CVE-2026-99145 in Linux
Summary
by MITRE • 10/28/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/xe: Don't transfer shrinker pages for pinned bos on purgeable state change
Pinned bos have their pages removed from the shrinker's shrinkable / purgeable counts on pin, and added back on unpin according to the bo's purgeable state at that time.
However, xe_bo_set_purgeable_shrinker() unconditionally transfers pages between the shrinkable and purgeable counts. If the purgeable state of a pinned bo changes, for example by userspace madvising DONTNEED on a VMA of a bo that is also pinned as a scanout buffer, this underflows one count and, after unpin, leaves the other one permanently inflated.
Only update the purgeable flag for pinned bos, and leave the page accounting to unpin.
(cherry picked from commit afe6bc012034123fd838328668e609bf57e46bd3)
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Analysis
by VulDB Data Team • 10/28/2026
The Linux kernel's graphics subsystem, specifically the DRM Xe driver, contains a logic error in memory management accounting that can lead to resource exhaustion and system instability. This vulnerability arises from an incorrect handling of buffer object states when transitioning between pinned and unpinned conditions while simultaneously altering their purgeable status. In modern operating systems, particularly those utilizing virtual memory techniques like demand paging, the kernel maintains strict accounting for which pages are considered shrinkable or purgeable by the memory reclaim subsystem. When a buffer object is pinned, meaning its physical pages must remain resident in RAM to prevent swapping out during active use such as display scanning, it should be excluded from these counts. Conversely, when unpinned, the system relies on the current state of the buffer to determine if those pages can be reclaimed under memory pressure.
The core technical flaw lies within the xe_bo_set_purgeable_shrinker function, which unconditionally transfers page accounting between shrinkable and purgeable categories regardless of whether the buffer object is currently pinned. This design fails to account for the temporal state of the pinning status at the moment of the operation. If a user space application modifies the madvise advice on a virtual memory area associated with a buffer that is also actively pinned as a scanout buffer, the kernel incorrectly adjusts these internal counters. Specifically, this action causes an underflow in one accounting count because it attempts to remove pages from a list where they are not currently tracked due to their pinned status. This mismatch disrupts the integrity of the memory management data structures used by the Linux kernel's page reclaim algorithms.
The operational impact of this vulnerability is significant for system stability and security posture. The immediate consequence is an underflow in one accounting metric, which can lead to negative integer values or wrap-around errors depending on the underlying implementation details. More critically, upon unpinning the buffer object later, the other count becomes permanently inflated because the initial adjustment was invalid. This inflation causes the kernel to believe there are more purgeable pages available than actually exist in physical memory. As a result, the memory reclaim subsystem may aggressively attempt to free non-existent or already freed resources, leading to potential crashes, data corruption, or severe performance degradation due to excessive and futile reclamation attempts. In extreme cases, this can trigger kernel panics or allow for denial-of-service conditions where system responsiveness is severely compromised under load.
From a vulnerability classification perspective, this issue aligns with CWE-190 Integer Overflow or Wraparound, as the incorrect accounting leads to erroneous numerical states in memory management structures. It also relates to CWE-400 Uncontrolled Resource Consumption, since the inflated purgeable count misleads the kernel into consuming resources incorrectly during reclamation cycles. In terms of ATT&CK mapping, this represents a weakness that could potentially be leveraged for Denial of Service against local users or processes with access to graphics hardware interfaces. The vulnerability highlights the complexity of maintaining consistency between user-space memory hints and kernel-side resource tracking mechanisms in high-performance computing environments like GPU drivers.
Mitigation strategies primarily involve applying the upstream kernel patch that corrects this logic error. The fix ensures that for pinned buffer objects, only the purgeable flag is updated without altering the shrinker page counts immediately. Instead, the actual transfer of pages between shrinkable and purgeable lists is deferred until the buffer object is unpinned. This approach guarantees that accounting adjustments occur when the memory state accurately reflects the residency requirements of the buffer. System administrators should ensure their Linux kernels are updated to include this fix from commit afe6bc012034123fd838328668e609bf57e46bd3 or later versions where it is integrated. For organizations running custom kernel builds, backporting this specific change to the xe driver source code is necessary to restore correct memory accounting behavior and prevent potential stability issues related to GPU memory management under dynamic madvise operations.