wifi: cfg80211: cancel rfkill_block work in wiphy_unregister()

There is a use-after-free error in cfg80211_shutdown_all_interfaces found
by syzkaller:

BUG: KASAN: use-after-free in cfg80211_shutdown_all_interfaces+0x213/0x220
Read of size 8 at addr ffff888112a78d98 by task kworker/0:5/5326
CPU: 0 UID: 0 PID: 5326 Comm: kworker/0:5 Not tainted 6.19.0-rc2 #2 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
Workqueue: events cfg80211_rfkill_block_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x116/0x1f0
 print_report+0xcd/0x630
 kasan_report+0xe0/0x110
 cfg80211_shutdown_all_interfaces+0x213/0x220
 cfg80211_rfkill_block_work+0x1e/0x30
 process_one_work+0x9cf/0x1b70
 worker_thread+0x6c8/0xf10
 kthread+0x3c5/0x780
 ret_from_fork+0x56d/0x700
 ret_from_fork_asm+0x1a/0x30
 </TASK>

The problem arises due to the rfkill_block work is not cancelled when wiphy
is being unregistered. In order to fix the issue cancel the corresponding
work in wiphy_unregister().

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 1f87f7d ("cfg80211: add rfkill support")
Cc: stable@vger.kernel.org
Signed-off-by: Daniil Dulov <d.dulov@aladdin.ru>
Link: https://patch.msgid.link/20260211082024.1967588-1-d.dulov@aladdin.ru
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: Daniil Dulov

net/wireless/core.c

@@ -1212,6 +1212,7 @@ void wiphy_unregister(struct wiphy *wiphy)
 	/* this has nothing to do now but make sure it's gone */
 	cancel_work_sync(&rdev->wiphy_work);
 
+	cancel_work_sync(&rdev->rfkill_block);
 	cancel_work_sync(&rdev->conn_work);
 	flush_work(&rdev->event_work);
 	cancel_delayed_work_sync(&rdev->dfs_update_channels_wk);