Subject: CVE-2021-47225: mac80211: fix deadlock in AP/VLAN handling

From: Greg Kroah-Hartman <[email-masked]>

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

The Linux kernel CVE team has assigned CVE-2021-47225 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.12 with commit a05829a7222e and fixed in 5.12.13 with commit 8043903fcb72
	Issue introduced in 5.12 with commit a05829a7222e and fixed in 5.13 with commit d5befb224edb

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-47225
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	net/mac80211/iface.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/8043903fcb72f545c52e3ec74d6fd82ef79ce7c5
	https://git.kernel.org/stable/c/d5befb224edbe53056c2c18999d630dafb4a08b9