linux-kernel - Re: [PATCH -next 3/5] landlock/selftests: add selftests for chmod and chown

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Date:   Sat, 27 Aug 2022 18:57:57 +0200
From:   Günther Noack <gnoack3000@...il.com>
To:     xiujianfeng <xiujianfeng@...wei.com>
Cc:     mic@...ikod.net, paul@...l-moore.com, jmorris@...ei.org,
        serge@...lyn.com, shuah@...nel.org, corbet@....net,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH -next 3/5] landlock/selftests: add selftests for chmod
 and chown

On Sat, Aug 27, 2022 at 07:14:30PM +0800, xiujianfeng wrote:
> Hi，
>
> 在 2022/8/23 3:26, Günther Noack 写道:
> > On Mon, Aug 22, 2022 at 07:46:59PM +0800, Xiu Jianfeng wrote:
> > > +TEST_F_FORK(layout1, unhandled_chmod)
> > > +{
> > > +	const struct rule rules[] = {
> > > +		{
> > > +			.path = file2_s3d1,
> > > +			.access = LANDLOCK_ACCESS_FS_READ_FILE |
> > > +				  LANDLOCK_ACCESS_FS_WRITE_FILE,
> > > +		},
> > > +		{
> > > +			.path = file3_s3d1,
> > > +			.access = LANDLOCK_ACCESS_FS_READ_FILE |
> > > +				  LANDLOCK_ACCESS_FS_WRITE_FILE,
> > > +		},
> > > +		{},
> > > +	};
> > > +	const int ruleset_fd =
> > > +		create_ruleset(_metadata, ACCESS_RW, rules);
> > > +
> > > +	ASSERT_LE(0, ruleset_fd);
> > > +	enforce_ruleset(_metadata, ruleset_fd);
> > > +	ASSERT_EQ(0, close(ruleset_fd));
> > > +
> > > +	ASSERT_EQ(0, test_chmod(file2_s3d1));
> > > +	ASSERT_EQ(0, test_fchmod(file2_s3d1));
> > > +	ASSERT_EQ(0, test_chmod(file3_s3d1));
> > > +	ASSERT_EQ(0, test_chmod(dir_s3d1));
> > > +}
> >
> > I missed it in the previous mail:
> >
> > There are also the chown variants lchown() and fchownat(), as well as
> > the chmod variant fchmodat(), which might be interesting to test,
> > especially the symlink scenarios.
> >
> > fchmodat() has a AT_SYMLINK_NOFOLLOW flag which does the chmod
> > equivalent to lchown().
> >
>
> man fchmodat shows as follows:
> ...
> AT_SYMLINK_NOFOLLOW
> If pathname is a symbolic link, do not dereference it: instead operate on
> the link itself. This flag is not currently implemented.
> ...
>
> so I suppose this can not be test. Please correct me if I am wrong.

Good point - I didn't realize that AT_SYMLINK_NOFOLLOW was not
implemented for fchmodat. In that case, this only applies to lchown.

—Günther

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