CVE-2026-98749 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
tty: serial: max3100: shut down timer before freeing port
max3100_shutdown() stops the polling timer but returns early during system suspend. If the SPI device is unbound before resume, the serial core does not call max3100_shutdown() again, so max3100_remove() frees the port while the timer remains armed. max3100_timeout() may then access the freed port and re-arm the timer.
Add final timer teardown to max3100_remove() and use timer_shutdown_sync() to prevent a racing callback from re-arming it. Also free the IRQ and destroy the workqueue there before freeing the port. Keep timer_delete_sync() in max3100_shutdown() so that a subsequent open() can re-arm the timer.
The workqueue is created before request_irq() and destroyed on both request_irq() failure and normal shutdown. Its presence at remove thus identifies the IRQ left registered when suspend bypasses shutdown.
Free the IRQ before destroying the workqueue, in both max3100_shutdown() and max3100_remove(), and cancel the pending work in between. free_irq() waits for a running interrupt handler to finish and no new handler can start afterwards, so a racing handler cannot queue work on a workqueue that is being destroyed; the force_end_work check in max3100_dowork() only narrows that window, as a handler delayed between the check and queue_work() could still run after the teardown has cleared the workqueue pointer. Cancelling the work also keeps destroy_workqueue() from waiting on a queued work item in case remove() ever runs while the freezable workqueue is still frozen, e.g. device removal during the resume window, before workqueues are thawed.
This issue was found by an in-house static analysis tool.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel driver for the MAX3100 serial interface chip contains a critical use-after-free vulnerability rooted in improper resource management during system suspend and device removal sequences. The core of the flaw lies in the interaction between the power management state machine and the driver's teardown logic. Specifically, when the system enters a suspended state, the max3100_shutdown function is invoked to halt operations; however, this routine returns early if it detects that the system is suspending rather than performing a full shutdown or removal. This design choice leaves certain resources in an inconsistent state because the expectation is that these resources will be cleaned up later during resume or device unbinding. The vulnerability manifests when an SPI device is unbound from its driver while the system remains suspended, thereby bypassing the normal resume path where max3100_shutdown would typically be called again to ensure complete cleanup. Consequently, when the kernel subsequently executes max3100_remove to free the serial port structure, it deallocates memory that is still actively referenced by an armed polling timer.
This race condition leads to a severe use-after-free scenario classified under CWE-416: Use After Free. Once the port data structure is freed, any subsequent execution of the max3100_timeout callback function results in access to invalid memory addresses. The timeout handler not only attempts to read from or write to the now-deallocated serial port context but also re-arms the timer, perpetuating a cycle of illegal memory accesses that can lead to kernel panics, data corruption, or potentially arbitrary code execution if an attacker can influence the timing and state of these operations. This aligns with ATT&CK technique T1059: Command and Scripting Interpreter in contexts where such instability allows for exploitation vectors leading to privilege escalation or denial of service against critical system services relying on serial communication stability.
The resolution involves a comprehensive restructuring of the resource teardown sequence within both max3100_shutdown and max3100_remove functions to ensure strict ordering and synchronization of hardware and software resources. The fix introduces timer_shutdown_sync in max3100_remove, which guarantees that any currently executing timer callback completes before the function proceeds, effectively preventing racing callbacks from re-arming the timer after it has been logically deleted via timer_delete_sync retained in shutdown for potential future open operations. This dual approach ensures that timers are safely managed regardless of whether they were stopped during suspend or require final cleanup during removal. By synchronizing these actions, the driver eliminates the window where a freed port could be accessed by asynchronous hardware interrupts or software timers.
Furthermore, the patch addresses related resource leaks and race conditions involving interrupt requests and workqueues. The IRQ is now explicitly freed before destroying the associated workqueue in both shutdown and remove paths. This ordering is critical because free_irq waits for any running interrupt handler to finish and prevents new handlers from starting, thereby ensuring that no racing handler can queue work on a workqueue that is simultaneously being destroyed. To further mitigate race conditions where an interrupt might be delayed between checking the need to end work and actually queuing it, pending work items are explicitly cancelled before destroying the workqueue. This prevents destroy_workqueue from hanging indefinitely if remove occurs while the freezable workqueue is still frozen during a resume window, addressing edge cases related to device removal timing that could otherwise cause system hangs or deadlocks.
These changes were identified through an in-house static analysis tool, highlighting the importance of automated code inspection in detecting complex concurrency bugs and lifecycle management errors within kernel drivers. The fix ensures robustness against both standard operational flows and exceptional power state transitions. By enforcing strict dependency ordering for timers, interrupts, and workqueues, the driver now adheres to best practices for resource safety as outlined in CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization. This comprehensive remediation stabilizes the MAX3100 serial interface under all system states, preventing memory corruption and ensuring reliable operation of embedded systems relying on this hardware component.