[v21,07/12] landlock: Support filesystem access-control

diff --git a/arch/Kconfig b/arch/Kconfig
index af14a567b493..05e9b26d6915 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -838,6 +838,13 @@  config COMPAT_32BIT_TIME
 config ARCH_NO_PREEMPT
 	bool
 
+config ARCH_EPHEMERAL_STATES
+	def_bool n
+	help
+	  An arch should select this symbol if it does not keep an internal kernel
+	  state for kernel objects such as inodes, 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 eb51fec75948..ed481bb3d500 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -5,6 +5,7 @@  menu "UML-specific options"
 config UML
 	bool
 	default y
+	select ARCH_EPHEMERAL_STATES
 	select ARCH_HAS_KCOV
 	select ARCH_NO_PREEMPT
 	select HAVE_ARCH_AUDITSYSCALL
diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
new file mode 100644
index 000000000000..9a1bbf18fb9f
--- /dev/null
+++ b/include/uapi/linux/landlock.h
@@ -0,0 +1,78 @@ 
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Landlock - UAPI headers
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#ifndef _UAPI__LINUX_LANDLOCK_H__
+#define _UAPI__LINUX_LANDLOCK_H__
+
+/**
+ * DOC: fs_access
+ *
+ * A set of actions on kernel objects may be defined by an attribute (e.g.
+ * &struct landlock_path_beneath_attr) and a bitmask of access.
+ *
+ * Filesystem flags
+ * ~~~~~~~~~~~~~~~~
+ *
+ * These flags enable to restrict a sandbox process to a set of actions on
+ * files and directories.  Files or directories opened before the sandboxing
+ * are not subject to these restrictions.
+ *
+ * A file can only receive these access rights:
+ *
+ * - %LANDLOCK_ACCESS_FS_EXECUTE: Execute a file.
+ * - %LANDLOCK_ACCESS_FS_WRITE_FILE: Open a file with write access.
+ * - %LANDLOCK_ACCESS_FS_READ_FILE: Open a file with read access.
+ *
+ * A directory can receive access rights related to files or directories.  This
+ * set of access rights is applied to the directory itself, and the directories
+ * beneath it:
+ *
+ * - %LANDLOCK_ACCESS_FS_READ_DIR: Open a directory or list its content.
+ * - %LANDLOCK_ACCESS_FS_CHROOT: Change the root directory of the current
+ *   process.
+ *
+ * However, the following access rights only apply to the content of a
+ * directory, not the directory itself:
+ *
+ * - %LANDLOCK_ACCESS_FS_REMOVE_DIR: Remove an empty directory or rename one.
+ * - %LANDLOCK_ACCESS_FS_REMOVE_FILE: Unlink (or rename) a file.
+ * - %LANDLOCK_ACCESS_FS_MAKE_CHAR: Create (or rename or link) a character
+ *   device.
+ * - %LANDLOCK_ACCESS_FS_MAKE_DIR: Create (or rename) a directory.
+ * - %LANDLOCK_ACCESS_FS_MAKE_REG: Create (or rename or link) a regular file.
+ * - %LANDLOCK_ACCESS_FS_MAKE_SOCK: Create (or rename or link) a UNIX domain
+ *   socket.
+ * - %LANDLOCK_ACCESS_FS_MAKE_FIFO: Create (or rename or link) a named pipe.
+ * - %LANDLOCK_ACCESS_FS_MAKE_BLOCK: Create (or rename or link) a block device.
+ * - %LANDLOCK_ACCESS_FS_MAKE_SYM: Create (or rename or link) a symbolic link.
+ *
+ * .. warning::
+ *
+ *   It is currently not possible to restrict some file-related actions
+ *   accessible through these syscall families: :manpage:`chdir(2)`,
+ *   :manpage:`truncate(2)`, :manpage:`stat(2)`, :manpage:`flock(2)`,
+ *   :manpage:`chmod(2)`, :manpage:`chown(2)`, :manpage:`setxattr(2)`,
+ *   :manpage:`ioctl(2)`, :manpage:`fcntl(2)`.
+ *   Future Landlock evolutions will enable to restrict them.
