[PATCH 4/7] selinux: Convert from sb_mount to granular mount hooks

[Stephen Smalley]

On Wed, Mar 18, 2026 at 2:44 PM Song Liu <song at kernel.org> wrote:
>
> Replace selinux_mount() with granular mount hooks, preserving the
> same permission checks:
>
> - mount_bind, mount_new, mount_change_type: FILE__MOUNTON
> - mount_remount, mount_reconfigure: FILESYSTEM__REMOUNT
> - mount_move: FILE__MOUNTON (reuses selinux_move_mount)
>
> The flags and data parameters are unused by SELinux.
>
> Code generated with the assistance of Claude, reviewed by human.
>
> Signed-off-by: Song Liu <song at kernel.org>

Not expecting you to do this, but after this lands, I think it would
make sense to revisit the SELinux checks and further specialize them
while providing backward compatibility.

Reviewed-by: Stephen Smalley <stephen.smalley.work at gmail.com>
Tested-by: Stephen Smalley <stephen.smalley.work at gmail.com

> ---
>  security/selinux/hooks.c | 47 ++++++++++++++++++++++++++++++----------
>  1 file changed, 35 insertions(+), 12 deletions(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index d8224ea113d1..415b5541ab9e 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2778,19 +2778,37 @@ static int selinux_sb_statfs(struct dentry *dentry)
>         return superblock_has_perm(cred, dentry->d_sb, FILESYSTEM__GETATTR, &ad);
>  }
>
> -static int selinux_mount(const char *dev_name,
> -                        const struct path *path,
> -                        const char *type,
> -                        unsigned long flags,
> -                        void *data)
> +static int selinux_mount_bind(const struct path *from, const struct path *to,
> +                             bool recurse)
>  {
> -       const struct cred *cred = current_cred();
> +       return path_has_perm(current_cred(), to, FILE__MOUNTON);
> +}
>
> -       if (flags & MS_REMOUNT)
> -               return superblock_has_perm(cred, path->dentry->d_sb,
> -                                          FILESYSTEM__REMOUNT, NULL);
> -       else
> -               return path_has_perm(cred, path, FILE__MOUNTON);
> +static int selinux_mount_new(struct fs_context *fc, const struct path *mp,
> +                            int mnt_flags, unsigned long flags, void *data)
> +{
> +       return path_has_perm(current_cred(), mp, FILE__MOUNTON);
> +}
> +
> +static int selinux_mount_remount(struct fs_context *fc, const struct path *mp,
> +                                int mnt_flags, unsigned long flags,
> +                                void *data)
> +{
> +       return superblock_has_perm(current_cred(), fc->root->d_sb,
> +                                  FILESYSTEM__REMOUNT, NULL);
> +}
> +
> +static int selinux_mount_reconfigure(const struct path *mp,
> +                                    unsigned int mnt_flags,
> +                                    unsigned long flags)
> +{
> +       return superblock_has_perm(current_cred(), mp->dentry->d_sb,
> +                                  FILESYSTEM__REMOUNT, NULL);
> +}
> +
> +static int selinux_mount_change_type(const struct path *mp, int ms_flags)
> +{
> +       return path_has_perm(current_cred(), mp, FILE__MOUNTON);
>  }
>
>  static int selinux_move_mount(const struct path *from_path,
> @@ -7449,7 +7467,12 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
>         LSM_HOOK_INIT(sb_kern_mount, selinux_sb_kern_mount),
>         LSM_HOOK_INIT(sb_show_options, selinux_sb_show_options),
>         LSM_HOOK_INIT(sb_statfs, selinux_sb_statfs),
> -       LSM_HOOK_INIT(sb_mount, selinux_mount),
> +       LSM_HOOK_INIT(mount_bind, selinux_mount_bind),
> +       LSM_HOOK_INIT(mount_new, selinux_mount_new),
> +       LSM_HOOK_INIT(mount_remount, selinux_mount_remount),
> +       LSM_HOOK_INIT(mount_reconfigure, selinux_mount_reconfigure),
> +       LSM_HOOK_INIT(mount_change_type, selinux_mount_change_type),
> +       LSM_HOOK_INIT(mount_move, selinux_move_mount),
>         LSM_HOOK_INIT(sb_umount, selinux_umount),
>         LSM_HOOK_INIT(sb_set_mnt_opts, selinux_set_mnt_opts),
>         LSM_HOOK_INIT(sb_clone_mnt_opts, selinux_sb_clone_mnt_opts),
> --
> 2.52.0
>