[PATCH v2 0/6] Landlock support for UML

[PATCH v2 0/6] Landlock support for UML

[Mickaël Salaün]

Hi,

Commit cb2c7d1a1776 ("landlock: Support filesystem access-control")
introduced a new ARCH_EPHEMERAL_INODES configuration, only enabled for
User-Mode Linux.  The reason was that UML's hostfs managed inodes in an
ephemeral way: from the kernel point of view, the same inode struct
could be created several times while being used by user space because
the kernel didn't hold references to inodes.  Because Landlock (and
probably other subsystems) ties properties (i.e. access rights) to inode
objects, it wasn't possible to create rules that match inodes and then
allow specific accesses.

This patch series fixes the way UML manages inodes according to the
underlying filesystem.  They are now properly handles as for other
filesystems, which enables to support Landlock (and probably other
features).

Changes since v1:
https://lore.kernel.org/r/20230309165455.175131-1-mic@digikod.net
- Remove Cc stable@ (suggested by Richard).
- Add Acked-by: Richard Weinberger to the first patch.
- Split the test patch into two patches: one for the common
  pseudo-filesystems, and another patch dedicated to hostfs.
- Remove CONFIG_SECURITY_PATH because it is useless for merge_config.sh
- Move CONFIG_HOSTFS to a new config.um file.
- Fix commit message spelling and test warnings.
- Improve prepare_layout_opt() with remove_path() call to avoid
  cascading errors when some tested filesystems are not supported.
- Remove cgroup-v1 tests because this filesystem cannot really be
  mounted several times.
- Add test coverage with and without kernel debug code, according to
  GCC 12 and GCC 13.

Regards,

Mickaël Salaün (6):
  hostfs: Fix ephemeral inodes
  selftests/landlock: Don't create useless file layouts
  selftests/landlock: Add supports_filesystem() helper
  selftests/landlock: Make mounts configurable
  selftests/landlock: Add tests for pseudo filesystems
  selftests/landlock: Add hostfs tests

 arch/Kconfig                               |   7 -
 arch/um/Kconfig                            |   1 -
 fs/hostfs/hostfs.h                         |   1 +
 fs/hostfs/hostfs_kern.c                    | 213 ++++++------
 fs/hostfs/hostfs_user.c                    |   1 +
 security/landlock/Kconfig                  |   2 +-
 tools/testing/selftests/landlock/config    |   9 +-
 tools/testing/selftests/landlock/config.um |   1 +
 tools/testing/selftests/landlock/fs_test.c | 387 +++++++++++++++++++--
 9 files changed, 478 insertions(+), 144 deletions(-)
 create mode 100644 tools/testing/selftests/landlock/config.um


base-commit: 858fd168a95c5b9669aac8db6c14a9aeab446375
-- 
2.41.0

[PATCH v2 1/6] hostfs: Fix ephemeral inodes

[Mickaël Salaün]

hostfs creates a new inode for each opened or created file, which
created useless inode allocations and forbade identifying a host file
with a kernel inode.

Fix this uncommon filesystem behavior by tying kernel inodes to host
file's inode and device IDs.  Even if the host filesystem inodes may be
recycled, this cannot happen while a file referencing it is opened,
which is the case with hostfs.  It should be noted that hostfs inode IDs
may not be unique for the same hostfs superblock because multiple host's
(backed) superblocks may be used.

Delete inodes when dropping them to force backed host's file descriptors
closing.

This enables to entirely remove ARCH_EPHEMERAL_INODES, and then makes
Landlock fully supported by UML.  This is very useful for testing
changes.

These changes also factor out and simplify some helpers thanks to the
new hostfs_inode_update() and the hostfs_iget() revamp: read_name(),
hostfs_create(), hostfs_lookup(), hostfs_mknod(), and
hostfs_fill_sb_common().

A following commit with new Landlock tests check this new hostfs inode
consistency.

Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
---
 arch/Kconfig              |   7 --
 arch/um/Kconfig           |   1 -
 fs/hostfs/hostfs.h        |   1 +
 fs/hostfs/hostfs_kern.c   | 213 +++++++++++++++++++-------------------
 fs/hostfs/hostfs_user.c   |   1 +
 security/landlock/Kconfig |   2 +-
 6 files changed, 109 insertions(+), 116 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 205fd23e0cad..49996ee9e33b 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1188,13 +1188,6 @@ config COMPAT_32BIT_TIME
 config ARCH_NO_PREEMPT
 	bool
 
-config ARCH_EPHEMERAL_INODES
-	def_bool n
-	help
-	  An arch should select this symbol if it doesn't keep track of inode
-	  instances on its own, but instead relies on something else (e.g. the
-	  host kernel for an UML kernel).
-
 config ARCH_SUPPORTS_RT
 	bool
 
diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index 541a9b18e343..4057d5267c6a 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -5,7 +5,6 @@ menu "UML-specific options"
 config UML
 	bool
 	default y
-	select ARCH_EPHEMERAL_INODES
 	select ARCH_HAS_FORTIFY_SOURCE
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_KCOV
diff --git a/fs/hostfs/hostfs.h b/fs/hostfs/hostfs.h
index 69cb796f6270..0239e3af3945 100644
--- a/fs/hostfs/hostfs.h
+++ b/fs/hostfs/hostfs.h
@@ -65,6 +65,7 @@ struct hostfs_stat {
 	unsigned long long blocks;
 	unsigned int maj;
 	unsigned int min;
+	dev_t dev;
 };
 
 extern int stat_file(const char *path, struct hostfs_stat *p, int fd);
diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
index 28b4f15c19eb..19496f732016 100644
--- a/fs/hostfs/hostfs_kern.c
+++ b/fs/hostfs/hostfs_kern.c
@@ -26,6 +26,7 @@ struct hostfs_inode_info {
 	fmode_t mode;
 	struct inode vfs_inode;
 	struct mutex open_mutex;
+	dev_t dev;
 };
 
 static inline struct hostfs_inode_info *HOSTFS_I(struct inode *inode)
@@ -182,14 +183,6 @@ static char *follow_link(char *link)
 	return ERR_PTR(n);
 }
 
