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

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On 2011-06-20T21:40:53+00:00 Simo wrote:

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).

Reply at:
https://bugs.launchpad.net/ubuntu/+source/eglibc/+bug/1057526/comments/0

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On 2011-06-20T22:33:00+00:00 Marko wrote:

It turned out that setting ai_family triggers this behaviour.

When calling getaddrinfo with ai_flags = AI_CANONNAME, ai_family =
AF_UNSPEC then the ai_canonname returned is as expected.

When calling getaddrinfo with ai_flags = AI_CANONNAME, ai_family =
AF_INET then the ai_canonname returned contains the PTR name of the
forward resolved IP address as described in comment 0.

Reply at:
https://bugs.launchpad.net/ubuntu/+source/eglibc/+bug/1057526/comments/1

------------------------------------------------------------------------
On 2011-12-06T17:47:52+00:00 errata-xmlrpc wrote:

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHSA-2011-1526.html

Reply at:
https://bugs.launchpad.net/ubuntu/+source/eglibc/+bug/1057526/comments/2


** Changed in: eglibc (Fedora)
       Status: Unknown => Fix Released

** Changed in: eglibc (Fedora)
   Importance: Unknown => Undecided

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

Title:
  getaddrinfo returns PTR name in ai_canonname when using DNS

Status in eglibc:
  Fix Released
Status in eglibc package in Ubuntu:
  Fix Released
Status in eglibc source package in Precise:
  Fix Released
Status in eglibc package in Debian:
  Fix Released
Status in eglibc package in Fedora:
  Fix Released

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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