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)

Bug: 25510821

Change-Id: Ic509a6efedc3da9ff40f2842fab5547d087f64de
Signed-off-by: Jouni Malinen <j@w1.fi>
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>
diff --git a/src/eap_peer/eap_pwd.c b/src/eap_peer/eap_pwd.c
index 267d0a5..976e017 100644
--- a/src/eap_peer/eap_pwd.c
+++ b/src/eap_peer/eap_pwd.c
@@ -760,7 +760,7 @@
 	/*
 	 * 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 "
@@ -772,7 +772,8 @@
 			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));
@@ -786,10 +787,8 @@
 	 * 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;
 	}