-static struct inode *hostfs_iget(struct super_block *sb)
-{
-	struct inode *inode = new_inode(sb);
-	if (!inode)
-		return ERR_PTR(-ENOMEM);
-	return inode;
-}
-
 static int hostfs_statfs(struct dentry *dentry, struct kstatfs *sf)
 {
 	/*
@@ -228,6 +221,7 @@ static struct inode *hostfs_alloc_inode(struct super_block *sb)
 		return NULL;
 	hi->fd = -1;
 	hi->mode = 0;
+	hi->dev = 0;
 	inode_init_once(&hi->vfs_inode);
 	mutex_init(&hi->open_mutex);
 	return &hi->vfs_inode;
@@ -240,6 +234,7 @@ static void hostfs_evict_inode(struct inode *inode)
 	if (HOSTFS_I(inode)->fd != -1) {
 		close_file(&HOSTFS_I(inode)->fd);
 		HOSTFS_I(inode)->fd = -1;
+		HOSTFS_I(inode)->dev = 0;
 	}
 }
 
@@ -265,6 +260,7 @@ static int hostfs_show_options(struct seq_file *seq, struct dentry *root)
 static const struct super_operations hostfs_sbops = {
 	.alloc_inode	= hostfs_alloc_inode,
 	.free_inode	= hostfs_free_inode,
+	.drop_inode	= generic_delete_inode,
 	.evict_inode	= hostfs_evict_inode,
 	.statfs		= hostfs_statfs,
 	.show_options	= hostfs_show_options,
@@ -512,18 +508,31 @@ static const struct address_space_operations hostfs_aops = {
 	.write_end	= hostfs_write_end,
 };
 
-static int read_name(struct inode *ino, char *name)
+static int hostfs_inode_update(struct inode *ino, const struct hostfs_stat *st)
+{
+	set_nlink(ino, st->nlink);
+	i_uid_write(ino, st->uid);
+	i_gid_write(ino, st->gid);
+	ino->i_atime =
+		(struct timespec64){ st->atime.tv_sec, st->atime.tv_nsec };
+	ino->i_mtime =
+		(struct timespec64){ st->mtime.tv_sec, st->mtime.tv_nsec };
+	ino->i_ctime =
+		(struct timespec64){ st->ctime.tv_sec, st->ctime.tv_nsec };
+	ino->i_size = st->size;
+	ino->i_blocks = st->blocks;
+	return 0;
+}
+
+static int hostfs_inode_set(struct inode *ino, void *data)
 {
+	struct hostfs_stat *st = data;
 	dev_t rdev;
-	struct hostfs_stat st;
-	int err = stat_file(name, &st, -1);
-	if (err)
-		return err;
 
 	/* Reencode maj and min with the kernel encoding.*/
-	rdev = MKDEV(st.maj, st.min);
+	rdev = MKDEV(st->maj, st->min);
 
-	switch (st.mode & S_IFMT) {
+	switch (st->mode & S_IFMT) {
 	case S_IFLNK:
 		ino->i_op = &hostfs_link_iops;
 		break;
@@ -535,7 +544,7 @@ static int read_name(struct inode *ino, char *name)
 	case S_IFBLK:
 	case S_IFIFO:
 	case S_IFSOCK:
-		init_special_inode(ino, st.mode & S_IFMT, rdev);
+		init_special_inode(ino, st->mode & S_IFMT, rdev);
 		ino->i_op = &hostfs_iops;
 		break;
 	case S_IFREG:
@@ -547,17 +556,42 @@ static int read_name(struct inode *ino, char *name)
 		return -EIO;
 	}
 
-	ino->i_ino = st.ino;
-	ino->i_mode = st.mode;
-	set_nlink(ino, st.nlink);
-	i_uid_write(ino, st.uid);
-	i_gid_write(ino, st.gid);
-	ino->i_atime = (struct timespec64){ st.atime.tv_sec, st.atime.tv_nsec };
-	ino->i_mtime = (struct timespec64){ st.mtime.tv_sec, st.mtime.tv_nsec };
-	ino->i_ctime = (struct timespec64){ st.ctime.tv_sec, st.ctime.tv_nsec };
-	ino->i_size = st.size;
-	ino->i_blocks = st.blocks;
-	return 0;
+	HOSTFS_I(ino)->dev = st->dev;
+	ino->i_ino = st->ino;
+	ino->i_mode = st->mode;
+	return hostfs_inode_update(ino, st);
+}
+
+static int hostfs_inode_test(struct inode *inode, void *data)
+{
+	const struct hostfs_stat *st = data;
+
+	return inode->i_ino == st->ino && HOSTFS_I(inode)->dev == st->dev;
+}
+
+static struct inode *hostfs_iget(struct super_block *sb, char *name)
+{
+	struct inode *inode;
+	struct hostfs_stat st;
+	int err = stat_file(name, &st, -1);
+
+	if (err)
+		return ERR_PTR(err);
+
+	inode = iget5_locked(sb, st.ino, hostfs_inode_test, hostfs_inode_set,
+			     &st);
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	if (inode->i_state & I_NEW) {
+		unlock_new_inode(inode);
+	} else {
+		spin_lock(&inode->i_lock);
+		hostfs_inode_update(inode, &st);
+		spin_unlock(&inode->i_lock);
+	}
+
+	return inode;
 }
 
 static int hostfs_create(struct mnt_idmap *idmap, struct inode *dir,
@@ -565,62 +599,48 @@ static int hostfs_create(struct mnt_idmap *idmap, struct inode *dir,
 {
 	struct inode *inode;
 	char *name;
-	int error, fd;
-
-	inode = hostfs_iget(dir->i_sb);
-	if (IS_ERR(inode)) {
-		error = PTR_ERR(inode);
-		goto out;
-	}
+	int fd;
 
