Bluetooth: use RCU for hci_conn_params and iterate safely in hci_sync

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

Bluetooth: use RCU for hci_conn_params and iterate safely in hci_sync

hci_update_accept_list_sync iterates over hdev->pend_le_conns and
hdev->pend_le_reports, and waits for controller events in the loop body,
without holding hdev lock.

Meanwhile, these lists and the items may be modified e.g. by
le_scan_cleanup. This can invalidate the list cursor or any other item
in the list, resulting to invalid behavior (eg use-after-free).

Use RCU for the hci_conn_params action lists. Since the loop bodies in
hci_sync block and we cannot use RCU or hdev->lock for the whole loop,
copy list items first and then iterate on the copy. Only the flags field
is written from elsewhere, so READ_ONCE/WRITE_ONCE should guarantee we
read valid values.

Free params everywhere with hci_conn_params_free so the cleanup is
guaranteed to be done properly.

This fixes the following, which can be triggered e.g. by BlueZ new
mgmt-tester case "Add + Remove Device Nowait - Success", or by changing
hci_le_set_cig_params to always return false, and running iso-tester:

==================================================================
BUG: KASAN: slab-use-after-free in hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2536 net/bluetooth/hci_sync.c:2723 net/bluetooth/hci_sync.c:2841)
Read of size 8 at addr ffff888001265018 by task kworker/u3:0/32

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc38 04/01/2014
Workqueue: hci0 hci_cmd_sync_work
Call Trace:
<TASK>
dump_stack_lvl (./arch/x86/include/asm/irqflags.h:134 lib/dump_stack.c:107)
print_report (mm/kasan/report.c:320 mm/kasan/report.c:430)
? __virt_addr_valid (./include/linux/mmzone.h:1915 ./include/linux/mmzone.h:2011 arch/x86/mm/physaddr.c:65)
? hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2536 net/bluetooth/hci_sync.c:2723 net/bluetooth/hci_sync.c:2841)
kasan_report (mm/kasan/report.c:538)
? hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2536 net/bluetooth/hci_sync.c:2723 net/bluetooth/hci_sync.c:2841)
hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2536 net/bluetooth/hci_sync.c:2723 net/bluetooth/hci_sync.c:2841)
? __pfx_hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2780)
? mutex_lock (kernel/locking/mutex.c:282)
? __pfx_mutex_lock (kernel/locking/mutex.c:282)
? __pfx_mutex_unlock (kernel/locking/mutex.c:538)
? __pfx_update_passive_scan_sync (net/bluetooth/hci_sync.c:2861)
hci_cmd_sync_work (net/bluetooth/hci_sync.c:306)
process_one_work (./arch/x86/include/asm/preempt.h:27 kernel/workqueue.c:2399)
worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2538)
? __pfx_worker_thread (kernel/workqueue.c:2480)
kthread (kernel/kthread.c:376)
? __pfx_kthread (kernel/kthread.c:331)
ret_from_fork (arch/x86/entry/entry_64.S:314)
</TASK>

Allocated by task 31:
kasan_save_stack (mm/kasan/common.c:46)
kasan_set_track (mm/kasan/common.c:52)
__kasan_kmalloc (mm/kasan/common.c:374 mm/kasan/common.c:383)
hci_conn_params_add (./include/linux/slab.h:580 ./include/linux/slab.h:720 net/bluetooth/hci_core.c:2277)
hci_connect_le_scan (net/bluetooth/hci_conn.c:1419 net/bluetooth/hci_conn.c:1589)
hci_connect_cis (net/bluetooth/hci_conn.c:2266)
iso_connect_cis (net/bluetooth/iso.c:390)
iso_sock_connect (net/bluetooth/iso.c:899)
__sys_connect (net/socket.c:2003 net/socket.c:2020)
__x64_sys_connect (net/socket.c:2027)
do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)

Freed by task 15:
kasan_save_stack (mm/kasan/common.c:46)
kasan_set_track (mm/kasan/common.c:52)
kasan_save_free_info (mm/kasan/generic.c:523)
__kasan_slab_free (mm/kasan/common.c:238 mm/kasan/common.c:200 mm/kasan/common.c:244)
__kmem_cache_free (mm/slub.c:1807 mm/slub.c:3787 mm/slub.c:3800)
hci_conn_params_del (net/bluetooth/hci_core.c:2323)
le_scan_cleanup (net/bluetooth/hci_conn.c:202)
process_one_work (./arch/x86/include/asm/preempt.
---truncated---