3.2.69-rc1 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> [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- net/mac80211/agg-rx.c | 8 ++++++-- net/mac80211/rx.c | 7 ++++--- net/mac80211/sta_info.h | 2 ++ 3 files changed, 12 insertions(+), 5 deletions(-) --- a/net/mac80211/agg-rx.c +++ b/net/mac80211/agg-rx.c @@ -49,8 +49,6 @@ static void ieee80211_free_tid_rx(struct 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); @@ -91,6 +89,12 @@ void ___ieee80211_stop_rx_ba_session(str 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); } --- a/net/mac80211/rx.c +++ b/net/mac80211/rx.c @@ -670,9 +670,10 @@ static void ieee80211_sta_reorder_releas 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); } --- a/net/mac80211/sta_info.h +++ b/net/mac80211/sta_info.h @@ -138,6 +138,7 @@ 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. @@ -160,6 +161,7 @@ struct tid_ampdu_rx { u16 buf_size; u16 timeout; u8 dialog_token; + bool removed; }; /** -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html