-	error = -ENOMEM;
 	name = dentry_name(dentry);
 	if (name == NULL)
-		goto out_put;
+		return -ENOMEM;
 
 	fd = file_create(name, mode & 0777);
-	if (fd < 0)
-		error = fd;
-	else
-		error = read_name(inode, name);
+	if (fd < 0) {
+		__putname(name);
+		return fd;
+	}
 
+	inode = hostfs_iget(dir->i_sb, name);
 	__putname(name);
-	if (error)
-		goto out_put;
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
 
 	HOSTFS_I(inode)->fd = fd;
 	HOSTFS_I(inode)->mode = FMODE_READ | FMODE_WRITE;
 	d_instantiate(dentry, inode);
 	return 0;
-
- out_put:
-	iput(inode);
- out:
-	return error;
 }
 
 static struct dentry *hostfs_lookup(struct inode *ino, struct dentry *dentry,
 				    unsigned int flags)
 {
-	struct inode *inode;
+	struct inode *inode = NULL;
 	char *name;
-	int err;
-
-	inode = hostfs_iget(ino->i_sb);
-	if (IS_ERR(inode))
-		goto out;
 
-	err = -ENOMEM;
 	name = dentry_name(dentry);
-	if (name) {
-		err = read_name(inode, name);
-		__putname(name);
-	}
-	if (err) {
-		iput(inode);
-		inode = (err == -ENOENT) ? NULL : ERR_PTR(err);
+	if (name == NULL)
+		return ERR_PTR(-ENOMEM);
+
+	inode = hostfs_iget(ino->i_sb, name);
+	__putname(name);
+	if (IS_ERR(inode)) {
+		if (PTR_ERR(inode) == -ENOENT)
+			inode = NULL;
+		else
+			return ERR_CAST(inode);
 	}
- out:
+
 	return d_splice_alias(inode, dentry);
 }
 
@@ -704,35 +724,23 @@ static int hostfs_mknod(struct mnt_idmap *idmap, struct inode *dir,
 	char *name;
 	int err;
 
-	inode = hostfs_iget(dir->i_sb);
-	if (IS_ERR(inode)) {
-		err = PTR_ERR(inode);
-		goto out;
-	}
-
-	err = -ENOMEM;
 	name = dentry_name(dentry);
 	if (name == NULL)
-		goto out_put;
+		return -ENOMEM;
 
 	err = do_mknod(name, mode, MAJOR(dev), MINOR(dev));
-	if (err)
-		goto out_free;
+	if (err) {
+		__putname(name);
+		return err;
+	}
 
-	err = read_name(inode, name);
+	inode = hostfs_iget(dir->i_sb, name);
 	__putname(name);
-	if (err)
-		goto out_put;
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
 
 	d_instantiate(dentry, inode);
 	return 0;
-
- out_free:
-	__putname(name);
- out_put:
-	iput(inode);
- out:
-	return err;
 }
 
 static int hostfs_rename2(struct mnt_idmap *idmap,
@@ -929,49 +937,40 @@ static int hostfs_fill_sb_common(struct super_block *sb, void *d, int silent)
 	sb->s_maxbytes = MAX_LFS_FILESIZE;
 	err = super_setup_bdi(sb);
 	if (err)
-		goto out;
+		return err;
 
 	/* NULL is printed as '(null)' by printf(): avoid that. */
 	if (req_root == NULL)
 		req_root = "";
 
-	err = -ENOMEM;
 	sb->s_fs_info = host_root_path =
 		kasprintf(GFP_KERNEL, "%s/%s", root_ino, req_root);
 	if (host_root_path == NULL)
-		goto out;
-
-	root_inode = new_inode(sb);
-	if (!root_inode)
-		goto out;
+		return -ENOMEM;
 
-	err = read_name(root_inode, host_root_path);
-	if (err)
-		goto out_put;
+	root_inode = hostfs_iget(sb, host_root_path);
+	if (IS_ERR(root_inode))
+		return PTR_ERR(root_inode);
 
 	if (S_ISLNK(root_inode->i_mode)) {
-		char *name = follow_link(host_root_path);
-		if (IS_ERR(name)) {
-			err = PTR_ERR(name);
-			goto out_put;
-		}
-		err = read_name(root_inode, name);
+		char *name;
+
+		iput(root_inode);
+		name = follow_link(host_root_path);
+		if (IS_ERR(name))
+			return PTR_ERR(name);
+
+		root_inode = hostfs_iget(sb, name);
 		kfree(name);
-		if (err)
-			goto out_put;
+		if (IS_ERR(root_inode))
+			return PTR_ERR(root_inode);
 	}
 
-	err = -ENOMEM;
 	sb->s_root = d_make_root(root_inode);
 	if (sb->s_root == NULL)
-		goto out;
+		return -ENOMEM;
 
 	return 0;
-
-out_put:
-	iput(root_inode);
-out:
-	return err;
 }
 
 static struct dentry *hostfs_read_sb(struct file_system_type *type,
diff --git a/fs/hostfs/hostfs_user.c b/fs/hostfs/hostfs_user.c
index 5ecc4706172b..840619e39a1a 100644
--- a/fs/hostfs/hostfs_user.c
+++ b/fs/hostfs/hostfs_user.c
@@ -36,6 +36,7 @@ static void stat64_to_hostfs(const struct stat64 *buf, struct hostfs_stat *p)
 	p->blocks = buf->st_blocks;
 	p->maj = os_major(buf->st_rdev);
 	p->min = os_minor(buf->st_rdev);
+	p->dev = buf->st_dev;
 }
 
 int stat_file(const char *path, struct hostfs_stat *p, int fd)
diff --git a/security/landlock/Kconfig b/security/landlock/Kconfig
index 8e33c4e8ffb8..c1e862a38410 100644
--- a/security/landlock/Kconfig
+++ b/security/landlock/Kconfig
@@ -2,7 +2,7 @@
 
 config SECURITY_LANDLOCK
 	bool "Landlock support"
-	depends on SECURITY && !ARCH_EPHEMERAL_INODES
+	depends on SECURITY
 	select SECURITY_PATH
 	help
 	  Landlock is a sandboxing mechanism that enables processes to restrict
-- 
2.41.0

[PATCH v2 2/6] selftests/landlock: Don't create useless file layouts

[Mickaël Salaün]

Add and use a layout0 test fixture to not populate the tmpfs filesystem
if it is not required for tests: unknown_access_rights, proc_nsfs,
unpriv and max_layers.

