Re: [PATCH 03/10] test: assert ro/rw, nosuid/suid, nodev/dev round-trip via fsmount

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, May 08, 2026 at 06:39:06PM +0200, Bernd Schubert via B4 Relay wrote:
> From: Bernd Schubert <bernd@bsbernd.com>
> 
> Assisted by ClaudeOpus 4.7
> Signed-off-by: Bernd Schubert <bernd@bsbernd.com>
> ---
>  test/test_mount_state.py | 70 ++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 62 insertions(+), 8 deletions(-)
> 
> diff --git a/test/test_mount_state.py b/test/test_mount_state.py
> index eacb7326..a7949ec3 100644
> --- a/test/test_mount_state.py
> +++ b/test/test_mount_state.py
> @@ -105,12 +105,66 @@ def test_mountinfo_subtype_fsname(tmpdir, output_checker, name):
>          'unexpected source: %r' % info['source']
>  
>  
> -@pytest.mark.parametrize('name', ('hello', 'hello_ll'))
> -def test_mountinfo_unprivileged_attrs(tmpdir, output_checker, name):
> -    if os.getuid() == 0:
> -        pytest.skip('only meaningful for unprivileged mounts via fusermount3')
> -    with hello_mount(tmpdir, output_checker, name) as mnt:
> -        info = parse_mountinfo(mnt)
> +# (label, options, must-be-in mount_options, must-NOT-be-in mount_options)
> +#
> +# Library defaults are MS_NOSUID|MS_NODEV (lib/mount.c:771,
> +# util/fusermount.c:988), so a no-options mount is expected to land
> +# with both attrs set. The negation forms (suid/dev) clear the default
> +# flags via lib/mount.c:set_mount_flag(), which on the new mount API
> +# path means MOUNT_ATTR_NOSUID/MOUNT_ATTR_NODEV are not set in the
> +# fsmount() call. Asserting their absence catches a routing bug where
> +# the negation wasn't honored.
> +ATTR_CASES = [
> +    ('default',  (),          ('rw', 'nosuid', 'nodev'), ('ro',)),
> +    ('ro',       ('ro',),     ('ro',),                   ('rw',)),
> +    ('nosuid',   ('nosuid',), ('nosuid',),               ()),
> +    ('nodev',    ('nodev',),  ('nodev',),                ()),
> +]
> +
> +# suid/dev are root-only: the kernel rejects MS_NOSUID/MS_NODEV being
> +# cleared for unprivileged mounts, and fusermount3 hard-codes them on
> +# anyway (util/fusermount.c:988).
> +ATTR_CASES_ROOT = [
> +    ('suid',     ('suid',),   (),                        ('nosuid',)),
> +    ('dev',      ('dev',),    (),                        ('nodev',)),
> +]
> +
> +
> +def _check_attrs(info, must_have, must_not_have):
>      assert info is not None
> -    assert 'nosuid' in info['mount_options']
> -    assert 'nodev'  in info['mount_options']
> +    for opt in must_have:
> +        assert opt in info['mount_options'], \
> +            '%r missing from mount_options=%r' % (opt, info['mount_options'])
> +    for opt in must_not_have:
> +        assert opt not in info['mount_options'], \
> +            'unexpected %r in mount_options=%r' % (opt, info['mount_options'])
> +
> +
> +@pytest.mark.parametrize('name', ('hello', 'hello_ll'))
> +@pytest.mark.parametrize('label,opts,must_have,must_not_have', ATTR_CASES,
> +                         ids=[c[0] for c in ATTR_CASES])
> +def test_mountinfo_attrs(tmpdir, output_checker, name,
> +                         label, opts, must_have, must_not_have):
> +    with hello_mount(tmpdir, output_checker, name, opts) as mnt:
> +        info = parse_mountinfo(mnt)
> +    _check_attrs(info, must_have, must_not_have)
> +    # ro/rw also surface in super_options; if we asked for ro the
> +    # superblock must agree. Catches a path that sets MOUNT_ATTR_RDONLY
> +    # but forgets the FSCONFIG-side MS_RDONLY (or vice versa).

Ehhh we're probably going to have to fix this again to handle the new
"ro=vfs"/"ro=fs" behaviors that util-linux 2.41 added.

/me is sad that this wasn't all that well publicized on fsdevel:
https://lore.kernel.org/linux-fsdevel/?q=%22ro%3Dvfs%22

The rest of the new tests look ok to me.
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> +    if 'ro' in must_have:
> +        assert 'ro' in info['super_options'], \
> +            'ro on mount but rw on superblock: super_options=%r' % \
> +                info['super_options']
> +
> +
> +@pytest.mark.parametrize('name', ('hello', 'hello_ll'))
> +@pytest.mark.parametrize('label,opts,must_have,must_not_have',
> +                         ATTR_CASES_ROOT,
> +                         ids=[c[0] for c in ATTR_CASES_ROOT])
> +def test_mountinfo_attrs_root(tmpdir, output_checker, name,
> +                              label, opts, must_have, must_not_have):
> +    if os.getuid() != 0:
> +        pytest.skip('clearing nosuid/nodev requires root')
> +    with hello_mount(tmpdir, output_checker, name, opts) as mnt:
> +        info = parse_mountinfo(mnt)
> +    _check_attrs(info, must_have, must_not_have)
> 
> -- 
> 2.53.0
> 
>