CVE-2026-93075 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
dax/fsdev: clear pgmap ops and owner on unbind
fsdev_dax_probe() sets pgmap->ops = &fsdev_pagemap_ops and pgmap->owner = dev_dax, but nothing ever clears them. For a dynamic device the pgmap is devm-allocated and freed on unbind, so this is harmless. For a static device the pgmap is the shared, long-lived one owned by the dax bus (kill_dev_dax() only NULLs dev_dax->pgmap for the non-static case), and device.c's probe sets only pgmap->type, never clearing ops/owner.
So after fsdev unbinds a static device the stale fsdev_pagemap_ops survives on the shared pgmap. If the device is then rebound to device_dax (MEMORY_DEVICE_GENERIC, which installs no ->memory_failure), or the fsdev_dax module is unloaded, a subsequent memory_failure on that pgmap dispatches through the stale -- and possibly freed -- handler.
Register a devm action that clears pgmap->ops and pgmap->owner on unbind, symmetric with setting them at probe, so the pgmap carries no fsdev state once fsdev is detached.
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Analysis
by VulDB Data Team • 09/18/2026
The Linux kernel vulnerability identified in the dax/fsdev subsystem represents a critical resource management flaw involving stale function pointers within persistent memory mapping structures. This issue arises from an asymmetry in how device driver resources are initialized and cleaned up during the lifecycle of a dynamic versus static device binding. During the probe phase, specifically within fsdev_dax_probe(), the code correctly assigns specific page map operations via pgmap->ops = &fsdev_pagemap_ops and sets the owner reference to dev_dax. However, the unbind routine fails to reverse these assignments for all device types. While dynamic devices utilize device-managed memory allocation that automatically frees the pgmap structure upon unbinding thereby mitigating direct exploitation of stale pointers through use-after-free scenarios on the struct itself, static devices present a significantly higher risk profile because they rely on shared, long-lived pgmap structures owned by the dax bus infrastructure.
The core technical flaw lies in the fact that for static devices, the kill_dev_dax function only NULLs out dev_dax->pgmap but does not clear the ops and owner fields within the underlying shared pgmap structure retained by the dax bus. Consequently, when a static device is unbound from fsdev while leaving its associated memory region mapped or accessible through other means, the stale pointer to fsdev_pagemap_ops remains embedded in this persistent data structure. This creates a dangerous state where subsequent operations targeting that memory range may inadvertently invoke handlers belonging to the detached driver module rather than appropriate generic handlers. The severity of this vulnerability is compounded by the potential for use-after-free conditions if the fsdev_dax kernel module is unloaded while references to these stale function pointers persist in active system paths or pending asynchronous work items.
The operational impact of this flaw centers on memory failure handling mechanisms within the Linux kernel's persistent memory subsystem. If a hardware error occurs and triggers a memory_failure call on an affected pgmap, the kernel will dispatch the request through the stale fsdev_pagemap_ops handler. In scenarios where the device has been rebound to device_dax with MEMORY_DEVICE_GENERIC type which installs no specific ->memory_failure handler or when the original module is unloaded, this leads to execution of freed code or invalid function calls. Such behavior can result in kernel panics, denial of service conditions, or potentially arbitrary code execution if an attacker can influence memory error injection vectors and control the state of the system during a failure event. This aligns with CWE-416 Use After Free as it involves accessing memory operations after they have become invalid due to improper cleanup, and also reflects CWE-209 Generation of Error Message Containing Sensitive Information if the crash leads to information disclosure via stack traces or core dumps exposing internal kernel structures.
From a threat modeling perspective using MITRE ATT&CK frameworks this vulnerability facilitates techniques related to Defense Evasion by allowing an attacker to cause system instability through crafted memory error conditions and potentially Impact on Availability via denial of service resulting from kernel crashes. It also touches upon Improper Neutralization of Special Elements used in an OS Command CWE-78 if the crash leads to exploitable states that could be chained with other vulnerabilities for privilege escalation though the primary vector remains stability compromise rather than direct command injection. The lack of proper state isolation between driver instances on shared hardware resources exemplifies a failure in enforcing strict boundaries during device lifecycle transitions which is critical for systems relying on persistent memory technologies like Intel Optane or NVDIMMs where data integrity and system reliability are paramount.
To mitigate this vulnerability developers must ensure that all references to dynamic driver-specific operations are explicitly cleared upon device unbinding regardless of whether the underlying pgmap structure persists in shared storage. The recommended remediation involves registering a devm action during the probe phase that specifically clears pgmap->ops and pgmap->owner fields when the device is detached from fsdev. This ensures symmetry between initialization and teardown phases preventing any residual state leakage into subsequent operations on the same memory region. System administrators should apply kernel patches addressing this specific issue in affected distributions immediately particularly those deploying static dax devices with persistent memory configurations. Regular auditing of driver unbind routines for completeness in resource cleanup is essential to prevent similar issues across other subsystems managing shared hardware resources and maintaining strict adherence to device lifecycle management protocols within the Linux kernel architecture.