Bluetooth: hci_conn: Lock parent access during enhanced SCO setup

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

Bluetooth: hci_conn: Lock parent access during enhanced SCO setup

Bluetooth: hci_conn: Lock parent access during enhanced SCO setup

hci_enhanced_setup_sync() runs on the request workqueue without the
hci_dev_lock held by its caller when setup was queued. Its CVSD
capability check and find_next_esco_param() dereference conn->parent
while the receive workqueue can unlink and release that parent.

The following interleaving can cause a use-after-free:

hci_enhanced_setup_sync() hci_disconn_complete_evt()
load conn->parent
hci_dev_lock()
hci_conn_del(ACL parent)
unlink SCO child
drop link's parent reference
clear child->parent
release ACL parent
bt_link_release()
kfree(parent)
hci_dev_unlock()
read parent->features[0][3]

The reference held for the queued SCO child does not keep its ACL parent
alive after unlinking. Commit 42de40abe25d ("Bluetooth: hci_conn: fix the
SCO setup context lifetime") protects the child stored in the queued
context, but leaves these parent accesses unprotected.

With a 40 ms diagnostic delay after loading conn->parent, an instrumented
kernel based on fd179f8a05be, which already contains 42de40abe25d,

BUG: KASAN: slab-use-after-free in hci_enhanced_setup_sync+0xda5/0xdf0
Read of size 1 at addr ffff888102204047 by task kworker/u17:0/93
Call Trace:
hci_enhanced_setup_sync+0xda5/0xdf0
hci_cmd_sync_work+0x13c/0x290
process_one_work+0x6b4/0x10e0

Allocated by task 92:
__hci_conn_add+0x304/0x1df0
hci_connect_acl+0x349/0x3e0
hci_connect_sco+0x3b/0x9a0
sco_sock_connect+0x475/0xca0

Freed by task 94:
kfree+0x121/0x3c0
bt_link_release+0x79/0xa0
device_release+0xc8/0x240
kobject_put+0x14d/0x280
hci_conn_del+0x524/0xe30
hci_disconn_complete_evt+0x403/0x8c0
hci_event_packet+0x71b/0xb20
hci_rx_work+0x293/0x730

The accessed address is 71 bytes into the freed ACL parent, at its
features[0][3] byte; the queued SCO child is a different object. The
diagnostic preserves the loaded parent across the delay, matching the
unmodified compiled capability check, and does not change the parent
references or teardown path.

Hold hci_dev_lock() across the codec switch, including every call to
find_next_esco_param(), and release it on all selection errors. Keep
configure_datapath_sync() outside the critical section because it waits
for HCI events. Preserve parameter selection and existing return values.