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Date: Wed, 16 Mar 2022 21:26:08 -0400
From: Paul Moore <paul@...l-moore.com>
To: Mickaël Salaün <mic@...ikod.net>
Cc: James Morris <jmorris@...ei.org>,
"Serge E . Hallyn" <serge@...lyn.com>,
Al Viro <viro@...iv.linux.org.uk>,
Jann Horn <jannh@...gle.com>,
Kees Cook <keescook@...omium.org>,
Konstantin Meskhidze <konstantin.meskhidze@...wei.com>,
Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org,
Mickaël Salaün <mic@...ux.microsoft.com>
Subject: Re: [PATCH v1 01/11] landlock: Define access_mask_t to enforce a
consistent access mask size
On Mon, Feb 21, 2022 at 4:15 PM Mickaël Salaün <mic@...ikod.net> wrote:
>
> From: Mickaël Salaün <mic@...ux.microsoft.com>
>
> 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.
>
> Signed-off-by: Mickaël Salaün <mic@...ux.microsoft.com>
> Link: https://lore.kernel.org/r/20220221212522.320243-2-mic@digikod.net
> ---
> security/landlock/fs.c | 19 ++++++++++---------
> security/landlock/fs.h | 2 +-
> security/landlock/limits.h | 2 ++
> security/landlock/ruleset.c | 6 ++++--
> security/landlock/ruleset.h | 17 +++++++++++++----
> 5 files changed, 30 insertions(+), 16 deletions(-)
>
> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> index 97b8e421f617..9de2a460a762 100644
> --- a/security/landlock/fs.c
> +++ b/security/landlock/fs.c
> @@ -150,7 +150,7 @@ static struct landlock_object *get_inode_object(struct inode *const inode)
> * @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;
> @@ -182,8 +182,8 @@ int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
>
> 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 path *const path,
> + const access_mask_t access_request, u64 layer_mask)
> {
> const struct landlock_rule *rule;
> const struct inode *inode;
> @@ -223,7 +223,8 @@ static inline u64 unmask_layers(
> }
>
> 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;
> @@ -308,7 +309,7 @@ static int check_access_path(const struct landlock_ruleset *const domain,
> }
>
> 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();
> @@ -511,7 +512,7 @@ static int hook_sb_pivotroot(const struct path *const old_path,
>
> /* 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:
> @@ -563,7 +564,7 @@ static int hook_path_link(struct dentry *const old_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;
> @@ -631,9 +632,9 @@ static int hook_path_rmdir(const struct path *const dir,
>
> /* 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. */
> diff --git a/security/landlock/fs.h b/security/landlock/fs.h
> index 187284b421c9..74be312aad96 100644
> --- a/security/landlock/fs.h
> +++ b/security/landlock/fs.h
> @@ -65,6 +65,6 @@ static inline struct landlock_superblock_security *landlock_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);
> + const struct path *const path, access_mask_t access_hierarchy);
>
> #endif /* _SECURITY_LANDLOCK_FS_H */
> diff --git a/security/landlock/limits.h b/security/landlock/limits.h
> index 2a0a1095ee27..458d1de32ed5 100644
> --- 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>
>
> @@ -17,5 +18,6 @@
>
> #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)
The line above, and the static_assert() in ruleset.h are clever. I'll
admit I didn't even know the hweightX() macros existed until looking
at this code :)
However, the LANDLOCK_NUM_ACCESS_FS is never really going to be used
outside the static_assert() in ruleset.h is it? I wonder if it would
be better to skip the extra macro and rewrite the static_assert like
this:
static_assert(BITS_PER_TYPE(access_mask_t) >=
__const_hweight64(LANDLOCK_MASK_ACCESS_FS));
If not, I might suggest changing LANDLOCK_NUM_ACCESS_FS to
LANDLOCK_BITS_ACCESS_FS or something similar.
> diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
> index 2d3ed7ec5a0a..7e7cac68e443 100644
> --- 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);
--
paul-moore.com
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