CVE-2026-53154mm/hugetlb: restore reservation on error in hugetlb folio copy paths

Official description

In the Linux kernel, the following vulnerability has been resolved: mm/hugetlb: restore reservation on error in hugetlb folio copy paths Two sites in mm/hugetlb.c allocate a hugetlb folio via alloc_hugetlb_folio() (consuming a VMA reservation) and then call copy_user_large_folio(), which became int-returning in commit 1cb9dc4b475c ("mm: hwpoison: support recovery from HugePage copy-on-write faults") and can now fail (e.g. -EHWPOISON on a hwpoisoned source page). On the failure path, folio_put() restores the global hugetlb pool count through free_huge_folio(), but the per-VMA reservation map entry is left marked consumed: - hugetlb_mfill_atomic_pte() resubmission path (UFFDIO_COPY) - copy_hugetlb_page_range() fork-time CoW path when hugetlb_try_dup_anon_rmap() fails (rare: pinned hugetlb anon folio under fork) User-visible effect: on UFFDIO_COPY into a private hugetlb VMA where the resubmission copy fails, the reservation for that address is leaked from the VMA's reserve map. A subsequent fault at the same address takes the no-reservation path, and under hugetlb pool pressure the task is SIGBUSed at an address it had previously reserved. The fork-time CoW path leaks the same way in the child VMA's reserve map, though it requires the much rarer combination of pinned hugetlb anon page + hwpoisoned source. Add the missing restore_reserve_on_error() call before folio_put() on both error paths.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/8d6e1dd3ad1340cd8b6d554b7aa93d8f0a1c6d38
• https://git.kernel.org/stable/c/e47bf16af3c45470ea32f2241fa69aefe0dd61bd
• https://git.kernel.org/stable/c/c72469ac0f274bde3f0df60a4584e14a123d0aa6
• https://git.kernel.org/stable/c/45e33d43243d71d089af42f5077b8213cee6610f
• https://git.kernel.org/stable/c/40c81856e622a9dc59294a90d169ac07ea25b0b0