CVE-2021-47225 Information

Description

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

Reference

https://git.kernel.org/stable/c/8043903fcb72f545c52e3ec74d6fd82ef79ce7c5 https://git.kernel.org/stable/c/d5befb224edbe53056c2c18999d630dafb4a08b9