[PATCH] wifi: mac80211: free AP_VLAN bc_buf SKBs outside IRQ lock

[PATCH] wifi: mac80211: free AP_VLAN bc_buf SKBs outside IRQ lock

[Cen Zhang]

ieee80211_do_stop() removes AP_VLAN packets from the parent AP
ps->bc_buf while holding ps->bc_buf.lock with IRQs disabled. It then
calls ieee80211_free_txskb() before dropping the lock.

ieee80211_free_txskb() is not just a passive SKB release. For SKBs with
TX status state it can report a dropped frame through cfg80211/nl80211,
and that path can reach netlink tap transmit. This is the same reason
the pending queue cleanup in ieee80211_do_stop() already unlinks SKBs
under the queue lock and frees them after IRQ state is restored.

The buggy scenario involves two paths, with each column showing the
order within that path:

AP_VLAN management TX:             AP_VLAN stop:
1. attach ACK-status state         1. clear the running state
2. queue a multicast SKB on        2. take ps->bc_buf.lock with IRQs
   parent ps->bc_buf                  disabled
                                   3. unlink the AP_VLAN SKB
                                   4. call ieee80211_free_txskb()

Unlink matching AP_VLAN SKBs from ps->bc_buf under the existing lock,
but move them to a local free queue. Drop the lock and restore IRQ state
before calling ieee80211_free_txskb().

WARNING: kernel/softirq.c:430 at __local_bh_enable_ip

Fixes: 397a7a24ef8c ("mac80211: free ps->bc_buf skbs on vlan device stop")
Assisted-by: Codex:gpt-5.5
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
---
 net/mac80211/iface.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index 086272c3ec08..43460a705a6b 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -588,6 +588,7 @@ static void ieee80211_do_stop(struct ieee80211_sub_if_data *sdata, bool going_do
 		WARN_ON(!list_empty(&sdata->u.ap.vlans));
 	} else if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN) {
 		/* remove all packets in parent bc_buf pointing to this dev */
+		__skb_queue_head_init(&freeq);
 		ps = &sdata->bss->ps;
 
 		spin_lock_irqsave(&ps->bc_buf.lock, flags);
@@ -595,10 +596,15 @@ static void ieee80211_do_stop(struct ieee80211_sub_if_data *sdata, bool going_do
 			if (skb->dev == sdata->dev) {
 				__skb_unlink(skb, &ps->bc_buf);
 				local->total_ps_buffered--;
-				ieee80211_free_txskb(&local->hw, skb);
+				__skb_queue_tail(&freeq, skb);
 			}
 		}
 		spin_unlock_irqrestore(&ps->bc_buf.lock, flags);
+
+		skb_queue_walk_safe(&freeq, skb, tmp) {
+			__skb_unlink(skb, &freeq);
+			ieee80211_free_txskb(&local->hw, skb);
+		}
 	}
 
 	if (going_down)
-- 
2.43.0