+ */
+#define LANDLOCK_ACCESS_FS_EXECUTE			(1ULL << 0)
+#define LANDLOCK_ACCESS_FS_WRITE_FILE			(1ULL << 1)
+#define LANDLOCK_ACCESS_FS_READ_FILE			(1ULL << 2)
+#define LANDLOCK_ACCESS_FS_READ_DIR			(1ULL << 3)
+#define LANDLOCK_ACCESS_FS_CHROOT			(1ULL << 4)
+#define LANDLOCK_ACCESS_FS_REMOVE_DIR			(1ULL << 5)
+#define LANDLOCK_ACCESS_FS_REMOVE_FILE			(1ULL << 6)
+#define LANDLOCK_ACCESS_FS_MAKE_CHAR			(1ULL << 7)
+#define LANDLOCK_ACCESS_FS_MAKE_DIR			(1ULL << 8)
+#define LANDLOCK_ACCESS_FS_MAKE_REG			(1ULL << 9)
+#define LANDLOCK_ACCESS_FS_MAKE_SOCK			(1ULL << 10)
+#define LANDLOCK_ACCESS_FS_MAKE_FIFO			(1ULL << 11)
+#define LANDLOCK_ACCESS_FS_MAKE_BLOCK			(1ULL << 12)
+#define LANDLOCK_ACCESS_FS_MAKE_SYM			(1ULL << 13)
+
+#endif /* _UAPI__LINUX_LANDLOCK_H__ */
diff --git a/security/landlock/Kconfig b/security/landlock/Kconfig
index 9ec7593a534a..487d88328d98 100644
--- a/security/landlock/Kconfig
+++ b/security/landlock/Kconfig
@@ -2,7 +2,7 @@ 
 
 config SECURITY_LANDLOCK
 	bool "Landlock support"
-	depends on SECURITY
+	depends on SECURITY && !ARCH_EPHEMERAL_STATES
 	select SECURITY_PATH
 	help
 	  Landlock is a safe sandboxing mechanism which enables processes to
diff --git a/security/landlock/Makefile b/security/landlock/Makefile
index f1d1eb72fa76..92e3d80ab8ed 100644
--- a/security/landlock/Makefile
+++ b/security/landlock/Makefile
@@ -1,4 +1,4 @@ 
 obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
 
 landlock-y := setup.o object.o ruleset.o \
-	cred.o ptrace.o
+	cred.o ptrace.o fs.o
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
new file mode 100644
index 000000000000..7d5df26c3441
--- /dev/null
+++ b/security/landlock/fs.c
@@ -0,0 +1,609 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - Filesystem management and hooks
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#include <linux/atomic.h>
+#include <linux/compiler_types.h>
+#include <linux/dcache.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/lsm_hooks.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/path.h>
+#include <linux/prefetch.h>
+#include <linux/rcupdate.h>
+#include <linux/spinlock.h>
+#include <linux/stat.h>
+#include <linux/types.h>
+#include <linux/wait_bit.h>
+#include <linux/workqueue.h>
+#include <uapi/linux/landlock.h>
+
+#include "common.h"
+#include "cred.h"
+#include "fs.h"
+#include "object.h"
+#include "ruleset.h"
+#include "setup.h"
+
+/* Underlying object management */
+
+static void release_inode(struct landlock_object *const object)
+	__releases(object->lock)
+{
+	struct inode *const inode = object->underobj;
+	struct super_block *sb;
+
+	if (!inode) {
+		spin_unlock(&object->lock);
+		return;
+	}
+
+	spin_lock(&inode->i_lock);
+	/*
+	 * Make sure that if the filesystem is concurrently unmounted,
+	 * hook_sb_delete() will wait for us to finish iput().
+	 */
+	sb = inode->i_sb;
+	atomic_long_inc(&landlock_superblock(sb)->inode_refs);
+	rcu_assign_pointer(landlock_inode(inode)->object, NULL);
+	spin_unlock(&inode->i_lock);
+	spin_unlock(&object->lock);
+	/*
+	 * Now, new rules can safely be tied to @inode.
+	 */
+
+	iput(inode);
+	if (atomic_long_dec_and_test(&landlock_superblock(sb)->inode_refs))
+		wake_up_var(&landlock_superblock(sb)->inode_refs);
+}
+
+static const struct landlock_object_underops landlock_fs_underops = {
+	.release = release_inode
+};
+
+/* Ruleset management */
+
+static struct landlock_object *get_inode_object(struct inode *const inode)
+{
+	struct landlock_object *object, *new_object;
+	struct landlock_inode_security *inode_sec = landlock_inode(inode);
+
+	rcu_read_lock();
+retry:
+	object = rcu_dereference(inode_sec->object);
+	if (object) {
+		if (likely(refcount_inc_not_zero(&object->usage))) {
+			rcu_read_unlock();
+			return object;
+		}
+		/*
+		 * We're racing with release_inode(), the object is going away.
