Bug#554188: getaddrinfo: times out when asking for v4 and v6 without single-request option

[Sam Hartman <hartmans@debian.org>]

Package: libc6
Version: 2.10.1-5
Severity: normal

Hi.  I've found that if I use MIT Kerberos, or any other application
that requests both v4 and v6 addresses at the same time I get a 5
second delay in each call to getaddrinfo with high probability.  There
is obviously a race condition: sometimes (order closer to 1/16 than
1/4 or 1/64) it returns quickly.  If you take a look at a packet
capture  at http://web.mit.edu/hartmans/Public/domain-simple.cap
you will see
* Two separate queries for AAAA and A records
* Responses to these queries
* five second delay
* retransmit of one of the queries
* a response

That's one call to getaddrinfo 

If I include the options single-request line in resolv.conf then things return fast as expected.

Tests were run against name servers that were on the local network (or
on localhost) with the responses already cached.

Here's sample c++ code:

std::string s = "kerberos.mit.edu";
bool numeric = false;

  addrinfo  hints;
  memset(&hints, 0, sizeof(hints));
  if (numeric)
    hints.ai_flags |= AI_NUMERICHOST;
  else hints.ai_flags |= AI_ADDRCONFIG;
  addrinfo *res;
  int ret = getaddrinfo(s.c_str(), NULL, &hints, &res);

If you set hints.ai_family to AF_INET6 or AF_INET then you get a fast response.



-- System Information:
Debian Release: squeeze/sid
  APT prefers testing
  APT policy: (500, 'testing'), (500, 'stable'), (40, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.30-2-amd64 (SMP w/2 CPU cores)
Locale: LANG=C, LC_CTYPE=C (charmap=ANSI_X3.4-1968)
Shell: /bin/sh linked to /bin/bash

Versions of packages libc6 depends on:
ii  libc-bin                      2.10.1-5   GNU C Library: Binaries
ii  libgcc1                       1:4.4.1-4  GCC support library

libc6 recommends no packages.

Versions of packages libc6 suggests:
ii  debconf [debconf-2.0]         1.5.26     Debian configuration management sy
ii  glibc-doc                     2.9-4      GNU C Library: Documentation
pn  locales                       <none>     (no description available)

-- debconf information:
  glibc/upgrade: true
  glibc/disable-screensaver:
  glibc/restart-failed:
* glibc/restart-services: spamassassin rsync postfix openbsd-inetd cups cron atd