[Bug 1849733] Re: resolved incorrectly limits TCP reply to edns0 payload

[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/1849733

Title:
  resolved incorrectly limits TCP reply to edns0 payload

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

Bug description:
  [impact]

  glibc's getaddrinfo() uses EDNS0 to talk to resolved, and it sets its
  payload limit to 1200.  When the response is larger than 1200,
  resolved will limit the response and set the truncate flag.  This
  causes getaddrinfo() to switch to TCP and request again, but glibc
  incorrectly keeps the EDNS0 RR opt, with the same 1200 payload limit.
  Most dns nameservers ignore EDNS0 payload limit for TCP, since per RFC
  it applies only to UDP, but resolved does not and again marks the
  response as truncated.  This prevents getaddrinfo() from being able to
  resolve any records with a response over 1200 bytes.

  [test case]

  use ping or telnet, which use getaddrinfo(), to lookup an A record
  with a lot of results, like toomany100.ddstreet.org

  $ telnet toomany100.ddstreet.org
  telnet: could not resolve toomany100.ddstreet.org/telnet: Temporary failure in name resolution

  [regression potential]

  any regression would likely result in failure to correctly lookup a
  hostname or to provide the correct response to a local client.

  [other info]

  note that on Bionic, this also requires backporting TCP pipelining
  support in the stub resolver.

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