Re: [RFC PATCH v3 04/18] fs: add ->s_master_keys to struct super_block

[Richard Weinberger <richard.weinberger@gmail.com>]

On Wed, Feb 20, 2019 at 7:55 AM Eric Biggers <ebiggers@kernel.org> wrote:
>
> From: Eric Biggers <ebiggers@google.com>
>
> Add an ->s_master_keys keyring to 'struct super_block'.  New fscrypt
> ioctls will allow adding and removing encryption keys from this keyring.
> This will enable solving multiple interrelated problems with how fscrypt
> keys are provided and managed currently, including:
>
> - Making the key status (which is currently per-process) match the
>   filesystem-level status of which encrypted files are "unlocked".
>
> - Supporting a proper API to remove encryption keys, "locking" the
>   corresponding encrypted files.
>
> - Caching an HMAC transform for each master key, allowing the use of
>   HKDF while still retaining good performance.
>
> - Preventing denial of service via keyctl_invalidate().
>
> Similar to the existing ->s_cop, the keyring is added to the VFS-level
> superblock struct rather than separately to the ext4, f2fs, and ubifs
> superblock structs so that it can be used by the shared code in
> fs/crypto/.  To minimize overhead, the keyring will only be allocated if
> userspace actually adds a key; otherwise will stay NULL.
>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>  fs/super.c         | 3 +++
>  include/linux/fs.h | 1 +
>  2 files changed, 4 insertions(+)
>
> diff --git a/fs/super.c b/fs/super.c
> index 48e25eba8465..7ca05dda905c 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -291,6 +291,9 @@ static void __put_super(struct super_block *s)
>                 security_sb_free(s);
>                 put_user_ns(s->s_user_ns);
>                 kfree(s->s_subtype);
> +#ifdef CONFIG_FS_ENCRYPTION
> +               key_put(s->s_master_keys);
> +#endif

Please wrap this in a static inline function such that you can get rid
of the ifdef here.
Just like put_user_ns() does.

-- 
Thanks,
//richard