+		 * Wait for release_inode(), then retry.
+		 */
+		spin_lock(&object->lock);
+		spin_unlock(&object->lock);
+		goto retry;
+	}
+	rcu_read_unlock();
+
+	/*
+	 * If there is no object tied to @inode, then create a new one (without
+	 * holding any locks).
+	 */
+	new_object = landlock_create_object(&landlock_fs_underops, inode);
+
+	spin_lock(&inode->i_lock);
+	object = rcu_dereference_protected(inode_sec->object,
+			lockdep_is_held(&inode->i_lock));
+	if (unlikely(object)) {
+		/* Someone else just created the object, bail out and retry. */
+		kfree(new_object);
+		spin_unlock(&inode->i_lock);
+
+		rcu_read_lock();
+		goto retry;
+	} else {
+		rcu_assign_pointer(inode_sec->object, new_object);
+		/*
+		 * @inode will be released by hook_sb_delete() on its
+		 * superblock shutdown.
+		 */
+		ihold(inode);
+		spin_unlock(&inode->i_lock);
+		return new_object;
+	}
+}
+
+/* All access rights which can be tied to files. */
+#define ACCESS_FILE ( \
+	LANDLOCK_ACCESS_FS_EXECUTE | \
+	LANDLOCK_ACCESS_FS_WRITE_FILE | \
+	LANDLOCK_ACCESS_FS_READ_FILE)
+
+/*
+ * @path: Should have been checked by get_path_from_fd().
+ */
+int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
+		const struct path *const path, u32 access_rights)
+{
+	int err;
+	struct landlock_rule rule = {};
+
+	/* Files only get access rights that make sense. */
+	if (!d_is_dir(path->dentry) && (access_rights | ACCESS_FILE) !=
+			ACCESS_FILE)
+		return -EINVAL;
+
+	/* Transforms relative access rights to absolute ones. */
+	access_rights |= _LANDLOCK_ACCESS_FS_MASK & ~ruleset->fs_access_mask;
+	rule.access = access_rights;
+	rule.object = get_inode_object(d_backing_inode(path->dentry));
+	mutex_lock(&ruleset->lock);
+	err = landlock_insert_rule(ruleset, &rule, false);
+	mutex_unlock(&ruleset->lock);
+	/*
+	 * No need to check for an error because landlock_insert_rule()
+	 * increments the refcount for the new rule, if any.
+	 */
+	landlock_put_object(rule.object);
+	return err;
+}
+
+/* Access-control management */
+
+static bool check_access_path_continue(
+		const struct landlock_ruleset *const domain,
+		const struct path *const path, const u32 access_request,
+		bool *const allow, u64 *const layer_mask)
+{
+	const struct landlock_rule *rule;
+	const struct inode *inode;
+	bool next = true;
+
+	prefetch(path->dentry->d_parent);
+	if (d_is_negative(path->dentry))
+		/* Continues to walk while there is no mapped inode. */
+		return true;
+	inode = d_backing_inode(path->dentry);
+	rcu_read_lock();
+	rule = landlock_find_rule(domain,
+			rcu_dereference(landlock_inode(inode)->object));
+	rcu_read_unlock();
+
+	/* Checks for matching layers. */
+	if (rule && (rule->layers | *layer_mask)) {
+		*allow = (rule->access & access_request) == access_request;
+		if (*allow) {
+			*layer_mask &= ~rule->layers;
+			/* Stops when a rule from each layer granted access. */
+			next = !!*layer_mask;
+		} else {
+			next = false;
+		}
+	}
+	return next;
+}
+
+static int check_access_path(const struct landlock_ruleset *const domain,
+		const struct path *const path, u32 access_request)
+{
+	bool allow = false;
+	struct path walker_path;
+	u64 layer_mask;
+
+	if (WARN_ON_ONCE(!domain || !path))
+		return 0;
+	/*
+	 * Allows access to pseudo filesystems that will never be mountable
+	 * (e.g. sockfs, pipefs), but can still be reachable through
+	 * /proc/self/fd .
