CVE-2026-80622 in Linux
Summary
by MITRE • 08/28/2026
In the Linux kernel, the following vulnerability has been resolved:
char: tlclk: fix use-after-free in tlclk_cleanup()
This patch improves the module cleanup process in the tlclk driver to prevent potential use-after-free and race conditions.
Currently, the file_operations structure does not specify the .owner field, which could allow the module to be unloaded while user-space processes are still interacting with the device. Additionally, the tlclk_cleanup() function frees the alarm_events memory before ensuring that blocked processes in the waitqueue are fully awakened and that the switchover_timer has completed.
To address these cases, this patch: - Sets '.owner = THIS_MODULE' in tlclk_fops to safely defer module unloading while the device is in use. - Updates tlclk_cleanup() to explicitly wake up all blocked readers (wake_up_all), properly release hardware I/O regions, and safely delete the timer (timer_delete_sync) prior to freeing memory.
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Analysis
by VulDB Data Team • 08/28/2026
The vulnerability identified within the Linux kernel's char:tlclk driver represents a critical class of concurrency-related defects that compromise system stability and data integrity through improper resource lifecycle management. Specifically, this issue manifests as a use-after-free condition coupled with race conditions during module cleanup operations. In complex operating systems like Linux, character device drivers must meticulously manage their interaction with user-space applications to prevent scenarios where kernel memory is accessed after it has been deallocated or when hardware resources are released while still in active use by pending I/O requests. The tlclk driver, which handles specific hardware clocking functions, lacked sufficient safeguards during its teardown phase, creating a window of opportunity for these dangerous states to occur under concurrent access patterns.
The root cause of this vulnerability lies primarily in the omission of the .owner field within the file_operations structure associated with the device. In Linux kernel programming, setting .owner = THIS_MODULE is a standard mechanism that ties the lifetime of the loadable module to the usage count of its devices. Without this assignment, the kernel does not prevent the driver from being unloaded while user-space processes still have open file descriptors or are actively performing I/O operations on the device. This oversight allows for a scenario where the module code and associated data structures can be removed from memory by an administrator or automated system process even though active threads in user space are attempting to interact with them, leading directly to use-after-free errors when those threads attempt to execute driver functions that no longer exist in valid memory regions.
Furthermore, the tlclk_cleanup() function exhibited a flawed sequence of operations regarding resource release and synchronization primitives. The original implementation proceeded to free the alarm_events memory structure before ensuring that all processes blocked on the device's waitqueue were fully awakened and before guaranteeing that any active hardware timers had completed their execution cycles. This premature deallocation means that if a process was sleeping in an interruptible sleep state waiting for data or events from this driver, it would remain suspended even after the cleanup began, potentially leading to deadlocks or undefined behavior when the system attempted to resume those tasks against freed memory contexts. Additionally, hardware I/O regions were not properly released before memory deallocation, which could result in resource leaks and conflicts with other drivers attempting to access the same physical addresses.
The operational impact of this vulnerability is significant for systems relying on stable kernel module loading and unloading cycles, particularly in environments where dynamic driver updates or frequent restarts are common. A successful exploitation scenario does not necessarily require malicious intent from an attacker; rather, it can be triggered by legitimate administrative actions combined with concurrent user activity. The use-after-free condition poses a severe risk as it allows for arbitrary code execution if the freed memory is reallocated and overwritten with controlled data before being accessed again. This aligns closely with CWE-416 (Use After Free), which describes situations where pointers are used after they have been freed, leading to crashes or privilege escalation. The race condition aspect also relates to CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization).
From a threat modeling perspective, this vulnerability can be mapped to MITRE ATT&CK techniques involving resource hijacking and exploitation of software vulnerabilities for initial access or persistence if an attacker can induce the specific timing conditions. The lack of proper synchronization allows an adversary who controls user-space processes interacting with the device to potentially influence kernel execution flow through carefully timed race windows, although exploiting this typically requires local access and precise timing control.
To mitigate these risks, the patch implements several critical corrections that restore robustness to the driver's lifecycle management. First, by explicitly setting .owner = THIS_MODULE in the tlclk_fops structure, the kernel now correctly increments a reference count whenever an application opens the device file. This ensures that the module cannot be unloaded until all open references are closed, effectively eliminating the primary vector for use-after-free during unloading operations. Second, the cleanup routine has been restructured to adhere to strict synchronization protocols. It now employs wake_up_all to ensure every process waiting on the waitqueue is notified and can proceed safely before any memory is touched. The hardware I/O regions are explicitly released only after all active interactions have ceased, preventing resource conflicts. Finally, timer_delete_sync is utilized instead of simple deletion functions, which guarantees that any pending timer callbacks have fully completed execution across all CPUs before the function returns, thereby ensuring no asynchronous code paths will attempt to access freed memory structures like alarm_events. These changes collectively enforce a safe shutdown sequence that respects both user-space concurrency and kernel-level synchronization requirements.