[RFC,v3,04/18] fs: add ->s_master_keys to struct super_block
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Message ID 20190220065249.32099-5-ebiggers@kernel.org
State Not Applicable
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Series
  • fscrypt: key management improvements
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Commit Message

Eric Biggers Feb. 20, 2019, 6:52 a.m. UTC
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(+)

Comments

Richard Weinberger Feb. 20, 2019, 11:19 p.m. UTC | #1
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.

Patch
diff mbox series

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
 		call_rcu(&s->rcu, destroy_super_rcu);
 	}
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ba7889bb9ef6..70d929ac89f9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1405,6 +1405,7 @@  struct super_block {
 	const struct xattr_handler **s_xattr;
 #ifdef CONFIG_FS_ENCRYPTION
 	const struct fscrypt_operations	*s_cop;
+	struct key		*s_master_keys; /* master crypto keys in use */
 #endif
 	struct hlist_bl_head	s_roots;	/* alternate root dentries for NFS */
 	struct list_head	s_mounts;	/* list of mounts; _not_ for fs use */