mac80211: clear sequence/fragment number in QoS-null frames

commit 864a6040 upstream.

Avoid leaking data by sending uninitialized memory and setting an
invalid (non-zero) fragment number (the sequence number is ignored
anyway) by setting the seq_ctrl field to zero.

Fixes: 3f52b7e3 ("mac80211: mesh power save basics")
Fixes: ce662b44 ("mac80211: send (QoS) Null if no buffered frames")
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
[bwh: Backported to 3.2: Drop change to mps_qos_null_get()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

net/mac80211/sta_info.c

@@ -1211,6 +1211,7 @@ static void ieee80211_send_null_response(struct ieee80211_sub_if_data *sdata,
 	memcpy(nullfunc->addr1, sta->sta.addr, ETH_ALEN);
 	memcpy(nullfunc->addr2, sdata->vif.addr, ETH_ALEN);
 	memcpy(nullfunc->addr3, sdata->vif.addr, ETH_ALEN);
+	nullfunc->seq_ctrl = 0;
 
 	skb->priority = tid;
 	skb_set_queue_mapping(skb, ieee802_1d_to_ac[tid]);