CVE-2024-35997 in Linux
Summary
by MITRE • 05/20/2024
In the Linux kernel, the following vulnerability has been resolved:
HID: i2c-hid: remove I2C_HID_READ_PENDING flag to prevent lock-up
The flag I2C_HID_READ_PENDING is used to serialize I2C operations. However, this is not necessary, because I2C core already has its own locking for that.
More importantly, this flag can cause a lock-up: if the flag is set in i2c_hid_xfer() and an interrupt happens, the interrupt handler (i2c_hid_irq) will check this flag and return immediately without doing anything, then the interrupt handler will be invoked again in an infinite loop.
Since interrupt handler is an RT task, it takes over the CPU and the flag-clearing task never gets scheduled, thus we have a lock-up.
Delete this unnecessary flag.
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Analysis
by VulDB Data Team • 01/17/2025
The vulnerability described in CVE-2024-35997 resides within the Linux kernel's HID (Human Interface Device) subsystem, specifically in the i2c-hid driver component. This issue represents a critical concurrency problem that can lead to system lock-ups and complete denial of service conditions. The vulnerability manifests in how the driver handles I2C (Inter-Integrated Circuit) communication operations through the HID interface, creating a scenario where improper locking mechanisms can cause system-wide paralysis. The problem is particularly severe because it affects the fundamental input device handling capabilities of Linux systems, potentially impacting desktop environments, servers, and embedded devices that rely on HID peripherals.
The technical flaw centers on the unnecessary I2C_HID_READ_PENDING flag that was implemented to serialize I2C operations within the driver. This flag was intended to manage concurrent access to I2C resources, but it was fundamentally flawed due to its redundancy with existing kernel infrastructure. The Linux I2C core already provides robust locking mechanisms for handling concurrent I2C operations, making the custom flag implementation not only unnecessary but actively harmful. The flag's presence creates a race condition scenario where the flag is set during the i2c_hid_xfer() function execution, but an interrupt event can cause the interrupt handler i2c_hid_irq to check this flag and return immediately without performing its intended work. This creates a pathological condition where the interrupt handler continuously invokes itself in an infinite loop, as the flag is never cleared due to the interrupt handler monopolizing CPU resources.
The operational impact of this vulnerability extends beyond simple system instability to encompass complete system lock-ups that can render devices unusable. When the interrupt handler enters this infinite loop, it operates as a real-time task that consumes CPU cycles exclusively, preventing the kernel scheduler from executing the task responsible for clearing the problematic flag. This creates a deadlock scenario where the system becomes unresponsive to user input and peripheral operations, effectively causing a denial of service condition. The vulnerability affects any Linux system utilizing HID devices connected via I2C bus, including laptops, desktop computers, servers, and embedded systems, making it particularly concerning for enterprise environments where system availability is critical. The lock-up condition can persist until manual intervention occurs, such as system reboot or power cycling, which can be disruptive in mission-critical applications.
The mitigation strategy for this vulnerability involves removing the redundant I2C_HID_READ_PENDING flag from the i2c-hid driver implementation, allowing the existing I2C core locking mechanisms to handle concurrent access properly. This change aligns with established kernel development practices that favor leveraging existing infrastructure rather than implementing redundant solutions. The fix addresses the root cause by eliminating the conflicting locking mechanism that was causing the interrupt handler to enter an infinite loop. System administrators and kernel maintainers should ensure that affected systems are updated with patched kernel versions that contain this fix. The solution demonstrates the importance of proper kernel concurrency management and highlights the risks associated with over-engineering locking mechanisms that can inadvertently create more problems than they solve. This vulnerability serves as a reminder of the critical importance of careful kernel development practices and the potential for seemingly minor concurrency issues to cause significant system-wide failures, aligning with CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) and ATT&CK technique T1490 (Inhibit System Recovery) through its potential to cause system lock-ups and denial of service conditions.