In the Linux kernel, the following vulnerability has been resolved: wifi: mac80211: refuse to make a monitor active when it has no queue A

In the Linux kernel, the following vulnerability has been resolved:

wifi: mac80211: refuse to make a monitor active when it has no queue

A monitor interface only gets a TXQ if it's created active, and one can't
be added later. Setting the flag on a down interface is still allowed, so
the driver is handed a monitor with no queue. ath9k dereferences it:

BUG: kernel NULL pointer dereference, address: 0000000000000066
RIP: 0010:ath_tx_node_init+0x49/0x170 [ath9k]
ath9k_add_interface+0x10c/0x140 [ath9k]
drv_add_interface+0x54/0x250 [mac80211]
ieee80211_do_open+0x32f/0x800 [mac80211]

Reached with CAP_NET_ADMIN by "iw dev X set monitor active" followed by
"ip link set X up". RTNL is held, so netlink operations block behind it.

Refuse the flag when there is no queue to give.