wifi: rtw89: fix race between cancel_hw_scan and hw_scan completion

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

wifi: rtw89: fix race between cancel_hw_scan and hw_scan completion

The rtwdev->scanning flag isn't protected by mutex originally, so
cancel_hw_scan can pass the condition, but suddenly hw_scan completion
unset the flag and calls ieee80211_scan_completed() that will free
local->hw_scan_req. Then, cancel_hw_scan raises null-ptr-deref and
use-after-free. Fix it by moving the check condition to where
protected by mutex.

KASAN: null-ptr-deref in range [0x0000000000000088-0x000000000000008f]
CPU: 2 PID: 6922 Comm: kworker/2:2 Tainted: G OE
Hardware name: LENOVO 2356AD1/2356AD1, BIOS G7ETB6WW (2.76 ) 09/10/2019
Workqueue: events cfg80211_conn_work [cfg80211]
RIP: 0010:rtw89_fw_h2c_scan_offload_be+0xc33/0x13c3 [rtw89_core]
Code: 00 45 89 6c 24 1c 0f 85 23 01 00 00 48 8b 85 20 ff ff ff 48 8d
RSP: 0018:ffff88811fd9f068 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffff88811fd9f258 RCX: 0000000000000001
RDX: 0000000000000011 RSI: 0000000000000001 RDI: 0000000000000089
RBP: ffff88811fd9f170 R08: 0000000000000000 R09: 0000000000000000
R10: ffff88811fd9f108 R11: 0000000000000000 R12: ffff88810e47f960
R13: 0000000000000000 R14: 000000000000ffff R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8881d6f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007531dfca55b0 CR3: 00000001be296004 CR4: 00000000001706e0
Call Trace:
<TASK>
? show_regs+0x61/0x73
? __die_body+0x20/0x73
? die_addr+0x4f/0x7b
? exc_general_protection+0x191/0x1db
? asm_exc_general_protection+0x27/0x30
? rtw89_fw_h2c_scan_offload_be+0xc33/0x13c3 [rtw89_core]
? rtw89_fw_h2c_scan_offload_be+0x458/0x13c3 [rtw89_core]
? __pfx_rtw89_fw_h2c_scan_offload_be+0x10/0x10 [rtw89_core]
? do_raw_spin_lock+0x75/0xdb
? __pfx_do_raw_spin_lock+0x10/0x10
rtw89_hw_scan_offload+0xb5e/0xbf7 [rtw89_core]
? _raw_spin_unlock+0xe/0x24
? __mutex_lock.constprop.0+0x40c/0x471
? __pfx_rtw89_hw_scan_offload+0x10/0x10 [rtw89_core]
? __mutex_lock_slowpath+0x13/0x1f
? mutex_lock+0xa2/0xdc
? __pfx_mutex_lock+0x10/0x10
rtw89_hw_scan_abort+0x58/0xb7 [rtw89_core]
rtw89_ops_cancel_hw_scan+0x120/0x13b [rtw89_core]
ieee80211_scan_cancel+0x468/0x4d0 [mac80211]
ieee80211_prep_connection+0x858/0x899 [mac80211]
ieee80211_mgd_auth+0xbea/0xdde [mac80211]
? __pfx_ieee80211_mgd_auth+0x10/0x10 [mac80211]
? cfg80211_find_elem+0x15/0x29 [cfg80211]
? is_bss+0x1b7/0x1d7 [cfg80211]
ieee80211_auth+0x18/0x27 [mac80211]
cfg80211_mlme_auth+0x3bb/0x3e7 [cfg80211]
cfg80211_conn_do_work+0x410/0xb81 [cfg80211]
? __pfx_cfg80211_conn_do_work+0x10/0x10 [cfg80211]
? __kasan_check_read+0x11/0x1f
? psi_group_change+0x8bc/0x944
? __kasan_check_write+0x14/0x22
? mutex_lock+0x8e/0xdc
? __pfx_mutex_lock+0x10/0x10
? __pfx___radix_tree_lookup+0x10/0x10
cfg80211_conn_work+0x245/0x34d [cfg80211]
? __pfx_cfg80211_conn_work+0x10/0x10 [cfg80211]
? update_cfs_rq_load_avg+0x3bc/0x3d7
? sched_clock_noinstr+0x9/0x1a
? sched_clock+0x10/0x24
? sched_clock_cpu+0x7e/0x42e
? newidle_balance+0x796/0x937
? __pfx_sched_clock_cpu+0x10/0x10
? __pfx_newidle_balance+0x10/0x10
? __kasan_check_read+0x11/0x1f
? psi_group_change+0x8bc/0x944
? _raw_spin_unlock+0xe/0x24
? raw_spin_rq_unlock+0x47/0x54
? raw_spin_rq_unlock_irq+0x9/0x1f
? finish_task_switch.isra.0+0x347/0x586
? __schedule+0x27bf/0x2892
? mutex_unlock+0x80/0xd0
? do_raw_spin_lock+0x75/0xdb
? __pfx___schedule+0x10/0x10
process_scheduled_works+0x58c/0x821
worker_thread+0x4c7/0x586
? __kasan_check_read+0x11/0x1f
kthread+0x285/0x294
? __pfx_worker_thread+0x10/0x10
? __pfx_kthread+0x10/0x10
ret_from_fork+0x29/0x6f
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1b/0x30
</TASK>