# CVE-2026-31575: mm/userfaultfd: fix hugetlb fault mutex hash calculation

Status: published. Published: 2026-04-24. Updated: 2026-11-05.

In the Linux kernel, the following vulnerability has been resolved:

mm/userfaultfd: fix hugetlb fault mutex hash calculation

In mfill_atomic_hugetlb(), linear_page_index() is used to calculate the
page index for hugetlb_fault_mutex_hash().  However, linear_page_index()
returns the index in PAGE_SIZE units, while hugetlb_fault_mutex_hash()
expects the index in huge page units.  This mismatch means that different
addresses within the same huge page can produce different hash values,
leading to the use of different mutexes for the same huge page.  This can
cause races between faulting threads, which can corrupt the reservation
map and trigger the BUG_ON in resv_map_release().

Fix this by introducing hugetlb_linear_page_index(), which returns the
page index in huge page granularity, and using it in place of
linear_page_index().

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ a08c7193e4f18dc8508f2d07d0de2c5b94cb39a3; < 5a525c43baaba0bf3063f86996ca3623b71e4172 (affected, git); ≥ a08c7193e4f18dc8508f2d07d0de2c5b94cb39a3; < 574501ede47ac439afd67ba9812bc66722d500ba (affected, git); ≥ a08c7193e4f18dc8508f2d07d0de2c5b94cb39a3; < 08282b1bf74c69fc8ecd25493e7fdb5460f01290 (affected, git); ≥ a08c7193e4f18dc8508f2d07d0de2c5b94cb39a3; < f4689fc089765d36c026063fb22d23533e883eb6 (affected, git); ≥ a08c7193e4f18dc8508f2d07d0de2c5b94cb39a3; < 0217c7fb4de4a40cee667eb21901f3204effe5ac (affected, git). Source: CNA: Linux
- Linux / Linux: 6.7 (affected); ≥ 0; < 6.7 (unaffected, semver); ≥ 6.12.84; ≤ 6.12.* (unaffected, semver); ≥ 6.18.24; ≤ 6.18.* (unaffected, semver); ≥ 6.19.14; ≤ 6.19.* (unaffected, semver); ≥ 7.0.1; ≤ 7.0.* (unaffected, semver); ≥ 7.1; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.12% as of 2026-11-05; percentile 1.99%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/5a525c43baaba0bf3063f86996ca3623b71e4172 (CNA: Linux)

- https://git.kernel.org/stable/c/574501ede47ac439afd67ba9812bc66722d500ba (CNA: Linux)

- https://git.kernel.org/stable/c/08282b1bf74c69fc8ecd25493e7fdb5460f01290 (CNA: Linux)

- https://git.kernel.org/stable/c/f4689fc089765d36c026063fb22d23533e883eb6 (CNA: Linux)

- https://git.kernel.org/stable/c/0217c7fb4de4a40cee667eb21901f3204effe5ac (CNA: Linux)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-31575; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-31575; retrieved 2026-11-05; source updated Not reported

Revision: 67e592f062c6fb39cdc26acfb28c8e78bb2b3f7549640f16fb0bbcc8705e8162

Canonical: https://y2.dev/cve/CVE-2026-31575

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

Collected public records only. Check source status for coverage and freshness.