UBUNTU-CVE-2026-80622: Use After Free
In the Linux kernel, the following vulnerability has been resolved: char: tlclk: fix use-after-free in tlclkcleanup() This patch improves the module cleanup process in the tlclk driver to prevent potential use-after-free and race conditions. Currently, the fileoperations 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 tlclkcleanup() function frees the alarmevents memory before ensuring that blocked processes in the waitqueue are fully awakened and that the switchovertimer has completed. To address these cases, this patch: - Sets '.owner = THISMODULE' in tlclkfops to safely defer module unloading while the device is in use. - Updates tlclkcleanup() to explicitly wake up all blocked readers (wakeupall), properly release hardware I/O regions, and safely delete the timer (timerdeletesync) prior to freeing memory.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Configuration
Update tlclk_cleanup() to wake all blocked readers, release hardware I/O regions, synchronously delete switchover_timer, and only then free alarm_events memory.
Linux kernel tlclk driver tlclk_cleanup() cleanup ordering = wake_up_all; release hardware I/O regions; timer_delete_sync(switchover_timer); free alarm_events - Configuration
Set the .owner field in the tlclk_fops file_operations structure to THIS_MODULE to defer module unloading while the device is in use.
Linux kernel tlclk driver tlclk_fops.owner = THIS_MODULE
Event History
Frequently Asked Questions
Who can exploit this issue?
An attacker needs local access and low-level privileges to interact with the affected tlclk device. The vulnerable driver is present in the listed Ubuntu kernel package variants.
What conditions trigger the vulnerability?
The issue can occur when the tlclk module is unloaded while user-space processes still use the device, or when cleanup frees alarm event memory before blocked readers and the switchover timer have fully completed.
What should be done if an updated kernel cannot be installed immediately?
Avoid unloading the tlclk module while any process may be interacting with its device, and prevent untrusted local users from accessing the device. Ensure processes using the driver are stopped before module cleanup.
How does the fix prevent exploitation?
The fix pins the module while its file operations are in use, wakes all blocked readers during cleanup, synchronously deletes the timer before freeing memory, and releases hardware I/O regions.