[Bug 1057526] Re: getaddrinfo returns PTR name in ai_canonname when using DNS

[Myllynen]

There seems to be two related issues but actually both on 12.10.

Some background information: on RHEL 6 both Firefox and ssh work as
expected (i.e., rdns setting in krb5.conf is respected meaning that if
DNS reverse mapping has not been set up properly then authentication
fails when rdns = true but succeeds with rdns = false). On F18 Firefox
works as expected but ssh fails, see
https://bugzilla.redhat.com/show_bug.cgi?id=863350.

On Ubuntu 12.04 both Firefox/ssh work as expected. However, on Ubuntu
12.10 both ssh and Firefox fail to authenticate regardless rdns = false
in krb5.conf.

I'd suggest you to test and verify with curl and/or Firefox to make sure
libc/krb5 are ok and once verified then investigate ssh in more detail
which seems to have an issue of its own.

** Bug watch added: Red Hat Bugzilla #863350
   https://bugzilla.redhat.com/show_bug.cgi?id=863350

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https://bugs.launchpad.net/bugs/1057526

Title:
  getaddrinfo returns PTR name in ai_canonname when using DNS

Status in “eglibc” package in Ubuntu:
  Incomplete
Status in “eglibc” source package in Precise:
  Incomplete
Status in “eglibc” package in Fedora:
  Unknown

Bug description:
  Got pinged about this, not fixed in 12.04 yet. From the Redhat bug:

  "We have verified that getaddrinfo() does reverse address calls to DNS
  when AI_CANONNAME is passed in hints.ai_flags and returns the PTR name
  of the forward resolved ip address as Canonical name.

  The canonical name is arguably not what is returned by the PTR record
  for various reasons. Aside the fact that PTR record are often not
  under control of the the same people that control the A name, A names
  can also be roundrobin names and return multiple addresses. Picking
  one and returnings its PTR as canonical name seem highly questionable.

  A CNAME -> A name resolution is welcome as the A name is arguably the
  Canonical name of a CNAME. But getaddrinfo shouldn't do PTR requests
  to the DNS.

  We found this when testing ssh+GSSAPI auth on laptops that can properly set the A record for their name usin dynamic DNS updates but cannot change the PTR record of whatever network they are currently travelling in.
  This breaks kerberos which needs the canonical (A record) name to construct the principal name used to request a ticket when rdns = false is set in krb5.conf and GSSAPITrustDNS is set to no in ssh (the default)."

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