Set EAPOL-Key Key Length field to 0 for group message 1/2 in RSN

P802.11i/D3.0 described the Key Length as having value 16 for the group
key handshake. However, this was changed to 0 in the published IEEE Std
802.11i-2004 amendment (and still remains 0 in the current standard IEEE
Std 802.11-2016). We need to maintain the non-zero value for WPA (v1)
cases, but the RSN case can be changed to 0 to be closer to the current
standard.

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

src/ap/wpa_auth.c

@@ -1484,9 +1484,11 @@ void __wpa_send_eapol(struct wpa_authenticator *wpa_auth,
 	WPA_PUT_BE16(key->key_info, key_info);
 
 	alg = pairwise ? sm->pairwise : wpa_auth->conf.wpa_group;
-	WPA_PUT_BE16(key->key_length, wpa_cipher_key_len(alg));
-	if (key_info & WPA_KEY_INFO_SMK_MESSAGE)
+	if ((key_info & WPA_KEY_INFO_SMK_MESSAGE) ||
+	    (sm->wpa == WPA_VERSION_WPA2 && !pairwise))
 		WPA_PUT_BE16(key->key_length, 0);
+	else
+		WPA_PUT_BE16(key->key_length, wpa_cipher_key_len(alg));
 
 	/* FIX: STSL: what to use as key_replay_counter? */
 	for (i = RSNA_MAX_EAPOL_RETRIES - 1; i > 0; i--) {