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-rw-r--r--MAINTAINERS1
-rw-r--r--arch/Kconfig7
-rw-r--r--arch/um/Kconfig1
-rw-r--r--include/uapi/linux/landlock.h76
-rw-r--r--security/landlock/Kconfig2
-rw-r--r--security/landlock/Makefile2
-rw-r--r--security/landlock/fs.c692
-rw-r--r--security/landlock/fs.h70
-rw-r--r--security/landlock/limits.h4
-rw-r--r--security/landlock/ruleset.c4
-rw-r--r--security/landlock/setup.c7
-rw-r--r--security/landlock/setup.h2
12 files changed, 866 insertions, 2 deletions
diff --git a/MAINTAINERS b/MAINTAINERS
index 87a2738dfdec..70ec117efa8a 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -10003,6 +10003,7 @@ L: linux-security-module@vger.kernel.org
S: Supported
W: https://landlock.io
T: git https://github.com/landlock-lsm/linux.git
+F: include/uapi/linux/landlock.h
F: security/landlock/
K: landlock
K: LANDLOCK
diff --git a/arch/Kconfig b/arch/Kconfig
index ecfd3520b676..8160ab7e3e03 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1013,6 +1013,13 @@ 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 c3030db3325f..57cfd9a1c082 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_INODES
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..b1a81b5a8b86
--- /dev/null
+++ b/include/uapi/linux/landlock.h
@@ -0,0 +1,76 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Landlock - User space API
+ *
+ * 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) including a bitmask of access.
+ *
+ * Filesystem flags
+ * ~~~~~~~~~~~~~~~~
+ *
+ * These flags enable to restrict a sandboxed 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. The
+ * following access right is applied to the directory itself, and the
+ * directories beneath it:
+ *
+ * - %LANDLOCK_ACCESS_FS_READ_DIR: Open a directory or list its content.
+ *
+ * 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:`utime(2)`, :manpage:`ioctl(2)`, :manpage:`fcntl(2)`,
+ * :manpage:`access(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_REMOVE_DIR (1ULL << 4)
+#define LANDLOCK_ACCESS_FS_REMOVE_FILE (1ULL << 5)
+#define LANDLOCK_ACCESS_FS_MAKE_CHAR (1ULL << 6)
+#define LANDLOCK_ACCESS_FS_MAKE_DIR (1ULL << 7)
+#define LANDLOCK_ACCESS_FS_MAKE_REG (1ULL << 8)
+#define LANDLOCK_ACCESS_FS_MAKE_SOCK (1ULL << 9)
+#define LANDLOCK_ACCESS_FS_MAKE_FIFO (1ULL << 10)
+#define LANDLOCK_ACCESS_FS_MAKE_BLOCK (1ULL << 11)
+#define LANDLOCK_ACCESS_FS_MAKE_SYM (1ULL << 12)
+
+#endif /* _UAPI_LINUX_LANDLOCK_H */
diff --git a/security/landlock/Kconfig b/security/landlock/Kconfig
index c1e862a38410..8e33c4e8ffb8 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_INODES
select SECURITY_PATH
help
Landlock is a sandboxing mechanism that enables processes to restrict
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..97b8e421f617
--- /dev/null
+++ b/security/landlock/fs.c
@@ -0,0 +1,692 @@
+// 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/bitops.h>
+#include <linux/bits.h>
+#include <linux/compiler_types.h>
+#include <linux/dcache.h>
+#include <linux/err.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/limits.h>
+#include <linux/list.h>
+#include <linux/lsm_hooks.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/path.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 "limits.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;
+ }
+
+ /*
+ * Protects against concurrent use by hook_sb_delete() of the reference
+ * to the underlying inode.
+ */
+ object->underobj = NULL;
+ /*
+ * Makes 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);
+ spin_unlock(&object->lock);
+ /*
+ * Because object->underobj was not NULL, hook_sb_delete() and
+ * get_inode_object() guarantee that it is safe to reset
+ * landlock_inode(inode)->object while it is not NULL. It is therefore
+ * not necessary to lock inode->i_lock.
