Bluetooth: MGMT: Fix UAF of hci_conn_params in add_device_complete

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

Bluetooth: MGMT: Fix UAF of hci_conn_params in add_device_complete

add_device_complete() runs from the hci_cmd_sync_work kworker, which
holds only hci_req_sync_lock and *not* hci_dev_lock. It calls
hci_conn_params_lookup() and then dereferences the returned object
(params->flags) without taking hci_dev_lock:

params = hci_conn_params_lookup(hdev, &cp->addr.bdaddr,
le_addr_type(cp->addr.type));
...
device_flags_changed(NULL, hdev, &cp->addr.bdaddr,
cp->addr.type, hdev->conn_flags,
params ? params->flags : 0);

hci_conn_params_lookup() walks hdev->le_conn_params and is documented to
require hdev->lock. A concurrent MGMT_OP_REMOVE_DEVICE
(remove_device()), which does run under hci_dev_lock, can call
hci_conn_params_free() to list_del() and kfree() the very object the
lookup returned, so the subsequent params->flags read touches freed
memory [0].

Hold hci_dev_lock() across the hci_conn_params_lookup() and the read of
params->flags (and the matching event emission) so the lookup result
cannot be freed by a concurrent remove_device() before it is used,
honouring the locking contract of hci_conn_params_lookup().

[0]: (trailing page/memory-state dump trimmed)
BUG: KASAN: slab-use-after-free in add_device_complete+0x358/0x3d8 net/bluetooth/mgmt.c:7671
Read of size 1 at addr ffff000017ab26c1 by task kworker/u9:8/388

CPU: 1 UID: 0 PID: 388 Comm: kworker/u9:8 Not tainted 7.0.11 #20 PREEMPT
Hardware name: linux,dummy-virt (DT)
Workqueue: hci0 hci_cmd_sync_work
Call trace:
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0xb4/0xd4 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0x118/0x5d8 mm/kasan/report.c:482
kasan_report+0xb0/0xf4 mm/kasan/report.c:595
__asan_report_load1_noabort+0x20/0x2c mm/kasan/report_generic.c:378
add_device_complete+0x358/0x3d8 net/bluetooth/mgmt.c:7671
hci_cmd_sync_work+0x14c/0x240 net/bluetooth/hci_sync.c:334
process_one_work+0x628/0xd38 kernel/workqueue.c:3289
process_scheduled_works kernel/workqueue.c:3372 [inline]
worker_thread+0x7a8/0xac0 kernel/workqueue.c:3453
kthread+0x39c/0x444 kernel/kthread.c:436
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:860

Allocated by task 3401:
kasan_save_stack+0x3c/0x64 mm/kasan/common.c:57
kasan_save_track+0x20/0x3c mm/kasan/common.c:78
kasan_save_alloc_info+0x40/0x54 mm/kasan/generic.c:570
poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
__kasan_kmalloc+0xd4/0xd8 mm/kasan/common.c:415
kasan_kmalloc include/linux/kasan.h:263 [inline]
__kmalloc_cache_noprof+0x1b0/0x458 mm/slub.c:5385
kmalloc_noprof include/linux/slab.h:950 [inline]
kzalloc_noprof include/linux/slab.h:1188 [inline]
hci_conn_params_add+0x10c/0x4b0 net/bluetooth/hci_core.c:2279
hci_conn_params_set net/bluetooth/mgmt.c:5162 [inline]
add_device+0x5b4/0xa54 net/bluetooth/mgmt.c:7755
hci_mgmt_cmd net/bluetooth/hci_sock.c:1721 [inline]
hci_sock_sendmsg+0x10b4/0x1dd0 net/bluetooth/hci_sock.c:1841
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg+0xe0/0x128 net/socket.c:742
sock_write_iter+0x250/0x390 net/socket.c:1195
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x66c/0xab0 fs/read_write.c:688
ksys_write+0x1fc/0x24c fs/read_write.c:740
__do_sys_write fs/read_write.c:751 [inline]
__se_sys_write fs/read_write.c:748 [inline]
__arm64_sys_write+0x70/0xa4 fs/read_write.c:748
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x84/0x2a8 arch/arm64/kernel/syscall.c:49
el0_svc_common.constprop.0+0xe4/0x294 arch/arm64/kernel/syscall.c:132
do_el0_svc+0x44/0x5c arch/arm64/kernel/syscall.c:151
el0_svc+0x38/0xac arch/arm64/kernel/entry-common.c:724
el0t_64_sync_handler+0xa0/0xe4 arch/arm64/kernel/entry-common.c:743
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Freed by task 3740:
kasan_save_stack+0x3c/0x64
---truncated---