Optional AP side workaround for key reinstallation attacks

This adds a new hostapd configuration parameter
wpa_disable_eapol_key_retries=1 that can be used to disable
retransmission of EAPOL-Key frames that are used to install
keys (EAPOL-Key message 3/4 and group message 1/2). This is
similar to setting wpa_group_update_count=1 and
wpa_pairwise_update_count=1, but with no impact to message 1/4
retries and with extended timeout for messages 4/4 and group
message 2/2 to avoid causing issues with stations that may use
aggressive power saving have very long time in replying to the
EAPOL-Key messages.

This option can be used to work around key reinstallation attacks
on the station (supplicant) side in cases those station devices
cannot be updated for some reason. By removing the
retransmissions the attacker cannot cause key reinstallation with
a delayed frame transmission. This is related to the station side
vulnerabilities CVE-2017-13077, CVE-2017-13078, CVE-2017-13079,
CVE-2017-13080, and CVE-2017-13081.

This workaround might cause interoperability issues and reduced
robustness of key negotiation especially in environments with
heavy traffic load due to the number of attempts to perform the
key exchange is reduced significantly. As such, this workaround
is disabled by default (unless overridden in build
configuration). To enable this, set the parameter to 1.

It is also possible to enable this in the build by default by
adding the following to the build configuration:

CFLAGS += -DDEFAULT_WPA_DISABLE_EAPOL_KEY_RETRIES=1

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

src/ap/wpa_auth.h

@@ -165,6 +165,7 @@ struct wpa_auth_config {
 	int wpa_ptk_rekey;
 	u32 wpa_group_update_count;
 	u32 wpa_pairwise_update_count;
+	int wpa_disable_eapol_key_retries;
 	int rsn_pairwise;
 	int rsn_preauth;
 	int eapol_version;