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

[Timo Aaltonen]

Public bug reported:

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)."

** Affects: eglibc (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: eglibc (Ubuntu Precise)
     Importance: Undecided
         Status: New

** Affects: eglibc (Fedora)
     Importance: Unknown
         Status: Unknown

** Also affects: eglibc (Ubuntu Precise)
   Importance: Undecided
       Status: New

** Bug watch added: Red Hat Bugzilla #714823
   https://bugzilla.redhat.com/show_bug.cgi?id=714823

** Also affects: eglibc (Fedora) via
   https://bugzilla.redhat.com/show_bug.cgi?id=714823
   Importance: Unknown
       Status: Unknown

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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:
  New
Status in “eglibc” source package in Precise:
  New
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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