NFC: NULL out the dev->rfkill to prevent UAF

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

NFC: NULL out the dev->rfkill to prevent UAF

Commit 3e3b5dfcd16a ("NFC: reorder the logic in nfc_{un,}register_device")
assumes the device_is_registered() in function nfc_dev_up() will help
to check when the rfkill is unregistered. However, this check only
take effect when device_del(&dev->dev) is done in nfc_unregister_device().
Hence, the rfkill object is still possible be dereferenced.

The crash trace in latest kernel (5.18-rc2):

[ 68.760105] ==================================================================
[ 68.760330] BUG: KASAN: use-after-free in __lock_acquire+0x3ec1/0x6750
[ 68.760756] Read of size 8 at addr ffff888009c93018 by task fuzz/313
[ 68.760756]
[ 68.760756] CPU: 0 PID: 313 Comm: fuzz Not tainted 5.18.0-rc2 #4
[ 68.760756] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 68.760756] Call Trace:
[ 68.760756] <TASK>
[ 68.760756] dump_stack_lvl+0x57/0x7d
[ 68.760756] print_report.cold+0x5e/0x5db
[ 68.760756] ? __lock_acquire+0x3ec1/0x6750
[ 68.760756] kasan_report+0xbe/0x1c0
[ 68.760756] ? __lock_acquire+0x3ec1/0x6750
[ 68.760756] __lock_acquire+0x3ec1/0x6750
[ 68.760756] ? lockdep_hardirqs_on_prepare+0x410/0x410
[ 68.760756] ? register_lock_class+0x18d0/0x18d0
[ 68.760756] lock_acquire+0x1ac/0x4f0
[ 68.760756] ? rfkill_blocked+0xe/0x60
[ 68.760756] ? lockdep_hardirqs_on_prepare+0x410/0x410
[ 68.760756] ? mutex_lock_io_nested+0x12c0/0x12c0
[ 68.760756] ? nla_get_range_signed+0x540/0x540
[ 68.760756] ? _raw_spin_lock_irqsave+0x4e/0x50
[ 68.760756] _raw_spin_lock_irqsave+0x39/0x50
[ 68.760756] ? rfkill_blocked+0xe/0x60
[ 68.760756] rfkill_blocked+0xe/0x60
[ 68.760756] nfc_dev_up+0x84/0x260
[ 68.760756] nfc_genl_dev_up+0x90/0xe0
[ 68.760756] genl_family_rcv_msg_doit+0x1f4/0x2f0
[ 68.760756] ? genl_family_rcv_msg_attrs_parse.constprop.0+0x230/0x230
[ 68.760756] ? security_capable+0x51/0x90
[ 68.760756] genl_rcv_msg+0x280/0x500
[ 68.760756] ? genl_get_cmd+0x3c0/0x3c0
[ 68.760756] ? lock_acquire+0x1ac/0x4f0
[ 68.760756] ? nfc_genl_dev_down+0xe0/0xe0
[ 68.760756] ? lockdep_hardirqs_on_prepare+0x410/0x410
[ 68.760756] netlink_rcv_skb+0x11b/0x340
[ 68.760756] ? genl_get_cmd+0x3c0/0x3c0
[ 68.760756] ? netlink_ack+0x9c0/0x9c0
[ 68.760756] ? netlink_deliver_tap+0x136/0xb00
[ 68.760756] genl_rcv+0x1f/0x30
[ 68.760756] netlink_unicast+0x430/0x710
[ 68.760756] ? memset+0x20/0x40
[ 68.760756] ? netlink_attachskb+0x740/0x740
[ 68.760756] ? __build_skb_around+0x1f4/0x2a0
[ 68.760756] netlink_sendmsg+0x75d/0xc00
[ 68.760756] ? netlink_unicast+0x710/0x710
[ 68.760756] ? netlink_unicast+0x710/0x710
[ 68.760756] sock_sendmsg+0xdf/0x110
[ 68.760756] __sys_sendto+0x19e/0x270
[ 68.760756] ? __ia32_sys_getpeername+0xa0/0xa0
[ 68.760756] ? fd_install+0x178/0x4c0
[ 68.760756] ? fd_install+0x195/0x4c0
[ 68.760756] ? kernel_fpu_begin_mask+0x1c0/0x1c0
[ 68.760756] __x64_sys_sendto+0xd8/0x1b0
[ 68.760756] ? lockdep_hardirqs_on+0xbf/0x130
[ 68.760756] ? syscall_enter_from_user_mode+0x1d/0x50
[ 68.760756] do_syscall_64+0x3b/0x90
[ 68.760756] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 68.760756] RIP: 0033:0x7f67fb50e6b3
...
[ 68.760756] RSP: 002b:00007f67fa91fe90 EFLAGS: 00000293 ORIG_RAX: 000000000000002c
[ 68.760756] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f67fb50e6b3
[ 68.760756] RDX: 000000000000001c RSI: 0000559354603090 RDI: 0000000000000003
[ 68.760756] RBP: 00007f67fa91ff00 R08: 00007f67fa91fedc R09: 000000000000000c
[ 68.760756] R10: 0000000000000000 R11: 0000000000000293 R12: 00007ffe824d496e
[ 68.760756] R13: 00007ffe824d496f R14: 00007f67fa120000 R15: 0000000000000003

[ 68.760756] </TASK>
[ 68.760756]
[ 68.760756] Allocated by task 279:
[ 68.760756] kasan_save_stack+0x1e/0x40
[
---truncated---