[PATCH v3 05/13] lib/crypto: md5: Provide a function for zeroizing hmac_md5 structures

[Thomas Huth <thuth@redhat.com>]

In certain cases crypto code functions need to zeroize their local
hmac_md5_key or hmac_md5_ctx structures after use to avoid leaking
sensitive material on the stack.
Provide hmac_md5_zeroize_key() and hmac_md5_zeroize_ctx() helper
functions that e.g. can be used with __cleanup() to automatically
zeroize the structure when it goes out of scope.

While we're at it, replace the related memzero_explicit() call in
lib/crypto/md5.c with a call to the new helper function.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 include/crypto/md5.h | 19 +++++++++++++++++++
 lib/crypto/md5.c     |  2 +-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/include/crypto/md5.h b/include/crypto/md5.h
index c47aedfe67ecd..1ed89c15b662c 100644
--- a/include/crypto/md5.h
+++ b/include/crypto/md5.h
@@ -4,6 +4,7 @@
 
 #include <crypto/hash.h>
 #include <linux/types.h>
+#include <linux/string.h>
 
 #define MD5_DIGEST_SIZE		16
 #define MD5_HMAC_BLOCK_SIZE	64
@@ -98,6 +99,15 @@ struct hmac_md5_key {
 	struct md5_block_state ostate;
 };
 
+/**
+ * hmac_md5_zeroize_key() - Zeroize an hmac_md5_key structure
+ * @key: The hmac_md5_key to zeroize
+ */
+static inline void hmac_md5_zeroize_key(struct hmac_md5_key *key)
+{
+	memzero_explicit(key, sizeof(*key));
+}
+
 /**
  * struct hmac_md5_ctx - Context for computing HMAC-MD5 of a message
  * @hash_ctx: private
@@ -108,6 +118,15 @@ struct hmac_md5_ctx {
 	struct md5_block_state ostate;
 };
 
+/**
+ * hmac_md5_zeroize_ctx() - Zeroize an hmac_md5_ctx structure
+ * @ctx: The hmac_md5_ctx context to zeroize
+ */
+static inline void hmac_md5_zeroize_ctx(struct hmac_md5_ctx *ctx)
+{
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+
 /**
  * hmac_md5_preparekey() - Prepare a key for HMAC-MD5
  * @key: (output) the key structure to initialize
diff --git a/lib/crypto/md5.c b/lib/crypto/md5.c
index 3d2b017a0525a..a8ee57600012d 100644
--- a/lib/crypto/md5.c
+++ b/lib/crypto/md5.c
@@ -271,7 +271,7 @@ void hmac_md5_final(struct hmac_md5_ctx *ctx, u8 out[MD5_DIGEST_SIZE])
 	cpu_to_le32_array(ctx->ostate.h, ARRAY_SIZE(ctx->ostate.h));
 	memcpy(out, ctx->ostate.h, MD5_DIGEST_SIZE);
 
-	memzero_explicit(ctx, sizeof(*ctx));
+	hmac_md5_zeroize_ctx(ctx);
 }
 EXPORT_SYMBOL_GPL(hmac_md5_final);
 
-- 
2.55.0