[PATCH] resolv: Add test for getaddrinfo returning FQDN in ai_canonname

[Florian Weimer]

* Sergey Kolosov:

> This test verifies that getaddrinfo returns a fully-qualified domain
> name in the ai_canonname field then AI_CANONNAME is set and search
> domains apply.

Overall the new test case looks good.

Does the test reproduce the original bug?  I think you can re-introduce
it with t his change:

diff --git a/nss/getaddrinfo.c b/nss/getaddrinfo.c
index 6726ace6fd..4150553bd7 100644
--- a/nss/getaddrinfo.c
+++ b/nss/getaddrinfo.c
@@ -977,7 +977,7 @@ try_simple_gethostbyname (const char *name, const struct addrinfo *req,
 {
   res->at = NULL;
 
-  if (req->ai_family != AF_INET || (req->ai_flags & AI_CANONNAME) != 0)
+  if (req->ai_family != AF_INET)
     return 0;
 
   int rc;

As far as I can tell, the upstream fix was this one:

commit b957ced8890a4438c8efe2c15e5abf4e327f25cf
Author: Andreas Schwab <schwab@suse.de>
Date:   Tue Oct 15 10:21:13 2013 +0200

    Don't use gethostbyaddr to determine canonical name

So please reference bug 15218 in the test case.

> diff --git a/resolv/tst-resolv-getaddrinfo-fqdn.c b/resolv/tst-resolv-getaddrinfo-fqdn.c
> new file mode 100644
> index 0000000000..18a71d6acf
> --- /dev/null
> +++ b/resolv/tst-resolv-getaddrinfo-fqdn.c
> @@ -0,0 +1,156 @@
> +/* Verify that getaddrinfo returns FQDN in ai_canonname,
> +   when AI_CANONNAME is requested and search domain apply.
> +   Copyright (C) 2025 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <resolv.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <support/check.h>
> +#include <support/check_nss.h>
> +#include <support/resolv_test.h>
> +#include <support/support.h>
> +
> +static void
> +response (const struct resolv_response_context *ctx,
> +          struct resolv_response_builder *b,
> +          const char *qname, uint16_t qclass, uint16_t qtype)
> +{
> +  if (strcmp (qname, "foo.site.example") == 0 ||
> +      strcmp (qname, "bar.foo.site.example") == 0 ||
> +      strcmp (qname, "site.example") == 0)

Style nit: Operators should be at the start of the following line, not
the end of the line.

> +char *
> +query_host (const char *host_name)

Could be static as well.

> +{
> +  int family[] = { AF_INET, AF_INET6, AF_UNSPEC };
> +  const char *family_names[] = { "AF_INET", "AF_INET6", "AF_UNSPEC" };
> +  char *canonname = NULL;
> +
> +  for (int i = 0; i < 3; i++)
> +    {
> +      struct addrinfo hints = {
> +        .ai_socktype = 0,
> +        .ai_protocol = 0,
> +        .ai_family = family[i],
> +        .ai_flags = AI_CANONNAME,
> +      };
> +      struct addrinfo *result, *current;
> +      int res = getaddrinfo (host_name, NULL, &hints, &result);
> +      if (res != 0)
> +        {
> +          FAIL_EXIT1 ("getaddrinfo(%s, %s): %s\n", host_name, family_names[i],
> +                      gai_strerror (res));
> +        }

The braces are unnecessary here, but I don't mind including them.

> +      else
> +        {
> +          int count = 0;
> +          for (current = result;
> +               current != NULL && current->ai_canonname != NULL;
> +               current = current->ai_next)
> +            {
> +              if (count > 0)
> +                FAIL_EXIT1 ("Exected exactly one cannoname\n");

Spelling: can[]o[n]name

> +              canonname =
> +                strndup (current->ai_canonname,
> +                         strlen (current->ai_canonname));

Please use xstrdup (strndup + strlen is strdup).  But see below.

> +              count++;
> +            }

It might be clearer to check count after the loop has run to completion.
You could also include the count in the error message.

> +/* test with site.example domain.  */
> +void
> +test_search_with_site_example_domain (void)
> +{
> +  struct resolv_test *aux = resolv_test_start 
> +    ((struct resolv_redirect_config)
> +     {
> +       .response_callback = response,
> +       .search = {"site.example"},
> +     });
> +
> +  TEST_COMPARE_STRING (query_host ("foo"), "foo.site.example");
> +  TEST_COMPARE_STRING (query_host ("bar.foo"), "bar.foo.site.example");


>From an interface perspective, it's easier to pass the expected
canonical name to the query_host function.  Then it's not necessary to
make a copy of the string at all.  You can also check that the name is
on the first struct addrinfo result (which is also required by the
interface).

Thanks,
Florian