+	 */
+	if ((path->dentry->d_sb->s_flags & SB_NOUSER) ||
+			(d_is_positive(path->dentry) &&
+			 unlikely(IS_PRIVATE(d_backing_inode(path->dentry)))))
+		return 0;
+	if (WARN_ON_ONCE(domain->nb_layers < 1))
+		return -EACCES;
+
+	layer_mask = GENMASK_ULL(domain->nb_layers - 1, 0);
+	/*
+	 * An access request which is not handled by the domain should be
+	 * allowed.
+	 */
+	access_request &= domain->fs_access_mask;
+	if (access_request == 0)
+		return 0;
+	walker_path = *path;
+	path_get(&walker_path);
+	/*
+	 * We need to walk through all the hierarchy to not miss any relevant
+	 * restriction.
+	 */
+	while (check_access_path_continue(domain, &walker_path, access_request,
+				&allow, &layer_mask)) {
+		struct dentry *parent_dentry;
+
+jump_up:
+		/*
+		 * Does not work with orphaned/private mounts like overlayfs
+		 * layers for now (cf. ovl_path_real() and ovl_path_open()).
+		 */
+		if (walker_path.dentry == walker_path.mnt->mnt_root) {
+			if (follow_up(&walker_path)) {
+				/* Ignores hidden mount points. */
+				goto jump_up;
+			} else {
+				/*
+				 * Stops at the real root.  Denies access
+				 * because not all layers have granted access.
+				 */
+				allow = false;
+				break;
+			}
+		}
+		if (unlikely(IS_ROOT(walker_path.dentry))) {
+			/*
+			 * Stops at disconnected root directories.  Only allows
+			 * access to internal filesystems (e.g. nsfs which is
+			 * reachable through /proc/self/ns).
+			 */
+			allow = !!(walker_path.mnt->mnt_flags & MNT_INTERNAL);
+			break;
+		}
+		parent_dentry = dget_parent(walker_path.dentry);
+		dput(walker_path.dentry);
+		walker_path.dentry = parent_dentry;
+	}
+	path_put(&walker_path);
+	return allow ? 0 : -EACCES;
+}
+
+static inline int current_check_access_path(const struct path *const path,
+		const u32 access_request)
+{
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+
+	if (!dom)
+		return 0;
+	return check_access_path(dom, path, access_request);
+}
+
+/* Super-block hooks */
+
+/*
+ * Release the inodes used in a security policy.
+ *
+ * Cf. fsnotify_unmount_inodes()
+ */
+static void hook_sb_delete(struct super_block *const sb)
+{
+	struct inode *inode, *iput_inode = NULL;
+
+	if (!landlock_initialized)
+		return;
+
+	spin_lock(&sb->s_inode_list_lock);
+	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+		struct landlock_inode_security *inode_sec =
+			landlock_inode(inode);
+		struct landlock_object *object;
+		bool do_put = false;
+
+		rcu_read_lock();
+		object = rcu_dereference(inode_sec->object);
+		if (!object) {
+			rcu_read_unlock();
+			continue;
+		}
+
+		spin_lock(&object->lock);
+		if (object->underobj) {
+			object->underobj = NULL;
+			do_put = true;
+			spin_lock(&inode->i_lock);
+			rcu_assign_pointer(inode_sec->object, NULL);
+			spin_unlock(&inode->i_lock);
+		}
+		spin_unlock(&object->lock);
+		rcu_read_unlock();
+		if (!do_put)
+			/*
+			 * A concurrent iput() in release_inode() is ongoing
+			 * and we will just wait for it to finish.
+			 */
+			continue;
+
+		/*
+		 * At this point, we own the ihold() reference that was
+		 * originally set up by get_inode_object(). Therefore we can
+		 * drop the list lock and know that the inode won't disappear
+		 * from under us until the next loop walk.
+		 */
+		spin_unlock(&sb->s_inode_list_lock);
+		/*
+		 * We can now actually put the previous inode, which is not
+		 * needed anymore for the loop walk.
+		 */
+		if (iput_inode)
+			iput(iput_inode);
+		iput_inode = inode;
+		spin_lock(&sb->s_inode_list_lock);
+	}
+	spin_unlock(&sb->s_inode_list_lock);
+	if (iput_inode)
+		iput(iput_inode);
+
+	/*
+	 * Wait for pending iput() in release_inode().
