[PATCH v3 02/13] lib/crypto: aes-xts: Provide function for zeroizing aes_xts_key

[Thomas Huth <thuth@redhat.com>]

In certain cases crypto code functions need to zeroize their local
aes_xts_key structures after use to avoid leaking sensitive material.
Provide an aes_xts_zeroize_key() helper function that e.g. can be
used with __cleanup() to automatically zeroize the struct when it
goes out of scope.

While we're at it, replace the related memzero_explicit() call in
lib/crypto/aes.c with a call to the new helper function.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 include/crypto/aes-xts.h | 13 +++++++++++--
 lib/crypto/aes.c         |  2 +-
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/include/crypto/aes-xts.h b/include/crypto/aes-xts.h
index b9e828265e58a..3a52e1cf40b57 100644
--- a/include/crypto/aes-xts.h
+++ b/include/crypto/aes-xts.h
@@ -22,6 +22,15 @@ struct aes_xts_key {
 	struct aes_enckey tweak_key;
 };
 
+/**
+ * aes_xts_zeroize_key() - Zeroize an aes_xts_key structure
+ * @key: The aes_xts_key to zeroize
+ */
+static inline void aes_xts_zeroize_key(struct aes_xts_key *key)
+{
+	memzero_explicit(key, sizeof(*key));
+}
+
 /**
  * aes_xts_preparekey() - Prepare a key for AES-XTS encryption and decryption
  * @key: (output) The key structure to initialize
@@ -30,8 +39,8 @@ struct aes_xts_key {
  * @flags: Optional flag XTS_FORBID_WEAK_KEYS to forbid keys whose two halves
  *	   are the same.
  *
- * Users should use memzero_explicit() to zeroize the key struct at the end of
- * its lifetime.  (But if this function fails, zeroization is unnecessary.)
+ * Users should use aes_xts_zeroize_key() to zeroize the key struct at the end
+ * of its lifetime.  (But if this function fails, zeroization is unnecessary.)
  *
  * Context: Any context.
  * Return:
diff --git a/lib/crypto/aes.c b/lib/crypto/aes.c
index 07c1d912ac365..34ef5deca0a79 100644
--- a/lib/crypto/aes.c
+++ b/lib/crypto/aes.c
@@ -1223,7 +1223,7 @@ int aes_xts_preparekey(struct aes_xts_key *key, const u8 *in_key,
 	return 0;
 
 out_zeroize:
-	memzero_explicit(key, sizeof(*key));
+	aes_xts_zeroize_key(key);
 	return err;
 }
 EXPORT_SYMBOL_GPL(aes_xts_preparekey);
-- 
2.55.0