mac80211: check the correct bit for EMA AP

An AP supporting EMA (Enhanced Multi-BSSID advertisement) should set
bit 83 in the extended capabilities IE (9.4.2.26 in the 802.11ax D5 spec).
So the *3rd* bit of the 10th byte should be checked.
Also, in one place, the wrong byte was checked.
(cfg80211_find_ie returns a pointer to the beginning of the IE,
 so the data really starts at ie[2], so the 10th byte
 should be ie[12]. To avoid this confusion, use cfg80211_find_elem
 instead).
Signed-off-by: Shaul Triebitz <shaul.triebitz@intel.com>
Link: https://lore.kernel.org/r/20200528213443.4316121fa2a3.I9745582f8d41ad8e689dac0fefcd70b276d7c1ea@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

include/linux/ieee80211.h

@@ -3082,7 +3082,7 @@ enum ieee80211_tdls_actioncode {
 #define WLAN_EXT_CAPA10_OBSS_NARROW_BW_RU_TOLERANCE_SUPPORT BIT(7)
 
 /* Defines support for enhanced multi-bssid advertisement*/
-#define WLAN_EXT_CAPA11_EMA_SUPPORT	BIT(1)
+#define WLAN_EXT_CAPA11_EMA_SUPPORT	BIT(3)
 
 /* TDLS specific payload type in the LLC/SNAP header */
 #define WLAN_TDLS_SNAP_RFTYPE	0x2

net/mac80211/mlme.c

@@ -5596,7 +5596,7 @@ int ieee80211_mgd_assoc(struct ieee80211_sub_if_data *sdata,
 		assoc_data->timeout_started = true;
 		assoc_data->need_beacon = true;
 	} else if (beacon_ies) {
-		const u8 *ie;
+		const struct element *elem;
 		u8 dtim_count = 0;
 
 		ieee80211_get_dtim(beacon_ies, &dtim_count,
@@ -5613,15 +5613,15 @@ int ieee80211_mgd_assoc(struct ieee80211_sub_if_data *sdata,
 			sdata->vif.bss_conf.sync_dtim_count = dtim_count;
 		}
 
-		ie = cfg80211_find_ext_ie(WLAN_EID_EXT_MULTIPLE_BSSID_CONFIGURATION,
-					  beacon_ies->data, beacon_ies->len);
-		if (ie && ie[1] >= 3)
-			sdata->vif.bss_conf.profile_periodicity = ie[4];
+		elem = cfg80211_find_ext_elem(WLAN_EID_EXT_MULTIPLE_BSSID_CONFIGURATION,
+					      beacon_ies->data, beacon_ies->len);
+		if (elem && elem->datalen >= 3)
+			sdata->vif.bss_conf.profile_periodicity = elem->data[2];
 
-		ie = cfg80211_find_ie(WLAN_EID_EXT_CAPABILITY,
-				      beacon_ies->data, beacon_ies->len);
-		if (ie && ie[1] >= 11 &&
-		    (ie[10] & WLAN_EXT_CAPA11_EMA_SUPPORT))
+		elem = cfg80211_find_elem(WLAN_EID_EXT_CAPABILITY,
+					  beacon_ies->data, beacon_ies->len);
+		if (elem && elem->datalen >= 11 &&
+		    (elem->data[10] & WLAN_EXT_CAPA11_EMA_SUPPORT))
 			sdata->vif.bss_conf.ema_ap = true;
 	} else {
 		assoc_data->timeout = jiffies;