+	 */
+	wait_var_event(&landlock_superblock(sb)->inode_refs, !atomic_long_read(
+				&landlock_superblock(sb)->inode_refs));
+}
+
+/*
+ * Because a Landlock security policy is defined according to the filesystem
+ * layout (i.e. the mount namespace), changing it may grant access to files not
+ * previously allowed.
+ *
+ * To make it simple, deny any filesystem layout modification by landlocked
+ * processes.  Non-landlocked processes may still change the namespace of a
+ * landlocked process, but this kind of threat must be handled by a system-wide
+ * access-control security policy.
+ *
+ * This could be lifted in the future if Landlock can safely handle mount
+ * namespace updates requested by a landlocked process.  Indeed, we could
+ * update the current domain (which is currently read-only) by taking into
+ * account the accesses of the source and the destination of a new mount point.
+ * However, it would also require to make all the child domains dynamically
+ * inherit these new constraints.  Anyway, for backward compatibility reasons,
+ * a dedicated user space option would be required (e.g. as a ruleset command
+ * option).
+ */
+static int hook_sb_mount(const char *const dev_name,
+		const struct path *const path, const char *const type,
+		const unsigned long flags, void *const data)
+{
+	if (!landlock_get_current_domain())
+		return 0;
+	return -EPERM;
+}
+
+static int hook_move_mount(const struct path *const from_path,
+		const struct path *const to_path)
+{
+	if (!landlock_get_current_domain())
+		return 0;
+	return -EPERM;
+}
+
+/*
+ * Removing a mount point may reveal a previously hidden file hierarchy, which
+ * may then grant access to files, which may have previously been forbidden.
+ */
+static int hook_sb_umount(struct vfsmount *const mnt, const int flags)
+{
+	if (!landlock_get_current_domain())
+		return 0;
+	return -EPERM;
+}
+
+static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts)
+{
+	if (!landlock_get_current_domain())
+		return 0;
+	return -EPERM;
+}
+
+/*
+ * pivot_root(2), like mount(2), changes the current mount namespace.  It must
+ * then be forbidden for a landlocked process.
+ *
+ * However, chroot(2) may be allowed because it only changes the relative root
+ * directory of the current process.
+ */
+static int hook_sb_pivotroot(const struct path *const old_path,
+		const struct path *const new_path)
+{
+	if (!landlock_get_current_domain())
+		return 0;
+	return -EPERM;
+}
+
+/* Path hooks */
+
+static inline u32 get_mode_access(const umode_t mode)
+{
+	switch (mode & S_IFMT) {
+	case S_IFLNK:
+		return LANDLOCK_ACCESS_FS_MAKE_SYM;
+	case 0:
+		/* A zero mode translates to S_IFREG. */
+	case S_IFREG:
+		return LANDLOCK_ACCESS_FS_MAKE_REG;
+	case S_IFDIR:
+		return LANDLOCK_ACCESS_FS_MAKE_DIR;
+	case S_IFCHR:
+		return LANDLOCK_ACCESS_FS_MAKE_CHAR;
+	case S_IFBLK:
+		return LANDLOCK_ACCESS_FS_MAKE_BLOCK;
+	case S_IFIFO:
+		return LANDLOCK_ACCESS_FS_MAKE_FIFO;
+	case S_IFSOCK:
+		return LANDLOCK_ACCESS_FS_MAKE_SOCK;
+	default:
+		WARN_ON_ONCE(1);
+		return 0;
+	}
+}
+
+/*
+ * Creating multiple links or renaming may lead to privilege escalations if not
+ * handled properly.  Indeed, we must be sure that the source doesn't gain more
+ * privileges by being accessible from the destination.  This is getting more
+ * complex when dealing with multiple layers.  The whole picture can be seen as
+ * a multilayer partial ordering problem.  A future version of Landlock will
+ * deal with that.
