[PATCH] resolv: Add test for getaddrinfo returning EAI_AGAIN on DNS failure

[H.J. Lu]

On Tue, Sep 16, 2025 at 12:43 PM Sergey Kolosov <skolosov@redhat.com> wrote:
>
> Test for BZ #16849. This test verifies that getaddrinfo correctly
> returns the EAI_AGAIN error code when DNS queries fail due to a network
> failure. The test queries with AF_INET, AF_INET6, AF_UNSPEC address
> families and expects getaddrinfo to return EAI_AGAIN in each case.
> ---
> To validate the test, I manually reverted the fix for BZ #16849 in
> nss/getaddrinfo.c, specifically the condition:

Is it possible to write a container test with network/DNS disabled?

>   -  if (h_errno == TRY_AGAIN)
>   +  if (status == NSS_STATUS_TRYAGAIN && h_errno == TRY_AGAIN)
>
> With this reversion in place, the test fails as expected (getaddrinfo
> returns EAI_NONAME instead of EAI_AGAIN), confirming that the test
> detects the broken behavior.
>
> With the fix present, the test passes.
> ---
>  resolv/Makefile                    |  2 +
>  resolv/tst-getaddrinfo-eai-again.c | 71 ++++++++++++++++++++++++++++++
>  2 files changed, 73 insertions(+)
>  create mode 100644 resolv/tst-getaddrinfo-eai-again.c
>
> diff --git a/resolv/Makefile b/resolv/Makefile
> index 8fa3398d76..4d6f0ebe82 100644
> --- a/resolv/Makefile
> +++ b/resolv/Makefile
> @@ -136,6 +136,7 @@ tests-static += tst-ns_rr_cursor
>  # These tests need libdl.
>  ifeq (yes,$(build-shared))
>  tests += \
> +  tst-getaddrinfo-eai-again \
>    tst-resolv-ai_idn \
>    tst-resolv-ai_idn-latin1 \
>    tst-resolv-ai_idn-nolibidn2 \
> @@ -280,6 +281,7 @@ $(objpfx)mtrace-tst-resolv-res_ninit.out: $(objpfx)tst-resolv-res_ninit.out
>
>  $(objpfx)tst-bug18665-tcp: $(objpfx)libresolv.so $(shared-thread-library)
>  $(objpfx)tst-bug18665: $(objpfx)libresolv.so $(shared-thread-library)
> +$(objpfx)tst-getaddrinfo-eai-again: $(objpfx)libresolv.so $(shared-thread-library)
>  $(objpfx)tst-resolv-ai_idn: $(objpfx)libresolv.so $(shared-thread-library)
>  $(objpfx)tst-resolv-ai_idn-latin1: \
>    $(objpfx)libresolv.so $(shared-thread-library)
> diff --git a/resolv/tst-getaddrinfo-eai-again.c b/resolv/tst-getaddrinfo-eai-again.c
> new file mode 100644
> index 0000000000..0c2d8deb96
> --- /dev/null
> +++ b/resolv/tst-getaddrinfo-eai-again.c
> @@ -0,0 +1,71 @@
> +/* Test for BZ #16849. Verify that getaddrinfo correctly returns
> +   EAI_AGAIN error code if DNS query fails due to a network failure.
> +   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>
> +
> +/* DNS stub callback that simulates a network failure.  */
> +static void
> +response (const struct resolv_response_context *ctx,
> +          struct resolv_response_builder *b,
> +          const char *qname, uint16_t qclass, uint16_t qtype)
> +{
> +}
> +
> +static void
> +query_host (const char *host_name)
> +{
> +  int family[] = { AF_INET, AF_INET6, AF_UNSPEC };
> +  const char *family_names[] = { "AF_INET", "AF_INET6", "AF_UNSPEC" };
> +
> +  for (int i = 0; i < 3; i++)
> +    {
> +      struct addrinfo hints = {
> +        .ai_socktype = 0,
> +        .ai_protocol = 0,
> +        .ai_family = family[i],
> +        .ai_flags = 0,
> +      };
> +      struct addrinfo *result;
> +      int res = getaddrinfo (host_name, NULL, &hints, &result);
> +      if (res != EAI_AGAIN)
> +        FAIL_EXIT1 ("getaddrinfo (%s, %s): %s\n should return EAI_AGAIN \n",
> +                    host_name, family_names[i], gai_strerror (res));
> +    }
> +}
> +
> +static int
> +do_test (void)
> +{
> +  struct resolv_test *aux = resolv_test_start
> +    ((struct resolv_redirect_config)
> +     {
> +       .response_callback = response,
> +     });
> +  query_host("site.example");
> +  resolv_test_end (aux);
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
> --
> 2.51.0
>


-- 
H.J.