wifi: mac80211: free AP_VLAN bc_buf SKBs outside IRQ lock

Summary

In the Linux kernel, the following vulnerability has been resolved: wifi: mac80211: free AP_VLAN bc_buf SKBs outside IRQ lock 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