cxl/port: Hold port reference until decoder release

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

cxl/port: Hold port reference until decoder release

KASAN + DEBUG_KOBJECT_RELEASE reports a potential use-after-free in

cxl_decoder_release() where it goes to reference its parent, a cxl_port,

to free its id back to port->decoder_ida.

BUG: KASAN: use-after-free in to_cxl_port+0x18/0x90 [cxl_core]

Read of size 8 at addr ffff888119270908 by task kworker/35:2/379

CPU: 35 PID: 379 Comm: kworker/35:2 Tainted: G OE 5.17.0-rc2+ #198

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015

Workqueue: events kobject_delayed_cleanup

Call Trace:

<TASK>

dump_stack_lvl+0x59/0x73

print_address_description.constprop.0+0x1f/0x150

? to_cxl_port+0x18/0x90 [cxl_core]

kasan_report.cold+0x83/0xdf

? to_cxl_port+0x18/0x90 [cxl_core]

to_cxl_port+0x18/0x90 [cxl_core]

cxl_decoder_release+0x2a/0x60 [cxl_core]

device_release+0x5f/0x100

kobject_cleanup+0x80/0x1c0

The device core only guarantees parent lifetime until all children are

unregistered. If a child needs a parent to complete its ->release()

callback that child needs to hold a reference to extend the lifetime of

the parent.