CVE-2026-97972
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
net: macb: put the "mdio" child node reference on success
macb_mii_init() holds the reference returned by of_get_child_by_name() for macb_mdiobus_register() and drops it only on the error paths, so every successful probe leaks a node reference. On a CM5, overlay removal after four bind cycles reports
OF: ERROR: memory leak, expected refcount 1 instead of 5
Drop the reference after registration, where __mdiobus_register() has already taken its own for the lifetime of the bus.
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Analysis
by VulDB Data Team • 09/25/2026
The Linux kernel networking subsystem contains a resource management flaw within the MACB Ethernet driver that results in an object reference leak during device initialization. This vulnerability is rooted in improper handling of Device Tree node references acquired through the Open Firmware API functions, specifically when initializing the Media Independent Interface (MII) bus for network hardware. The core issue lies in the macb_mii_init function, which retrieves a child node named mdio using of_get_child_by_name and subsequently passes this reference to macb_mdiobus_register. While the driver correctly releases the reference on error paths where registration fails, it neglects to decrement the reference count upon successful completion of the probe operation. This oversight violates standard kernel resource management practices which dictate that every increment in a reference counter must have a corresponding decrement when the object is no longer needed by the caller.
From a technical perspective, this defect constitutes an improper cleanup mechanism for allocated resources, aligning with CWE-401: Missing Release of Resource after Effective Lifetime. The function __mdiobus_register internally takes its own reference to ensure the bus structure remains valid during its operational lifetime within the kernel networking stack. Consequently, when macb_mii_init retains the original node reference returned by of_get_child_by_name without releasing it, the system accumulates orphaned references that are never freed. This leads to a gradual accumulation of unreleased memory structures associated with the device tree nodes, creating a persistent leak in the kernel's internal data structures rather than general RAM exhaustion, although both can occur depending on frequency and scale.
The operational impact of this vulnerability is most observable during dynamic configuration changes involving Device Tree overlays, particularly on platforms like the CM5 where such operations are common. When an overlay containing network device definitions is removed after multiple bind cycles, the kernel detects a discrepancy in reference counts because the leaked references prevent proper cleanup of the node hierarchy. The system logs errors indicating that memory leaks have occurred, with expected refcounts significantly lower than actual values due to these accumulated unreleased nodes. Over time, repeated binding and unbinding operations can lead to increased memory consumption within the kernel space, potentially degrading system performance or causing instability in resource-constrained embedded environments where such drivers are frequently deployed.
To mitigate this vulnerability, developers must ensure that reference counts are balanced correctly during all execution paths of device initialization routines. Specifically, after successfully registering the MDIO bus via __mdiobus_register, which assumes ownership and maintains its own reference for the duration of the bus lifecycle, the driver should explicitly drop the initial node reference obtained from of_get_child_by_name using of_node_put. This adjustment aligns with ATT&CK technique T1078: Valid Accounts if viewed through the lens of maintaining system integrity against resource exhaustion attacks that could lead to denial-of-service conditions. By correcting this logic, the kernel maintains proper accounting of device tree nodes and prevents the accumulation of stale references during normal operational cycles involving dynamic hardware configuration changes.