CVE-2026-89953 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
mtd: mtdoops: free page bitmap when the backing MTD is removed
mtdoops_notify_add() allocates oops_page_used when the configured MTD device is registered. mtdoops_notify_remove() detaches from that device but leaves the bitmap allocated. If the same MTD device is later registered again, the add path allocates a new bitmap and overwrites the old pointer, leaking one vmalloc allocation per remove/add cycle.
This is only visible when the backing MTD device can disappear and be registered again while mtdoops remains loaded, so the usual static MTD case does not expose it.
Free the bitmap after unregistering the dumper and flushing the pending workers, then clear the pointer and page count before a later attach can allocate fresh state. Clearing the pointer also keeps the module exit path from freeing the same bitmap a second time after a remove event.
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Analysis
by VulDB Data Team • 09/16/2026
The Linux kernel's Memory Technology Device (MTD) subsystem includes a component known as mtdoops, which is designed to capture and store kernel oops or panic messages on non-volatile storage devices such as flash memory. This mechanism ensures that critical debugging information survives system crashes where volatile RAM would be lost. A specific resource management flaw was identified within the lifecycle handling of this module when interacting with dynamically registered MTD devices. The vulnerability centers on improper cleanup procedures during device detachment, leading to a persistent memory leak in kernel space.
The technical root cause lies in the interaction between the mtdoops driver and the underlying MTD framework's notification system. When an MTD device is added or registered while the mtdoops module is active, the function mtdoops_notify_add() allocates a bitmap structure named oops_page_used to track which pages on the storage medium have been written with crash data. This allocation utilizes vmalloc for kernel memory management. However, when the backing MTD device is removed or detached from the system, the corresponding cleanup routine mtdoops_notify_remove() detaches the driver from the device but fails to release this allocated bitmap. Consequently, the pointer to the previously allocated memory remains in place without being freed, resulting in a direct loss of kernel heap resources.
This vulnerability manifests specifically under conditions where an MTD device is dynamically removed and subsequently re-registered while the mtdoops module remains loaded in the kernel space. In such scenarios, each remove-and-add cycle triggers a new allocation for oops_page_used without freeing the previous instance. The old pointer is overwritten by the new allocation, rendering the original memory block unreachable and permanently leaked until the system is rebooted or the module is unloaded. This issue does not typically affect static MTD configurations where devices are present at boot time and do not undergo hot-plug removal events, making it a niche but significant flaw for systems relying on dynamic storage configuration.
From an operational perspective, this memory leak contributes to gradual kernel memory exhaustion over time in affected environments. While individual leaks may be small relative to total system RAM, repeated cycles of device attachment and detachment can accumulate sufficient leaked vmalloc space to degrade performance or trigger out-of-memory conditions within the kernel's internal allocator limits. This aligns with CWE-401, which describes a missing release of memory after effective use, and falls under the broader category of resource management errors that compromise system stability and reliability over extended uptime periods.
To mitigate this vulnerability, developers must ensure that all dynamically allocated resources are properly released during device detachment sequences. The fix involves modifying mtdoops_notify_remove() to explicitly free the oops_page_used bitmap after unregistering the dumper and flushing any pending worker threads associated with writing crash data. Additionally, it is critical to clear the pointer variable and reset page count metrics immediately following the deallocation. This practice prevents double-free errors during module exit paths by ensuring that subsequent attachment operations allocate fresh state rather than attempting to reuse or free stale pointers. Adhering to these cleanup protocols ensures robust resource lifecycle management consistent with industry best practices for kernel driver development, such as those outlined in ATT&CK techniques related to persistence and defense evasion through system compromise via memory corruption or exhaustion.