EAP-pwd peer: Fix last fragment length validation

All but the last fragment had their length checked against the remaining
room in the reassembly buffer. This allowed a suitably constructed last
fragment frame to try to add extra data that would go beyond the buffer.
The length validation code in wpabuf_put_data() prevents an actual
buffer write overflow from occurring, but this results in process
termination. (CVE-2015-5315)

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

src/eap_peer/eap_pwd.c

@@ -903,7 +903,7 @@ eap_pwd_process(struct eap_sm *sm, void *priv, struct eap_method_ret *ret,
 	/*
 	 * buffer and ACK the fragment
 	 */
-	if (EAP_PWD_GET_MORE_BIT(lm_exch)) {
+	if (EAP_PWD_GET_MORE_BIT(lm_exch) || data->in_frag_pos) {
 		data->in_frag_pos += len;
 		if (data->in_frag_pos > wpabuf_size(data->inbuf)) {
 			wpa_printf(MSG_INFO, "EAP-pwd: Buffer overflow attack "
@@ -916,7 +916,8 @@ eap_pwd_process(struct eap_sm *sm, void *priv, struct eap_method_ret *ret,
 			return NULL;
 		}
 		wpabuf_put_data(data->inbuf, pos, len);
-
+	}
+	if (EAP_PWD_GET_MORE_BIT(lm_exch)) {
 		resp = eap_msg_alloc(EAP_VENDOR_IETF, EAP_TYPE_PWD,
 				     EAP_PWD_HDR_SIZE,
 				     EAP_CODE_RESPONSE, eap_get_id(reqData));
@@ -930,10 +931,8 @@ eap_pwd_process(struct eap_sm *sm, void *priv, struct eap_method_ret *ret,
 	 * we're buffering and this is the last fragment
 	 */
 	if (data->in_frag_pos) {
-		wpabuf_put_data(data->inbuf, pos, len);
 		wpa_printf(MSG_DEBUG, "EAP-pwd: Last fragment, %d bytes",
 			   (int) len);
-		data->in_frag_pos += len;
 		pos = wpabuf_head_u8(data->inbuf);
 		len = data->in_frag_pos;
 	}