+ */
+static int hook_path_link(struct dentry *const old_dentry,
+		const struct path *const new_dir,
+		struct dentry *const new_dentry)
+{
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+
+	if (!dom)
+		return 0;
+	/* The mount points are the same for old and new paths, cf. EXDEV. */
+	if (old_dentry->d_parent != new_dir->dentry)
+		/* For now, forbid reparenting. */
+		return -EACCES;
+	if (unlikely(d_is_negative(old_dentry)))
+		return -EACCES;
+	return check_access_path(dom, new_dir,
+			get_mode_access(d_backing_inode(old_dentry)->i_mode));
+}
+
+static inline u32 maybe_remove(const struct dentry *const dentry)
+{
+	if (d_is_negative(dentry))
+		return 0;
+	return d_is_dir(dentry) ? LANDLOCK_ACCESS_FS_REMOVE_DIR :
+		LANDLOCK_ACCESS_FS_REMOVE_FILE;
+}
+
+static int hook_path_rename(const struct path *const old_dir,
+		struct dentry *const old_dentry,
+		const struct path *const new_dir,
+		struct dentry *const new_dentry)
+{
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+
+	if (!dom)
+		return 0;
+	/* The mount points are the same for old and new paths, cf. EXDEV. */
+	if (old_dir->dentry != new_dir->dentry)
+		/* For now, forbid reparenting. */
+		return -EACCES;
+	if (WARN_ON_ONCE(d_is_negative(old_dentry)))
+		return -EACCES;
+	/* RENAME_EXCHANGE is handled because directories are the same. */
+	return check_access_path(dom, old_dir, maybe_remove(old_dentry) |
+			maybe_remove(new_dentry) |
+			get_mode_access(d_backing_inode(old_dentry)->i_mode));
+}
+
+static int hook_path_mkdir(const struct path *const dir,
+		struct dentry *const dentry, const umode_t mode)
+{
+	return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_DIR);
+}
+
+static int hook_path_mknod(const struct path *const dir,
+		struct dentry *const dentry, const umode_t mode,
+		const unsigned int dev)
+{
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+
+	if (!dom)
+		return 0;
+	return check_access_path(dom, dir, get_mode_access(mode));
+}
+
+static int hook_path_symlink(const struct path *const dir,
+		struct dentry *const dentry, const char *const old_name)
+{
+	return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_SYM);
+}
+
+static int hook_path_unlink(const struct path *const dir,
+		struct dentry *const dentry)
+{
+	return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_FILE);
+}
+
+static int hook_path_rmdir(const struct path *const dir,
+		struct dentry *const dentry)
+{
+	return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_DIR);
+}
+
+static int hook_path_chroot(const struct path *const path)
+{
+	return current_check_access_path(path, LANDLOCK_ACCESS_FS_CHROOT);
+}
+
+/* File hooks */
+
+static inline u32 get_file_access(const struct file *const file)
+{
+	u32 access = 0;
+
+	if (file->f_mode & FMODE_READ) {
+		/* A directory can only be opened in read mode. */
+		if (S_ISDIR(file_inode(file)->i_mode))
+			return LANDLOCK_ACCESS_FS_READ_DIR;
+		access = LANDLOCK_ACCESS_FS_READ_FILE;
+	}
+	/*
+	 * A LANDLOCK_ACCESS_FS_APPEND could be added but we also need to check
+	 * fcntl(2).
+	 */
+	if (file->f_mode & FMODE_WRITE)
+		access |= LANDLOCK_ACCESS_FS_WRITE_FILE;
+	/* __FMODE_EXEC is indeed part of f_flags, not f_mode. */
+	if (file->f_flags & __FMODE_EXEC)
+		access |= LANDLOCK_ACCESS_FS_EXECUTE;
+	return access;
+}
+
+static int hook_file_open(struct file *const file)
+{
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+
+	if (!dom)
+		return 0;
+	/*
+	 * Because a file may be opened with O_PATH, get_file_access() may
+	 * return 0.  This case will be handled with a future Landlock
+	 * evolution.
