hkdf zeroization fix

Reviewed-by: Paul Yang <yang.yang@baishancloud.com>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/7106)

(cherry picked from commit 64ed55ab033f1bfa795d46f0ecc61c313204b418)

1 files changed, 4 insertions, 4 deletions

diff --git a/crypto/kdf/hkdf.c b/crypto/kdf/hkdf.c
index 00b95b5a88..6d38a2fded 100644
--- a/crypto/kdf/hkdf.c
+++ b/crypto/kdf/hkdf.c
@@ -234,6 +234,7 @@ static unsigned char *HKDF_Expand(const EVP_MD *evp_md,
                                   unsigned char *okm, size_t okm_len)
 {
     HMAC_CTX *hmac;
+    unsigned char *ret = NULL;
 
     unsigned int i;
 
@@ -283,11 +284,10 @@ static unsigned char *HKDF_Expand(const EVP_MD *evp_md,
 
         done_len += copy_len;
     }
-
-    HMAC_CTX_free(hmac);
-    return okm;
+    ret = okm;
 
  err:
+    OPENSSL_cleanse(prev, sizeof(prev));
     HMAC_CTX_free(hmac);
-    return NULL;
+    return ret;
 }