CVE-2023-52771 in Linux
Summary
by MITRE • 05/21/2024
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.
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Analysis
by VulDB Data Team • 09/23/2025
The vulnerability CVE-2023-52771 resides within the Linux kernel's Compute Express Link (CXL) subsystem, specifically affecting the cxl_mem driver's handling of endpoint removal operations. This issue manifests as a race condition between the delete_endpoint() function and parent device unregistration processes, creating potential system instability and memory corruption scenarios. The CXL subsystem manages complex port hierarchies connecting endpoints to the root of a CXL topology, where each port including the endpoint port is attached to the cxl_port driver, establishing a structured lineage that must be carefully managed during device lifecycle operations.
The technical flaw stems from inadequate synchronization mechanisms during the cleanup process when either individual ports or entire memory devices undergo removal events. The delete_endpoint() callback attempts to distinguish between complete hierarchy teardown scenarios versus partial teardown caused by ancestor port removals, but fails to properly acquire the device_lock() of the endpoint's parent device. This oversight creates a critical race condition where the parent device reference may be freed while still being accessed, leading to use-after-free conditions and subsequent system crashes. The kernel's spinlock subsystem detects these invalid memory accesses, generating critical error messages indicating spinlock corruption and triggering system panics that can result in complete system hang or reboot.
The operational impact of this vulnerability extends beyond simple system stability concerns, potentially affecting data integrity and system availability in environments relying on CXL memory subsystems. Attackers could potentially exploit this race condition to cause denial of service conditions or in more sophisticated scenarios, leverage the memory corruption for privilege escalation attacks. The vulnerability specifically impacts systems utilizing RCH (Root Complex Hierarchy) topologies where the parent device locking mechanism requires special handling, as the standard cxl_mem_find_port() function may not always return the correct parent device reference needed for proper locking operations. This issue affects the broader CXL ecosystem and could compromise the reliability of high-performance computing systems, data center infrastructure, and server platforms that depend on CXL memory expansion capabilities.
Mitigation strategies should focus on implementing proper reference counting mechanisms to prevent premature device freeing and ensuring correct parent device locking during endpoint removal operations. System administrators should apply kernel updates containing the patched CXL subsystem code immediately, as the vulnerability can be exploited to cause system crashes and potential data loss. The fix requires maintaining proper reference counts on parent devices throughout the removal lifecycle and using the correct device parent reference endpoint->dev.parent instead of relying solely on cxl_mem_find_port() return values for locking operations. Organizations using CXL-enabled systems should monitor their kernel versions and ensure all patches are applied, particularly in production environments where system stability and data integrity are paramount. This vulnerability aligns with CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) and could be mapped to ATT&CK technique T1499.001 (Endpoint Termination) in threat modeling contexts, representing a critical security concern for enterprise computing infrastructures.