Bluetooth: hci_conn: Fix UAF in hci_enhanced_setup_sync

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

Bluetooth: hci_conn: Fix UAF in hci_enhanced_setup_sync

This checks if the ACL connection remains valid as it could be destroyed
while hci_enhanced_setup_sync is pending on cmd_sync leading to the
following trace:

BUG: KASAN: slab-use-after-free in hci_enhanced_setup_sync+0x91b/0xa60
Read of size 1 at addr ffff888002328ffd by task kworker/u5:2/37

CPU: 0 UID: 0 PID: 37 Comm: kworker/u5:2 Not tainted 6.11.0-rc6-01300-g810be445d8d6 #7099
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-2.fc40 04/01/2014
Workqueue: hci0 hci_cmd_sync_work
Call Trace:
<TASK>
dump_stack_lvl+0x5d/0x80
? hci_enhanced_setup_sync+0x91b/0xa60
print_report+0x152/0x4c0
? hci_enhanced_setup_sync+0x91b/0xa60
? __virt_addr_valid+0x1fa/0x420
? hci_enhanced_setup_sync+0x91b/0xa60
kasan_report+0xda/0x1b0
? hci_enhanced_setup_sync+0x91b/0xa60
hci_enhanced_setup_sync+0x91b/0xa60
? __pfx_hci_enhanced_setup_sync+0x10/0x10
? __pfx___mutex_lock+0x10/0x10
hci_cmd_sync_work+0x1c2/0x330
process_one_work+0x7d9/0x1360
? __pfx_lock_acquire+0x10/0x10
? __pfx_process_one_work+0x10/0x10
? assign_work+0x167/0x240
worker_thread+0x5b7/0xf60
? __kthread_parkme+0xac/0x1c0
? __pfx_worker_thread+0x10/0x10
? __pfx_worker_thread+0x10/0x10
kthread+0x293/0x360
? __pfx_kthread+0x10/0x10
ret_from_fork+0x2f/0x70
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30
</TASK>

Allocated by task 34:
kasan_save_stack+0x30/0x50
kasan_save_track+0x14/0x30
__kasan_kmalloc+0x8f/0xa0
__hci_conn_add+0x187/0x17d0
hci_connect_sco+0x2e1/0xb90
sco_sock_connect+0x2a2/0xb80
__sys_connect+0x227/0x2a0
__x64_sys_connect+0x6d/0xb0
do_syscall_64+0x71/0x140
entry_SYSCALL_64_after_hwframe+0x76/0x7e

Freed by task 37:
kasan_save_stack+0x30/0x50
kasan_save_track+0x14/0x30
kasan_save_free_info+0x3b/0x60
__kasan_slab_free+0x101/0x160
kfree+0xd0/0x250
device_release+0x9a/0x210
kobject_put+0x151/0x280
hci_conn_del+0x448/0xbf0
hci_abort_conn_sync+0x46f/0x980
hci_cmd_sync_work+0x1c2/0x330
process_one_work+0x7d9/0x1360
worker_thread+0x5b7/0xf60
kthread+0x293/0x360
ret_from_fork+0x2f/0x70
ret_from_fork_asm+0x1a/0x30