CVE-2017-8071 in Linux
Summary
by MITRE
drivers/hid/hid-cp2112.c in the Linux kernel 4.9.x before 4.9.9 uses a spinlock without considering that sleeping is possible in a USB HID request callback, which allows local users to cause a denial of service (deadlock) via unspecified vectors.
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Analysis
by VulDB Data Team • 08/25/2024
The vulnerability identified as CVE-2017-8071 resides within the Linux kernel's USB HID driver implementation, specifically in the hid-cp2112.c file that manages Silicon Laboratories CP2112 USB-to-SPI bridge devices. This flaw represents a classic concurrency issue where improper locking mechanisms create conditions that can lead to system instability and complete service disruption. The vulnerability affects Linux kernel versions 4.9.x prior to 4.9.9, making it a significant concern for systems running these kernel versions where USB HID devices are actively utilized.
The technical root cause of this vulnerability stems from the improper use of spinlocks within the USB HID request callback context. Spinlocks are designed for scenarios where the locked resource is expected to be held for very brief periods, typically in interrupt contexts or other non-sleeping environments. However, in this case, the driver employs spinlocks while processing USB HID requests that may involve operations capable of sleeping or blocking, creating a fundamental mismatch between the locking mechanism and the actual execution context. According to CWE-667, this represents an improper locking scenario where a spinlock is used inappropriately, leading to potential deadlock conditions. The USB HID subsystem's callback execution context may legitimately sleep during device communication operations, which directly conflicts with the spinlock's non-sleeping nature.
The operational impact of this vulnerability manifests as a potential deadlock condition that can result in complete system denial of service. Local users with access to the affected system can exploit this weakness by triggering specific USB HID device operations that cause the kernel to enter a deadlock state. This occurs because the spinlock prevents other kernel threads from executing while the sleeping USB HID request callback attempts to acquire the same lock, creating a circular dependency that halts system responsiveness. The ATT&CK framework categorizes this as a privilege escalation technique through kernel exploitation, as local users can leverage this vulnerability to gain system control through denial of service attacks. The vulnerability is particularly concerning because it requires no special privileges beyond local system access and can be triggered through normal USB HID device operations.
Mitigation strategies for CVE-2017-8071 focus on upgrading to Linux kernel versions 4.9.9 or later where the issue has been resolved through proper locking implementation. The fix involves replacing the inappropriate spinlock usage with mutexes or other locking primitives that can safely handle sleeping operations within the USB HID callback context. System administrators should prioritize patching affected systems, particularly those running kernel versions 4.9.0 through 4.9.8, as these are most vulnerable to exploitation. Additionally, organizations should implement monitoring for unusual system behavior that might indicate a deadlock condition, as the vulnerability's impact is typically subtle and may not be immediately apparent. The solution aligns with industry best practices for kernel security where proper synchronization primitives are selected based on the execution context and potential blocking behaviors of the operations involved. Regular kernel updates and security audits should be maintained to prevent similar concurrency issues from arising in other kernel subsystems.