Cleanse the key log buffer.

Reviewed-by: NMatthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/7564)

(cherry picked from commit e931f370aa38d8645b35fb8d6260cb44d37b6b61)

ssl/ssl_lib.c

@@ -5117,7 +5117,7 @@ static int nss_keylog_int(const char *prefix,
      * hexadecimal, so we need a buffer that is twice their lengths.
      */
     prefix_len = strlen(prefix);
-    out_len = prefix_len + (2*parameter_1_len) + (2*parameter_2_len) + 3;
+    out_len = prefix_len + (2 * parameter_1_len) + (2 * parameter_2_len) + 3;
     if ((out = cursor = OPENSSL_malloc(out_len)) == NULL) {
         SSLfatal(ssl, SSL_AD_INTERNAL_ERROR, SSL_F_NSS_KEYLOG_INT,
                  ERR_R_MALLOC_FAILURE);
@@ -5141,7 +5141,7 @@ static int nss_keylog_int(const char *prefix,
     *cursor = '\0';
 
     ssl->ctx->keylog_callback(ssl, (const char *)out);
-    OPENSSL_free(out);
+    OPENSSL_clear_free(out, out_len);
     return 1;
 
 }