CVE-2021-47225

In the Linux kernel, the following vulnerability has been resolved:
mac80211: fix deadlock in AP/VLAN handling Syzbot reports that when you
have AP_VLAN interfaces that are up and close the AP interface they belong
to, we get a deadlock. No surprise - since we dev_close() them with the
wiphy mutex held, which goes back into the netdev notifier in cfg80211 and
tries to acquire the wiphy mutex there. To fix this, we need to do two
things: 1) prevent changing iftype while AP_VLANs are up, we can’t easily
fix this case since cfg80211 already calls us with the wiphy mutex held,
but change_interface() is relatively rare in drivers anyway, so changing
iftype isn’t used much (and userspace has to fall back to down/change/up
anyway) 2) pull the dev_close() loop over VLANs out of the wiphy mutex
section in the normal stop case