EAP-TLS server: Clear temporary buffer during EMSK derivation

Now that EMSK derivation is taken into use with ERP, it is better to
make sure the temporary MSK + EMSK buffer does not get left in heap
after use.

Signed-off-by: Jouni Malinen <j@w1.fi>

src/eap_server/eap_server_tls.c

@@ -287,7 +287,7 @@ static u8 * eap_tls_get_emsk(struct eap_sm *sm, void *priv, size_t *len)
 		if (emsk)
 			os_memcpy(emsk, eapKeyData + EAP_TLS_KEY_LEN,
 				  EAP_EMSK_LEN);
-		os_free(eapKeyData);
+		bin_clear_free(eapKeyData, EAP_TLS_KEY_LEN + EAP_EMSK_LEN);
 	} else
 		emsk = NULL;