EAP-AKA: Validate RES Length field in AT_RES

This change breaks interoperability with older wpa_supplicant versions
(everything up to and including wpa_supplicant 0.5.10 and 0.6.5) which
incorrectly used this field as number of bytes, not bits, in RES.

src/eap_common/eap_sim_common.c

@@ -517,6 +517,7 @@ int eap_sim_parse_attr(const u8 *start, const u8 *end,
 			break;
 		case EAP_SIM_AT_RES:
 			wpa_printf(MSG_DEBUG, "EAP-SIM: AT_RES");
+			attr->res_len_bits = WPA_GET_BE16(apos);
 			apos += 2;
 			alen -= 2;
 			if (!aka || alen < EAP_AKA_MIN_RES_LEN ||

src/eap_common/eap_sim_common.h

@@ -137,6 +137,7 @@ struct eap_sim_attrs {
 	const u8 *checkcode;
 	size_t num_chal, version_list_len, encr_data_len;
 	size_t next_pseudonym_len, next_reauth_id_len, identity_len, res_len;
+	size_t res_len_bits;
 	size_t checkcode_len;
 	enum eap_sim_id_req id_req;
 	int notification, counter, selected_version, client_error_code;

src/eap_server/eap_aka.c

@@ -666,10 +666,19 @@ static void eap_aka_process_challenge(struct eap_sm *sm,
 		return;
 	}
 
-	if (attr->res == NULL || attr->res_len != data->res_len ||
+	/*
+	 * AT_RES is padded, so verify that there is enough room for RES and
+	 * that the RES length in bits matches with the expected RES.
+	 */
+	if (attr->res == NULL || attr->res_len < data->res_len ||
+	    attr->res_len_bits != data->res_len * 8 ||
 	    os_memcmp(attr->res, data->res, data->res_len) != 0) {
 		wpa_printf(MSG_WARNING, "EAP-AKA: Challenge message did not "
-			   "include valid AT_RES");
+			   "include valid AT_RES (attr len=%lu, res len=%lu "
+			   "bits, expected %lu bits)",
+			   (unsigned long) attr->res_len,
+			   (unsigned long) attr->res_len_bits,
+			   (unsigned long) data->res_len);
 		data->notification = EAP_SIM_GENERAL_FAILURE_BEFORE_AUTH;
 		eap_aka_state(data, NOTIFICATION);
 		return;