iwlwifi: mvm: fix a NULL pointer dereference of error in recovery

Sometimes, we can have an firmware crash while trying to
recover from a previous firmware problem.
When that happens, lots of things can go wrong. For example
the stations don't get added properly to mvm->fw_id_to_mac_id.

Mac80211 tries to stop A-MPDU upon reconfig but in case of
a firmware crash we will bail out fairly early and in the
end, we won't delete the A-MPDU Rx timeout.
When that timer expired after a double firmware crash,
we end up dereferencing mvm->fw_id_to_mac_id[sta_id]
which is NULL.

Fixes: 10b2b2019d81 ("iwlwifi: mvm: add infrastructure for tracking BA session in driver")
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/sta.c b/drivers/net/wireless/intel/iwlwifi/mvm/sta.c
index 4df5f13..4a6df45 100644 (file)
--- a/drivers/net/wireless/intel/iwlwifi/mvm/sta.c
+++ b/drivers/net/wireless/intel/iwlwifi/mvm/sta.c
@@ -277,6 +277,18 @@ static void iwl_mvm_rx_agg_session_expired(unsigned long data)
 
        /* Timer expired */
        sta = rcu_dereference(ba_data->mvm->fw_id_to_mac_id[ba_data->sta_id]);
+
+       /*
+        * sta should be valid unless the following happens:
+        * The firmware asserts which triggers a reconfig flow, but
+        * the reconfig fails before we set the pointer to sta into
+        * the fw_id_to_mac_id pointer table. Mac80211 can't stop
+        * A-MDPU and hence the timer continues to run. Then, the
+        * timer expires and sta is NULL.
+        */
+       if (!sta)
+               goto unlock;
+
        mvm_sta = iwl_mvm_sta_from_mac80211(sta);
        ieee80211_stop_rx_ba_session_offl(mvm_sta->vif,
                                          sta->addr, ba_data->tid);