mac80211: fix rcu-unsafe pointer dereference

This patch fixes a potential crash (null-pointer de-
reference) which was introduced in my previous patch:
 "mac80211: AMPDU rx reorder timeout timer"

During a BA teardown, the pointer to the soon-to-be-gone
tid_ampdu_rx element will be nullified. Therefore the
release timer mechanism has to be careful not to
accidentally access the item without any RCU protection.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index e1844f7085de..e67deb48af5c 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -2479,6 +2479,11 @@ void ieee80211_release_reorder_timeout(struct sta_info *sta, int tid)
 {
         struct sk_buff_head frames;
         struct ieee80211_rx_data rx = { };
+        struct tid_ampdu_rx *tid_agg_rx;
+
+        tid_agg_rx = rcu_dereference(sta->ampdu_mlme.tid_rx[tid]);
+        if (!tid_agg_rx)
+                return;
 
         __skb_queue_head_init(&frames);
 
@@ -2493,10 +2498,9 @@ void ieee80211_release_reorder_timeout(struct sta_info *sta, int tid)
                      test_bit(SCAN_OFF_CHANNEL, &sta->local->scanning)))
                 rx.flags |= IEEE80211_RX_IN_SCAN;
 
-        spin_lock(&sta->ampdu_mlme.tid_rx[tid]->reorder_lock);
-        ieee80211_sta_reorder_release(&sta->local->hw,
-                sta->ampdu_mlme.tid_rx[tid], &frames);
-        spin_unlock(&sta->ampdu_mlme.tid_rx[tid]->reorder_lock);
+        spin_lock(&tid_agg_rx->reorder_lock);
+        ieee80211_sta_reorder_release(&sta->local->hw, tid_agg_rx, &frames);
+        spin_unlock(&tid_agg_rx->reorder_lock);
 
         ieee80211_rx_handlers(&rx, &frames);
 }