IPv6 reverse lookup broken (possibly by glibc-2.30.patch)

[Matthias Ferdinand]

On Ubuntu 20.04 with glibc-2.31, sendmail fails to verify IPv6 client addresses (reverse-then-forward-lookup) and refuses to accept incoming mail:

May 20 16:42:50 mx sm-mta[161617]: ruleset=check_relay, arg1=[IPv6:2a04:6c0:0:0:0:0:bad:0], arg2=IPv6:2a04:6c0:0:0:0:0:bad:0, relay=hektik.14v.de [IPv6:2a04:6c0:0:0:0:0:bad:0] (may be forged), reject=451 4.1.8 Possibly forged hostname for IPv6:2a04:6c0:0:0:0:0:bad:0

No such problem on Ubuntu 18.04 (glibc-2.27).

It seems the patch "glibc-2.30.patch" fixes the FTBS problem, but does not provide an alternate method for IPv6 reverse lookups.

I checked with tcpdump and the forward lookups are always for "A" records instead of "AAAA".

There is already some #ifdef in conf.c, function sm_getipnodebyname() for gethostbyname2().

If I add
  #define HAS_GETHOSTBYNAME2 1
before that, reverse lookups for IPv6 do work again as expected.

[Matthias Ferdinand (mf+ubuntu1)]

Hi,

please find attached patch for debian/configure.ac.

It removes the test for getaddrinfo() (not used in sendmail), and adds a test for gethostbyname2(), adding -DHAS_GETHOSTBYNNAME2=1 to sm_envdef when found.

Regards
Matthias Ferdinand

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "configure.ac snippet to test for gethostbyname2() and to define HAS_GETHOSTBYNAME2" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[Launchpad Janitor (janitor)]

This bug was fixed in the package sendmail - 8.15.2-19

---------------
sendmail (8.15.2-19) unstable; urgency=medium

  * QA upload.
  * Fix IPv6 reverse lookups with glibc 2.30, thanks to Matthias Ferdinand.
    (Closes: #961538) (LP: #1879738)
  * Do not ship files generated by autoreconf.
  * Run autoreconf on debian/ at build time.
  * Switch to debhelper-compat (= 13).
  * Move /usr/lib/sm.bin/ to /usr/libexec/sendmail/.
  * Update Lintian overrides.

 -- Andreas Beckmann <email address hidden> Tue, 26 May 2020 01:48:43 +0200