mac80211: fix fast-rx encryption check

stable inclusion
from stable-5.10.14
commit 20790b2534f2057345ffd75e77c9758e4d94407e
bugzilla: 48051

--------------------------------

[ Upstream commit 622d3b4e ]

When using WEP, the default unicast key needs to be selected, instead of
the STA PTK.
Signed-off-by: NFelix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20201218184718.93650-5-nbd@nbd.nameSigned-off-by: NJohannes Berg <johannes.berg@intel.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

net/mac80211/rx.c

@@ -4191,6 +4191,8 @@ void ieee80211_check_fast_rx(struct sta_info *sta)
 
 	rcu_read_lock();
 	key = rcu_dereference(sta->ptk[sta->ptk_idx]);
+	if (!key)
+		key = rcu_dereference(sdata->default_unicast_key);
 	if (key) {
 		switch (key->conf.cipher) {
 		case WLAN_CIPHER_SUITE_TKIP: