Re: [PATCH] kernel: Add Mount Option For Efivarfs

[Ard Biesheuvel]

On Tue, 22 Aug 2023 at 18:24, Jiao Zhou <jiaozhou@xxxxxxxxxx> wrote:
>
> Add uid and gid in efivarfs's mount option, so that
> we can mount the file system with ownership. This approach
> is used by a number of other filesystems that don't have
> native support for ownership
>
> Signed-off-by: Jiao Zhou <jiaozhou@xxxxxxxxxx>
> ---
>
>  fs/efivarfs/inode.c    |  4 ++++
>  fs/efivarfs/internal.h |  9 +++++++
>  fs/efivarfs/super.c    | 54 ++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 67 insertions(+)
>
> diff --git a/fs/efivarfs/inode.c b/fs/efivarfs/inode.c
> index b973a2c03dde..86175e229b0f 100644
> --- a/fs/efivarfs/inode.c
> +++ b/fs/efivarfs/inode.c
> @@ -20,9 +20,13 @@ struct inode *efivarfs_get_inode(struct super_block *sb,
>                                 const struct inode *dir, int mode,
>                                 dev_t dev, bool is_removable)
>  {
> +       struct efivarfs_fs_info *fsi = sb->s_fs_info;
>         struct inode *inode = new_inode(sb);
> +       struct efivarfs_mount_opts *opts = &fsi->mount_opts;
>
>         if (inode) {
> +               inode->i_uid = opts->uid;
> +               inode->i_gid = opts->gid;
>                 inode->i_ino = get_next_ino();
>                 inode->i_mode = mode;
>                 inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
> diff --git a/fs/efivarfs/internal.h b/fs/efivarfs/internal.h
> index 8ebf3a6a8aa2..2c7b6b24df19 100644
> --- a/fs/efivarfs/internal.h
> +++ b/fs/efivarfs/internal.h
> @@ -48,6 +48,15 @@ bool efivar_validate(efi_guid_t vendor, efi_char16_t *var_name, u8 *data,
>  bool efivar_variable_is_removable(efi_guid_t vendor, const char *name,
>                                   size_t len);
>
> +struct efivarfs_mount_opts {
> +       kuid_t uid;
> +       kgid_t gid;
> +};
> +
> +struct efivarfs_fs_info {
> +       struct efivarfs_mount_opts mount_opts;
> +};
> +
>  extern const struct file_operations efivarfs_file_operations;
>  extern const struct inode_operations efivarfs_dir_inode_operations;
>  extern bool efivarfs_valid_name(const char *str, int len);
> diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
> index e028fafa04f3..e3c81fac8208 100644
> --- a/fs/efivarfs/super.c
> +++ b/fs/efivarfs/super.c
> @@ -8,6 +8,7 @@
>  #include <linux/efi.h>
>  #include <linux/fs.h>
>  #include <linux/fs_context.h>
> +#include <linux/fs_parser.h>
>  #include <linux/module.h>
>  #include <linux/pagemap.h>
>  #include <linux/ucs2_string.h>
> @@ -60,10 +61,27 @@ static int efivarfs_statfs(struct dentry *dentry, struct kstatfs *buf)
>
>         return 0;
>  }
> +static int efivarfs_show_options(struct seq_file *m, struct dentry *root)
> +{
> +       struct super_block *sb = root->d_sb;
> +       struct efivarfs_fs_info *sbi = sb->s_fs_info;
> +       struct efivarfs_mount_opts *opts = &sbi->mount_opts;
> +
> +       /* Show partition info */
> +       if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
> +               seq_printf(m, ",uid=%u",
> +                               from_kuid_munged(&init_user_ns, opts->uid));
> +       if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
> +               seq_printf(m, ",gid=%u",
> +                               from_kgid_munged(&init_user_ns, opts->gid));
> +       return 0;
> +}
> +
>  static const struct super_operations efivarfs_ops = {
>         .statfs = efivarfs_statfs,
>         .drop_inode = generic_delete_inode,
>         .evict_inode = efivarfs_evict_inode,
> +       .show_options   = efivarfs_show_options,
>  };
>
>  /*
> @@ -225,6 +243,40 @@ static int efivarfs_destroy(struct efivar_entry *entry, void *data)
>         return 0;
>  }
>
> +enum {
> +       Opt_uid, Opt_gid,
> +};
> +
> +static const struct fs_parameter_spec efivarfs_parameters[] = {
> +       fsparam_u32("uid",                      Opt_uid),
> +       fsparam_u32("gid",                      Opt_gid),
> +};
> +

The kasan report seems to suggest that this array needs a trailing
empty entry {}


> +static int efivarfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
> +{
> +       struct efivarfs_fs_info *sbi = fc->s_fs_info;
> +       struct efivarfs_mount_opts *opts = &sbi->mount_opts;
> +       struct fs_parse_result result;
> +       int opt;
> +
> +       opt = fs_parse(fc, efivarfs_parameters, param, &result);
> +       if (opt < 0)
> +               return opt;
> +
> +       switch (opt) {
> +       case Opt_uid:
> +               opts->uid = make_kuid(current_user_ns(), result.uint_32);
> +               break;
> +       case Opt_gid:
> +               opts->gid = make_kgid(current_user_ns(), result.uint_32);
> +               break;
> +       default:
> +               return -EINVAL;
> +       }
> +
> +       return 0;
> +}
> +
>  static int efivarfs_fill_super(struct super_block *sb, struct fs_context *fc)
>  {
>         struct inode *inode = NULL;
> @@ -271,6 +323,7 @@ static int efivarfs_get_tree(struct fs_context *fc)
>
>  static const struct fs_context_operations efivarfs_context_ops = {
>         .get_tree       = efivarfs_get_tree,
> +       .parse_param    = efivarfs_parse_param,
>  };
>
>  static int efivarfs_init_fs_context(struct fs_context *fc)
> @@ -295,6 +348,7 @@ static struct file_system_type efivarfs_type = {
>         .name    = "efivarfs",
>         .init_fs_context = efivarfs_init_fs_context,
>         .kill_sb = efivarfs_kill_sb,
> +       .parameters             = efivarfs_parameters,
>  };
>
>  static __init int efivarfs_init(void)
> --
> 2.42.0.rc1.204.g551eb34607-goog
>