Balint Reczey ]
  * Merge to Ubuntu from Debian experimental
  * Refresh patches:
    - Dropped changes:
      * udevadm trigger: do not propagate EACCES and ENODEV.
        File: debian/patches/udevadm-trigger-do-not-propagate-EACCES-and-ENODEV.patch
        https://git.launchpad.net/~ubuntu-core-dev/ubuntu/+source/systemd/commit/?id=334e3fdc904de05105c78763c88220c1976d1946
      * Pass personality test even when i386 userland runs on amd64 kernel
        File: debian/patches/debian/UBUNTU-test-Pass-personality-test-even-when-i386-userland-runs-o.patch
        https://git.launchpad.net/~ubuntu-core-dev/ubuntu/+source/systemd/commit/?id=42e0bfc426f19430f6768ef4922a9531a345765f

systemd (243-3) experimental; urgency=medium

  * Import patches from v243-stable branch (up to ef677436aa)

 -- Balint Reczey <rbalint at ubuntu.com>  Wed, 30 Oct 2019 15:19:33 +0100

** Changed in: systemd (Ubuntu Focal)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1849658

Title:
  resolved fallback to TCP fails for truncated UDP replies

Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Disco:
  In Progress
Status in systemd source package in Eoan:
  In Progress
Status in systemd source package in Focal:
  Fix Released

Bug description:
  [impact]

  for DNS UDP replies larger than 512 bytes, fallback to TCP is used.
  For example 'host toomany.ddstreet.org'.

  Due to a bug in resolved in refcounting DNS stream types, the refcount
  underflows for type 0 streams (which resolved uses to talk to upstream
  nameservers), resulting in resolved being unable to fallback to TCP to
  handle truncated UDP replies.

  [test case]

  ubuntu at sf247344-upstream:~$ dig +noanswer +noedns toomany.ddstreet.org
  ;; Truncated, retrying in TCP mode.

  ; <<>> DiG 9.11.3-1ubuntu1.9-Ubuntu <<>> +noanswer +noedns toomany.ddstreet.org
  ;; global options: +cmd
  ;; Got answer:
  ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2683
  ;; flags: qr rd ra; QUERY: 1, ANSWER: 40, AUTHORITY: 0, ADDITIONAL: 0

  ;; QUESTION SECTION:
  ;toomany.ddstreet.org.		IN	A

  ;; Query time: 0 msec
  ;; SERVER: 127.0.0.53#53(127.0.0.53)
  ;; WHEN: Thu Oct 24 11:40:29 UTC 2019
  ;; MSG SIZE  rcvd: 678

  ubuntu at sf247344-upstream:~$ sudo resolvectl flush-caches
  ubuntu at sf247344-upstream:~$ dig +noanswer +noedns toomany.ddstreet.org

  ; <<>> DiG 9.11.3-1ubuntu1.9-Ubuntu <<>> +noanswer +noedns toomany.ddstreet.org
  ;; global options: +cmd
  ;; connection timed out; no servers could be reached

  [regression potential]

  very low, as this only properly sets the stream type in the DnsStream
  object; any regression would be a failure to be able to use TCP for
  DNS requests or replies.

  [other info]

  https://github.com/systemd/systemd/pull/13838

  The commit adding stream types is not present in x/b, so this is
  needed only for disco and later.

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