[PATCH] nss: Use gethostbyname4_r when requesting IPv6 addresses (bug 14413)

[Patrick Griffis]

If getaddrinfo() is called with family of AF_INET6 it would return IPv6
addresses lacking scope_id information.

This was a regression caused by bug 14505. That patch avoided calling
gethostbyname4_r unless AF_UNSPEC is passed. The reasoning was that
gethostbyname4_r has no ability to only ask for a specific family.
That is true however gethostbyname3_r returns a list of hostent structs
which lack scope_id information.

The solution is to always use gethostbyname4_r if IPv6 is requested.
This does have the downside of IPv4 addresses being looked up by
modules even when they are not needed.
---
 nss/getaddrinfo.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/nss/getaddrinfo.c b/nss/getaddrinfo.c
index 6726ace6fd..67f7223ac7 100644
--- a/nss/getaddrinfo.c
+++ b/nss/getaddrinfo.c
@@ -644,9 +644,12 @@ get_nss_addresses (const char *name, const struct addrinfo *req,
       no_data = 0;
       nss_gethostbyname4_r *fct4 = NULL;
 
-      /* gethostbyname4_r sends out parallel A and AAAA queries and
-	 is thus only suitable for PF_UNSPEC.  */
-      if (req->ai_family == PF_UNSPEC)
+      /* The gethostbyname4_r API is always expected to return both address families
+       * which means we would prefer gethostbyname3_r when requesting only IPv4 addresses.
+       * Unfortunately when requesting IPv6 only we have to use this API for link-local
+       * information (scope_id is not in the hostent struct).
+       * This means we may collect unncessary IPv4 addresses. */
+      if (req->ai_family != AF_INET)
 	fct4 = __nss_lookup_function (nip, "gethostbyname4_r");
 
       if (fct4 != NULL)
@@ -856,6 +859,11 @@ get_nss_addresses (const char *name, const struct addrinfo *req,
       /* If both requests timed out report this.  */
       if (no_data == EAI_AGAIN && no_inet6_data == EAI_AGAIN)
 	result = -EAI_AGAIN;
+      else if (req->ai_family == AF_INET6 && !res->got_ipv6)
+        /* If only IPv6 addresses were requested and we only got IPv4 addresses
+         * we ignore those. This is less accurate but matches previous behavior.
+         * The cause of this is commented above when using gethostbyname4_r */
+        result = -EAI_NONAME;
       else
 	/* We made requests but they turned out no data.  The name
 	   is known, though.  */
-- 
2.51.0