This doesn't change these tests but it speeds up their setup and makes
them less prone to error.  This prepare the ground for a next commit.

Signed-off-by: Mickaël Salaün <mic@digikod.net>
---
 tools/testing/selftests/landlock/fs_test.c | 26 +++++++++++++++++-----
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index b6c4be3faf7a..0438651f61d2 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -231,6 +231,20 @@ static void cleanup_layout(struct __test_metadata *const _metadata)
 	EXPECT_EQ(0, remove_path(TMP_DIR));
 }
 
+/* clang-format off */
+FIXTURE(layout0) {};
+/* clang-format on */
+
+FIXTURE_SETUP(layout0)
+{
+	prepare_layout(_metadata);
+}
+
+FIXTURE_TEARDOWN(layout0)
+{
+	cleanup_layout(_metadata);
+}
+
 static void create_layout1(struct __test_metadata *const _metadata)
 {
 	create_file(_metadata, file1_s1d1);
@@ -510,7 +524,7 @@ TEST_F_FORK(layout1, file_and_dir_access_rights)
 	ASSERT_EQ(0, close(ruleset_fd));
 }
 
-TEST_F_FORK(layout1, unknown_access_rights)
+TEST_F_FORK(layout0, unknown_access_rights)
 {
 	__u64 access_mask;
 
@@ -608,7 +622,7 @@ static void enforce_ruleset(struct __test_metadata *const _metadata,
 	}
 }
 
-TEST_F_FORK(layout1, proc_nsfs)
+TEST_F_FORK(layout0, proc_nsfs)
 {
 	const struct rule rules[] = {
 		{
@@ -657,11 +671,11 @@ TEST_F_FORK(layout1, proc_nsfs)
 	ASSERT_EQ(0, close(path_beneath.parent_fd));
 }
 
-TEST_F_FORK(layout1, unpriv)
+TEST_F_FORK(layout0, unpriv)
 {
 	const struct rule rules[] = {
 		{
-			.path = dir_s1d2,
+			.path = TMP_DIR,
 			.access = ACCESS_RO,
 		},
 		{},
@@ -1301,12 +1315,12 @@ TEST_F_FORK(layout1, inherit_superset)
 	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
 }
 
-TEST_F_FORK(layout1, max_layers)
+TEST_F_FORK(layout0, max_layers)
 {
 	int i, err;
 	const struct rule rules[] = {
 		{
-			.path = dir_s1d2,
+			.path = TMP_DIR,
 			.access = ACCESS_RO,
 		},
 		{},
-- 
2.41.0

[PATCH v2 3/6] selftests/landlock: Add supports_filesystem() helper

[Mickaël Salaün]

Replace supports_overlayfs() with supports_filesystem() to be able to
check several filesystems.  This will be useful in a following commit.

Only check for overlay filesystem once in the setup step, and then rely
on self->skip_test.

Cc: Guenter Roeck <groeck@chromium.org>
Cc: Jeff Xu <jeffxu@google.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
---
 tools/testing/selftests/landlock/fs_test.c | 36 ++++++++++++++--------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 0438651f61d2..c1e655fc06bb 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -107,8 +107,10 @@ static bool fgrep(FILE *const inf, const char *const str)
 	return false;
 }
 
-static bool supports_overlayfs(void)
+static bool supports_filesystem(const char *const filesystem)
 {
+	char str[32];
+	int len;
 	bool res;
 	FILE *const inf = fopen("/proc/filesystems", "r");
 
@@ -119,7 +121,12 @@ static bool supports_overlayfs(void)
 	if (!inf)
 		return true;
 
-	res = fgrep(inf, "nodev\toverlay\n");
+	len = snprintf(str, sizeof(str), "nodev\t%s\n", filesystem);
+	if (len >= sizeof(str))
+		/* Ignores too-long filesystem names. */
+		return true;
+
+	res = fgrep(inf, str);
 	fclose(inf);
 	return res;
 }
@@ -4044,14 +4051,17 @@ static const char (*merge_sub_files[])[] = {
  *         └── work
  */
 
-/* clang-format off */
-FIXTURE(layout2_overlay) {};
-/* clang-format on */
+FIXTURE(layout2_overlay)
+{
+	bool skip_test;
+};
 
 FIXTURE_SETUP(layout2_overlay)
 {
-	if (!supports_overlayfs())
-		SKIP(return, "overlayfs is not supported");
+	if (!supports_filesystem("overlay")) {
+		self->skip_test = true;
+		SKIP(return, "overlayfs is not supported (setup)");
+	}
 
 	prepare_layout(_metadata);
 
@@ -4089,8 +4099,8 @@ FIXTURE_SETUP(layout2_overlay)
 
 FIXTURE_TEARDOWN(layout2_overlay)
 {
-	if (!supports_overlayfs())
-		SKIP(return, "overlayfs is not supported");
+	if (self->skip_test)
+		SKIP(return, "overlayfs is not supported (teardown)");
 
 	EXPECT_EQ(0, remove_path(lower_do1_fl3));
 	EXPECT_EQ(0, remove_path(lower_dl1_fl2));
@@ -4123,8 +4133,8 @@ FIXTURE_TEARDOWN(layout2_overlay)
 
 TEST_F_FORK(layout2_overlay, no_restriction)
 {
-	if (!supports_overlayfs())
-		SKIP(return, "overlayfs is not supported");
+	if (self->skip_test)
+		SKIP(return, "overlayfs is not supported (test)");
 
 	ASSERT_EQ(0, test_open(lower_fl1, O_RDONLY));
 	ASSERT_EQ(0, test_open(lower_dl1, O_RDONLY));
@@ -4289,8 +4299,8 @@ TEST_F_FORK(layout2_overlay, same_content_different_file)
 	size_t i;
 	const char *path_entry;
 
-	if (!supports_overlayfs())
-		SKIP(return, "overlayfs is not supported");
+	if (self->skip_test)
+		SKIP(return, "overlayfs is not supported (test)");
 
 	/* Sets rules on base directories (i.e. outside overlay scope). */
 	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, layer1_base);
-- 
2.41.0

[PATCH v2 4/6] selftests/landlock: Make mounts configurable

[Mickaël Salaün]

Add a new struct mnt_opt to define a mount point with the mount_opt()
helper.  This doesn't change tests but prepare for the next commit.

