[Patch] [BZ 14505] Avoid unwanted A lookups on IPV6 only host

[Jeff Law]

As mentioned in the BZ, when looking up a name via getaddrinfo with 
AI_ADDRCONFIG on an IPv6 only host, IN A queries are being sent. 
According to RFC 3493, they should not.

The issue is gaih_inet calls gethostbyname4 which issues both A and AAAA 
queries.

If we look up in getaddrinfo we see that when the AI_ADDRCONFIG hint is 
set, we look at the configured interfaces and set the ai_family flag to 
either PF_INET or PF_INET6 if only one type of interface is configured. 
  If both kinds of interfaces are enabled the hint should continue to be 
AF_UNSPEC.

We then pass that information down to gaih_inet where we can trivially 
query it before calling gethostbyname4.  That's precisely what this 
patch implements.





-------------- next part --------------
2012-08-21  Jeff Law <law@redhat.com>

	
	[BZ #14505]
	* sysdeps/posix/getaddrinfo.c (gaih_inet): If the caller has
	requested either A or AAAA requests explicitly, then do not use
	gethostbyname4 as it sends out both A and AAAA requests.

diff -Nrup a/sysdeps/posix/getaddrinfo.c b/sysdeps/posix/getaddrinfo.c
--- a/sysdeps/posix/getaddrinfo.c	2012-08-21 13:43:07.291667596 -0600
+++ b/sysdeps/posix/getaddrinfo.c	2012-08-21 13:48:19.840427211 -0600
@@ -832,7 +832,13 @@ gaih_inet (const char *name, const struc
 	      no_data = 0;
 	      nss_gethostbyname4_r fct4
 		= __nss_lookup_function (nip, "gethostbyname4_r");
-	      if (fct4 != NULL)
+
+	      /* gethostbyname4 sends out parallel queries.  If we are
+		 suppressing either IPV4 or IPV6 by asking for a specific
+		 protocol, then gethostbyname4 is not appropriate.  */
+	      if (fct4 != NULL
+		  && !(req->ai_family == PF_INET6
+		       || req->ai_family == PF_INET))
 		{
 		  int herrno;