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

[Adhemerval Zanella Netto]

On 07/10/25 16:12, 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.

This seems to triggers regressions on CI [1].

[1] https://www.delorie.com/trybots/32bit/52756/nss-tst-nss-files-hosts-multi.out

> ---
>  nss/getaddrinfo.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/nss/getaddrinfo.c b/nss/getaddrinfo.c
> index 6726ace6fd..f448222821 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 != PF_INET)
>  	fct4 = __nss_lookup_function (nip, "gethostbyname4_r");
>  
>        if (fct4 != NULL)