Signed-off-by: Mickaël Salaün <mic@digikod.net>
---
 tools/testing/selftests/landlock/fs_test.c | 45 +++++++++++++++++++---
 1 file changed, 40 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index c1e655fc06bb..737047a81547 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -213,7 +213,26 @@ static int remove_path(const char *const path)
 	return err;
 }
 
-static void prepare_layout(struct __test_metadata *const _metadata)
+struct mnt_opt {
+	const char *const source;
+	const char *const type;
+	const unsigned long flags;
+	const char *const data;
+};
+
+const struct mnt_opt mnt_tmp = {
+	.type = "tmpfs",
+	.data = "size=4m,mode=700",
+};
+
+static int mount_opt(const struct mnt_opt *const mnt, const char *const target)
+{
+	return mount(mnt->source ?: mnt->type, target, mnt->type, mnt->flags,
+		     mnt->data);
+}
+
+static void prepare_layout_opt(struct __test_metadata *const _metadata,
+			       const struct mnt_opt *const mnt)
 {
 	disable_caps(_metadata);
 	umask(0077);
@@ -225,11 +244,27 @@ static void prepare_layout(struct __test_metadata *const _metadata)
 	 */
 	set_cap(_metadata, CAP_SYS_ADMIN);
 	ASSERT_EQ(0, unshare(CLONE_NEWNS));
-	ASSERT_EQ(0, mount("tmp", TMP_DIR, "tmpfs", 0, "size=4m,mode=700"));
+	ASSERT_EQ(0, mount_opt(mnt, TMP_DIR))
+	{
+		TH_LOG("Failed to mount the %s filesystem: %s", mnt->type,
+		       strerror(errno));
+		/*
+		 * FIXTURE_TEARDOWN() is not called when FIXTURE_SETUP()
+		 * failed, so we need to explicitly do a minimal cleanup to
+		 * avoid cascading errors with other tests that don't depend on
+		 * the same filesystem.
+		 */
+		remove_path(TMP_DIR);
+	}
 	ASSERT_EQ(0, mount(NULL, TMP_DIR, NULL, MS_PRIVATE | MS_REC, NULL));
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 }
 
+static void prepare_layout(struct __test_metadata *const _metadata)
+{
+	prepare_layout_opt(_metadata, &mnt_tmp);
+}
+
 static void cleanup_layout(struct __test_metadata *const _metadata)
 {
 	set_cap(_metadata, CAP_SYS_ADMIN);
@@ -269,7 +304,7 @@ static void create_layout1(struct __test_metadata *const _metadata)
 	create_file(_metadata, file1_s3d1);
 	create_directory(_metadata, dir_s3d2);
 	set_cap(_metadata, CAP_SYS_ADMIN);
-	ASSERT_EQ(0, mount("tmp", dir_s3d2, "tmpfs", 0, "size=4m,mode=700"));
+	ASSERT_EQ(0, mount_opt(&mnt_tmp, dir_s3d2));
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 
 	ASSERT_EQ(0, mkdir(dir_s3d3, 0700));
@@ -4068,7 +4103,7 @@ FIXTURE_SETUP(layout2_overlay)
 	create_directory(_metadata, LOWER_BASE);
 	set_cap(_metadata, CAP_SYS_ADMIN);
 	/* Creates tmpfs mount points to get deterministic overlayfs. */
-	ASSERT_EQ(0, mount("tmp", LOWER_BASE, "tmpfs", 0, "size=4m,mode=700"));
+	ASSERT_EQ(0, mount_opt(&mnt_tmp, LOWER_BASE));
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 	create_file(_metadata, lower_fl1);
 	create_file(_metadata, lower_dl1_fl2);
@@ -4078,7 +4113,7 @@ FIXTURE_SETUP(layout2_overlay)
 
 	create_directory(_metadata, UPPER_BASE);
 	set_cap(_metadata, CAP_SYS_ADMIN);
-	ASSERT_EQ(0, mount("tmp", UPPER_BASE, "tmpfs", 0, "size=4m,mode=700"));
+	ASSERT_EQ(0, mount_opt(&mnt_tmp, UPPER_BASE));
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 	create_file(_metadata, upper_fu1);
 	create_file(_metadata, upper_du1_fu2);
-- 
2.41.0

[PATCH v2 5/6] selftests/landlock: Add tests for pseudo filesystems

[Mickaël Salaün]

Add generic and read-only tests for 6 pseudo filesystems to make sure
they have a consistent inode management, which is required for
Landlock's file hierarchy identification:
- tmpfs
- ramfs
- cgroup2
- proc
- sysfs

Update related kernel configuration to support these new filesystems,
remove useless CONFIG_SECURITY_PATH, and sort all entries.  If these
filesystems are not supported by the kernel running tests, the related
tests are skipped.

