wifi: mac80211: fix BA session teardown race

As previously reported by Alexander, whose commit 69403bad97aa
("wifi: mac80211: sdata can be NULL during AMPDU start") I'm
reverting as part of this commit, there's a race between station
destruction and aggregation setup, where the aggregation setup
can happen while the station is being removed and queue the work
after ieee80211_sta_tear_down_BA_sessions() has already run in
__sta_info_destroy_part1(), and thus the worker will run with a
now freed station. In his case, this manifested in a NULL sdata
pointer, but really there's no guarantee whatsoever.

The real issue seems to be that it's possible at all to have a
situation where this occurs - we want to stop the BA sessions
when doing _part1, but we cannot be sure, and WLAN_STA_BLOCK_BA
isn't necessarily effective since we don't know that the setup
isn't concurrently running and already got past the check.

Simply call ieee80211_sta_tear_down_BA_sessions() again in the
second part of station destruction, since at that point really
nothing else can hold a reference to the station any more.

Also revert the sdata checks since those are just misleading at
this point.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/net/mac80211/agg-tx.c b/net/mac80211/agg-tx.c
index 0627abb09f0e4b29e07da15e54bfce4549fc109d..b8a278355e18ee9dceaa62659846e0686b2050df 100644 (file)
--- a/net/mac80211/agg-tx.c
+++ b/net/mac80211/agg-tx.c
@@ -497,7 +497,7 @@ void ieee80211_tx_ba_session_handle_start(struct sta_info *sta, int tid)
 {
        struct tid_ampdu_tx *tid_tx;
        struct ieee80211_local *local = sta->local;
-       struct ieee80211_sub_if_data *sdata;
+       struct ieee80211_sub_if_data *sdata = sta->sdata;
        struct ieee80211_ampdu_params params = {
                .sta = &sta->sta,
                .action = IEEE80211_AMPDU_TX_START,
@@ -525,7 +525,6 @@ void ieee80211_tx_ba_session_handle_start(struct sta_info *sta, int tid)
         */
        synchronize_net();
 
-       sdata = sta->sdata;
        params.ssn = sta->tid_seq[tid] >> 4;
        ret = drv_ampdu_action(local, sdata, &params);
        tid_tx->ssn = params.ssn;
@@ -539,9 +538,6 @@ void ieee80211_tx_ba_session_handle_start(struct sta_info *sta, int tid)
                 */
                set_bit(HT_AGG_STATE_DRV_READY, &tid_tx->state);
        } else if (ret) {
-               if (!sdata)
-                       return;
-
                ht_dbg(sdata,
                       "BA request denied - HW unavailable for %pM tid %d\n",
                       sta->sta.addr, tid);

diff --git a/net/mac80211/driver-ops.c b/net/mac80211/driver-ops.c
index 919300750527d7c401bf9e405be787bf5eb5d017..169dbbca54b6fa774bcf1e043576b1e7568ae8b1 100644 (file)
--- a/net/mac80211/driver-ops.c
+++ b/net/mac80211/driver-ops.c
@@ -409,9 +409,6 @@ int drv_ampdu_action(struct ieee80211_local *local,
        might_sleep();
        lockdep_assert_wiphy(local->hw.wiphy);
 
-       if (!sdata)
-               return -EIO;
-
        sdata = get_bss_sdata(sdata);
        if (!check_sdata_in_driver(sdata))
                return -EIO;

diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index abcc280acd3846fe5c7d614860b254424ad26012..2a61269a4b54d209c4ad6a2ae1853964aa2dd6c7 100644 (file)
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -1385,6 +1385,20 @@ static void __sta_info_destroy_part2(struct sta_info *sta, bool recalc)
         *       after _part1 and before _part2!
         */
 
+       /*
+        * There's a potential race in _part1 where we set WLAN_STA_BLOCK_BA
+        * but someone might have just gotten past a check, and not yet into
+        * queuing the work/creating the data/etc.
+        *
+        * Do another round of destruction so that the worker is certainly
+        * canceled before we later free the station.
+        *
+        * Since this is after synchronize_rcu()/synchronize_net() we're now
+        * certain that nobody can actually hold a reference to the STA and
+        * be calling e.g. ieee80211_start_tx_ba_session().
+        */
+       ieee80211_sta_tear_down_BA_sessions(sta, AGG_STOP_DESTROY_STA);
+
        might_sleep();
        lockdep_assert_wiphy(local->hw.wiphy);