[PATCH 5.18 787/879] landlock: Define access_mask_t to enforce a consistent access mask size

Greg Kroah-Hartman
2022-06-08T01:42:04Z

From: Mickaël Salaün <mic@digikod.net>

commit 5f2ff33e10843ef51275c8611bdb7b49537aba5d upstream.

Create and use the access_mask_t typedef to enforce a consistent access
mask size and uniformly use a 16-bits type. This will helps transition
to a 32-bits value one day.

Add a build check to make sure all (filesystem) access rights fit in.
This will be extended with a following commit.

Reviewed-by: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20220506161102.525323-2-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
security/landlock/fs.c | 19 +++++++++++--------
security/landlock/fs.h | 2 +-
security/landlock/limits.h | 2 ++
security/landlock/ruleset.c | 6 ++++--
security/landlock/ruleset.h | 16 ++++++++++++----
5 files changed, 30 insertions(+), 15 deletions(-)

--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -152,7 +152,8 @@ retry:
* @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)
+ const struct path *const path,
+ access_mask_t access_rights)
{
int err;
struct landlock_object *object;
@@ -184,7 +185,8 @@ int landlock_append_fs_rule(struct landl

static inline u64 unmask_layers(const struct landlock_ruleset *const domain,
const struct path *const path,
- const u32 access_request, u64 layer_mask)
+ const access_mask_t access_request,
+ u64 layer_mask)
{
const struct landlock_rule *rule;
const struct inode *inode;
@@ -224,7 +226,8 @@ static inline u64 unmask_layers(const st
}

static int check_access_path(const struct landlock_ruleset *const domain,
- const struct path *const path, u32 access_request)
+ const struct path *const path,
+ const access_mask_t access_request)
{
bool allowed = false;
struct path walker_path;
@@ -309,7 +312,7 @@ jump_up:
}

static inline int current_check_access_path(const struct path *const path,
- const u32 access_request)
+ const access_mask_t access_request)
{
const struct landlock_ruleset *const dom =
landlock_get_current_domain();
@@ -512,7 +515,7 @@ static int hook_sb_pivotroot(const struc

/* Path hooks */

-static inline u32 get_mode_access(const umode_t mode)
+static inline access_mask_t get_mode_access(const umode_t mode)
{
switch (mode & S_IFMT) {
case S_IFLNK:
@@ -565,7 +568,7 @@ static int hook_path_link(struct dentry
get_mode_access(d_backing_inode(old_dentry)->i_mode));
}

-static inline u32 maybe_remove(const struct dentry *const dentry)
+static inline access_mask_t maybe_remove(const struct dentry *const dentry)
{
if (d_is_negative(dentry))
return 0;
@@ -635,9 +638,9 @@ static int hook_path_rmdir(const struct

/* File hooks */

-static inline u32 get_file_access(const struct file *const file)
+static inline access_mask_t get_file_access(const struct file *const file)
{
- u32 access = 0;
+ access_mask_t access = 0;

if (file->f_mode & FMODE_READ) {
/* A directory can only be opened in read mode. */
--- a/security/landlock/fs.h
+++ b/security/landlock/fs.h
@@ -66,6 +66,6 @@ __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);
+ access_mask_t access_hierarchy);

#endif /* _SECURITY_LANDLOCK_FS_H */
--- a/security/landlock/limits.h
+++ b/security/landlock/limits.h
@@ -9,6 +9,7 @@
#ifndef _SECURITY_LANDLOCK_LIMITS_H
#define _SECURITY_LANDLOCK_LIMITS_H

+#include <linux/bitops.h>
#include <linux/limits.h>
#include <uapi/linux/landlock.h>

@@ -19,6 +20,7 @@

#define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_MAKE_SYM
#define LANDLOCK_MASK_ACCESS_FS ((LANDLOCK_LAST_ACCESS_FS << 1) - 1)
+#define LANDLOCK_NUM_ACCESS_FS __const_hweight64(LANDLOCK_MASK_ACCESS_FS)

/* clang-format on */

--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -45,7 +45,8 @@ static struct landlock_ruleset *create_r
return new_ruleset;
}

-struct landlock_ruleset *landlock_create_ruleset(const u32 fs_access_mask)
+struct landlock_ruleset *
+landlock_create_ruleset(const access_mask_t fs_access_mask)
{
struct landlock_ruleset *new_ruleset;

@@ -228,7 +229,8 @@ static void build_check_layer(void)

/* @ruleset must be locked by the caller. */
int landlock_insert_rule(struct landlock_ruleset *const ruleset,
- struct landlock_object *const object, const u32 access)
+ struct landlock_object *const object,
+ const access_mask_t access)
{
struct landlock_layer layers[] = { {
.access = access,
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -9,13 +9,20 @@
#ifndef _SECURITY_LANDLOCK_RULESET_H
#define _SECURITY_LANDLOCK_RULESET_H

+#include <linux/bitops.h>
+#include <linux/build_bug.h>
#include <linux/mutex.h>
#include <linux/rbtree.h>
#include <linux/refcount.h>
#include <linux/workqueue.h>

+#include "limits.h"
#include "object.h"

+typedef u16 access_mask_t;
+/* Makes sure all filesystem access rights can be stored. */
+static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS);
+
/**
* struct landlock_layer - Access rights for a given layer
*/
@@ -28,7 +35,7 @@ struct landlock_layer {
* @access: Bitfield of allowed actions on the kernel object. They are
* relative to the object type (e.g. %LANDLOCK_ACTION_FS_READ).
*/
- u16 access;
+ access_mask_t access;
};

/**
@@ -135,19 +142,20 @@ struct landlock_ruleset {
* layers are set once and never changed for the
* lifetime of the ruleset.
*/
- u16 fs_access_masks[];
+ access_mask_t fs_access_masks[];
};
};
};

-struct landlock_ruleset *landlock_create_ruleset(const u32 fs_access_mask);
+struct landlock_ruleset *
+landlock_create_ruleset(const access_mask_t fs_access_mask);

void landlock_put_ruleset(struct landlock_ruleset *const ruleset);
void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset);

int landlock_insert_rule(struct landlock_ruleset *const ruleset,
struct landlock_object *const object,
- const u32 access);
+ const access_mask_t access);

struct landlock_ruleset *
landlock_merge_ruleset(struct landlock_ruleset *const parent,