Expanding variants, this adds 25 new tests for layout3_fs:
- tag_inode_dir_parent
- tag_inode_dir_mnt
- tag_inode_dir_child
- tag_inode_dir_file
- release_inodes

Test coverage for security/landlock with kernel debug code:
- 94.7% of 835 lines according to gcc/gcov-12
- 93.0% of 852 lines according to gcc/gcov-13

Test coverage for security/landlock without kernel debug code:
- 95.5% of 624 lines according to gcc/gcov-12
- 93.1% of 641 lines according to gcc/gcov-13

Signed-off-by: Mickaël Salaün <mic@digikod.net>
---
 tools/testing/selftests/landlock/config    |   9 +-
 tools/testing/selftests/landlock/fs_test.c | 254 ++++++++++++++++++++-
 2 files changed, 259 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/landlock/config b/tools/testing/selftests/landlock/config
index 0f0a65287bac..3dc9e438eab1 100644
--- a/tools/testing/selftests/landlock/config
+++ b/tools/testing/selftests/landlock/config
@@ -1,7 +1,10 @@
+CONFIG_CGROUPS=y
+CONFIG_CGROUP_SCHED=y
 CONFIG_OVERLAY_FS=y
-CONFIG_SECURITY_LANDLOCK=y
-CONFIG_SECURITY_PATH=y
+CONFIG_PROC_FS=y
 CONFIG_SECURITY=y
+CONFIG_SECURITY_LANDLOCK=y
 CONFIG_SHMEM=y
-CONFIG_TMPFS_XATTR=y
+CONFIG_SYSFS=y
 CONFIG_TMPFS=y
+CONFIG_TMPFS_XATTR=y
diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 737047a81547..2911b5241583 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -121,6 +121,10 @@ static bool supports_filesystem(const char *const filesystem)
 	if (!inf)
 		return true;
 
+	/* filesystem can be null for bind mounts. */
+	if (!filesystem)
+		return true;
+
 	len = snprintf(str, sizeof(str), "nodev\t%s\n", filesystem);
 	if (len >= sizeof(str))
 		/* Ignores too-long filesystem names. */
@@ -243,7 +247,7 @@ static void prepare_layout_opt(struct __test_metadata *const _metadata,
 	 * for tests relying on pivot_root(2) and move_mount(2).
 	 */
 	set_cap(_metadata, CAP_SYS_ADMIN);
-	ASSERT_EQ(0, unshare(CLONE_NEWNS));
+	ASSERT_EQ(0, unshare(CLONE_NEWNS | CLONE_NEWCGROUP));
 	ASSERT_EQ(0, mount_opt(mnt, TMP_DIR))
 	{
 		TH_LOG("Failed to mount the %s filesystem: %s", mnt->type,
@@ -318,11 +322,13 @@ static void remove_layout1(struct __test_metadata *const _metadata)
 	EXPECT_EQ(0, remove_path(file1_s1d3));
 	EXPECT_EQ(0, remove_path(file1_s1d2));
 	EXPECT_EQ(0, remove_path(file1_s1d1));
+	EXPECT_EQ(0, remove_path(dir_s1d3));
 
 	EXPECT_EQ(0, remove_path(file2_s2d3));
 	EXPECT_EQ(0, remove_path(file1_s2d3));
 	EXPECT_EQ(0, remove_path(file1_s2d2));
 	EXPECT_EQ(0, remove_path(file1_s2d1));
+	EXPECT_EQ(0, remove_path(dir_s2d2));
 
 	EXPECT_EQ(0, remove_path(file1_s3d1));
 	EXPECT_EQ(0, remove_path(dir_s3d3));
@@ -4482,4 +4488,250 @@ TEST_F_FORK(layout2_overlay, same_content_different_file)
 	}
 }
 
