[PATCH v2 08/13] lib/crypto: sha1: Provide functions for zeroizing hmac_sha1 structures

[Thomas Huth]

In certain cases crypto code needs to zeroize their local hmac_sha1_key
or hmac_sha1_ctx structures after use to avoid leaking sensitive material.
Provide hmac_sha1_zeroize_key() and hmac_sha1_zeroize_ctx() helper
functions that e.g. can be used with __cleanup() to automatically zeroize
the structures when they go out of scope.

While we're at it, replace the related memzero_explicit() call in
lib/crypto/sha1.c with a call to the new helper function.

Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx>
---
 include/crypto/sha1.h | 19 +++++++++++++++++++
 lib/crypto/sha1.c     |  2 +-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/include/crypto/sha1.h b/include/crypto/sha1.h
index 4d973e016cd69..bc0046bffeaee 100644
--- a/include/crypto/sha1.h
+++ b/include/crypto/sha1.h
@@ -7,6 +7,7 @@
 #define _CRYPTO_SHA1_H
 
 #include <linux/types.h>
+#include <linux/string.h>
 
 #define SHA1_DIGEST_SIZE        20
 #define SHA1_BLOCK_SIZE         64
@@ -96,6 +97,15 @@ struct hmac_sha1_key {
 	struct sha1_block_state ostate;
 };
 
+/**
+ * hmac_sha1_zeroize_key() - Zeroize an hmac_sha1_key structure
+ * @key: The hmac_sha1_key to zeroize
+ */
+static inline void hmac_sha1_zeroize_key(struct hmac_sha1_key *key)
+{
+	memzero_explicit(key, sizeof(*key));
+}
+
 /**
  * struct hmac_sha1_ctx - Context for computing HMAC-SHA1 of a message
  * @sha_ctx: private
@@ -106,6 +116,15 @@ struct hmac_sha1_ctx {
 	struct sha1_block_state ostate;
 };
 
+/**
+ * hmac_sha1_zeroize_ctx() - Zeroize an hmac_sha1_ctx structure
+ * @ctx: The hmac_sha1_ctx context to zeroize
+ */
+static inline void hmac_sha1_zeroize_ctx(struct hmac_sha1_ctx *ctx)
+{
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+
 /**
  * hmac_sha1_preparekey() - Prepare a key for HMAC-SHA1
  * @key: (output) the key structure to initialize
diff --git a/lib/crypto/sha1.c b/lib/crypto/sha1.c
index b687b89d97cb4..c4361ef77166e 100644
--- a/lib/crypto/sha1.c
+++ b/lib/crypto/sha1.c
@@ -275,7 +275,7 @@ void hmac_sha1_final(struct hmac_sha1_ctx *ctx, u8 out[SHA1_DIGEST_SIZE])
 	for (size_t i = 0; i < SHA1_DIGEST_SIZE; i += 4)
 		put_unaligned_be32(ctx->ostate.h[i / 4], out + i);
 
-	memzero_explicit(ctx, sizeof(*ctx));
+	hmac_sha1_zeroize_ctx(ctx);
 }
 EXPORT_SYMBOL_GPL(hmac_sha1_final);
 
-- 
2.55.0