[PATCH] fscrypt: add comments that describe the HKDF info strings

[PATCH] fscrypt: add comments that describe the HKDF info strings

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

Each HKDF context byte is associated with a specific format of the
remaining part of the application-specific info string.  Add comments so
that it's easier to keep track of what these all are.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/fscrypt_private.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index 5bb40d0109c8..0f154bdbc14b 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -312,13 +312,13 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
  * outputs are unique and cryptographically isolated, i.e. knowledge of one
  * output doesn't reveal another.
  */
-#define HKDF_CONTEXT_KEY_IDENTIFIER	1
-#define HKDF_CONTEXT_PER_FILE_ENC_KEY	2
-#define HKDF_CONTEXT_DIRECT_KEY		3
-#define HKDF_CONTEXT_IV_INO_LBLK_64_KEY	4
-#define HKDF_CONTEXT_DIRHASH_KEY	5
-#define HKDF_CONTEXT_IV_INO_LBLK_32_KEY	6
-#define HKDF_CONTEXT_INODE_HASH_KEY	7
+#define HKDF_CONTEXT_KEY_IDENTIFIER	1 /* info=<empty>		*/
+#define HKDF_CONTEXT_PER_FILE_ENC_KEY	2 /* info=file_nonce		*/
+#define HKDF_CONTEXT_DIRECT_KEY		3 /* info=mode_num		*/
+#define HKDF_CONTEXT_IV_INO_LBLK_64_KEY	4 /* info=mode_num||fs_uuid	*/
+#define HKDF_CONTEXT_DIRHASH_KEY	5 /* info=file_nonce		*/
+#define HKDF_CONTEXT_IV_INO_LBLK_32_KEY	6 /* info=mode_num||fs_uuid	*/
+#define HKDF_CONTEXT_INODE_HASH_KEY	7 /* info=<empty>		*/
 
 int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context,
 			const u8 *info, unsigned int infolen,
-- 
2.27.0

Re: [PATCH] fscrypt: add comments that describe the HKDF info strings

[Eric Biggers]

On Wed, Jul 08, 2020 at 02:55:29PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> Each HKDF context byte is associated with a specific format of the
> remaining part of the application-specific info string.  Add comments so
> that it's easier to keep track of what these all are.
> 
> Signed-off-by: Eric Biggers <ebiggers@google.com>

Applied to fscrypt.git#master for 5.9.