+	 */
+	return current_check_access_path(&file->f_path, get_file_access(file));
+}
+
+static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
+	LSM_HOOK_INIT(sb_delete, hook_sb_delete),
+	LSM_HOOK_INIT(sb_mount, hook_sb_mount),
+	LSM_HOOK_INIT(move_mount, hook_move_mount),
+	LSM_HOOK_INIT(sb_umount, hook_sb_umount),
+	LSM_HOOK_INIT(sb_remount, hook_sb_remount),
+	LSM_HOOK_INIT(sb_pivotroot, hook_sb_pivotroot),
+
+	LSM_HOOK_INIT(path_link, hook_path_link),
+	LSM_HOOK_INIT(path_rename, hook_path_rename),
+	LSM_HOOK_INIT(path_mkdir, hook_path_mkdir),
+	LSM_HOOK_INIT(path_mknod, hook_path_mknod),
+	LSM_HOOK_INIT(path_symlink, hook_path_symlink),
+	LSM_HOOK_INIT(path_unlink, hook_path_unlink),
+	LSM_HOOK_INIT(path_rmdir, hook_path_rmdir),
+	LSM_HOOK_INIT(path_chroot, hook_path_chroot),
+
+	LSM_HOOK_INIT(file_open, hook_file_open),
+};
+
+__init void landlock_add_hooks_fs(void)
+{
+	security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
+			LANDLOCK_NAME);
+}
diff --git a/security/landlock/fs.h b/security/landlock/fs.h
new file mode 100644
index 000000000000..58b462eb7f10
--- /dev/null
+++ b/security/landlock/fs.h
@@ -0,0 +1,60 @@ 
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - Filesystem management and hooks
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#ifndef _SECURITY_LANDLOCK_FS_H
+#define _SECURITY_LANDLOCK_FS_H
+
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/rcupdate.h>
+#include <uapi/linux/landlock.h>
+
+#include "ruleset.h"
+#include "setup.h"
+
+#define _LANDLOCK_ACCESS_FS_LAST	LANDLOCK_ACCESS_FS_MAKE_SYM
+#define _LANDLOCK_ACCESS_FS_MASK	((_LANDLOCK_ACCESS_FS_LAST << 1) - 1)
+
+struct landlock_inode_security {
+	/*
+	 * @object: Weak pointer to an allocated object.  All writes (i.e.
+	 * creating a new object or removing one) are protected by the
+	 * underlying inode->i_lock.  Disassociating @object from the inode is
+	 * additionally protected by @object->lock, from the time @object's
+	 * usage refcount drops to zero to the time this pointer is nulled out.
+	 * Cf. release_inode().
+	 */
+	struct landlock_object __rcu *object;
+};
+
+struct landlock_superblock_security {
+	/*
+	 * @inode_refs: References to Landlock underlying objects.
+	 * Cf. struct super_block->s_fsnotify_inode_refs .
+	 */
+	atomic_long_t inode_refs;
+};
+
+static inline struct landlock_inode_security *landlock_inode(
+		const struct inode *const inode)
+{
+	return inode->i_security + landlock_blob_sizes.lbs_inode;
+}
+
+static inline struct landlock_superblock_security *landlock_superblock(
+		const struct super_block *const superblock)
+{
+	return superblock->s_security + landlock_blob_sizes.lbs_superblock;
+}
+
+__init void landlock_add_hooks_fs(void);
+
+int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
+		const struct path *const path, u32 access_hierarchy);
+
+#endif /* _SECURITY_LANDLOCK_FS_H */
diff --git a/security/landlock/setup.c b/security/landlock/setup.c
index 5e7540fdeefa..722cbea82324 100644
--- a/security/landlock/setup.c
+++ b/security/landlock/setup.c
@@ -11,17 +11,24 @@ 
 
 #include "common.h"
 #include "cred.h"
+#include "fs.h"
 #include "ptrace.h"
 #include "setup.h"
 
+bool landlock_initialized __lsm_ro_after_init = false;
+
 struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = {
 	.lbs_cred = sizeof(struct landlock_cred_security),
+	.lbs_inode = sizeof(struct landlock_inode_security),
+	.lbs_superblock = sizeof(struct landlock_superblock_security),
 };
 
 static int __init landlock_init(void)
 {
 	landlock_add_hooks_cred();
 	landlock_add_hooks_ptrace();
+	landlock_add_hooks_fs();
+	landlock_initialized = true;
 	pr_info("Up and running.\n");
 	return 0;
 }
diff --git a/security/landlock/setup.h b/security/landlock/setup.h
index 9fdbf33fcc33..1daffab1ab4b 100644
--- a/security/landlock/setup.h
+++ b/security/landlock/setup.h
@@ -11,6 +11,8 @@ 
 
 #include <linux/lsm_hooks.h>
 
+extern bool landlock_initialized;
+
 extern struct lsm_blob_sizes landlock_blob_sizes;
 
 #endif /* _SECURITY_LANDLOCK_SETUP_H */