+FIXTURE(layout3_fs)
+{
+	bool has_created_dir;
+	bool has_created_file;
+	char *dir_path;
+	bool skip_test;
+};
+
+FIXTURE_VARIANT(layout3_fs)
+{
+	const struct mnt_opt mnt;
+	const char *const file_path;
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(layout3_fs, tmpfs) {
+	/* clang-format on */
+	.mnt = mnt_tmp,
+	.file_path = file1_s1d1,
+};
+
+FIXTURE_VARIANT_ADD(layout3_fs, ramfs) {
+	.mnt = {
+		.type = "ramfs",
+		.data = "mode=700",
+	},
+	.file_path = TMP_DIR "/dir/file",
+};
+
+FIXTURE_VARIANT_ADD(layout3_fs, cgroup2) {
+	.mnt = {
+		.type = "cgroup2",
+	},
+	.file_path = TMP_DIR "/test/cgroup.procs",
+};
+
+FIXTURE_VARIANT_ADD(layout3_fs, proc) {
+	.mnt = {
+		.type = "proc",
+	},
+	.file_path = TMP_DIR "/self/status",
+};
+
+FIXTURE_VARIANT_ADD(layout3_fs, sysfs) {
+	.mnt = {
+		.type = "sysfs",
+	},
+	.file_path = TMP_DIR "/kernel/notes",
+};
+
+FIXTURE_SETUP(layout3_fs)
+{
+	struct stat statbuf;
+	const char *slash;
+	size_t dir_len;
+
+	if (!supports_filesystem(variant->mnt.type)) {
+		self->skip_test = true;
+		SKIP(return, "this filesystem is not supported (setup)");
+	}
+
+	slash = strrchr(variant->file_path, '/');
+	ASSERT_NE(slash, NULL);
+	dir_len = (size_t)slash - (size_t)variant->file_path;
+	ASSERT_LT(0, dir_len);
+	self->dir_path = malloc(dir_len + 1);
+	self->dir_path[dir_len] = '\0';
+	strncpy(self->dir_path, variant->file_path, dir_len);
+
+	prepare_layout_opt(_metadata, &variant->mnt);
+
+	/* Creates directory when required. */
+	if (stat(self->dir_path, &statbuf)) {
+		set_cap(_metadata, CAP_DAC_OVERRIDE);
+		EXPECT_EQ(0, mkdir(self->dir_path, 0700))
+		{
+			TH_LOG("Failed to create directory \"%s\": %s",
+			       self->dir_path, strerror(errno));
+			free(self->dir_path);
+			self->dir_path = NULL;
+		}
+		self->has_created_dir = true;
+		clear_cap(_metadata, CAP_DAC_OVERRIDE);
+	}
+
+	/* Creates file when required. */
+	if (stat(variant->file_path, &statbuf)) {
+		int fd;
+
+		set_cap(_metadata, CAP_DAC_OVERRIDE);
+		fd = creat(variant->file_path, 0600);
+		EXPECT_LE(0, fd)
+		{
+			TH_LOG("Failed to create file \"%s\": %s",
+			       variant->file_path, strerror(errno));
+		}
+		EXPECT_EQ(0, close(fd));
+		self->has_created_file = true;
+		clear_cap(_metadata, CAP_DAC_OVERRIDE);
+	}
+}
+
+FIXTURE_TEARDOWN(layout3_fs)
+{
+	if (self->skip_test)
+		SKIP(return, "this filesystem is not supported (teardown)");
+
+	if (self->has_created_file) {
+		set_cap(_metadata, CAP_DAC_OVERRIDE);
+		/*
+		 * Don't check for error because the file might already
+		 * have been removed (cf. release_inode test).
+		 */
+		unlink(variant->file_path);
+		clear_cap(_metadata, CAP_DAC_OVERRIDE);
+	}
+
+	if (self->has_created_dir) {
+		set_cap(_metadata, CAP_DAC_OVERRIDE);
+		/*
+		 * Don't check for error because the directory might already
+		 * have been removed (cf. release_inode test).
+		 */
+		rmdir(self->dir_path);
+		clear_cap(_metadata, CAP_DAC_OVERRIDE);
+	}
+	free(self->dir_path);
+	self->dir_path = NULL;
+
+	cleanup_layout(_metadata);
+}
+
+static void layer3_fs_tag_inode(struct __test_metadata *const _metadata,
+				FIXTURE_DATA(layout3_fs) * self,
+				const FIXTURE_VARIANT(layout3_fs) * variant,
+				const char *const rule_path)
+{
+	const struct rule layer1_allow_read_file[] = {
+		{
+			.path = rule_path,
+			.access = LANDLOCK_ACCESS_FS_READ_FILE,
+		},
+		{},
+	};
+	const struct landlock_ruleset_attr layer2_deny_everything_attr = {
+		.handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE,
+	};
+	const char *const dev_null_path = "/dev/null";
+	int ruleset_fd;
+
+	if (self->skip_test)
+		SKIP(return, "this filesystem is not supported (test)");
+
+	/* Checks without Landlock. */
+	EXPECT_EQ(0, test_open(dev_null_path, O_RDONLY | O_CLOEXEC));
+	EXPECT_EQ(0, test_open(variant->file_path, O_RDONLY | O_CLOEXEC));
+
+	ruleset_fd = create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_FILE,
+				    layer1_allow_read_file);
+	EXPECT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	EXPECT_EQ(EACCES, test_open(dev_null_path, O_RDONLY | O_CLOEXEC));
+	EXPECT_EQ(0, test_open(variant->file_path, O_RDONLY | O_CLOEXEC));
+
+	/* Forbids directory reading. */
+	ruleset_fd =
+		landlock_create_ruleset(&layer2_deny_everything_attr,
+					sizeof(layer2_deny_everything_attr), 0);
+	EXPECT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	/* Checks with Landlock and forbidden access. */
+	EXPECT_EQ(EACCES, test_open(dev_null_path, O_RDONLY | O_CLOEXEC));
+	EXPECT_EQ(EACCES, test_open(variant->file_path, O_RDONLY | O_CLOEXEC));
+}
+
+/* Matrix of tests to check file hierarchy evaluation. */
+
+TEST_F_FORK(layout3_fs, tag_inode_dir_parent)
+{
+	/* The current directory must not be the root for this test. */
+	layer3_fs_tag_inode(_metadata, self, variant, ".");
+}
+
+TEST_F_FORK(layout3_fs, tag_inode_dir_mnt)
+{
+	layer3_fs_tag_inode(_metadata, self, variant, TMP_DIR);
+}
+
+TEST_F_FORK(layout3_fs, tag_inode_dir_child)
+{
+	layer3_fs_tag_inode(_metadata, self, variant, self->dir_path);
+}
+
+TEST_F_FORK(layout3_fs, tag_inode_file)
+{
+	layer3_fs_tag_inode(_metadata, self, variant, variant->file_path);
+}
+
+/* Light version of layout1.release_inodes */
+TEST_F_FORK(layout3_fs, release_inodes)
+{
+	const struct rule layer1[] = {
+		{
+			.path = TMP_DIR,
+			.access = LANDLOCK_ACCESS_FS_READ_DIR,
+		},
+		{},
+	};
+	int ruleset_fd;
+
+	if (self->skip_test)
+		SKIP(return, "this filesystem is not supported (test)");
+
+	/* Clean up for the teardown to not fail. */
+	if (self->has_created_file)
+		EXPECT_EQ(0, remove_path(variant->file_path));
+
+	if (self->has_created_dir)
+		/* Don't check for error because of cgroup specificities. */
+		remove_path(self->dir_path);
+
+	ruleset_fd =
+		create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_DIR, layer1);
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Unmount the filesystem while it is being used by a ruleset. */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, umount(TMP_DIR));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	/* Replaces with a new mount point to simplify FIXTURE_TEARDOWN. */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, mount_opt(&mnt_tmp, TMP_DIR));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks that access to the new mount point is denied. */
+	ASSERT_EQ(EACCES, test_open(TMP_DIR, O_RDONLY));
+}
+
 TEST_HARNESS_MAIN
-- 
2.41.0

[PATCH v2 6/6] selftests/landlock: Add hostfs tests

[Mickaël Salaün]

Add tests for the hostfs filesystems to make sure it has a consistent
inode management, which is required for Landlock's file hierarchy
identification.  This adds 5 new tests for layout3_fs with the hostfs
variant.

Add hostfs to the new (architecture-specific) config.um file.

The hostfs filesystem, only available for an User-Mode Linux kernel, is
special because we cannot explicitly mount it.  The layout3_fs.hostfs
variant tests are skipped if the current test directory is not backed by
this filesystem.

