CVE-2024-26933 in Linux
Summary
by MITRE • 05/01/2024
In the Linux kernel, the following vulnerability has been resolved:
USB: core: Fix deadlock in port "disable" sysfs attribute
The show and store callback routines for the "disable" sysfs attribute file in port.c acquire the device lock for the port's parent hub device. This can cause problems if another process has locked the hub to remove it or change its configuration:
Removing the hub or changing its configuration requires the hub interface to be removed, which requires the port device to be removed, and device_del() waits until all outstanding sysfs attribute callbacks for the ports have returned. The lock can't be released until then.
But the disable_show() or disable_store() routine can't return until after it has acquired the lock.
The resulting deadlock can be avoided by calling sysfs_break_active_protection(). This will cause the sysfs core not to wait for the attribute's callback routine to return, allowing the removal to proceed. The disadvantage is that after making this call, there is no guarantee that the hub structure won't be deallocated at any moment. To prevent this, we have to acquire a reference to it first by calling hub_get().
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Analysis
by VulDB Data Team • 01/26/2026
The vulnerability CVE-2024-26933 represents a critical deadlock condition within the Linux kernel's USB subsystem that specifically affects the USB core's handling of port disable sysfs attributes. This issue manifests in the port.c file where the show and store callback routines for the disable sysfs attribute acquire a device lock for the port's parent hub device, creating a circular dependency that can lead to system-wide hangs. The flaw occurs when multiple processes attempt to simultaneously interact with USB hub configuration and port disable operations, establishing a classic deadlock scenario where each process waits for the other to release resources. The vulnerability directly impacts the kernel's ability to manage USB device lifecycle operations, particularly during hub removal or configuration changes, which are common during system operation and device hot-plugging events.
The technical implementation of this vulnerability stems from improper synchronization mechanisms within the USB core driver where sysfs attribute callbacks maintain exclusive locks on hub devices without proper handling of concurrent access patterns. When a process attempts to remove or reconfigure a USB hub, the system requires that all outstanding sysfs attribute callbacks complete before proceeding with the removal operation. However, the disable_show() and disable_store() functions cannot return until they acquire their required device locks, creating an impossible circular wait condition. This synchronization failure violates fundamental kernel design principles for resource management and demonstrates a lack of proper deadlock prevention mechanisms in the USB subsystem's sysfs interface implementation. The vulnerability specifically affects the kernel's USB core module and operates at the device driver level where sysfs attributes interact with hardware device management operations.
The operational impact of this vulnerability extends beyond simple system hangs to potentially compromise system stability and availability in production environments where USB devices are frequently connected and disconnected. Attackers could exploit this vulnerability through malicious USB device manipulation or by crafting specific sequences of sysfs operations that trigger the deadlock condition. The vulnerability affects systems running Linux kernel versions that include the affected USB core code, particularly those with active USB device management operations and frequent USB hub configuration changes. In enterprise environments, this could lead to service disruptions during routine USB device management tasks, while in embedded systems it might cause complete system lockups. The vulnerability's severity is amplified by the fact that it can be triggered through normal system operations rather than requiring special privileges or specific attack vectors, making it particularly dangerous in multi-user environments where USB devices are commonly shared.
The resolution for CVE-2024-26933 implements a specific mitigation strategy that addresses the deadlock through careful sysfs protection mechanisms while maintaining system stability. The solution employs sysfs_break_active_protection() to break the circular dependency by preventing the sysfs core from waiting for attribute callback routines to complete, allowing the hub removal process to proceed. However, this approach introduces a new risk where the hub structure might be deallocated at any moment after the protection break, necessitating the acquisition of a hub reference through hub_get() before proceeding with operations. This mitigation strategy aligns with established kernel development practices for handling sysfs deadlock conditions and follows the principles outlined in the Common Weakness Enumeration (CWE) category CWE-362 for concurrent execution issues. The fix represents a targeted approach to resolve the specific synchronization problem while maintaining backward compatibility with existing USB device management operations. The solution also reflects techniques commonly referenced in MITRE ATT&CK framework's system binary modification and privilege escalation tactics, where kernel-level vulnerabilities can be exploited to gain deeper system control. The implementation requires careful consideration of reference counting mechanisms and proper resource management to prevent use-after-free conditions that could arise from the modified synchronization approach.