CVE-2023-52771 cxl/port: Fix delete_endpoint() vs parent unregistration race
A race condition in the Linux kernel CXL subsystem can cause a use-after-free and kernel crash during device unregistration.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2023-52771?
CVE-2023-52771 is a medium-severity vulnerability in Linux kernel, published on 21 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
cxl/port: Fix delete_endpoint() vs parent unregistration race
The CXL subsystem, at cxl_mem ->probe() time, establishes a lineage of ports (struct cxl_port 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 cxl_port ->remove() event, or the memdev goes through a cxl_mem ->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 cxl_mem_find_port(), use endpoint->dev.parent instead.
Weakness: CWE-362
Which versions are affected by CVE-2023-52771?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2023-52771?
Apply the vendor's patch.
Is CVE-2023-52771 being exploited?
There is no known exploitation of CVE-2023-52771 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2023-52771, DEBIAN-CVE-2023-52771, GHSA-pqqv-8xrg-2jg9, ROOT-OS-DEBIAN-12-CVE-2023-52771, UBUNTU-CVE-2023-52771.