[PATCH 3.16.y-ckt 128/144] mac80211: fix RX A-MPDU session reorder timer deletion

[Luis Henriques]

3.16.7-ckt10 -stable review patch.  If anyone has any objections, please let me know.

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

From: Johannes Berg <johannes.berg@xxxxxxxxx>

commit 788211d81bfdf9b6a547d0530f206ba6ee76b107 upstream.

There's an issue with the way the RX A-MPDU reorder timer is
deleted that can cause a kernel crash like this:

 * tid_rx is removed - call_rcu(ieee80211_free_tid_rx)
 * station is destroyed
 * reorder timer fires before ieee80211_free_tid_rx() runs,
   accessing the station, thus potentially crashing due to
   the use-after-free

The station deletion is protected by synchronize_net(), but
that isn't enough -- ieee80211_free_tid_rx() need not have
run when that returns (it deletes the timer.) We could use
rcu_barrier() instead of synchronize_net(), but that's much
more expensive.

Instead, to fix this, add a field tracking that the session
is being deleted. In this case, the only re-arming of the
timer happens with the reorder spinlock held, so make that
code not rearm it if the session is being deleted and also
delete the timer after setting that field. This ensures the
timer cannot fire after ___ieee80211_stop_rx_ba_session()
returns, which fixes the problem.

Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 net/mac80211/agg-rx.c   | 8 ++++++--
 net/mac80211/rx.c       | 7 ++++---
 net/mac80211/sta_info.h | 2 ++
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/net/mac80211/agg-rx.c b/net/mac80211/agg-rx.c
index 31bf2586fb84..9608c6e65887 100644
--- a/net/mac80211/agg-rx.c
+++ b/net/mac80211/agg-rx.c
@@ -49,8 +49,6 @@ static void ieee80211_free_tid_rx(struct rcu_head *h)
 		container_of(h, struct tid_ampdu_rx, rcu_head);
 	int i;
 
-	del_timer_sync(&tid_rx->reorder_timer);
-
 	for (i = 0; i < tid_rx->buf_size; i++)
 		dev_kfree_skb(tid_rx->reorder_buf[i]);
 	kfree(tid_rx->reorder_buf);
@@ -93,6 +91,12 @@ void ___ieee80211_stop_rx_ba_session(struct sta_info *sta, u16 tid,
 
 	del_timer_sync(&tid_rx->session_timer);
 
+	/* make sure ieee80211_sta_reorder_release() doesn't re-arm the timer */
+	spin_lock_bh(&tid_rx->reorder_lock);
+	tid_rx->removed = true;
+	spin_unlock_bh(&tid_rx->reorder_lock);
+	del_timer_sync(&tid_rx->reorder_timer);
+
 	call_rcu(&tid_rx->rcu_head, ieee80211_free_tid_rx);
 }
 
diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index a70f4ce4f652..07fb67803097 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -792,9 +792,10 @@ static void ieee80211_sta_reorder_release(struct ieee80211_sub_if_data *sdata,
 
  set_release_timer:
 
-		mod_timer(&tid_agg_rx->reorder_timer,
-			  tid_agg_rx->reorder_time[j] + 1 +
-			  HT_RX_REORDER_BUF_TIMEOUT);
+		if (!tid_agg_rx->removed)
+			mod_timer(&tid_agg_rx->reorder_timer,
+				  tid_agg_rx->reorder_time[j] + 1 +
+				  HT_RX_REORDER_BUF_TIMEOUT);
 	} else {
 		del_timer(&tid_agg_rx->reorder_timer);
 	}
diff --git a/net/mac80211/sta_info.h b/net/mac80211/sta_info.h
index 4acc5fc402fa..5a600151ba5a 100644
--- a/net/mac80211/sta_info.h
+++ b/net/mac80211/sta_info.h
@@ -162,6 +162,7 @@ struct tid_ampdu_tx {
  * @dialog_token: dialog token for aggregation session
  * @rcu_head: RCU head used for freeing this struct
  * @reorder_lock: serializes access to reorder buffer, see below.
+ * @removed: this session is removed (but might have been found due to RCU)
  *
  * This structure's lifetime is managed by RCU, assignments to
  * the array holding it must hold the aggregation mutex.
@@ -185,6 +186,7 @@ struct tid_ampdu_rx {
 	u16 buf_size;
 	u16 timeout;
 	u8 dialog_token;
+	bool removed;
 };
 
 /**
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