CVE-2026-90404 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
platform/chrome: cros_ec_debugfs: Unregister panic notifier
cros_ec_debugfs_probe() registers notifier_panic with the EC panic notifier chain. The remove path tears down debugfs and the console log, but leaves the notifier registered. A later panic notification can call back into the removed instance and queue work that accesses released data.
Unregister the panic notifier before tearing down the debugfs and console log state.
This issue was found by a static analysis tool.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability identified in the Linux kernel's Chrome OS EC (Embedded Controller) debug filesystem driver represents a classic use-after-free scenario arising from improper resource cleanup during module removal or device unbinding. The cros_ec_debugfs_probe function initializes the debugging interface by registering a panic notifier, specifically notifi_panic, with the embedded controller's panic notification chain. This mechanism allows the kernel to invoke specific callbacks when a system-wide panic occurs, enabling critical data preservation such as console logs and debug information before the system halts. However, the corresponding remove path for this driver contains a logical flaw in its teardown sequence. While it correctly proceeds to destroy the debugfs entries and release associated console log buffers, it fails to unregister the previously registered panic notifier from the EC's notification chain. This oversight creates a dangling pointer situation where the kernel retains a reference to a callback function that resides within memory regions scheduled for immediate deallocation or already freed by the time of removal completion.
The operational impact of this flaw is triggered when a system-wide panic event occurs after the driver has been unloaded but before the kernel's garbage collection mechanisms have fully reclaimed all associated memory structures, or more critically, if the notifier chain still holds references to functions in modules that are being removed concurrently during runtime unbinding scenarios. When the panic handler iterates through its list of registered notifiers and invokes the callback for cros_ec_debugfs, it attempts to execute code within a module instance that is no longer valid. This leads to undefined behavior, typically manifesting as kernel oopses or full system crashes due to accessing released data structures. The static analysis tool identified this by tracing the lifecycle of the notifier registration and observing its absence in the cleanup routine, highlighting a discrepancy between initialization and termination logic. Such vulnerabilities compromise system stability and reliability, particularly in embedded environments where panic handling is crucial for post-mortem debugging but must not itself cause secondary failures that obscure the original root cause or prevent proper logging.
From a security and standards perspective, this issue aligns with CWE-416, Use After Free, as it involves referencing memory after it has been freed due to incorrect ordering of resource release operations. It also relates to CWE-390, Detection of Error Condition Without Action, in the sense that the driver detects the need for cleanup but fails to perform a necessary step (unregistering the notifier) before proceeding with other teardown actions. In terms of MITRE ATT&CK mapping, while this is primarily a stability issue rather than an exploit vector for privilege escalation or data exfiltration by external attackers, it falls under T1499, Endpoint Denial of Service, as it can be leveraged to crash the system if triggered via panic conditions. The vulnerability underscores the importance of strict adherence to initialization and cleanup symmetry in kernel drivers, ensuring that every registration has a corresponding unregistration performed before any dependent resources are destroyed.
Mitigation for this vulnerability requires modifying the cros_ec_debugfs_remove function to explicitly call unregister_panic_notifier or the specific EC equivalent prior to destroying debugfs entries and releasing console log buffers. This ensures that no pending panic events can invoke callbacks into freed memory regions. Developers should adopt a defensive programming approach where resource acquisition is strictly paired with release in reverse order of acquisition, often encapsulated within helper functions to prevent such omissions during code maintenance or refactoring. Additionally, static analysis tools and dynamic testing frameworks like KASAN (Kernel Address Sanitizer) can be employed in development pipelines to detect these types of lifecycle mismatches early. For existing deployments, applying the kernel patch that corrects this ordering is essential to maintain system integrity, especially on Chrome OS devices where embedded controller interactions are frequent and panic logging is a critical diagnostic feature. Ensuring robust error handling paths during driver removal prevents race conditions between module unloading and asynchronous events like panics, thereby preserving both security posture and operational continuity.