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

[Carlos O'Donell]

On 10/24/25 8:23 PM, Patrick Griffis wrote:
> 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.

Patrick,

This still fails pre-commit CI as noted by Adhemerval in an earlier post.

https://patchwork.sourceware.org/project/glibc/patch/20251025002359.2093627-1-pgriffis@igalia.com/

Have you had a chance to look into the regression?


> ---
>   nss/getaddrinfo.c | 18 +++++++++++++++---
>   1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/nss/getaddrinfo.c b/nss/getaddrinfo.c
> index 6726ace6fd..e7064ea9f5 100644
> --- a/nss/getaddrinfo.c
> +++ b/nss/getaddrinfo.c
> @@ -610,6 +610,7 @@ get_nss_addresses (const char *name, const struct addrinfo *req,
>     struct resolv_context *res_ctx = NULL;
>     bool do_merge = false;
>     int result = 0;
> +  bool got_ipv4 = false;
>   
>     no_more = !__nss_database_get (nss_database_hosts, &nip);
>   
> @@ -644,9 +645,12 @@ 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)
> @@ -700,6 +704,9 @@ get_nss_addresses (const char *name, const struct addrinfo *req,
>   
>   	      while (*pat != NULL)
>   		{
> +		  if ((*pat)->family == AF_INET)
> +		        got_ipv4 = true;
> +
>   		  if ((*pat)->family == AF_INET
>   		      && req->ai_family == AF_INET6
>   		      && (req->ai_flags & AI_V4MAPPED) != 0)
> @@ -856,6 +863,11 @@ 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 && got_ipv4)
> +        /* 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.  */


-- 
Cheers,
Carlos.