+ */
+ rcu_assign_pointer(landlock_inode(inode)->object, NULL);
+ /*
+ * Now, new rules can safely be tied to @inode with get_inode_object().
+ */
+
+ 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 are 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);
+ if (IS_ERR(new_object))
+ return new_object;
+
+ /*
+ * Protects against concurrent calls to get_inode_object() or
+ * hook_sb_delete().
+ */
+ spin_lock(&inode->i_lock);
+ if (unlikely(rcu_access_pointer(inode_sec->object))) {
+ /* Someone else just created the object, bail out and retry. */
+ spin_unlock(&inode->i_lock);
+ kfree(new_object);
+
+ rcu_read_lock();
+ goto retry;
+ }
+
+ /*
+ * @inode will be released by hook_sb_delete() on its superblock
+ * shutdown, or by release_inode() when no more ruleset references the
+ * related object.
+ */
+ ihold(inode);
+ rcu_assign_pointer(inode_sec->object, new_object);
+ spin_unlock(&inode->i_lock);
+ return new_object;
+}
+
+/* All access rights that 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_object *object;
+
+ /* Files only get access rights that make sense. */
+ if (!d_is_dir(path->dentry) && (access_rights | ACCESS_FILE) !=
+ ACCESS_FILE)
+ return -EINVAL;
+ if (WARN_ON_ONCE(ruleset->num_layers != 1))
+ return -EINVAL;
+
+ /* Transforms relative access rights to absolute ones. */
+ access_rights |= LANDLOCK_MASK_ACCESS_FS & ~ruleset->fs_access_masks[0];
+ object = get_inode_object(d_backing_inode(path->dentry));
+ if (IS_ERR(object))
+ return PTR_ERR(object);
+ mutex_lock(&ruleset->lock);
+ err = landlock_insert_rule(ruleset, object, access_rights);
+ mutex_unlock(&ruleset->lock);
+ /*
+ * No need to check for an error because landlock_insert_rule()
+ * increments the refcount for the new object if needed.
+ */
+ landlock_put_object(object);
+ return err;
+}
+
+/* Access-control management */
+
+static inline u64 unmask_layers(
+ const struct landlock_ruleset *const domain,
+ const struct path *const path, const u32 access_request,
+ u64 layer_mask)
+{
+ const struct landlock_rule *rule;
+ const struct inode *inode;
+ size_t i;
+
+ if (d_is_negative(path->dentry))
+ /* Ignore nonexistent leafs. */
+ return layer_mask;
+ inode = d_backing_inode(path->dentry);
+ rcu_read_lock();
+ rule = landlock_find_rule(domain,
+ rcu_dereference(landlock_inode(inode)->object));
+ rcu_read_unlock();
+ if (!rule)
+ return layer_mask;
+
+ /*
+ * An access is granted if, for each policy layer, at least one rule
+ * encountered on the pathwalk grants the requested accesses,
+ * regardless of their position in the layer stack. We must then check
+ * the remaining layers for each inode, from the first added layer to
+ * the last one.
+ */
+ for (i = 0; i < rule->num_layers; i++) {
+ const struct landlock_layer *const layer = &rule->layers[i];
+ const u64 layer_level = BIT_ULL(layer->level - 1);
+
+ /* Checks that the layer grants access to the full request. */
+ if ((layer->access & access_request) == access_request) {
+ layer_mask &= ~layer_level;
+
+ if (layer_mask == 0)
+ return layer_mask;
+ }
+ }
+ return layer_mask;
+}
+
+static int check_access_path(const struct landlock_ruleset *const domain,
+ const struct path *const path, u32 access_request)
+{
+ bool allowed = false;
+ struct path walker_path;
+ u64 layer_mask;
+ size_t i;
+
+ /* Make sure all layers can be checked. */
+ BUILD_BUG_ON(BITS_PER_TYPE(layer_mask) < LANDLOCK_MAX_NUM_LAYERS);
+
+ if (!access_request)
+ return 0;
+ 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/<pid>/fd/<file-descriptor> .
