wifi: mac80211: ensure beacon is non-S1G prior to extracting the beacon timestamp field

Logic inside ieee80211_rx_mgmt_beacon accesses the
mgmt->u.beacon.timestamp field without first checking whether the beacon
received is non-S1G format.

Fix the problem by checking the beacon is non-S1G format to avoid access
of the mgmt->u.beacon.timestamp field.

Signed-off-by: Richard Kinder <richard.kinder@gmail.com>
Link: https://msgid.link/20240328005725.85355-1-richard.kinder@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: rkinder2023

net/mac80211/mlme.c

@@ -6193,7 +6193,8 @@ static void ieee80211_rx_mgmt_beacon(struct ieee80211_link_data *link,
 			link->u.mgd.dtim_period = elems->dtim_period;
 		link->u.mgd.have_beacon = true;
 		ifmgd->assoc_data->need_beacon = false;
-		if (ieee80211_hw_check(&local->hw, TIMING_BEACON_ONLY)) {
+		if (ieee80211_hw_check(&local->hw, TIMING_BEACON_ONLY) &&
+		    !ieee80211_is_s1g_beacon(hdr->frame_control)) {
 			link->conf->sync_tsf =
 				le64_to_cpu(mgmt->u.beacon.timestamp);
 			link->conf->sync_device_ts =