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

[Launchpad Bug Tracker]

This bug was fixed in the package systemd - 240-6ubuntu5.8

---------------
systemd (240-6ubuntu5.8) disco; urgency=medium

  [ Victor Tapia ]
  * d/p/resolved_disable-connection-downgrade-when-DNSSEC-yes.patch
    Fix regression introduced by
    resolved-Mitigate-DVE-2018-0001-by-retrying-NXDOMAIN-with.patch when
    DNSSEC=yes (LP: #1796501)

  [ Dan Streetman ]
  * d/p/lp1840640-shared-seccomp-add-sync_file_range2.patch:
    allow sync_file_range2 in nspawn container (LP: #1840640)
  * d/p/lp1847527-journal-remote-do-not-request-Content-Length-if-Tran.patch:
    do not request Content-Length if Transfer-Encoding is chunked
    (LP: #1847527)
  * d/t/storage: fix flaky test
    (LP: #1847815)
  * d/p/lp1843381-dell_passthrough_skip_rename_retry.patch,
    debian/extra/rules/73-usb-net-by-mac.rules:
    fix rename delay for systems using "Dell MAC passthrough"
    (LP: #1843381)
  * d/p/lp1849733/0001-resolved-if-we-can-t-append-EDNS-OPT-RR-then-indicat.patch,
    d/p/lp1849733/0002-resolved-don-t-let-EDNS0-OPT-dgram-size-affect-TCP.patch:
    ignore EDNS0 payload limit when responding over TCP (LP: #1849733)
  * d/p/lp1849658-resolved-set-stream-type-during-DnsStream-creation.patch:
    - Fix bug in refcounting TCP stream types (LP: #1849658)
  * d/extra/dhclient-enter-resolved-hook:
    - only restart resolved if dhclient conf changed (LP: #1805183)

  [ Balint Reczey ]
  * d/p/test-execute-Filter-dev-.lxc-in-exec-dynamicuser-statedir.patch:
    fix test breakage due to running in nested lxd container
    (LP: #1845337)

 -- Dan Streetman <ddstreet at canonical.com>  Fri, 04 Oct 2019 09:06:58
-0400

** Changed in: systemd (Ubuntu Disco)
       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 Bionic:
  Fix Committed
Status in systemd source package in Disco:
  Fix Released
Status in systemd source package in Eoan:
  Fix Released
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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