[Bug 1897744] Re: VerifyHostKeyDNS not working due to missing trust-ad flag

[Daniel von Obernitz]

Hello Brian,

I installed version

245.4-4ubuntu3.3   from   focal-proposed

on my focal systems, did some restarts, checked the content of the
/etc/resolv.conf (trust-ad was always present). Connection to servers
using sshfp is working without authenticity question except those
servers without sshfp key in DNS. So everything works as it is supposed
to.

Thanks a lot and I have changed the tag for focal.

Daniel

** Tags removed: verification-needed-focal
** Tags added: verification-done-focal

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Title:
  VerifyHostKeyDNS not working due to missing trust-ad flag

Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Focal:
  Fix Committed

Bug description:
  [impact]

  without trust-ad resolv.conf option, glibc will strip AD from systemd-
  resolved responses. one thing this will prevent working is ssh
  VerifyHostKeyDNS

  [test case]

  see
  https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1898590/comments/7

  [regression potential]

  regressions would likely involve DNS lookup failures, probably if
  DNSSEC is enabled but possibly even without, and likely when the
  application requesting the dns lookup processes the response AD.

  [scope]

  this is needed only in focal.

  glibc first stripped the AD in version 2.31, so this is not needed in
  bionic or earlier.

  this was added upstream in commit a742f9828ea which was included in
  v246, so this is fixed already in groovy.

  [original description]

  Hi,

  1)
  Description:	Ubuntu 20.04.1 LTS
  Release:	20.04

  2)
  systemd:        245.4-4ubuntu3.2

  3)
  I set VerifyHostKeyDNS to YES and hosts are automatically verified via sshfp.

  4)
  I still get the security question
  Matching host key fingerprint found in DNS.
  Are you sure you want to continue connecting (yes/no/[fingerprint])?

  The issue is known and fixed in systemd v246.
  https://github.com/systemd/systemd/pull/16072

  Best regards
  Daniel

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