CVE-2026-80766 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
HID: uclogic: fix use-after-free of inrange_timer on remove
uclogic_remove() cancels the pen in-range timer and then stops the device:
timer_delete_sync(&drvdata->inrange_timer); hid_hw_stop(hdev);
timer_delete_sync() only guarantees the timer is idle at that instant. uclogic_raw_event_pen() keeps delivering pen reports until hid_hw_stop() stops the transport several lines later, and every report with pen->inrange == UCLOGIC_PARAMS_PEN_INRANGE_NONE re-arms the timer:
mod_timer(&drvdata->inrange_timer, jiffies + msecs_to_jiffies(100));
A report landing between the timer_delete_sync() call and the transport teardown in hid_hw_stop() re-arms inrange_timer after it was cancelled. uclogic_remove() then returns and the devm drvdata is freed, while hid_hw_stop() has already freed the input device drvdata->pen_input points at, so when the timer fires ~100 ms later uclogic_inrange_timeout() dereferences freed memory -- a use-after-free in timer-softirq context.
Swapping the two calls is not a fix: stopping the device first frees drvdata->pen_input via hidinput_disconnect() while the timer may still be pending, so a timer already armed before removal fires on the freed input device in the window before timer_delete_sync() runs.
Use timer_shutdown_sync() before hid_hw_stop() instead. It cancels the timer, waits for a running callback while pen_input is still valid, and prevents any further re-arming -- a later mod_timer() from an in-flight report is silently ignored -- so the timer is provably dead before hid_hw_stop() frees the inputs. This is the ordering the timer core documents for this "timer re-armed from another path" teardown case.
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Analysis
by VulDB Data Team • 09/04/2026
The Linux kernel HID uclogic driver contains a critical use-after-free vulnerability within its device removal sequence, specifically involving the management of the pen in-range timer and associated input devices. This flaw arises from an incorrect ordering of operations during the cleanup phase when a UCLogic tablet is disconnected or removed from the system. The original implementation attempted to cancel the pending timer using timer_delete_sync followed by stopping the hardware transport via hid_hw_stop. However, this sequence fails to account for asynchronous events that may occur in the narrow window between these two calls. Specifically, while timer_delete_sync ensures the timer callback does not execute at that exact moment, it does not prevent new timers from being armed if a report arrives during the teardown process.
The technical root cause lies in how pen reports are processed after the cancellation signal is issued. The uclogic_raw_event_pen function continues to deliver pen status updates until hid_hw_stop fully halts the device transport layer. If an incoming report indicates that the pen is no longer in range, indicated by a specific parameter value, it triggers a re-arm of the inrange_timer with a one-hundred-millisecond timeout. Because this re-arming occurs after timer_delete_sync has been called but before hid_hw_stop completes its teardown, the system ends up with an active timer referencing data structures that are about to be freed or have already been partially deallocated by the subsequent hardware stop routine.
This race condition leads to a severe use-after-free vulnerability in kernel softirq context. When uclogic_remove returns after initiating the shutdown sequence, the device managed resources including drvdata are released via devm mechanisms. Simultaneously, hid_hw_stop frees the input device structure pointed to by drvdata->pen_input through hidinput_disconnect. If an in-flight report had re-armed the timer just before these structures were freed, the scheduled timeout will eventually fire approximately one hundred milliseconds later. At that point, uclogic_inrange_timeout attempts to dereference memory addresses belonging to the now-freed pen input device and driver data, resulting in undefined behavior, potential kernel panics, or arbitrary code execution depending on how the freed memory is reused by other subsystems.
The vulnerability aligns with CWE-416, Use After Free, as it involves accessing memory after it has been made available for reuse without ensuring that no references to that memory remain active. From a threat modeling perspective using MITRE ATT&CK, this could be leveraged in scenarios where an attacker controls the physical device or can manipulate USB HID reports to trigger specific timing conditions, potentially leading to privilege escalation if the kernel crashes into exploitable states or leaks sensitive information through corrupted memory structures. The impact is particularly acute because it occurs during a standard administrative action like unplugging a peripheral, making it difficult for users to reproduce consistently but highly dangerous when triggered by rapid device removals or high-frequency report streams.
A naive fix involving simply swapping the order of hid_hw_stop and timer deletion proves insufficient due to similar race conditions in reverse. Stopping the hardware first frees the input device while timers might still be pending from previous operations, leading to callbacks executing against freed memory before they can be safely canceled. The correct resolution requires using timer_shutdown_sync prior to calling hid_hw_stop. This function not only cancels any pending timer but also waits for any currently running callback to complete while ensuring that no new instances of the timer can be armed during this window. By guaranteeing that all timer activity ceases and is fully synchronized before the input device structures are destroyed, the kernel ensures memory safety throughout the teardown process.
This fix adheres strictly to the Linux kernel documentation regarding proper shutdown sequences for timers that may be re-armed from other execution paths. It demonstrates a deep understanding of asynchronous event handling in high-concurrency environments like USB HID drivers. For system administrators and developers, this highlights the importance of using synchronized shutdown primitives rather than simple cancellation calls when dealing with hardware resources that have dependent lifecycle states. Maintaining strict ordering between resource deallocation and timer management is essential to prevent subtle concurrency bugs that can compromise system stability and security in production Linux environments.