Patch "mwifiex: Fix possible ABBA deadlock" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    mwifiex: Fix possible ABBA deadlock

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mwifiex-fix-possible-abba-deadlock.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 03531e27350ebc6472975aa9699a1313f8c3b15a
Author: Brian Norris <briannorris@xxxxxxxxxxxx>
Date:   Mon Nov 29 16:47:34 2021 -0800

    mwifiex: Fix possible ABBA deadlock
    
    [ Upstream commit 1b8bb8919ef81bfc8873d223b9361f1685f2106d ]
    
    Quoting Jia-Ju Bai <baijiaju1990@xxxxxxxxx>:
    
      mwifiex_dequeue_tx_packet()
         spin_lock_bh(&priv->wmm.ra_list_spinlock); --> Line 1432 (Lock A)
         mwifiex_send_addba()
           spin_lock_bh(&priv->sta_list_spinlock); --> Line 608 (Lock B)
    
      mwifiex_process_sta_tx_pause()
         spin_lock_bh(&priv->sta_list_spinlock); --> Line 398 (Lock B)
         mwifiex_update_ralist_tx_pause()
           spin_lock_bh(&priv->wmm.ra_list_spinlock); --> Line 941 (Lock A)
    
    Similar report for mwifiex_process_uap_tx_pause().
    
    While the locking expectations in this driver are a bit unclear, the
    Fixed commit only intended to protect the sta_ptr, so we can drop the
    lock as soon as we're done with it.
    
    IIUC, this deadlock cannot actually happen, because command event
    processing (which calls mwifiex_process_sta_tx_pause()) is
    sequentialized with TX packet processing (e.g.,
    mwifiex_dequeue_tx_packet()) via the main loop (mwifiex_main_process()).
    But it's good not to leave this potential issue lurking.
    
    Fixes: f0f7c2275fb9 ("mwifiex: minor cleanups w/ sta_list_spinlock in cfg80211.c")
    Cc: Douglas Anderson <dianders@xxxxxxxxxxxx>
    Reported-by: TOTE Robot <oslab@xxxxxxxxxxxxxxx>
    Link: https://lore.kernel.org/linux-wireless/0e495b14-efbb-e0da-37bd-af6bd677ee2c@xxxxxxxxx/
    Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
    Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
    Signed-off-by: Kalle Valo <kvalo@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/YaV0pllJ5p/EuUat@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/net/wireless/marvell/mwifiex/sta_event.c b/drivers/net/wireless/marvell/mwifiex/sta_event.c
index 5fdffb114913d..fd12093863801 100644
--- a/drivers/net/wireless/marvell/mwifiex/sta_event.c
+++ b/drivers/net/wireless/marvell/mwifiex/sta_event.c
@@ -364,10 +364,12 @@ static void mwifiex_process_uap_tx_pause(struct mwifiex_private *priv,
 		sta_ptr = mwifiex_get_sta_entry(priv, tp->peermac);
 		if (sta_ptr && sta_ptr->tx_pause != tp->tx_pause) {
 			sta_ptr->tx_pause = tp->tx_pause;
+			spin_unlock_bh(&priv->sta_list_spinlock);
 			mwifiex_update_ralist_tx_pause(priv, tp->peermac,
 						       tp->tx_pause);
+		} else {
+			spin_unlock_bh(&priv->sta_list_spinlock);
 		}
-		spin_unlock_bh(&priv->sta_list_spinlock);
 	}
 }
 
@@ -399,11 +401,13 @@ static void mwifiex_process_sta_tx_pause(struct mwifiex_private *priv,
 			sta_ptr = mwifiex_get_sta_entry(priv, tp->peermac);
 			if (sta_ptr && sta_ptr->tx_pause != tp->tx_pause) {
 				sta_ptr->tx_pause = tp->tx_pause;
+				spin_unlock_bh(&priv->sta_list_spinlock);
 				mwifiex_update_ralist_tx_pause(priv,
 							       tp->peermac,
 							       tp->tx_pause);
+			} else {
+				spin_unlock_bh(&priv->sta_list_spinlock);
 			}
-			spin_unlock_bh(&priv->sta_list_spinlock);
 		}
 	}
 }