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CVE-2026-89593: hugetlb: only adjust reservation during unmapping if mapcount is 0

• Severity: high (CVSS 7.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-11 · updated 2026-10-19

Description

In the Linux kernel, the following vulnerability has been resolved: hugetlb: only adjust reservation during unmapping if mapcount is 0 Since df7a6d1f6405, __unmap_hugepage_range can adjust reservations. In the case of folio mapped in both a parent and a child, if the parent unmaps the range first, the reservation adjustment will result in an underflow of the reserved count. Once the child unmaps the range, the count is restored. Change __unmap_hugepage_range() to check the mapcount before adjusting the reservation.

Affected products

• Linux kernel: 6.9 — fixed in 7.3

How to fix

Upgrade to a fixed version: Linux kernel 7.3. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/0f001491e5a2ec69aa9d5dd6b799e5742245f9ea
• https://git.kernel.org/stable/c/5120b1e048d48596ffaec1a8412012a91adba73b
• https://git.kernel.org/stable/c/a3c65af20cceb7f997847727636b4017326f845d
• https://git.kernel.org/stable/c/b0b1b9ca80b795ed2223e76dd787db7067121fb9

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