+ */
+ 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->num_layers < 1))
+ return -EACCES;
+
+ /* Saves all layers handling a subset of requested accesses. */
+ layer_mask = 0;
+ for (i = 0; i < domain->num_layers; i++) {
+ if (domain->fs_access_masks[i] & access_request)
+ layer_mask |= BIT_ULL(i);
+ }
+ /* An access request not handled by the domain is allowed. */
+ if (layer_mask == 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 (true) {
+ struct dentry *parent_dentry;
+
+ layer_mask = unmask_layers(domain, &walker_path,
+ access_request, layer_mask);
+ if (layer_mask == 0) {
+ /* Stops when a rule from each layer grants access. */
+ allowed = true;
+ break;
+ }
+
+jump_up:
+ 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.
+ */
+ allowed = 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/<pid>/ns/<namespace>).
+ */
+ allowed = !!(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 allowed ? 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);
+}
+
+/* Inode hooks */
+
+static void hook_inode_free_security(struct inode *const inode)
+{
+ /*
+ * All inodes must already have been untied from their object by
+ * release_inode() or hook_sb_delete().
+ */
+ WARN_ON_ONCE(landlock_inode(inode)->object);
+}
+
+/* Super-block hooks */
+
+/*
+ * Release the inodes used in a security policy.
+ *
+ * Cf. fsnotify_unmount_inodes() and invalidate_inodes()
+ */
+static void hook_sb_delete(struct super_block *const sb)
+{
+ struct inode *inode, *prev_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_object *object;
+
+ /* Only handles referenced inodes. */
+ if (!atomic_read(&inode->i_count))
+ continue;
+
+ /*
+ * Protects against concurrent modification of inode (e.g.
+ * from get_inode_object()).
+ */
+ spin_lock(&inode->i_lock);
+ /*
+ * Checks I_FREEING and I_WILL_FREE to protect against a race
+ * condition when release_inode() just called iput(), which
+ * could lead to a NULL dereference of inode->security or a
+ * second call to iput() for the same Landlock object. Also
+ * checks I_NEW because such inode cannot be tied to an object.
+ */
+ if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
+ spin_unlock(&inode->i_lock);
+ continue;
+ }
+
+ rcu_read_lock();
+ object = rcu_dereference(landlock_inode(inode)->object);
+ if (!object) {
+ rcu_read_unlock();
+ spin_unlock(&inode->i_lock);
+ continue;
+ }
+ /* Keeps a reference to this inode until the next loop walk. */
+ __iget(inode);
+ spin_unlock(&inode->i_lock);
+
+ /*
+ * If there is no concurrent release_inode() ongoing, then we
+ * are in charge of calling iput() on this inode, otherwise we
+ * will just wait for it to finish.
+ */
+ spin_lock(&object->lock);
+ if (object->underobj == inode) {
+ object->underobj = NULL;
+ spin_unlock(&object->lock);
+ rcu_read_unlock();
+
+ /*
+ * Because object->underobj was not NULL,
+ * release_inode() and get_inode_object() guarantee
+ * that it is safe to reset
+ * landlock_inode(inode)->object while it is not NULL.
+ * It is therefore not necessary to lock inode->i_lock.
+ */
+ rcu_assign_pointer(landlock_inode(inode)->object, NULL);
+ /*
+ * At this point, we own the ihold() reference that was
+ * originally set up by get_inode_object() and the
+ * __iget() reference that we just set in this loop
+ * walk. Therefore the following call to iput() will
+ * not sleep nor drop the inode because there is now at
+ * least two references to it.
+ */
+ iput(inode);
+ } else {
+ spin_unlock(&object->lock);
+ rcu_read_unlock();
+ }
+
+ if (prev_inode) {
+ /*
+ * At this point, we still own the __iget() reference
+ * that we just set in this loop walk. 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 inode reference from the
+ * previous loop walk, which is not needed anymore.
