[Bug 673708] Re: getaddrinfo and AI_PASSIVE is broken for net.ipv6.bindv6only=0

[Pavel Šimerda]

Upstream bug report:

http://sourceware.org/bugzilla/show_bug.cgi?id=14967

More information:

https://fedoraproject.org/wiki/Networking/NameResolution#Binding_to_the_INADDR_ANY_and.2For_in6addr_any_addresses

** Bug watch added: Sourceware.org Bugzilla #14967
   http://sourceware.org/bugzilla/show_bug.cgi?id=14967

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Title:
  getaddrinfo and AI_PASSIVE is broken for net.ipv6.bindv6only=0

Status in “eglibc” package in Ubuntu:
  New

Bug description:
  When calling getaddrinfo and specifying AF_UNSPEC and AI_PASSIVE it
  returns both IPv4 and IPv6 addresses when the sysctl
  net.ipv6.bindv6only = 0. Proper app behavior for AI_PASSIVE should be
  to bind and listen to all returned addresses, but the kernel does not
  allow binding to a V4 and V6 address with the same port. In this case
  getaddrinfo should return only a IPv4 or only a IPv6 address.

  Illustrated with python because I'm lazy:

  >>> resx = socket.getaddrinfo(None,'1234',0,socket.SOCK_STREAM,0,socket.AI_PASSIVE)
  >>> print resx
  [(2, 1, 6, '', ('0.0.0.0', 1234)), (10, 1, 6, '', ('::', 1234, 0, 0))]

  >>> res = resx[0]
  >>> fd = socket.socket(res[0],res[1],res[2])
  >>> fd.bind(res[4]);    

  >>> res = resx[1]
  >>> fd2 = socket.socket(res[0],res[1],res[2])
  >>> fd2.bind(res[4]);
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "<string>", line 1, in bind
  socket.error: [Errno 98] Address already in use

  At least in earlier Ubuntu releases this case returned the IPv6
  address first, so most apps which don't properly use all addresses
  'worked' but it was still wrong to return both addresses.  The new
  behavior breaks IPv6 in various cases, with no possible app work-
  around!

  Apps should not be expected to 'sense' if the system is bindv6only.
  getaddrinfo  AF_UNSPEC/AI_PASSIVE should return v6 only for an IPv6
  enabled bindv6only = 0 host and both IPv6 and IPv4 (in any order) for
  an IPv6 enabled bindv6only= host.

  At a minimum the old sorting behavior of putting v6 first should be
  restored! Real apps depend on this!

  I've noted various other bugs in this same theme:
  http://sources.redhat.com/bugzilla/show_bug.cgi?id=9981
  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=573456

  So here is one for Ubuntu with a bit more clarity on the exact
  problem.

  ProblemType: Bug
  DistroRelease: Ubuntu 10.10
  Package: libc6 2.12.1-0ubuntu8
  ProcVersionSignature: Ubuntu 2.6.35-22.35-generic 2.6.35.4
  Uname: Linux 2.6.35-22-generic x86_64
  Architecture: amd64
  Date: Wed Nov 10 12:52:08 2010
  InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release amd64 (20101007)
  ProcEnviron:
   PATH=(custom, no user)
   LANG=C
   SHELL=/bin/bash
  SourcePackage: eglibc

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