Constant time memory comparison.

CVE-2014-4731.

Non-constant time comparisons usually require millions of packets
in order to get enough statistics.  This is VERY hard to do with
WiFi or wired 802.1X.  The delays on switch port open / close
are on the order of seconds.

src/modules/rlm_eap/types/rlm_eap_pwd/rlm_eap_pwd.c

@@ -370,7 +370,7 @@ static int mod_authenticate (void *arg, eap_handler_t *handler)
 		if ((id->prf != EAP_PWD_DEF_PRF) ||
 		    (id->random_function != EAP_PWD_DEF_RAND_FUN) ||
 		    (id->prep != EAP_PWD_PREP_NONE) ||
-		    (memcmp(id->token, (char *)&pwd_session->token, 4)) ||
+		    (CRYPTO_memcmp(id->token, (char *)&pwd_session->token, 4)) ||
 		    (id->group_num != ntohs(pwd_session->group_num))) {
 			RDEBUG2("pwd id response is invalid");
 			return 0;
@@ -561,7 +561,7 @@ static int mod_authenticate (void *arg, eap_handler_t *handler)
 			RDEBUG2("pwd exchange cannot compute peer's confirm");
 			return 0;
 		}
-		if (memcmp(peer_confirm, buf, SHA256_DIGEST_LENGTH)) {
+		if (CRYPTO_memcmp(peer_confirm, buf, SHA256_DIGEST_LENGTH)) {
 			RDEBUG2("pwd exchange fails: peer confirm is incorrect!");
 			return 0;
 		}