+ */
+ iput(prev_inode);
+ cond_resched();
+ spin_lock(&sb->s_inode_list_lock);
+ }
+ prev_inode = inode;
+ }
+ spin_unlock(&sb->s_inode_list_lock);
+
+ /* Puts the inode reference from the last loop walk, if any. */
+ if (prev_inode)
+ iput(prev_inode);
+ /* Waits 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
+ * topology (i.e. the mount namespace), changing it may grant access to files
+ * not previously allowed.
+ *
+ * To make it simple, deny any filesystem topology 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 flag).
+ */
+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. Moreover, it can be used to restrict the
+ * view of the filesystem.
+ */
+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)
+ /* Gracefully forbids reparenting. */
+ return -EXDEV;
+ if (unlikely(d_is_negative(old_dentry)))
+ return -ENOENT;
+ 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)
+ /* Gracefully forbids reparenting. */
+ return -EXDEV;
+ if (unlikely(d_is_negative(old_dentry)))
+ return -ENOENT;
+ /* 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);
+}
+
+/* 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;
+ }
+ 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 check_access_path(dom, &file->f_path, get_file_access(file));
+}
+
+static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
+ LSM_HOOK_INIT(inode_free_security, hook_inode_free_security),
+
+ 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(file_open, hook_file_open),
+};
+
+__init void landlock_add_fs_hooks(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..187284b421c9
--- /dev/null
+++ b/security/landlock/fs.h
@@ -0,0 +1,70 @@
+/* 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 "ruleset.h"
+#include "setup.h"
+
+/**
+ * struct landlock_inode_security - Inode security blob
+ *
+ * Enable to reference a &struct landlock_object tied to an inode (i.e.
+ * underlying object).
+ */
+struct landlock_inode_security {
+ /**
+ * @object: Weak pointer to an allocated object. All assignments of a
+ * new object are protected by the underlying inode->i_lock. However,
+ * atomically disassociating @object from the inode is only 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() and
+ * hook_sb_delete()). Indeed, such disassociation doesn't require
+ * inode->i_lock thanks to the careful rcu_access_pointer() check
+ * performed by get_inode_object().
+ */
+ struct landlock_object __rcu *object;
+};
+
+/**
+ * struct landlock_superblock_security - Superblock security blob
+ *
+ * Enable hook_sb_delete() to wait for concurrent calls to release_inode().
+ */
+struct landlock_superblock_security {
+ /**
+ * @inode_refs: Number of pending inodes (from this superblock) that
+ * are being released by release_inode().
+ * 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_fs_hooks(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/limits.h b/security/landlock/limits.h
index b734f597bb0e..2a0a1095ee27 100644
--- a/security/landlock/limits.h
+++ b/security/landlock/limits.h
@@ -10,8 +10,12 @@
#define _SECURITY_LANDLOCK_LIMITS_H
#include <linux/limits.h>
+#include <uapi/linux/landlock.h>
#define LANDLOCK_MAX_NUM_LAYERS 64
#define LANDLOCK_MAX_NUM_RULES U32_MAX
+#define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_MAKE_SYM
+#define LANDLOCK_MASK_ACCESS_FS ((LANDLOCK_LAST_ACCESS_FS << 1) - 1)
+
#endif /* _SECURITY_LANDLOCK_LIMITS_H */
diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index 2e616f6d5274..ec72b9262bf3 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -116,9 +116,11 @@ static void build_check_ruleset(void)
.num_rules = ~0,
.num_layers = ~0,
};
+ typeof(ruleset.fs_access_masks[0]) fs_access_mask = ~0;
BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
+ BUILD_BUG_ON(fs_access_mask < LANDLOCK_MASK_ACCESS_FS);
}
/**
@@ -217,9 +219,11 @@ static void build_check_layer(void)
{
const struct landlock_layer layer = {
.level = ~0,
+ .access = ~0,
};
BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS);
+ BUILD_BUG_ON(layer.access < LANDLOCK_MASK_ACCESS_FS);
}
/* @ruleset must be locked by the caller. */
diff --git a/security/landlock/setup.c b/security/landlock/setup.c
index a5d6ef334991..f8e8e980454c 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_cred_hooks();
landlock_add_ptrace_hooks();
+ landlock_add_fs_hooks();
+ 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 */