Clarify the TODO comment regarding PMKID KDE in EAPOL-Key msg 1/4

Make it clear that the consideration should be only for the IBSS case
and in infrastructure BSS case, PMKID KDE should not be added due to
risks involved with exposing this to stations that do not know the
passphrase.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>

src/ap/wpa_auth.c

@@ -2026,8 +2026,18 @@ SM_STATE(WPA_PTK, PTKSTART)
 	wpa_auth_logger(sm->wpa_auth, sm->addr, LOGGER_DEBUG,
 			"sending 1/4 msg of 4-Way Handshake");
 	/*
-	 * TODO: Could add PMKID even with WPA2-PSK, but only if there is only
-	 * one possible PSK for this STA.
+	 * For infrastructure BSS cases, it is better for the AP not to include
+	 * the PMKID KDE in EAPOL-Key msg 1/4 since it could be used to initiate
+	 * offline search for the passphrase/PSK without having to be able to
+	 * capture a 4-way handshake from a STA that has access to the network.
+	 *
+	 * For IBSS cases, addition of PMKID KDE could be considered even with
+	 * WPA2-PSK cases that use multiple PSKs, but only if there is a single
+	 * possible PSK for this STA. However, this should not be done unless
+	 * there is support for using that information on the supplicant side.
+	 * The concern about exposing PMKID unnecessarily in infrastructure BSS
+	 * cases would also apply here, but at least in the IBSS case, this
+	 * would cover a potential real use case.
 	 */
 	if (sm->wpa == WPA_VERSION_WPA2 &&
 	    (wpa_key_mgmt_wpa_ieee8021x(sm->wpa_key_mgmt) ||