CVE-2023-52771

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

cxl/port: Fix delete_endpoint() vs parent unregistration race

The CXL subsystem, at cxlmem ->probe() time, establishes a lineage of ports (struct cxlport objects) between an endpoint and the root of a CXL topology. Each port including the endpoint port is attached to the cxl_port driver.

Given that setup, it follows that when either any port in that lineage goes through a cxlport ->remove() event, or the memdev goes through a cxlmem ->remove() event. The hierarchy below the removed port, or the entire hierarchy if the memdev is removed needs to come down.

The delete_endpoint() callback is careful to check whether it is being called to tear down the hierarchy, or if it is only being called to teardown the memdev because an ancestor port is going through ->remove().

That care needs to take the device_lock() of the endpoint's parent. Which requires 2 bugs to be fixed:

1/ A reference on the parent is needed to prevent use-after-free scenarios like this signature:

BUG: spinlock bad magic on CPU#0, kworker/u56:0/11
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20230524-3.fc38 05/24/2023
Workqueue: cxl_port detach_memdev [cxl_core]
RIP: 0010:spin_bug+0x65/0xa0
Call Trace:
  do_raw_spin_lock+0x69/0xa0
 __mutex_lock+0x695/0xb80
 delete_endpoint+0xad/0x150 [cxl_core]
 devres_release_all+0xb8/0x110
 device_unbind_cleanup+0xe/0x70
 device_release_driver_internal+0x1d2/0x210
 detach_memdev+0x15/0x20 [cxl_core]
 process_one_work+0x1e3/0x4c0
 worker_thread+0x1dd/0x3d0

2/ In the case of RCH topologies, the parent device that needs to be locked is not always @port->dev as returned by cxlmemfind_port(), use endpoint->dev.parent instead.