[PATCH v4] misc: add a new test for gethostname

[Martin Coufal]

Please disregard this email, the changes made in the v4 are wrong.

On Tue, May 26, 2026 at 9:11 AM Martin Coufal <mcoufal@redhat.com> wrote:
>
> Add a simple test that runs in a UTS namespace: checks gethostname
> after various sethostname values (including empty and HOST_NAME_MAX),
> verifies ENAMETOOLONG when the buffer is too small for a maximal name,
> EINVAL when sethostname is given a name longer than HOST_NAME_MAX.
> ---
> v4 changes:
> * try to resolve 32b trybot failure with sethostname not permitted in
>   UTS namespace - test and fail as unsupported in case it's not
>   permitted.
> ---
>  misc/Makefile          |   1 +
>  misc/tst-gethostname.c | 118 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 119 insertions(+)
>  create mode 100644 misc/tst-gethostname.c
>
> diff --git a/misc/Makefile b/misc/Makefile
> index b38e983ed7..3937b5d5ea 100644
> --- a/misc/Makefile
> +++ b/misc/Makefile
> @@ -245,6 +245,7 @@ tests := \
>    tst-empty \
>    tst-error1 \
>    tst-fdset \
> +  tst-gethostname \
>    tst-getusershell \
>    tst-hsearch \
>    tst-insremque \
> diff --git a/misc/tst-gethostname.c b/misc/tst-gethostname.c
> new file mode 100644
> index 0000000000..d8349846ea
> --- /dev/null
> +++ b/misc/tst-gethostname.c
> @@ -0,0 +1,118 @@
> +/* Basic test for gethostname.
> +   Copyright (C) 2024-2026 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 <errno.h>
> +#include <limits.h>
> +#include <sched.h>
> +#include <string.h>
> +#include <support/check.h>
> +#include <support/namespace.h>
> +#include <unistd.h>
> +
> +#ifndef HOST_NAME_MAX
> +#define HOST_NAME_MAX 64
> +#endif
> +
> +#define MAX_LEN_INCREASE 10
> +
> +
> +static int
> +do_test (void)
> +{
> +  char default_hostname[HOST_NAME_MAX + 1] = "\0";
> +  char hostname[HOST_NAME_MAX + 1] = "\0";
> +  char generated_hostname[HOST_NAME_MAX + MAX_LEN_INCREASE + 1] = "\0";
> +
> +  /* sethostname needs support_become_root for namespace privileges. */
> +    support_become_root ();
> +    if (!support_in_uts_namespace () || !support_can_chroot ())
> +      return EXIT_UNSUPPORTED;
> +
> +/* Enter a UTS namespace so sethostname does not affect the host.  */
> +#ifdef CLONE_NEWUTS
> +  if (unshare (CLONE_NEWUTS) != 0)
> +    FAIL_UNSUPPORTED ("unshare (CLONE_NEWUTS): %m");
> +#else
> +  FAIL_UNSUPPORTED ("CLONE_NEWUTS not supported");
> +#endif
> +
> +  /* Check default hostname is not an empty string.  */
> +  TEST_VERIFY_EXIT (gethostname (default_hostname, sizeof (default_hostname))
> +                   == 0);
> +  TEST_VERIFY (strlen (default_hostname) > 0);
> +
> +  /* Check that sethostname is permitted in the UTS namespace.  */
> +  if (sethostname ("a", 1) != 0)
> +    FAIL_UNSUPPORTED ("sethostname: %m");
> +  TEST_VERIFY_EXIT (sethostname (default_hostname, strlen (default_hostname))
> +                   == 0);
> +
> +  /* input: ''
> +     expected output: '' */
> +  TEST_VERIFY_EXIT (sethostname ("", 0) == 0);
> +  TEST_VERIFY (gethostname (hostname, sizeof (hostname)) == 0);
> +  TEST_VERIFY (strlen (hostname) == 0);
> +
> +  /* input: 'a'
> +     expected output: 'a' */
> +  TEST_VERIFY_EXIT (sethostname ("a", strlen ("a")) == 0);
> +  TEST_VERIFY (gethostname (hostname, sizeof (hostname)) == 0);
> +  TEST_COMPARE (strlen (hostname), 1);
> +  TEST_VERIFY (strcmp (hostname, "a") == 0);
> +
> +  /* input: abc.def.ghi
> +     expected output: abc.def.ghi */
> +  TEST_VERIFY_EXIT (sethostname ("abc.def.ghi", strlen ("abc.def.ghi")) == 0);
> +  TEST_VERIFY (gethostname (hostname, sizeof (hostname)) == 0);
> +  TEST_COMPARE (strlen (hostname), strlen ("abc.def.ghi"));
> +  TEST_VERIFY (strcmp (hostname, "abc.def.ghi") == 0);
> +
> +  /* input: exactly HOST_NAME_MAX
> +     expected output: exactly HOST_NAME_MAX, gethostname returns -1, errno set */
> +  for (int i = 0; i < HOST_NAME_MAX; i++)
> +    {
> +      /* Generate hostname of length == HOST_NAME_MAX.  */
> +      generated_hostname[i] = 'a' + i % 26;
> +    }
> +  TEST_VERIFY_EXIT (sethostname
> +                   (generated_hostname, strlen (generated_hostname)) == 0);
> +  errno = 0;
> +  TEST_VERIFY (gethostname (hostname, HOST_NAME_MAX) == -1);
> +  TEST_COMPARE (errno, ENAMETOOLONG);
> +  TEST_COMPARE (strlen (hostname), HOST_NAME_MAX);
> +  TEST_VERIFY (strcmp (hostname, generated_hostname) == 0);
> +
> +  /* input: longer than HOST_NAME_MAX
> +     expected output: sethostname fails, return -1, errno set */
> +  for (int i = 0; i < HOST_NAME_MAX + MAX_LEN_INCREASE; i++)
> +    {
> +      /* Generate hostname LONGER than HOST_NAME_MAX.  */
> +      generated_hostname[i] = 'a' + i % 26;
> +    }
> +  errno = 0;
> +  TEST_VERIFY (sethostname (generated_hostname, strlen (generated_hostname))
> +              == -1);
> +  TEST_COMPARE (errno, EINVAL);
> +
> +  /* Restore default hostname.  */
> +  TEST_VERIFY_EXIT (sethostname (default_hostname, strlen (default_hostname))
> +                   == 0);
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
> --
> 2.53.0
>