mwifiex: bring down link before deleting interface

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

mwifiex: bring down link before deleting interface

We can deadlock when rmmod'ing the driver or going through firmware

reset, because the cfg80211_unregister_wdev() has to bring down the link

for us, ... which then grab the same wiphy lock.

nl80211_del_interface() already handles a very similar case, with a nice

description:

/*

* We hold RTNL, so this is safe, without RTNL opencount cannot

* reach 0, and thus the rdev cannot be deleted.

*

* We need to do it for the dev_close(), since that will call

* the netdev notifiers, and we need to acquire the mutex there

* but don't know if we get there from here or from some other

* place (e.g. "ip link set ... down").

*/

mutex_unlock(&rdev->wiphy.mtx);

...

Do similarly for mwifiex teardown, by ensuring we bring the link down

first.

Sample deadlock trace:

[ 247.103516] INFO: task rmmod:2119 blocked for more than 123 seconds.

[ 247.110630] Not tainted 5.12.4 #5

[ 247.115796] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

[ 247.124557] task:rmmod state:D stack: 0 pid: 2119 ppid: 2114 flags:0x00400208

[ 247.133905] Call trace:

[ 247.136644] __switch_to+0x130/0x170

[ 247.140643] __schedule+0x714/0xa0c

[ 247.144548] schedule_preempt_disabled+0x88/0xf4

[ 247.149714] __mutex_lock_common+0x43c/0x750

[ 247.154496] mutex_lock_nested+0x5c/0x68

[ 247.158884] cfg80211_netdev_notifier_call+0x280/0x4e0 [cfg80211]

[ 247.165769] raw_notifier_call_chain+0x4c/0x78

[ 247.170742] call_netdevice_notifiers_info+0x68/0xa4

[ 247.176305] __dev_close_many+0x7c/0x138

[ 247.180693] dev_close_many+0x7c/0x10c

[ 247.184893] unregister_netdevice_many+0xfc/0x654

[ 247.190158] unregister_netdevice_queue+0xb4/0xe0

[ 247.195424] _cfg80211_unregister_wdev+0xa4/0x204 [cfg80211]

[ 247.201816] cfg80211_unregister_wdev+0x20/0x2c [cfg80211]

[ 247.208016] mwifiex_del_virtual_intf+0xc8/0x188 [mwifiex]

[ 247.214174] mwifiex_uninit_sw+0x158/0x1b0 [mwifiex]

[ 247.219747] mwifiex_remove_card+0x38/0xa0 [mwifiex]

[ 247.225316] mwifiex_pcie_remove+0xd0/0xe0 [mwifiex_pcie]

[ 247.231451] pci_device_remove+0x50/0xe0

[ 247.235849] device_release_driver_internal+0x110/0x1b0

[ 247.241701] driver_detach+0x5c/0x9c

[ 247.245704] bus_remove_driver+0x84/0xb8

[ 247.250095] driver_unregister+0x3c/0x60

[ 247.254486] pci_unregister_driver+0x2c/0x90

[ 247.259267] cleanup_module+0x18/0xcdc [mwifiex_pcie]