The layout3_fs.hostfs.tag_inode_dir_child and
layout3_fs.hostfs.tag_inode_file tests pass thanks to a previous commit
fixing hostfs inode management.  Without this fix, the deny-by-default
policy would apply and all access requests would be denied.

Signed-off-by: Mickaël Salaün <mic@digikod.net>
---
 tools/testing/selftests/landlock/config.um |  1 +
 tools/testing/selftests/landlock/fs_test.c | 28 +++++++++++++++++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/landlock/config.um

diff --git a/tools/testing/selftests/landlock/config.um b/tools/testing/selftests/landlock/config.um
new file mode 100644
index 000000000000..40937c0395d6
--- /dev/null
+++ b/tools/testing/selftests/landlock/config.um
@@ -0,0 +1 @@
+CONFIG_HOSTFS=y
diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 2911b5241583..83d565569512 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -10,6 +10,7 @@
 #define _GNU_SOURCE
 #include <fcntl.h>
 #include <linux/landlock.h>
+#include <linux/magic.h>
 #include <sched.h>
 #include <stdio.h>
 #include <string.h>
@@ -19,6 +20,7 @@
 #include <sys/sendfile.h>
 #include <sys/stat.h>
 #include <sys/sysmacros.h>
+#include <sys/vfs.h>
 #include <unistd.h>
 
 #include "common.h"
@@ -135,6 +137,19 @@ static bool supports_filesystem(const char *const filesystem)
 	return res;
 }
 
+static bool cwd_matches_fs(unsigned int fs_magic)
+{
+	struct statfs statfs_buf;
+
+	if (!fs_magic)
+		return true;
+
+	if (statfs(".", &statfs_buf))
+		return true;
+
+	return statfs_buf.f_type == fs_magic;
+}
+
 static void mkdir_parents(struct __test_metadata *const _metadata,
 			  const char *const path)
 {
@@ -4500,6 +4515,7 @@ FIXTURE_VARIANT(layout3_fs)
 {
 	const struct mnt_opt mnt;
 	const char *const file_path;
+	unsigned int cwd_fs_magic;
 };
 
 /* clang-format off */
@@ -4538,13 +4554,23 @@ FIXTURE_VARIANT_ADD(layout3_fs, sysfs) {
 	.file_path = TMP_DIR "/kernel/notes",
 };
 
+FIXTURE_VARIANT_ADD(layout3_fs, hostfs) {
+	.mnt = {
+		.source = TMP_DIR,
+		.flags = MS_BIND,
+	},
+	.file_path = TMP_DIR "/dir/file",
+	.cwd_fs_magic = HOSTFS_SUPER_MAGIC,
+};
+
 FIXTURE_SETUP(layout3_fs)
 {
 	struct stat statbuf;
 	const char *slash;
 	size_t dir_len;
 
-	if (!supports_filesystem(variant->mnt.type)) {
+	if (!supports_filesystem(variant->mnt.type) ||
+	    !cwd_matches_fs(variant->cwd_fs_magic)) {
 		self->skip_test = true;
 		SKIP(return, "this filesystem is not supported (setup)");
 	}
-- 
2.41.0

Re: [PATCH v2 0/6] Landlock support for UML

[Mickaël Salaün]

I've push this series into -next. Thanks Richard!

On 12/06/2023 21:14, Mickaël Salaün wrote:
> Hi,
> 
> Commit cb2c7d1a1776 ("landlock: Support filesystem access-control")
> introduced a new ARCH_EPHEMERAL_INODES configuration, only enabled for
> User-Mode Linux.  The reason was that UML's hostfs managed inodes in an
> ephemeral way: from the kernel point of view, the same inode struct
> could be created several times while being used by user space because
> the kernel didn't hold references to inodes.  Because Landlock (and
> probably other subsystems) ties properties (i.e. access rights) to inode
> objects, it wasn't possible to create rules that match inodes and then
> allow specific accesses.
> 
> This patch series fixes the way UML manages inodes according to the
> underlying filesystem.  They are now properly handles as for other
> filesystems, which enables to support Landlock (and probably other
> features).
> 
> Changes since v1:
> https://lore.kernel.org/r/20230309165455.175131-1-mic@digikod.net
> - Remove Cc stable@ (suggested by Richard).
> - Add Acked-by: Richard Weinberger to the first patch.
> - Split the test patch into two patches: one for the common
>    pseudo-filesystems, and another patch dedicated to hostfs.
> - Remove CONFIG_SECURITY_PATH because it is useless for merge_config.sh
> - Move CONFIG_HOSTFS to a new config.um file.
> - Fix commit message spelling and test warnings.
> - Improve prepare_layout_opt() with remove_path() call to avoid
>    cascading errors when some tested filesystems are not supported.
> - Remove cgroup-v1 tests because this filesystem cannot really be
>    mounted several times.
> - Add test coverage with and without kernel debug code, according to
>    GCC 12 and GCC 13.
> 
> Regards,
> 
> Mickaël Salaün (6):
>    hostfs: Fix ephemeral inodes
>    selftests/landlock: Don't create useless file layouts
>    selftests/landlock: Add supports_filesystem() helper
>    selftests/landlock: Make mounts configurable
>    selftests/landlock: Add tests for pseudo filesystems
>    selftests/landlock: Add hostfs tests
> 
>   arch/Kconfig                               |   7 -
>   arch/um/Kconfig                            |   1 -
>   fs/hostfs/hostfs.h                         |   1 +
>   fs/hostfs/hostfs_kern.c                    | 213 ++++++------
>   fs/hostfs/hostfs_user.c                    |   1 +
>   security/landlock/Kconfig                  |   2 +-
>   tools/testing/selftests/landlock/config    |   9 +-
>   tools/testing/selftests/landlock/config.um |   1 +
>   tools/testing/selftests/landlock/fs_test.c | 387 +++++++++++++++++++--
>   9 files changed, 478 insertions(+), 144 deletions(-)
>   create mode 100644 tools/testing/selftests/landlock/config.um
> 
> 
> base-commit: 858fd168a95c5b9669aac8db6c14a9aeab446375